Gas separation with binary-cooperative heterogeneous membranes

Domain: chemistry
Published: 2026-02-28
Editorial outcome: major_revision

Abstract
Advanced polymer membranes exhibit competitive performance in gas separation. However, rationally designing a polymer membrane with high gas separation performance and structural robustness simultaneously remains challenging. Herein, we present a microzone interfacial polymerization approach to reconstruct the polymer network through the rearrangement of attached functional groups, forming a heterogeneous structure with a crumpled morphology. Unlike common crumpled membranes with homogeneous structures, the heterogeneous structure with a discovered microphase separation endows the membrane with independent and cooperative dual-function regions. The peaks, with more amides as CO2-philic sites, are functionalized as fast CO2 transport channels, whereas the stress release effect via the deformation process maintains a high free volume. Valleys, with more rigid phenyls, demonstrate both enhanced CO2 diffusion and compaction resistance. The cooperative effects of dual-function regions significantly improve the structural robustness, and the optimized membrane exhibits an approximately 300% increase in CO2 permeance and CO2/N2 selectivity compared with its homogeneous counterparts under 1.0 MPa, which is also one order of magnitude greater than that of state-of-the-art membranes. This approach offers a potential pathway for developing more durable polymer membranes suited for harsh environments, which could expand the range of gas separations feasible with membrane technology.

Introduction
Separation processes, such as evaporation and distillation, which are widely used in gas and liquid separations, are energy intensive1. Membrane separation technology, as an alternative, typically consumes an order of magnitude less energy and has attracted extensive interest2-7. Currently, polymer membranes still dominate industrial membranes8-10. Various advanced strategies, focused on designing the membrane structure at the molecular level aimed at increasing the gas diffusion or solubility ability or constructing sub-nanometer channels, are conducted to remarkably improve gas permselectivity11-13. However, gas separation membranes are mostly applied under operating pressure, and the polymer structure is easily destroyed owing to compaction or plasticization effects, which reduces the separation performance despite the high low-pressure performance.

Strengthening the interchain interactions in the polymer network is a common strategy to suppress the movement of polymer segments14, 15. Examples of hydrogen bonds16, metal‒ligand bonds17, and ionic or Coulombic interactions18 are implemented to effectively dissipate energy and protect the original network stability under external stresses. Other strategies, such as interpenetrating multiple networks, including those with prior mechanical rupture, demonstrate similar effects19. However, the introduction of the above interactions inevitably sacrifices the free volume and inhibits the transfer of gas molecules, and is capable of forming crystallization areas as stress concentration sites, which tend to form nonselective defects. Bones or teeth in organisms, with alternating arrangements of inorganic phases (hydroxyapatite) and organic phases (collagen), consistently exhibit mechanical robustness. The cooperative effects of the two phases explain the structural stability, which can effectively release external stresses20-24. Inspired by this, accurately constructing independent and cooperative functions within polymer networks is an effective approach to improve gas separation performance while maintaining structural stability, especially under operation pressure.

Herein, we designed a heterogeneous polymer membrane through reconstruction of the polymer network, which was achieved using a microzone interfacial polymerization (IP) technique. A microphase separation phenomenon was discovered by detecting the distribution of functional groups, whereas the peaks were composed of more amide groups and the valleys had more phenyl groups. The resulting cooperative effect endows the membrane with stress release and compaction resistance abilities and enhances CO2 transport and diffusion abilities. This results in gas separation performance compared with that of state-of-the-art membranes.

Results
Construction and characterization of heterogeneous structures

A heterogeneous structure was constructed through a microzone ISP strategy (Supplementary Figs. 1 and 2). In this work, we conducted IP reactions in microzones, i.e., micropores, distributed in a polydimethylsiloxane (PDMS) layer after immersion in an organic phase solution. The swollen micropores (Supplementary Figs. 3c, 4, 5), formed through solvent-induced swelling mechanism (see Supplementary Fig.4 for details), are conducive to anchoring organic phase monomers (trimesoyl chloride (TMC)) because of the capillary effect instead of remaining on the surface of the PDMS layer (Supplementary Fig. 15). In Supplementary Fig. 6, the non-uniform concentration gradient of TMC monomers in the swelling PDMS was qualitatively analyzed by Raman depth imaging, where the red areas indicate the regions with a relatively high concentration of TMC monomers. The advantages and purpose of microzone IP reactions are threefold. First, compared with the common liquid‒liquid IP process, the construction of microreaction zones is conducive to the uniform distribution of TMC monomers, avoiding the disordered arrangement resulting from interfacial disturbances caused by exothermic reactions. Second, refining the macroscopic liquid‒liquid reactions into numerous microreaction units effectively inhibits the reaction rate, making the IP reactions controllable. Third, the IP reactions, which occur at the microporosity, provide more binding sites to enhance the interaction between the selective polymer layer and the PDMS layer. This simple strategy is able to fabricate large-area heterogeneous membranes with a membrane area of 350 cm2 (Supplementary Fig. 7).

The microphase separation phenomenon in the heterogeneous structure was confirmed by atomic force microscopy-infrared spectroscopy (AFM-IR) (Supplementary Figs. 8, 9). The heterogeneous structures (Fig. 1a) are observed on the basis of the detection groups of amide groups (C=O, C–N) from Fig. 1d2 to Fig. 1f2 and the phenyl groups (C=C, C–H) from Fig. 1d3 to Fig. 1f3. The PT-4 and PT-5 membranes have homogeneous structures (Figs. 1b, 1g2-1h2, and 1g3-1h3). The above results demonstrated that the amide groups mostly accumulated at the peaks rather than at the valleys, whereas the phenyl groups showed the opposite trend. However, this phenomenon cannot be observed using Fourier transform infrared (FTIR) spectroscopy, as shown in Supplementary Fig. 10c. The heterogeneous structure caused by the liquid‒liquid (L‒L) microzone IP reactions (Fig. 1c, Zone-1) can be obtained within a residence time of 160 s, which was deemed the waiting time after pouring out the TMC solution. In this process, the n-hexane in the micropores carries the TMC monomers to the L-L interfaces (Supplementary Fig. 11, Zone-1), which subsequently promotes the IP reactions, forming a convex structure. The heterogeneous structure, reflected as a crumpled morphology, was characterized by AFM (Fig. 1d1-f1, Supplementary Fig. 12a1-c3) and scanning electron microscopy (SEM, Supplementary Figs. 13a-c, 14a-c). Beyond 160 s (Fig. 1c, Zone-2), a homogeneous structure with a smooth morphology (Figs. 1g1 and Fig.1h1; Supplementary Figs. 12d1-e3, 13d-e, and 14d-e), shown as PT-4 and PT-5 membranes, was achieved from the liquid‒solid (L‒S) microzone IP reactions (Supplementary Fig. 11, Zone-2), caused by the confined movement of TMC monomers to contact piperazine (PIP) monomers. The membranes fabricated with PIP concentrations of 0.2 and 0.3 wt% are shown in Supplementary Fig. 19 and exhibit the same variation tendency as membranes fabricated with a PIP concentration of 0.1 wt%.

The microphase separation phenomenon is attributed to the change in crosslinking density from the PT-1 to the PT-5 membranes, which was analysed using X-ray photoelectron spectroscopy (XPS). As shown in Supplementary Table 1, the degree of crosslinking of heterogeneous membranes (PT-1 to PT-3) is significantly greater than that of homogeneous membranes (PT-4 and PT-5), indicating the formation of dense structures. Moreover, the increase in the O/N ratio from the PT-1 to PT-3 membranes indicates an increase in linear crosslinking structures in the resultant PA membranes. This suggests that the acyl chloride groups on the PDMS surface were partially hydrolysed to form carboxyl groups when in contact with the PIP solution, reducing the crosslinking density. Hence, the composition differences at the peaks and valleys stem from the variations initiated at the micropores and surface on the PDMS layer in the IP processes, which subsequently changed the crosslinking density.

Formation mechanism of heterogeneous structure

The formation mechanism of the heterogeneous structure, explained as the L‒L microzone IP reaction, was illustrated by Raman scanning spectroscopy. We detected different functional groups by adjusting the Raman focusing mode to observe the microphase separation phenomenon. In the autofocus mode, the Raman laser focuses on the highest location of the membrane surface, which is the peak in the crumpled morphology. Discrete red points, representing C=O or C-N groups in the nascent polyamide films (Fig. 2a1), appear at the initial contact of PIP and TMC monomers (Fig. 2a1-1). This produces large polyamide films through continuous IP reactions (Fig. 2a2), as reflected by the dense red points in Fig. 2a2-1. In Fig. 2a3-1, adjacent large polyamide films are capable of decreasing the surface energy, followed by incorporation with other adjacent polyamide films to obtain the final crumpled morphology (Fig. 2a3). In fixed focus mode, the Raman laser is limited to the mPSf surface, which is regarded as the valley in the crumpled morphology. Unlike the results in Fig. 2a1-1 to 2a3-1, dense red points, representing the C=C or C-H groups in Fig. 2a4-1, appear immediately on the mPSf surface, followed by a decrease in density with continuous reaction in Fig. 2a5-1, which indicates the growth of nascent polyamide films (Fig. 2a5). The disappearance of the red points indicates the cavity structure of growing polyamide films. The significant decrease in the red point density in Fig. 2a6-1 reflects the incorporation of polyamide films, which results in peaks with a crumpled morphology corresponding with the results in Fig. 2a3-1. The formation mechanism of the homogeneous structure, as reflected by the smooth morphology, is explained by the L-S IP reaction shown in Fig. 2b. As shown in Fig. 2b1 to Fig. 2b3, the absence of solvents in the micropores makes it difficult to induce TMC to contact PIP consecutively to participate in the IP reaction; therefore, the formed polyamide films are difficult to grow or incorporate further. The final smooth morphology is obtained through the compact packing of polyamide films, which shows the gradual densification of red points in the Raman signals from Fig. 2(b1-1) to Fig. 2(b3-1). Here, the result is independent of the selected functional groups.

Mechanical properties of heterogeneous membranes

The cooperative effects of deformation and compaction resistance explain the mechanical properties of heterogeneous membranes, which can effectively alleviate both horizontal and vertical stresses. Tensile tests were performed to simulate the horizontal stresses on the membrane (Supplementary Fig. 20). The sample was stretched to a fixed value, held for 15 s, and then recovered. This process was repeated twice. As shown in Fig. 3b, the average tension force from the PT-1 to PT-5 membranes gradually increased from 840 ± 20 to 2650 ± 20 mN. Specifically, the tension force of the PT-1, PT-2 and PT-3 membranes gradually decreases with increasing holding time, and parts of the crumpled morphology became smooth under a stretched state (Supplementary Fig. 21), indicating that the crumpled morphology is capable of releasing stress. Within one hundred cycles of stretch tests (Fig. 3a1-a6, Supplementary Fig. 22), no visible cracks or fragmentation of the PT-1 to PT-3 membranes were observed, whereas the PT-4 and PT-5 membranes exhibited obvious cracks after five cycles (Fig. 3a7–a10). These results reflect the deformation characteristics of the crumpled morphology, thus effectively avoiding membrane defects, which is also confirmed by the tensile tests shown in Supplementary Fig. 23. Gold nanoparticle retention tests were also conducted to visually analyse the deformation behaviour of the peaks, and the detailed process is shown in the Supplementary Information. As shown in Fig. 3e and Supplementary Fig.16, gold nanoparticles were used as the markers, accompanied by a high-speed gas flow to strike the membrane. The deformation effect of the peaks effectively releases compressive stress, which is verified by narrowing the peak width from d1 to d2 to d3 (Figs. 3f1–3f3 and 3f1-1– 3f3-1) from atmospheric pressure to high pressure.

AFM height images and their corresponding quantitative nanomechanical maps were used to simulate the vertical stresses on the membrane surface, original SEM cross-section images were shown in Fig.3c and Supplementary Figs 17, 18. Four parameters are shown in Fig. 3d: the indentation depth, which reflects the deformation space when the membrane is closely attached to the substrate (mPSf membrane); the crumpled distance, which reflects the crumpled density; the crumpled height, which indicates the fluctuation degree of the crumpled structure; and the Young’s modulus, which reflects the difficulty in deformation. As shown in Supplementary Fig. 44e, the average crumpled heights from the PT-1 to PT-5 membranes gradually decreased from 128.2 ± 3.2 to 95.1 ± 2.3 nm and then rapidly decreased to 3.3 ± 0.2 nm. This finding suggests the disappearance of the crumpled morphology. The increase in the crumpled distance increases from 12.1 ± 1.3 to 125.1 ± 3.3 nm, which demonstrates a decrease in the crumpled density. AFM mechanical phase diagrams verify the mechanical microphase separation (Fig. 3g), demonstrating that the Young’s modulus at the peaks (yellow domains) is lower than that at the valleys (purple domains). We further used the AFM mechanical mode to compare the peaks and valleys in detail. In Fig. 3h, the Young’s moduli at the peaks from the PT-1 to PT-3 membranes are lower than those at the valleys, reflecting a greater indentation depth at the peaks than at the valleys. The indentation depth changes with attached force on the AFM tip, but the calculated Young’s modulus is almost independent of attached force (Supplementary Figs.44a-c). However, the PT-4 and PT-5 membranes, which have relatively low Young’s moduli, are compressible. Specifically, the indentation depth at valleys is lower than that in homogeneous membranes (PT-4 and PT-5). This result shows the enhanced compression resistance because of microphase separation, which increases the distribution of rigid groups at the valleys.

Gas separation performance of heterogeneous membranes

The heterogeneous membrane demonstrated gas separation performance under operating pressure. In Fig. 4a, at a pressure of 1.0 MPa, the CO2 permeance increases from 2350 GPU to 2967 GPU from the PT-1 to PT-3 membranes and then rapidly decreases to 706 GPU (PT-5 membrane). However, the CO2/N2 selectivity decreases slowly and then rapidly from the PT-1 to the PT-3 to the PT-5 membranes. The PT-3 membrane exhibited the highest CO2 permeance and acceptable CO2/N2 selectivity. The gas separation performance of the mPSf membrane is almost independent of pressure, indicating that pressure has no effect on the performance of PT membranes (Supplementary Fig. 26). The CO2/N2 separation performance with pressure is shown in Supplementary Figs. 27 and 28, and the CO2 and N2 permeance tested with pure gas is shown in Supplementary Fig. 35. Both the CO2 permeance and CO2/N2 selectivity of the PT-1, PT-2 and PT-3 membranes decrease slightly at low pressure and remain constant at operation pressure, but those of the PT-4 and PT-5 membranes decrease rapidly. According to the pressure cycle measurements in Supplementary Fig. 29, the heterogeneous membrane shows the same performance during increased and decreased pressures. On the basis of the pressure stability tests in Supplementary Fig. 30, the membrane performance is unchanged under the same pressure within a certain time. The PT-3 membrane treated at 120 °C for 4 h to simulate the real temperature of the flue gases in Supplementary Fig. 31 shows the same performance as that at room temperature, whereas the performance of the PT-5 membrane greatly decreases. The stretch tests also revealed the performance stability of heterogeneous membranes at different tensile rates (Fig. 4b and Supplementary Fig. 32). Fig. 4c and Supplementary Table 4 compare the heterogeneous membranes in this study with other state-of-the-art membranes under 1.0 MPa reported in the literatures that demonstrate great advantages in terms of gas separation performance. Moreover, the PT-1, PT-2 and PT-3 membranes also exhibited CO2/CH4 and CH4/N2 separation abilities within 3.0 MPa (Supplementary Fig. 33). The CH4/N2 separation ability is attributed to a high CH4/N2 solubility selectivity, which was obtained through deconvoluting the CH4 and N2 permeability into solubility and diffusivity coefficients on the basis of the solution‒diffusion model (Supplementary Fig. 34, Table 2, Table 3). Meanwhile, within operation pressure (from 1.0 to 3.0 MPa), the crumpled structure still cannot be squeezed onto the mPSf membrane (Supplementary Fig.44d).

The rearrangement of functional groups at the peaks and valleys endows the crumpled membrane with independent and cooperative dual-function regions. These regions can improve the membrane performance through increased gas diffusion and increased pressure resistance. Gold nanoparticle retention tests (Supplementary Fig. 36) were conducted to provide visual evidence of the diffusion difference in the heterogeneous structure (Supplementary Figs. 37 to 39). We fabricated a homogeneous crumpled membrane (Supplementary Fig. 8f to 8f3) with a common L-L IP reaction to compare the gas transfer behaviour with that of a heterogeneous crumpled membrane at 1.0 MPa, and the results are shown in Fig. 4d and Fig. 4e. In this process, gases can pass through the membrane, whereas the gold nanoparticles remain on the surface. Moreover, the gold nanoparticles, which have the same charge as the PT membranes in Supplementary Table 5, cannot be adsorbed on the membrane surface. Hence, the retention of gold nanoparticles was used to judge the gas transfer rate. In Fig. 4e, the coverages of the gold nanoparticles at both the peaks and valleys of the heterogeneous membranes are greater than those of the homogeneous membranes within a fixed time, which demonstrates that the heterogeneous structure is critical for improving gas transfer. In this structure, more amide groups accumulate at the peaks, remarkably increasing the CO2 solubility and constructing rapid gas transfer channels, whereas the phenyl groups in valleys maintain a high free volume due to steric hindrance effects. This is beneficial for improving the gas diffusion ability, especially under operating pressure. The largest coverage rate of gold nanoparticles in the PT-3 membrane explains the highest CO2 permeance shown in Fig. 4a. The rapid decrease in the CO2/N2 selectivity of the PT-4 and PT-5 membranes is mainly attributed to the facilitated transport mechanism25-27.

Two-dimensional (2D) resistance models28 and COMSOL Multiphysics simulations were introduced to better understand the gas transport behaviour in heterogeneous structures. In the resistance model shown in the Supplementary Information, the relationship describing gas permeation through a polymer membrane via Fick’s law is mathematically equivalent to Ohm’s law, which describes current flow through a resistor. Hence, the gas permeation rate is inversely proportional to the gas transport resistance. In Supplementary Fig. 40, the resistances of the heterogeneous crumpled membrane (R1), homogeneous crumpled membrane (R2) and homogeneous smooth membrane (R3) were calculated as R=1/BiA (R, B and A represent the gas transport resistance, gas permeance and surface area, respectively), and the results are shown in Supplementary Table 6. The results show that with increasing operation pressure, the gas transport resistance of the homogeneous structure increases rapidly, whereas that of the heterogeneous structure increases slowly. The series resistance model29 was also introduced to analyze the heterogeneous crumpled structure compared with the counterparts. From Supplementary Fig. 41 and Table 7, the result shows that CO2 permeance of selective layer is obviously higher than corresponding composite membranes, which indicates the total resistance of the composite membrane is mainly decided by the selective layer. Meanwhile, the CO2 permeance of heterogeneous polyamide layers is remarkably higher than the homogeneous counterparts, indicating the heterogeneous structure endows polyamide with enhanced gas permeation ability. Moreover, the mPSf membrane, which has a low resistance compared with other membranes with PA layers, has almost no effect on the overall resistance. We also Numerical simulations of the gas diffusion rate on the membrane permeate side using COMSOL Multiphysics were conducted to analyse this process, and the calculation method is described in the Supplementary Information and Supplementary Fig. 42. In Fig. 4f, the gas diffusion rate through the peaks is significantly higher than that through the valleys. Similar to the results in Fig. 4e, the PT-3 membrane also has the highest gas diffusion rate, which is also attributed to the low crosslinking density compared with those of the PT-1 and PT-2 membranes (Supplementary Table 1). Furthermore, the heterogeneous structure can effectively avoid the production of stress concentration points between peaks and valleys (Supplementary Fig. 43), which is vital for decreasing the number of membrane defects, especially under consecutive stress effects.

To analyse the economic advantages of heterogeneous membranes for CO2 capture, a typical two-stage membrane process was simulated on the basis of the assumptions of our previous study30. The detailed calculation process and a comparison of all the membranes are shown in Supplementary Fig. 45 and Table 8. The CO2 capture energy consumption (Supplementary Fig. 45a) decreases with pressure and then increases, as explained in our previous report31. As shown in Supplementary Fig. 45b, the membrane area requirements decrease with pressure due to the increased driving force. Overall, the CO2 capture cost decreases with pressure (Supplementary Fig. 45c). The PT-3 membrane has a minimum CO2 capture cost of $26.2 per tonne of CO2 at 0.8 MPa, which shows good potential for CO2 capture.

Methods
Preparation of the mPSf membrane

Polydimethylsiloxane (PDMS, 0.25 g, 0.5 wt.%), dibutyltin dilaurate (DBD, 0.2 g, 0.4%) and tetraethyl orthosilicate (TEOS, 0.2 g, 0.4 wt.%) were dissolved in n-heptane and stirred at 35 °C for 30 min under humidified conditions, thus obtaining PDMS prepolymer solution. PDMS, DBD and TEOS were used as monomers, catalysts and crosslinking agents, respectively, in the crosslinking reaction. The PSf ultrafiltration support was immersed in sodium dodecyl sulphate (SDS, 0.5 wt%) solution to remove organic solvent retained in the membrane pores, followed by drying at 60 °C for 10 h. The treated PSf membrane was coated with a PDMS solution, with a preset wet coating thickness (the gap between the PSf support and coating knife) of 200 μm (gap accuracy ± 5 μm), whereas the thickness of the PDMS layer in the mPSf membrane was approximately 100 nm. The casting membranes were dried at 30 °C and 40% RH in an artificial climate chamber (Climacell 222R, Germany) for at least two hours. The treated PSf support was denoted as the modified PSf (mPSf) membrane.

Fabrication of heterogeneous crumpled membranes

The membrane was fabricated using a microzone interfacial polymerization (IP) process. The aqueous phase solution was fabricated with 0.1-0.3 wt% PIP and 0.1 wt% Na2CO3, and 0.1 wt% TMC dissolved in hexane was used as the organic phase solution. The amide groups formed using the IP reaction constitute the repeating units in the polymer segments of the crumpled membrane. The prepared solutions were sealed and stored in a water bath at 25 °C for 30 min to avoid solvent evaporation. First, the mPSf membrane, which was clamped between two Teflon frames, was immersed in 30 mL of TMC solution for 3 min. Then, the excess solution was removed. Then, the membrane was incubated for 30 s, 60 s, 120 s, 200 s and 240 s as the residence time. Then, the treated mPSf membrane was immediately soaked in 50 mL of PIP solution for 15 min. Subsequently, the resulting membrane was washed thoroughly with deionized water and dried at 30 °C and 40% RH for 12 h. The obtained heterogeneous membrane with a crumpled morphology was attached to the mPSf membrane, forming a selective layer of the membrane. The membranes fabricated with different residence times of 30 s, 60 s, 120 s, 200 s and 240 s were named the PT-1, PT-2, PT-3, PT-4 and PT-5 membranes, respectively. Among them, the PT-1, PT-2 and PT-3 membranes have heterogeneous structures with crumpled morphologies, whereas the PT-4 and PT-5 membranes are homogeneous with smooth morphologies.

Fabrication of homogeneous crumpled membranes

The membrane was fabricated via a common liquid‒liquid interfacial polymerization process. The aqueous phase solution was fabricated with 0.1 wt% PIP and 0.1 wt% Na2CO3 (A solution), and 0.1 wt% TMC dissolved in hexane (B solution) was used as the organic phase solution. The prepared solutions were sealed and stored in a water bath at 25 °C for 30 min to avoid solvent evaporation. First, 50 mL of A solution was poured into the beaker, and then 50 mL of B solution was slowly added and left for 15 min. A polyamide film was formed at the interface of the two phases, after which it was extracted with a substrate. The obtained homogeneous crumpled membrane, attached to a mPSf membrane, was used to compare the mixed-gas separation performance with heterogeneous counterpart. While, the resultant homogeneous crumpled membrane, attached to a PSf support, was used to compare the pure-gas selectivity with heterogeneous counterpart to judge the gas transfer mechanism. The resulting membrane was washed thoroughly with deionized water and dried at 30 °C and 40% RH for 12 h.

Characterizations of the membranes

The morphology of the membranes was characterized using scanning electron microscopy (SEM, nano-SEM 430, FEI, USA) and atomic force microscopy (AFM, Bruker, Dimension IconXR, Germany). AFM was also used to characterize the membrane surface morphology and obtain information, including indentation, crumpled height and crumpled distance. AFM-IR (Bruker, Anasys nanoIR3s, Germany) nanoinfrared spectroscopy was used to perform microzone chemical analysis to characterize the microphase separation of the functional groups. Fourier transform infrared (FTIR) spectroscopy of the membranes in the wavenumber range of 400 cm−1 to 4000 cm−1 was performed using an FTS-6000 instrument (Bio-Rad, USA). X-ray photoelectron spectroscopy (XPS, ESCALAB 250Xi, Thermo Fischer, USA) was used to characterize the element composition and degree of crosslinking of the crumpled membrane with Al Kα radiation. X-ray diffraction (XRD) analysis (2θ=10° to 50°) was performed at room temperature with a Bruker-AXS D8 diffractometer with a Cu Kα (λ=1.54 Å) radiation detector. Raman spectroscopy (Renishaw, inVia Qontor, Britain) was used to analyse the TMC distribution in the swollen PDMS layer and the C=O, C=C, C-H and C-N groups in the membrane. A Raman scanning model, which is based on different functional groups, was used to demonstrate the formation process of peaks and valleys in the crumpled structure. Gold nanoparticle retention tests were conducted to provide visual evidence of the difference in gas diffusion between the peaks and valleys of the heterogeneous structure, and the detailed testing process is described in the Supplementary Information. N2 adsorption-desorption isotherms of the swelling PDMS layer were performed on BSD-660M (Beishide Instrument, China) at 77 K, and the pore size distribution of the PDMS layer was calculated based on the Barrett-Joyner-Halenda (BJH) model. The swelling PDMS layer was peeled off the mPSf membrane by immersing into N, N-dimethylformamide (DMF) to eliminate the influence of PSf substrate on the analysis of pore size. Subsequently, the PDMS layer was rinsed with ethanol and vacuum degassed at 25 ℃ for 10 h to remove the residual solvent before testing.

Mechanical property measurement

The membrane was cut into a square of 1 cm × 1 cm, and the effect of vertical force was tested by atomic force microscopy (AFM, Bruker, Dimension IconXR, Germany). The effect of horizontal stretch tension was tested using a mechanical test module in an AES-4SD flexible electronic device comprehensive test platform with different stretch rates. The mechanical properties, including the Young’s modulus, were gauged using peak force quantitative nanomechanical mapping (PF-QNM) imaging via AFM. The RTESPA-525-30 was used as the AFM tip to conduct the PF-QNM experiment, which is composed of 0.01-0.025 Ωcm Antimony (n)-doped Si with an aluminium reflective coating on the backside of the cantilever. The tip and cantilever parameters are presented below. The tip parameters included a tip height of 10-15 μm and an end curvature radius of 30 nm; the cantilever parameters included a cantilever thickness of 5.75 μm, a cantilever length of 125 μm, a cantilever width of 40 μm, a cantilever frequency of 525 kHz, and a spring constant of 200 N/m. The selected tip with a large spring constant of 200 N/m has a hardness property that is beneficial for rapid scanning. Moreover, the cantilever is difficult to deform and can truly reflect the indentation depth. A selected tip with a high resonance frequency of 525 kHz quickly reaches the equilibrium state. Thus, for the crumpled structure with a large undulation, the morphology can be rapidly detected. This is consistent with the SEM results, indicating that the crumpled structure is close to the PSf support. A selected tip with a curvature radius of 30 nm can avoid damage to the ultrathin sample surface caused by the contact between the tip side and the sample. In this work, the applied force on the membrane surface via AFM tips converted to the gas pressure is large enough to squeeze the peaks tightly on the mPSf surface, and the testing process was shown in Supplementary Fig.44. Hence, the tested Young's modulus of the peak, similar to the valley, was also obtained via pressing the peaks tightly on the mPSf support, which can eliminate the influence of morphology on the test results. Before and after performing each test, the deflection sensitivity calibration was performed on a sapphire sample that was assumed to have a less than 5% error. Meanwhile, the tip radius was calibrated using a standard highly oriented pyrolytic graphite film (18 GPa). This calibrated tip radius (35 ± 3 nm), which accounts for tip blunting, was used for all subsequent contact area calculation and modulus extractions from our samples.

Gas permselectivity test

The gas permselectivity of the membranes was tested with custom-made testing equipment27. The feed gas passed through a humidifier at 35 °C and a dehumidifier at ambient temperature successively so that the feed gas was saturated with water vapour before it entered the test unit. Thus, in this study, the humidified conditions were 100% relative humidity. The structure of the membrane cell is shown in Supplementary Fig. 24. The detailed gas permeance (R) is expressed in units of GPU, and the CO2/N2 (CH4) selectivity equals the CO2 permeance divided by the N2 (CH4) permeance.

The permeance is calculated via Eq. (1) as follows:

R = Qi / (A⋅ΔPi) (1)

where Q represents the permeate flow rate through the membrane, A is the effective membrane area, and ΔP is the partial pressure difference between the upstream and downstream sides of the membrane. A was calculated using the following two methods because of the crumpled morphology with different membrane surfaces. One is the real area obtained from the AFM results in Supplementary Fig. 25, and the other is the fixed area of the membrane cell. In the main text, all the performances were calculated with real areas.

The single-gas permeabilities P (Barrer) of the crumpled membranes were evaluated using a Labthink VAC-V2(EX) apparatus based on the constant volume/variable-pressure method. In this work, we utilized the stacked PA layers, with a thickness of about 50 μm to perform the time-lag measurements, which can effectively eliminate the impact of porous support. The PA layer was delaminated from the composite membrane by immersing it in n-hexane to remove the mPSf support, which will not damage the PA layer. The peeled PA layer with a surface area of 30 cm2 should be carefully transferred with a glass plate, then this process was repeated to accumulate more PA layers. The stacked PA layers were treated at 120 ℃ in a vacuum and then compressed at 3.0 MPa before testing to remove the residual solvent. To reduce the workload, after collecting some PA layers, we folded them several times to increase the effective thickness. The measurement was carried out on circular membrane samples fabricated by masking with adhesive aluminium foil with an effective exposed area of 3.14 cm2. The diffusivity coefficient D (cm2 s−1) was calculated using the time lag method as expressed in Eq. (2):

D = l^2 / (6θ) (2)

where l is the membrane thickness and θ is the time lag of the permeability measurement.

The solubility coefficient S (cm3 (STP) cm−3 cmHg−1) was calculated from the ratio of the gas permeability coefficient to the diffusivity coefficient using Eq. (3) as follows:

S = P / D (3)

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "Comments on the manuscript NCOMMS-25-15480\nThis manuscript presents an experimental study on the preparation and characterization of membranes, focuses on the\ndevelopment of advanced polymer membranes for gas separation aiming to simultaneously enhance separation\nperformance and structural robustness. The authors introduce a novel “micro-zone interfacial polymerization” technique to\nreconstruct the polymer network, yielding a “heterogeneous, crumpled morphology”. This structure exhibits microphase\nseparation, where the “peak regions”, enriched with amide groups, function as fast CO₂ transport channels and, on the other\nhand, the “valley regions”, containing more rigid phenyl groups, contribute to improved CO₂ diffusion and pressure-induced\ncompaction resistance. The cooperative effect of these dual-function zones significantly enhances mechanical resilience\nand gas separation efficiency.\nThe topic is interesting but the manuscript presents a series of weaknesses and some aspects that should be clarified.\nAmong them are following:\n1) Please consider having a professional English editor review the document before final submission.\n2) Throughout the manuscript, the authors discuss the application of their membranes for high-pressure gas separation.\nHowever, most of the experiments are performed at 1.0 MPa, which can hardly be considered high pressure in the field of\ngas separation. High pressures could be in the range of 80-150 bar, so the manuscript could mislead.\n3) The abstract in its current format seems too long (lines 10 to 61). Perhaps this text could be divided into an abstract with\nthe main ideas and another section serving as an introduction.\n4) The meaning of some expressions is not entirely clear. What do the authors mean by \"structural ability\" (line 40)? What do\nthe authors mean by \"gas diffusion ability\" (line 45)? The same goes for \"dense micropores\" (line 67).\n5) Lines 330-332, the authors write: “The treated PSf membrane was coated with PDMS solution, using a pre-set wet coating\nthickness (the gap between the support and coating knife) of 200 μm”. Does this mean that the mPSf membrane has a dense\nPDMS layer of around 200 μm?\n6) The role of each of the materials used in the preparation of the membranes (PDMS, TEOS, DBD, TMC, PIP) should be\nmore clearly identified, whether in the structure of the membrane or in its functionalization.\n7) Some abbreviations are used in the main body of the manuscript and are only defined in the supplementary material (e.g.,\nPIP).\n8) Regarding gas permselectivity tests: The manuscript should explain why the feed gas mixture must have 100% relative\nhumidity. How much water permeates through the membrane? Working with moisture-saturated gas streams can be\nproblematic in industrial operations.\n9) The format of references should be carefully reviewed. For example, the authors' names in references 1 and 3.\n10) Supplementary information (page 18), Figures S20 (a) and (b). Can the decrease in CO2 permeance with pressure be\nattributed to a facilitated transport mechanism?\n11) Supplementary information (page 34). The assumed price for the membrane module ($50/m2) is very low. There are\nmany reliable references that show much higher prices. For example, Baker (IEChR 47, 2008, 2109) and Lin et al (JMS 493\n(2015) 794) report that “The membrane skid has an estimated installed cost of $500/m2 membrane area, which includes\nmembrane modules, module housings, valves, instrumentation, piping and frame structures”. Therefore, I suggest that the\ncosts be recalculated using a more realistic value for the membrane cost.", "reviewer_2": "Wang et al. reported an interfacial polymerization strategy to create a heterogeneous crumpled polymer membrane with\nmicrophase separation. The authors claimed that the dual-functional regions enhanced the CO2 transport and structural\nrobustness. Overall, this paper is interesting but the quality of current version is far from satisfactory. More solid evidence is\nneed to clarify whether the heterogeneity is on the surface or in the bulk film. The formation mechanism of such wrinkled\nstructure with heterogeneous composition also requires further investigation. In addition, the following issues should be\nproperly addressed after major revision.\nDirect evidence from compositional characterization is needed to support the claim that “the heterogeneous structure with a\ndiscovered microphase separation”. AFM-IR may only reveal the surface composition rather than the bulk composition of the\nfilm. Rearrangement of functional groups towards the surface or a complete contrast of bulk composition in the microscale\nregions needs to be clarified. ToF-SIMS depth profiling maybe helpful for such analysis.\nThe schematic in Fig S1 is misleading. I don’t think there are such micro-trench structures formed in the PDMS in the first\nstep of TMC soaking and evaporation. More evidence is needed to show if there are such “micro-zones” in the PDMS, if the\nauthors would like to define the IP synthesis in this way. Fig. S4 suggest that the pore structures are connected rather than\nindividual channels, which contradicts to the schematic in Fig S1. The resolution of Fig S4 is also very low. Cross-sectional\nTEM with high-resolution EDX mapping could provide more detailed information about TMC distribution in PDMS, which is\ncritical for understanding this IP synthesis.\nIn Fig. 1, why does the weight of PDMS decrease with increased residence time of swelling PDMS layer? Shouldn’t there be\nmore TMC loaded into the polymer matrix with longer soaking time?\nThe crumpled morphology observed in PT-1, PT-2, and PT-3 closely resembles Turing patterns, and previous studies have\nreported Turing structures in polyimide membranes (Science, 360, 518-521 (2018)). Can the authors clarify whether the\nformation of such crumpled morphology in PT-1, PT-2, and PT-3 can be explained by the reaction-diffusion theory?\nThe authors stated that “Young’s modulus at peaks from PT-1 to PT-3 membranes are lower than that at valleys.” Could this\nbe attributed to the proximity of the valleys to the substrate and the overall thin nature of the membrane, leading to a\nsignificant substrate effect? How do the authors account for and minimize such substrate-induced artifacts in modulus\nmeasurement? The indentation depth of less than 10 nm for the valley in Fig. 3h is also problematic as surface effect may\nbecome dominant.\nFig. 3b and Fig. S15: Conducting tensile tests on membranes with a supporting substrate may not accurately reflect the\nmechanical properties of the crumpled film. Stress–strain curves are needed to better interpret the mechanical properties.\nThe authors stated that “The largest coverage rate of gold nanoparticles in the PT-3 membrane explains the highest CO2\npermeance in Fig.4a.” So do PT-1 to PT-3 exhibit higher surface area than PT-4 to PT-5? Could the authors quantify this\ndifference in surface area and examine whether the magnitude of increase correlates with the observed enhancement in gas\npermeance? A direct comparison would provide better insight into the structure-property relationship.\nThe schematic in Scheme S1 indicates that both humidifier and dehumidifier are placed before the test cell. However, if the\ngoal is to measure CO2/N2 separation under 100% relative humidity conditions, why is the dehumidifier positioned before\nthe test cell rather than before gas chromatography (GC) to protect it? Additionally, “Sweep” in Scheme S2 was mistakenly\nwritten as “Sweap”.\nWhile Figure S24 presents the trend in CO2 permeance, the corresponding variation in CO2/N2 selectivity is not explicitly\ndiscussed. Could the authors provide the data and analyze whether selectivity follows a similar or distinct trend?\nFigure S25 shows a decrease in both CO2 permeance and selectivity between 0.1-1MPa, followed by an increase in\npermeance and a decrease in selectivity beyond 1.0 MPa. Could the authors elaborate on the underlying mechanisms\nresponsible for this observation?", "reviewer_3": "This manuscript describes the preparation, characterization and separation performance of polyamide membranes made by\ncontrolled interfacial polymerization between a swollen PDMS film with acyl chloride in contact with an aqueous diamine\nsolution. This procedure yields highly permeable and selective membranes with a wrinkled surface morphology. The\nseparation performance is discussed in correlation with the membrane morphology and microstructure. The results are\nsupported by a range of different morphological, compositional and mechanical studies, as well as computational methods.\nThe gas separation performance is excellent, above the state of the art, with high permeance and high selectivity.\nOverall the work is done well and the results are convincing and occasionally exceed the state of the art. Nevertheless, not\nall results and points in the discussion are completely clear.\nThese points need to be improved before it may become suitable for publication. Some specific remarks that require a\nrevision of the manuscript are given below:\nThe relatively high permeance of the membranes can at least in part be ascribed to the roughness of the surface, and thus to\nthe effective increase in the surface area. A similar approach has already been applied by the group of Matthias Wessling to\nenhance mass transport in hollow fibres (e.g. https://doi.org/10.1016/j.memsci.2005.02.022,\nhttps://doi.org/10.1016/j.memsci.2009.10.003). This must be discussed in the state of the art.\nEvident errors:\nCO2 permeance (ca. 2000 for PT1, Fig S25A) and CH4 permeance (ca. 1200 for PT-1, Fig S25C) does not lead to a\nCO2/CH4 selectivity of almost 10 but to less than 2! Apparently there is an evident error in some of the measurements or\ncalculations, which should be checked and where necessary corrected throughout the manuscript.\nSpecific points:\nThe manuscript claims to have produced a micro-phase separated membrane with the peaks composed of more amide\ngroups and the valleys with more phenyl groups (line 57-58). Since the amide groups are covalently bonded to the phenyl\ngroups of TMC, this statement must be further explained. The only way to change the ratio of amide groups and phenyl\ngroups is by a different cross-link density or by the formation of free carboxylic acid groups instead of amide groups from the\nreaction of the corresponding acyl chloride with water instead of amine. In this sense, the cross-link density is likely more\nimportant than the composition as such. Also, the confinement of the PDMS is fundamental for the transport properties and\nshould be discussed more accurately. Does the interfacial polymerization also penetrate within the PDMS layer? PDMS\nitself has a CO2/N2 selectivity equal to ca. 11-12 (-). The very strong positive deviation from this value indicates that the\nPDMS is no longer the main resistance in the film.\nFigure S1 is not completely clear and should also show the PSF support. Besides the top surface images, also the cross\nsections of the membranes should be shown, indicating clearly the thickness of each active layer. In this light, the sampling\ndepth of IR is typically a few micrometers. Therefore, the analysis shows not only the active layer but also the support and/or\nthe top-layer, which may lead to erroneous conclusions related to presumed microphase separation. Please discuss in more\ndetail.\nFigure S25 (SI line 340) shows unlikely high selectivity CH4/N2. Since CH4 is larger than N2, diffusion selectivity is strongly\nin favour of N2 (e.g. Teplyakov and Meares, doi: 10.1016/0950-4214(90)80030-O), and the selectivity must apparently be\nbased on solubility selectivity. Is there any evidence for this? Please discuss.\nFig S30 caption “…is based on the difference of Young's modulus between the peaks and valleys”: Is there indeed any proof\nfor the differences in modulus? How can the authors exclude that indentation of the peaks is easier because of empty space\nbelow the peaks, whereas the valleys rest on the support and need to be compressed rather than just bent? Please discuss\nthe mechanical properties also in terms of morphology and not only in terms of microstructure.\nFig. S24: The increase in permeance is ascribed to the appearance of defects in samples PT-4 and PT-5. However, both\nsamples have a lower permeance than the samples PT-1, 2 and 3. Defects would first of all increase the permeance of the\nslowest species.\nThe authors should specify in the experimental part what kind of tip is used for the AFM analysis and what this means for the\nanalysis of the results.\nEspecially in non-homogeneous microphase separated polymers, the tip size, type and cantilever properties are crucial for\nthe result that should be expected and should therefore be mentioned (see for instance M. Longo, et al., Polymer, 156 (2018)\n22–29. doi:10.1016/j.polymer.2018.09.043.\nIn this light, the conclusion in line 189-191 that Young’s modulus in the peaks is lower than that in the valleys may not be\ncorrect. The deformation measured in the peaks reflect both the indentation and the deformation of the entire thin film,\nwhereas the deformation in the valleys reflects only the indentation.\nGold nanoparticles are dispersed in the feed and the deposition on the surface is discussed as presumed evidence of the\nhigh low rate of the gas across the membrane. However, the dimensions of the nanoparticles are said to be 5 nm, whereas\nthe smallest scale bar in Fig S27 is 200 nm. Thus, the particles are not visible at this scale. Figure d1-1 and d2-1 show an\nirregular morphology with small depressions between thin ‘walls’. The changes seen from figure d1 to d1-1 and d2 to d2-1\nare a different surface morphology with features up to 50 nm and do not represent the 5 nm nanoparticles.\nFurthermore, what is the linear perpendicular flow velocity of the gas on the membrane? Is this sufficient to overcome gravity\nand act as the main driving force for particle transport, rather than gravity or electrostatic interactions?\nOverall, the proof of the gas flow profile through the membrane, with preference for the higher areas, seems insufficient on\nthe one hand, but perhaps not particularly relevant on the other hand. Proof of the collocation of the particles on the tops and\nnot on the valleys of the crumpled membrane surface requires the demonstration of the cross-sectional image of the\nmembrane, appropriately made by embedding the surface in a resin (without moving the nanoparticles) and subsequent\nTEM analysis of s thin slice of this sample.\nThe transport model in Figure S28 does not have a strong scientific basis. The origin of the coefficients 2 and 3 is unclear\nand should be justified quantitatively. Instead, it makes more sense to express the transport in terms of ‘true’ effective surface\narea and effective membrane thickness (of the effective dense skin). The role of the individual components (PDMS and\npolyamide) should also be discussed in terms of more common models such as mixed matrix or resistances in series.\nLine 246-247: please explain what is meant with “The cooperative effects of functional groups rearrangement at peaks and\nvalleys, explain the heterogeneous membranes with excellent gas separation performance”.\nCommercial membranes for gas separation are normally produced by a continuous process and are often formed by hollow\nfibres as well as flat sheet membranes. A brief discussion on the feasibility of continuous production and the possible use of\nhollow fibre configuration should be added.\nMinor issues:\nFig. S7: the text in the IR spectra is too small to identify the peaks.\nEnglish language needs radical improvement.\nThe article is sometimes difficult to follow because of repetitions and not always logical order of the data and the discussion.\nOverall conclusion:\nThe manuscript may be suitable for publication, but the obvious mistakes must be corrected and all weaknesses should be\nimproved or properly justified. This will require a major revision of the present manuscript."}, "author_response": "General reply: We thank the reviewer for noting the novelty and the significance of our\nwork. We also appreciate the reviewer’s suggestions and comments to help improve the\nquality of our manuscript.\n1. Please consider having a professional English editor review the document before\nfinal submission.\nReply: The language has been polished by a professional English editing policy.\n2. Throughout the manuscript, the authors discuss the application of their membranes\nfor high-pressure gas separation. However, most of the experiments are performed at\n1.0 MPa, which can hardly be considered high pressure in the field of gas separation.\nHigh pressures could be in the range of 80-150 bar, so the manuscript could mislead.\nReply: Agree. We have modified “high-pressure gas separation” as “gas separation\nunder operation pressure”. We tested the separation performance of CO /N performed\n2 2\nwithin 1.0 MPa to simulate the flue gas. Meanwhile, we tested the separation\nperformance of CO /CH and CH /N within 3.0 MPa to simulate the natural gas and\n2 4 4 2\nshale gas.\n3. The abstract in its current format seems too long (lines 10 to 61). Perhaps this text\ncould be divided into an abstract with the main ideas and another section serving as an\nintroduction.\nReply: We are very sorry for this misunderstanding caused by the missing blank\nbetween Abstract and Introduction. In the revised manuscript, we have added a blank\nbetween Abstract (lines 10-28) and Introduction (lines 30-64).\n4. The meaning of some expressions is not entirely clear. What do the authors mean by\n\"structural ability\" (line 40)? What do the authors mean by \"gas diffusion ability\" (line\n45)? The same goes for \"dense micropores\" (line 67).\nReply: Agree. In line 42, we have modified “enhance the structural ability” as\n“suppress the movement of polymer segment”; In line 47, we have modified “gas\ndiffusion ability” as “inhibit the transfer of gas molecules”; In line 71, we have modified\n“dense micropores” as “swollen micropores”.\n5. Lines 330-332, the authors write: “The treated PSf membrane was coated with PDMS\nsolution, using a pre-set wet coating thickness (the gap between the support and coating\nknife) of 200 μm”. Does this mean that the mPSf membrane has a dense PDMS layer\nof around 200 μm?\nReply: We’re sorry for the misunderstanding caused by unclear description in the\nMethods. The real thickness of the dense PDMS layer is about 100 nm, shown in\nSupplementary Fig. 19. The mPSf membrane was fabricated by coating PDMS solution\nonto the PSf support via a homemade blade coating machine with the gap setting\nbetween the blade and the PSf support of 200 μm. Hence, the wet coating thickness of\n200 μm means the thickness of the PDMS solution. The modifications are shown in the\nMethods (line 367-369) in the main text, Supplementary Fig. 19 in revised\nSupplementary Information.\n6. The role of each of the materials used in the preparation of the membranes (PDMS,\nTEOS, DBD, TMC, PIP) should be more clearly identified, whether in the structure of\nthe membrane or in its functionalization.\nReply: Polydimethylsiloxane (PDMS), dibutyltin dilaurate (DBD) and tetraethyl\northosilicate (TEOS) were deemed as the monomer, catalyst and crosslinking agent to\nparticipate the crosslinking reaction to construct the PDMS layer on the polysulfone\n(PSf) support. The crosslinking PDMS network is dedicated to forming the reaction\nsites (micropores) to construct the heterogeneous membrane structure in the micro-zone\ninterfacial polymerization (IP) process.\n1,3,5-benzenetricarboxylic acid chloride (TMC) and piperazine (PIP) were used as the\norganic and aqueous monomers to participate the interfacial polymerization (IP)\nreaction. The formed amide groups constitute the repeating units in the polymer\nsegments of crumpled membrane. We have added above information on line 360-364\nand 377-378 in revised main text with yellow highlight.\n7. Some abbreviations are used in the main body of the manuscript and are only defined\nin the supplementary material (e.g., PIP).\nReply: All the abbreviations used in the main body of the manuscript were marked with\ntheir full names at the first appearance. The modifications are shown in line 88, 95, 114\nin revised main text with yellow highlight.\n8.1 Regarding gas permselectivity tests: The manuscript should explain why the feed\ngas mixture must have 100% relative humidity. Working with moisture-saturated gas\nstreams can be problematic in industrial operations.\nReply: The feed gas with a 100 %RH in this work is to simulate the real flue gases,\nwhich usually contains a certain amount of water vapor. Meanwhile, the temperature of\nflue gases is obviously lower than that of coal combustion, causing the gas streams with\na 100 %RH.\n8.2 How much water permeates through the membrane?\nReply: The water content in the permeate side of the membrane was calculated by the\nfollowing equations. And the result shows that the water content is 23.25 g/Nm3.\n𝑅𝐻\n𝑃 = ×𝑃\n𝐻2𝑂 100 𝑠𝑎𝑡\n𝑃 𝑀\n𝑤𝑎𝑡𝑒𝑟 𝑐𝑜𝑛𝑡𝑒𝑛𝑡 (𝑔/𝑁𝑚3) = 𝐻2𝑂 × 𝐻2𝑂 ×𝜌\n𝑃 −𝑃 𝑀 𝑑𝑟𝑦\n𝑡𝑜𝑡𝑎𝑙 𝐻2𝑂 𝑑𝑟𝑦\n𝑃 ×𝑀\n𝑠𝑡𝑑 𝑑𝑟𝑦\n𝑃 =\n𝑑𝑟𝑦 𝑅 ×𝑇\n𝑠𝑡𝑑\nwhere P is the partial pressure of water vapor; P is the saturated water vapor\nH2O sat\npressure; M\nH2O\nis molar mass of water; M\ndry\nis the average molar mass of dry gas; ρ\nis the density of dry gas. P is the standard pressure and T is the standard\ndry std std\ntemperature.\n9. The format of references should be carefully reviewed. For example, the authors'\nnames in references 1 and 3.\nReply: We have corrected the wrong formats and carefully checked other references.\nThe modifications are shown in References in revised main text with yellow highlight.\n10. Supplementary Information (page 18), Figures S20 (a) and (b). Can the decrease in\nCO permeance with pressure be attributed to a facilitated transport mechanism?\n2\nrather than facilitated transport mechanism. If the facilitated transport mechanism is\nfollowed, the gas permeance decreases with pressure rapidly then kept constant, which\nwas discussed in our previous work (Chem. Eng. J, 2013, 225, 744). However, in\nSupplementary Fig. 27 (original Supplementary Fig. 20), the CO permeance slightly\n2\ndecreased at the initial pressure then kept constant. This phenomenon also demonstrates\nthe heterogeneous structure in the polymer membrane can effectively enhance the gas\npermeation under high pressure.\n11. Supplementary Information (page 34). The assumed price for the membrane module\n($50/m2) is very low. There are many reliable references that show much higher prices.\nFor example, Baker (IEChR 47, 2008, 2109) and Lin et al (JMS 493 (2015) 794) report\nthat “The membrane skid has an estimated installed cost of $500/m2 membrane area,\nwhich includes membrane modules, module housings, valves, instrumentation, piping\nand frame structures”. Therefore, I suggest that the costs be recalculated using a more\nrealistic value for the membrane cost.\nReply: The assumed price for the membrane module ($50/m2) is reasonable in this\nwork. Baker’s and Lin’s works aimed at treating natural gas and syngas respectively,\nwhich are in a high-pressure environment (> 30 bar). High skid costs arise from many\npressure vessels, pipes, flanges, and valves.\nThe economic analysis in this work was aimed at treating flue gases (within 10 bar).\nHence, the plastic membrane shells can meet the separation requirements and greatly\nreduce the costs. While, the membrane skid cost (about 50 $/m2) used in flue gases was\nalso reported in previous works (J Membrane Sci. 2019, 581, 195; Ind. Eng. Chem. Res.\n2018, 57, 15963).\nReviewer #2:\nWang et al. reported an interfacial polymerization strategy to create a heterogeneous\ncrumpled polymer membrane with microphase separation. The authors claimed that the\ndual-functional regions enhanced the CO transport and structural robustness. Overall,\n2\nthis paper is interesting but the quality of current version is far from satisfactory. More\nsolid evidence is need to clarify whether the heterogeneity is on the surface or in the\nbulk film. The formation mechanism of such wrinkled structure with heterogeneous\ncomposition also requires further investigation. In addition, the following issues should\nbe properly addressed after major revision.\nGeneral reply: We thank the reviewer for noting the novelty and the significance of our\nwork. We also appreciate the reviewer’s suggestions and comments to help improve the\nquality of our manuscript.\n1. Direct evidence from compositional characterization is needed to support the claim\nthat “the heterogeneous structure with a discovered microphase separation”. AFM-IR\nmay only reveal the surface composition rather than the bulk composition of the film.\nRearrangement of functional groups towards the surface or a complete contrast of bulk\ncomposition in the microscale regions needs to be clarified. ToF-SIMS depth profiling\nmaybe helpful for such analysis.\nReply: In this work, the thickness of crumpled layer is about 60 nm (Supplementary\nFig. 19). Hence, AFM-IR characterization, with a sampling depth of several\nmicrometers, can reveal the bulk composition of the crumpled layer rather than only\nsurface composition. The AFM-IR technology combines a high nanoscale resolution\nwith a high chemical sensitivity of infrared spectroscopy. The microscopic morphology\ninformation of the surface was obtained via AFM by touching the sample surface via\nthe probe, which cannot damage the samples. While, the infrared spectrum detects the\nthermal expansion signals of the samples and converts into the infrared absorption\nspectrum in the micro-area. This combination enables AFM-IR to identify and image\nthe chemical composition of materials at the nanoscale, which has been widely adopted\nand recognized for identifying subtle structural differences within the nanoscale\n(Nature, 2023, 620, 545-551; Nat. Mater. 2023, 22, 873-879; Nat. Commun. 2023, 14,\n3941). Hence, in this work, AFM-IR characterization can fully reflect the composition\ndifferences at peaks and valleys in the crumpled structure.\nThe strength of ToF-SIMS lies in its high accuracy and capability for atomic-layer\nthickness detection; however, its limitation is a low microstructure resolution. Although\ntheoretical resolution can reach as low as 100 nm provided from the instrument\nmanufacturer, recent reports demonstrate that the practical resolution remains at the\nmicrometer scale (Nature, 2024, 632, 528-535; Nature, 2024, 628, 299-305; Nat.\nEnergy 2023, 8, 934-945; Nat. Commun. 2024, 15, 7516). In my work, the maximum\ndistance between peak and valley in the crumpled structure is about 50 nm. We also\nconducted TOF-SIMs characterizations with different instruments (IONTOF, TOF.\nSIMS 5, Germany; ULVAC-PHI, PHI nanoTOF 3+, Japan), but it was difficult to\ndistinguish the peak and valley locations in the crumpled structures.\n2.1 The schematic in Fig S1 is misleading. I don’t think there are such micro-trench\nstructures formed in the PDMS in the first step of TMC soaking and evaporation. More\nevidence is needed to show if there are such “micro-zones” in the PDMS, if the authors\nwould like to define the IP synthesis in this way.\nReply: I’m sorry for this misunderstanding, but the micro-trench structures were\nformed in the soaking process in TMC solution, which was further detected by AFM\nmorphology and pore structure analyses. The ScanAsyst-Air* tip, with a small tip\nradius of 2 nm, was adopted to distinguish the surface morphology of the PDMS/PSf\n(mPSf) membrane. In Supplementary Fig. 4a and 4b, the Rq and Ra of PDMS/PSf\n(mPSf) membrane are all higher than those of mPSf membrane after soaking in TMC\nsolutions, indicating the increased roughness of the soaked PDMS layer in the mPSf\nmembrane. In Supplementary Fig. 4c, the variation range of height in the original mPSf\nmembrane is obviously lower than that of the soaked mPSf membrane, which is\nconsistent with the roughness results. Meanwhile, the peak width with a narrow range\nof about 10 nm indicates the formation of pore structure in the PDMS layer, which is\nverified by the pore diameter distribution via gas adsorption tests. The PSf membrane\nwas first removed to avoid affecting the test results. In Supplementary Fig. 5, the narrow\ndistribution of pore diameter indicates the uniformity of the pore structure, while it\ncannot be discovered in that of original PDMS layer. Above results demonstrate the\nsoaked mPSf membrane in TMC solution enables the formation of micro-trench\nstructure on the PDMS layer. The modifications are shown in Supplementary Figs. 4\nand 5.\n2.2 Fig.4 suggest that the pore structures are connected rather than individual channels,\nwhich contradicts to the schematic in Fig S1. The resolution of Fig S4 is also very low.\nReply: The results in Supplementary Figs. 4 and 5 show the swollen PDMS layer with\nindividual pore channels, which are consistent with that shown in Supplementary Fig.\n1. I’m sorry for the misunderstanding shown in Supplementary Fig. 6 (original\nSupplementary Fig. 4) with the following reasons. First, compared with PDMS surface,\nthe increased density of red dots at the inner part of PDMS layer indicates more TMC\nmonomers are accumulated on the pore walls, which seems like the connected channels\nto some extent; Second, a small amount of TMC monomers is embedded into PDMS\nsegments during the swelling process, which further causes an increased density of red\ndots.\nWe conducted a Raman depth-profiling of the swollen PDMS membrane to observe the\nTMC distributions in Supplementary Fig. 6. Raman depth-profiling at different\nlocations were shown at Supplementary Fig. 6a1 and 6a2, in which the color indicates\nthe distribution of TMC monomers. The red regions with a boundary indicate that TMC\nmonomers are mostly accumulated in the micropores of PDMS layer. The modifications\nare shown in Supplementary Fig. 6 in revised Supplementary Information with yellow\nhighlight.\n2.3 Cross-sectional TEM with high-resolution EDX mapping could provide more\ndetailed information about TMC distribution in PDMS, which is critical for\nunderstanding this IP synthesis.\nReply: We conducted a TEM-EDX characterization to analyze the distribution of TMC\nmonomers in the PDMS layer via detecting the Cl elements, shown in Supplementary\nFig. 17. The result is similar with that in original Supplementary Fig.4, which is\nattributed to the same reasons mentioned in 2.2. The results in Supplementary Figs. 4\nand 5 show the swollen PDMS layer with individual channels. The modifications are\nshown in Supplementary Fig. 17.\n3.1 In Fig. 1, why does the weight of PDMS decrease with increased residence time of\nswelling PDMS layer?\nReply: The weight decrease of the swelling PDMS layer is attributed to the evaporation\nof n-hexane, and the membrane weight remains unchanged until the solvent is\ncompletely evaporated.\n3.2 Shouldn’t there be more TMC loaded into the polymer matrix with longer soaking\ntime?\nReply: If the soaking time is further increased, excessive swelling of PDMS layer\ndamages the integrity of membrane structure, leading to the monomer loss or affecting\nthe monomer distribution, which ultimately impacts the formation of crumpled\nstructure. In Fig. R1, with the increase of soaking time after 3 min, the CO /N\n2 2\nselectivity of mPSf membrane rapidly decreases, which indicate the damage of\nmembrane structure.\nFig. R1 The CO /N separation performance of mPSf membrane with soaking time.\n2 2\n4. The crumpled morphology observed in PT-1, PT-2, and PT-3 closely resembles\nTuring patterns, and previous studies have reported Turing structures in polyimide\nmembranes (Science, 360, 518-521 (2018)). Can the authors clarify whether the\nformation of such crumpled morphology in PT-1, PT-2, and PT-3 can be explained by\nthe reaction-diffusion theory?\nReply: In this work, we synthesized a polyamide membrane with a crumpled\nmorphology, which is similar to Turing structure to some extent. However, our work\naims at constructing heterogeneous structure at peaks and valleys within polymer\nmembranes for gas separation under high pressure. Although they still exhibit crumpled\nmorphology, for the purpose of avoiding controversy, we do not conduct in-depth\nanalysis to judge whether they belong to the Turing structure.\nCurrently, since the first publication of the Turing membrane (Science, 2018, 360, 518),\nextensive researches on Turing structures, with new construction mechanisms, were\nconducted in the membranes (Science, 2024, 385, 647; Sci. Adv. 2024, 10, eadr9260;\nAngew. Chem. Int. Ed. 2025, 64, e202503090), greatly promoting the influence of\nTuring structure in separation membranes.\nBoth our work and Zhang’s work (Science, 2018, 360, 518) fabricated polymer\nmembrane via interfacial polymerization (IP) reaction, which can be explained by the\nreaction-diffusion theory. However, the formation mechanism of the crumpled\nmorphology (similar to the Turing structure) in our work is different with that in\nZhang’s work. 1. We constructed micropores (microzones) in the intermediate layer\n(PDMS) with a swelling method, as the IP reaction sites, to enrich organic phase\nmonomers (TMC). Variations in IP reaction rates between the micropores and PDMS\nsurface result in the formation of a crumpled structure; 2. We constructed peaks and\nvalleys in the crumpled morphology with heterogeneous structures to enable the peaks\nand valleys with individual values at structural stability and gas transfer respectively.\nIn terms of structure, peaks can effectively relieve external stresses through\ndeformation behavior; while the valleys, composed of more rigid groups, enhance the\ncompactness resistance to maintain a high free volume. In terms of gas transfer, peaks\nwith more amides form CO -philic channels which increase the CO permeation, while\n2 2\nthe valleys maintain high CO diffusion ability. The cooperative effects of dual-function\n2\nregions in polymer membrane enhance the separation ability and structural stability\nsimultaneously; 3. The heterogeneous crumpled membrane provided a 300% increase\nin CO permeance and CO /N selectivity compared to homogeneous counterparts,\n2 2 2\nwhich also achieved one order of magnitude higher than that of state-of-the-art\nmembranes under real operation pressure. Meanwhile, the heterogeneous membrane\nalso shows excellent CO /CH separation performance.\n2 4\n5.1 The authors stated that “Young’s modulus at peaks from PT-1 to PT-3 membranes\nare lower than that at valleys.” Could this be attributed to the proximity of the valleys\nto the substrate and the overall thin nature of the membrane, leading to a significant\nsubstrate effect?\nReply: We’re very sorry for this misunderstanding caused by the unclear description of\nYoung’s modulus testing methods. In this work, the applied force on the membrane\nsurface via AFM tips converted to the gas pressure is 0.15 GPa, which is large enough\nto squeeze the peaks tightly on the mPSf surface in the calculation of Young’s modulus.\nHence, the tested Young's modulus of the peak, similar to the valley, was also obtained\nvia pressing the peaks tightly on the mPSf support, which can eliminate the influence\nof morphology on the test results. Additionally, the indentation depths at the peaks of\nPT-1, PT-2 and PT-3 membranes, shown in Fig. 3h, were calculated by subtracting the\ncorresponding crumpled heights in Fig. 3d. We apologize again for the\nmisunderstanding, and the modifications are shown in, line 230-231 and 446-450, Fig.\n3c and 3h in revised main text with yellow highlight.\n5.2 How do the authors account for and minimize such substrate-induced artifacts in\nmodulus measurement?\nReply: Based on the discussion in 5.1. The Young’s modulus, both at the peaks and\nvalleys, was tested under the condition that the peaks and valleys are tightly adhered to\nthe mPSf membrane. Meanwhile, the mPSf membrane (substrate) with a tested Young’s\nmodulus of 28 GPa is higher that of the crumpled membrane. Hence, the obtained\nYoung’s modulus at the valleys cannot be affected by the substrate effect.\n5.3 The indentation depth of less than 10 nm for the valley in Fig. 3h is also problematic\nas surface effect may become dominant.\nReply: Based on the discussions in 5.1 and 5.2, the indentation depth of less than 10\nnm for the valley in Fig. 3h is correct, which cannot be affected by the substrate effect.\n6.1 Fig. 3b and Fig.15: Conducting tensile tests on membranes with a supporting\nsubstrate may not accurately reflect the mechanical properties of the crumpled film.\nReply: In previous reports, tensile tests of multilayer composite materials can\neffectively reflect the influence of a certain layer on the overall mechanical properties\n(J Membrane Sci. 2025, 727, 124121; Polymer 2023, 265, 125599;Polymer 2024, 314,\n127695; J. Appl. Polym. Sci. 2019, 136, 48131). The mechanical properties of\nmultilayer composite materials depend on the overall performance of the interaction\nreactions among each layer. Additionally, multilayer composite materials are used as a\nwhole in practical applications. Hence, testing the performance of a certain layer alone\nis insufficient to reflect the overall mechanical performance of the composite materials.\nIn this work, the tensile test reflects the crumpled layer is deformable and recoverable,\nwhich also belongs to the mechanical properties. We fabricated a composite membrane\nwith a crumpled selective layer. The mechanical properties of the composite membrane\nmainly depend on the supporting layer (mPSf membrane). If the crumpled layer is\nremoved from the composite membrane to test the mechanical properties, there are two\nfollowing problems: 1. The crumpled layer with a thickness of 60 nm is liable to be\ndamaged by external forces during sample fabrication; 2. After being removed, the\nbinding form between the crumpled layer and the mPSf membrane was disrupted,\nleading to the change of mechanical properties. Meanwhile, the composite membranes\nwere directly used to conduct gas separation test rather than individual crumpled layer.\nHence, testing the mechanical properties of the composite membrane can reflect the\nreal mechanical properties.\n6.2 Stress–strain curves are needed to better interpret the mechanical properties.\nReply: We conducted stress-strain tests to interpret the mechanical properties. In\nSupplementary Fig. 24, the result shows that the mechanical properties gradually\nincrease from PT-1 to PT-3 membranes. Meanwhile, the elongation at break of all\nmembranes is within 20%-22%, which indicates that tensile strength of the crumpled\nmembranes is mainly determined by the PSf support. The modifications are shown in\nSupplementary Fig. 24.\n7.1 The authors stated that “The largest coverage rate of gold nanoparticles in the PT-3\nmembrane explains the highest CO permeance in Fig.4a.” So do PT-1 to PT-3 exhibit\n2\nhigher surface area than PT-4 to PT-5?\nReply: Agree. The surface areas of PT-1 to PT-3 membranes, detected by AFM, are all\nhigher than those of PT-4 and PT-5 membranes, which was shown in Supplementary\nFig. 25a with a fixed test area of 25 μm2. Meanwhile, the relative increase rate of PT-1\nto PT-5 membranes compared with mPSf membrane was shown in Supplementary Fig.\n25b. The modifications are shown in Supplementary Fig. 25.\n7.2 And examine whether the magnitude of increase correlates with the observed\nenhancement in gas permeance? A direct comparison would provide better insight into\nthe structure-property relationship.\nReply: There is no direct correlation between surface area and observed CO\n2\npermeance. We compared the relative increase multiples between surface area and gas\npermeance from PT-1 to PT-5 membranes in Supplementary Fig. 28, among which gas\npermeance and membrane area of PT-5 membrane is deemed as a reference. In\nSupplementary Fig. 28a, the relative increase multiples of CO permeance from PT-1\n2\nto PT-3 membrane are remarkably higher than that of PT-4 and PT-5 membranes, while\nthat of surface area from PT-1 to PT-3 membrane show no corresponding changes. For\nexample, under 1.0 MPa, the CO permeance of PT-1 membrane (3015 GPU) is 12.35\n2\ntimes higher than that of PT-5 membrane (244 GPU), whereas the surface area of PT-1\nmembrane is only 1.29 times higher than that of PT-5 membrane. Hence, the increase\nof CO permeance shows no direct correlation with surface area. Based on above results,\n2\nit can be deduced that the heterogeneous structure rather than membrane surface area\nexplains the polymer membrane with excellent gas separation performance especially\nunder high pressure. The modifications are shown in Supplementary Fig. 28 with\nyellow highlight in revised Supplementary Information.\n8. The schematic in Scheme S1 indicates that both humidifier and dehumidifier are\nplaced before the test cell. However, if the goal is to measure CO /N separation under\n2 2\n100% relative humidity conditions, why is the dehumidifier positioned before the test\ncell rather than before gas chromatography (GC) to protect it? Additionally, “Sweep”\nin Scheme S2 was mistakenly written as “Sweap”.\nReply: After passing through the humidifier, the feed gases simultaneously carry water\nvapor and partial liquid water molecules especially under high pressure. The liquid\nwater molecules will accumulate on the membrane surface during the gas diffusion\nprocess, hindering the gas transfer. Hence, the dehumidifier was introduced and\npositioned before the test cell to remove liquid water molecules.\nThe injection port temperature in the gas chromatography (GC) was set at 200 ℃ to\nremove the permeate water molecules, which can protect the chromatographic column\nfrom the influence of water molecules. Hence, a dehumidifier is not essential to be\nplaced before GC to protect it.\nThanks for your careful inspection, we have modified the “sweap” to “sweep”. In\naddition, we have carefully checked all the spelling mistakes both in the main text and\nSupplementary Information. The modification is shown in Scheme S2 with yellow\nhighlight in revised Supplementary Information.\n9. While Figure S24 presents the trend in CO permeance, the corresponding variation\n2\nin CO /N selectivity is not explicitly discussed. Could the authors provide the data and\n2 2\nanalyze whether selectivity follows a similar or distinct trend?\nReply: The CO /N selectivity was shown in the Fig. 4b in the main text. The CO /N\n2 2 2 2\nselectivity of PT-1, PT-2, PT-3 membranes is independent of stretch ratios, which shows\nthe similar trend with CO permeance. While, the CO /N selectivity of PT-4 and PT-5\n2 2 2\nmembranes decreases with stretch ratio, which shows the opposite trend with CO\n2\npermeance. The reason is attributed to the enlarged segment spacing appeared at the\nstretch process, showing low stress-resistance ability of the homogeneous structure in\nthe PT-4 and PT-5 membranes.\n10. Figure S25 shows a decrease in both CO permeance and selectivity between 0.1-\n2\n1MPa, followed by an increase in permeance and a decrease in selectivity beyond 1.0\nMPa. Could the authors elaborate on the underlying mechanisms responsible for this\nobservation?\nReply: In Supplementary Fig. 33 (original Supplementary Fig. 25), an increase in\npermeance and a decrease in selectivity beyond 1.0 MPa was appeared on the PT-4 and\nPT-5 membranes. This phenomenon can be explained by the plasticization effect, which\nwas always appeared at glassy polymers (Chem. Soc. Rev., 2024, 53, 2435; Chem. Rev.\n2018, 118, 5871; Prog. Polym. Sci., 2019, 91, 80).\nThe main reason for the plasticization effect is attributed to the strong interactions\nbetween glassy polymer membranes with condensable gases (CO ), leading to the\n2\nremarkable increase of gas solubility in the membranes. And, more gas molecules\ndissolve in the membranes that weaken the interforce of the polymer segments,\nresulting in an increase in the free volume. Therefore, the plasticization phenomenon\nof the polymer membranes will increase the gas permeation, shown as the increase of\nCO permeance with pressure beyond 1.0 MPa in Supplementary Fig. 33a and 33b.\n4\nthan that of CO , thereby deteriorating the CO /CH selectivity. Meanwhile, the similar\n2 2 4\nvariation also appears in the CH /N separation in Supplementary Fig. 33c and 33d. The\n4 2\nmodifications are shown in Supplementary Fig. 33 with yellow highlight in revised\nSupplementary Information.\nReviewer #3:\nThis manuscript describes the preparation, characterization and separation performance\nof polyamide membranes made by controlled interfacial polymerization between a\nswollen PDMS film with acyl chloride in contact with an aqueous diamine solution.\nThis procedure yields highly permeable and selective membranes with a wrinkled\nsurface morphology. The separation performance is discussed in correlation with the\nmembrane morphology and microstructure. The results are supported by a range of\ndifferent morphological, compositional and mechanical studies, as well as\ncomputational methods. The gas separation performance is excellent, above the state of\nthe art, with high permeance and high selectivity.\nOverall, the work is done well and the results are convincing and occasionally exceed\nthe state of the art. Nevertheless, not all results and points in the discussion are\ncompletely clear.\nThese points need to be improved before it may become suitable for publication. Some\nspecific remarks that require a revision of the manuscript are given below:\nGeneral reply: We sincerely appreciate this reviewer for praising comments and\ndetailed suggestions regarding the improvement of our manuscript. The following\ncontents are our point-by-point responses to the concerns raised by the reviewer.\n1.The relatively high permeance of the membranes can at least in part be ascribed to\nthe roughness of the surface, and thus to the effective increase in the surface area. A\nsimilar approach has already been applied by the group of Matthias Wessling to enhance\nmass transport in hollow fibers (e.g. https://doi.org/10.1016/j.memsci.2005.02.022,\nhttps://doi.org/10.1016/j.memsci.2009.10.003). This must be discussed in the state of\nthe art.\nReply: In this work, the relatively high permeance caused by increased surface area in\nboth homogeneous and heterogeneous crumpled structures only occurs at a low\npressure (<0.2 MPa), while the CO permeance of PT-1 to PT-3 and homogeneous\n2\nmembranes is obviously higher than that of PT-4 and PT-5 membranes. However, with\nthe increase of operation pressure, except PT-1 to PT-3 membranes, the gas permeance\nof the membranes with homogeneous structures decrease rapidly. Hence, in our work,\nthere is no direct correlation between surface area and gas permeance especially under\nhigh pressure. We compared the relative increase multiples between surface area and\ngas permeance from PT-1 to PT-5 membranes in Supplementary Fig. 28, among which\ngas permeance and membrane area of PT-5 membrane is deemed as a reference. In\nSupplementary Fig. 28a, the relative increase multiples of CO permeance from PT-1\n2\nto PT-3 membrane are remarkably higher than that of PT-4 and PT-5 membranes, while\nthat of surface area from PT-1 to PT-3 membrane show no corresponding changes. For\nexample, under 1.0 MPa, the CO permeance of PT-1 membrane (3015 GPU) is 12.35\n2\ntimes higher than that of PT-5 membrane (244 GPU), whereas the surface area of PT-1\nmembrane is only 1.29 times higher than that of PT-5 membrane. Above results\nindicates the heterogeneous structure explains the polymer membrane with excellent\ngas separation performance especially under high pressure rather than surface area.\nOur work aims at constructing the heterogeneous structure at peaks and valleys in a\ncrumpled morphology to break through the obstacle of polymer membranes with a low\ngas separation ability under high pressure. Although the fabricated membrane still\ndemonstrates a crumpled morphology, this is a common phenomenon in the interfacial\npolymerization reactions. However, it is difficult to simultaneously achieve high gas\npermeation and separation ability of polymer membranes under high pressure only with\nan increased surface area. The modifications are shown in Supplementary Figs. 27 and\n28 in revised Supplementary Information.\nEvident errors:\n2. CO permeance (ca. 2000 for PT-1, Fig S25a) and CH permeance (ca. 1200 for PT-\n2 4\n1, Fig S25c) does not lead to a CO /CH selectivity of almost 10 but to less than 2!\n2 4\nApparently, there is an evident error in some of the measurements or calculations, which\nshould be checked and where necessary corrected throughout the manuscript.\nReply: I’m sorry for this misunderstanding caused by the unclear description. The\ncalculation results shown in Supplementary Fig. 33 (original Supplementary Fig. 25)\nare correct. The results of CO /CH separation performance were shown in\n2 4\nSupplementary Fig. 33a (CO permeance) and Supplementary Fig. 33b (CO /CH\n2 2 4\nselectivity). While, the CH /N separation performance was shown in Supplementary\n4 2\nFig. 33c (CH permeance) and Supplementary Fig. S33d (CH /N selectivity). The\n4 4 2\nmentioned performances about CO permeance (ca. 2000 for PT-1, Supplementary Fig.\n2\n33a) and CH permeance (ca. 1200 for PT-1, Fig S33c) were not tested from the same\n4\nfeed gas. The CO /CH selectivity was obtained from the CO permeance in\n2 4 2\nSupplementary Fig. 33a and CH permeance in Supplementary Fig. 33c. We added the\n4 2\nrevised Supplementary Information.\nMeanwhile, we have carefully checked all the data both in the main text and\nSupplementary Information.\nSpecific points:\n3.1 The manuscript claims to have produced a micro-phase separated membrane with\nthe peaks composed of more amide groups and the valleys with more phenyl groups\n(line 57-58). Since the amide groups are covalently bonded to the phenyl groups of\nTMC, this statement must be further explained. The only way to change the ratio of\namide groups and phenyl groups is by a different cross-link density or by the formation\nof free carboxylic acid groups instead of amide groups from the reaction of the\ncorresponding acyl chloride with water instead of amine. In this sense, the cross-link\ndensity is likely more important than the composition as such.\nReply: Agree. We consider that the composition differences at peaks and valleys stem\nfrom the variations initiated at the micropores and the surface of the PDMS layer in the\nIP process, which in turn change the crosslinking density. We conducted XPS to analyze\nthe crosslinking degree of PT-1 to PT-5 membranes, and the results were shown in\nSupplementary Table 1. The crosslinking degrees of heterogeneous membranes (PT-1\nto PT-3) are significantly higher than that of homogeneous membranes (PT-4 and PT-\n5), indicating the formation of dense structure. The crosslinking degrees gradually\ndecrease from PT-1 to PT-3, resulting in a gradual increase in gas permeation ability\nshown in Supplementary Fig. 27b, which also explains the PT-3 membrane with the\nhighest gas permeance. Meanwhile, the increase of O/N ratio from PT-1 to PT-3\nmembranes indicates an increase of linear crosslinking structures in the PA membranes\n(Chem. Phys. Lett., 2009, 478, 56), which suggests that the acyl chloride groups on the\nPDMS surface partially hydrolyzed to form carboxyl groups when contacting with the\nPIP aqueous solution, reducing the crosslinking density. The modifications are shown\nin line 112-123 and 321-323 in revised main text, Supplementary Table 1 in revised\nSupplementary Information with yellow highlight.\n3.2 Does the interfacial polymerization also penetrate within the PDMS layer?\nReply: The interfacial polymerization does not penetrate within the PDMS layer. We\ncharacterized the cross-section morphology of the PT-1, PT-2 and PT-3 membranes in\nSupplementary Fig. 19. The PDMS layer, with a thickness of about 105 nm, shows a\nclear boundary between the PA layer and PSf support. The PDMS layer was used to\nconstruct IP reaction sites in the construction of the crumpled structure. The\nmodifications are shown in Supplementary Fig. 19 in revised Supplementary\nInformation.\n3.3 Also, the confinement of the PDMS is fundamental for the transport properties and\nshould be discussed more accurately. PDMS itself has a CO /N selectivity equal to ca.\n2 2\n11-12 (-). The very strong positive deviation from this value indicates that the PDMS\nis no longer the main resistance in the film.\nReply: Agree. In the crumpled membrane, PA layer in the PT membrane is the main\nresistance of gas separation rather than PDMS layer in mPSf membrane. In\nSupplementary Fig. 26, the mPSf membrane (composed of PDMS layer and PSf\nsupport), with a higher CO permeance of 7000 GPU and lower CO /N selectivity of\n2 2 2\n5 within 1.0 MPa compared with those of PT membranes, shows no impact on the\nseparation performance of PT membranes.\n4.1 Figure S1 is not completely clear and should also show the PSF support. Besides\nthe top surface images, also the cross sections of the membranes should be shown,\nindicating clearly the thickness of each active layer.\nReply: We have added the PSf support in Supplementary Fig. 1. The cross-section\nimages of were shown in Supplementary Fig. 19. The crumpled membranes are\ncomposed of three parts, PA layer (~60 nm), PDMS layer (~105 nm) and PSf support.\nAlthough all the figures show a PSf thickness of 5 μm, the actual thickness is\napproximately 30 μm. The modifications are shown in Supplementary Fig. 1 and Fig.\n19 in revised Supplementary Information.\n4.2 In this light, the sampling depth of IR is typically a few micrometers. Therefore, the\nanalysis shows not only the active layer but also the support and/or the top-layer, which\nmay lead to erroneous conclusions related to presumed microphase separation. Please\ndiscuss in more detail.\nReply: The IR tests with a sampling depth of a few micrometers including all the three\nparts in the membranes. We detected the mPSf membrane (including PDMS layer and\nPSf support) and PSf support via AFM-IR respectively. No amide groups (C=O, C-N)\nexist in both PDMS and PSf layers, which demonstrates almost no signals in\nSupplementary Fig. 10a1 and 10b1. While, phenyl groups (C=C, C-H) exist in both\nPDMS and PSf layers, showing uniform signals in Supplementary Fig. 10a2 and 10b2.\nThese uniform signals are deemed as the background signals during the testing process,\nand have been deducted. Hence, it will not affect the relative content of phenyl groups\nat the peaks and valleys. The modifications are shown in Supplementary Fig. 10 in\nrevised Supplementary Information.\n5. Figure S25 (SI line 340) shows unlikely high selectivity CH4/N2. Since CH4 is larger\nthan N2, diffusion selectivity is strongly in favour of N2 (e.g. Teplyakov and Meares,\ndoi: 10.1016/0950-4214(90)80030-O), and the selectivity must apparently be based on\nsolubility selectivity. Is there any evidence for this? Please discuss.\nReply: The high CH /N selectivity is attributed to a high CH /N solubility selectivity\n4 2 4 2\nthan diffusivity selectivity, which was obtained through deconvoluting the CH and N\n4 2\npermeability into solubility and diffusivity coefficient (Eq.(1)) based on the solution-\nd solution-\ndiffusion model (Eq.(2)), and the results were shown in Supplementary Table 2. The\ncalculation process was shown as follows.\nThe single-gas permeabilities P (Barrer) of the crumpled membranes were evaluated\nusing a Labthink VAC-V2(EX) apparatus. The diffusivity coefficient D (cm2 s−1) was\ncalculated by the time-lag method using the following Eq. (1):\nD=l/6θ2 (1)\nwhere θ is the time-lag of the permeability measurement.\nThe solubility coefficient S (cm3 (STP) cm−3 cmHg−1) was calculated by the ratio of\ngas permeability to diffusivity coefficient as the following Eq. (2):\nS=P/D (2)\nThe modifications are shown in line 260-263 and 471-479 in revised main text,\nSupplementary Table 2 in revised Supplementary Information with yellow highlight.\n6.1 Fig S30 caption “…is based on the difference of Young's modulus between the\npeaks and valleys”: Is there indeed any proof for the differences in modulus?\nReply: The simulation process, shown in Supplementary Fig. 40 (original\nSupplementary Fig. 30), was based on the difference of Young's modulus between the\npeaks and valleys, and the tested results of Young’s modulus were shown in Fig. 3h.\n6.2 How can the authors exclude that indentation of the peaks is easier because of empty\nspace below the peaks, whereas the valleys rest on the support and need to be\ncompressed rather than just bent? Please discuss the mechanical properties also in terms\nof morphology and not only in terms of microstructure.\nReply: We’re sorry for this misunderstanding caused by the unclear description of\nYoung’s modulus testing methods. The applied force on the membrane surface via AFM\ntips is calculated as the gas pressure of 0.15 GPa, which is large enough to squeeze the\npeaks tightly on the mPSf surface in the calculation of Young’s modulus.\nHence, the tested Young's modulus of the peak, similar to the valley, was also obtained\nvia pressing the peaks tightly on the mPSf support, which can eliminate the influence\nof morphology on the test results. Additionally, the indentation depths at the peaks in\nthe PT-1, PT-2 and PT-3 membranes, shown in Fig. 3h, were calculated by subtracting\nthe corresponding crumpled heights in Fig. 3d, which show a large indentation at the\npeaks than valleys.\nThe modifications are shown in line 199-200, 230-231 and 446-450 in revised main\ntext with yellow highlight.\n7. Fig.24: The increase in permeance is ascribed to the appearance of defects in samples\nPT-4 and PT-5. However, both samples have a lower permeance than the samples PT-1,\n2 and 3. Defects would first of all increase the permeance of the slowest species.\nReply: We modified “defects” as “enlarged segment spacing”. In Supplementary Fig.\n32 (original Supplementary Fig. 24), the increase rates of N permeance of PT-4 and\n2 2 2\nselectivity shown in Fig. 4b in the main text. Hence, the enlarged segment spacing first\nof all increase the slowest species (N ). The modifications are shown in Supplementary\n8. The authors should specify in the experimental part what kind of tip is used for the\nAFM analysis and what this means for the analysis of the results.\nReply: In this work, the AFM analysis was used to obtain the membrane morphology\nand mechanical properties. The RTESPA-525-30 was selected as the AFM tip, which\nis composed of 0.01-0.025 Ωcm Antimony (n) doped Si with Aluminum reflective\ncoating on the backside of the cantilever.\nAccording to the reported Young’s module of the polyamide materials in the literatures\n(Appl. Surf. Sci, 2020, 505, 144415; Macromolecules, 2022, 55, 2051; J Membrane Sci.,\n2021, 619, 118788), we initially determined the scope of the Young's modulus about\nthe crumpled polyamide membranes to select the matching tip. Hence, in this work, the\nRTESPA-525-30 tip, with a Young's modulus range within 10 GPa, was selected to\nconduct the AFM mechanical tests. The obtained Young’s moduli of both peaks and\nvalleys in the crumpled membranes, shown in Fig. 3g in the main text, were within this\nrange, which also truly reflect the mechanical properties of the crumpled membranes.\nMeanwhile, the indentation depth is regarded as another important basis to evaluate the\ntip selection, and the results shown in Fig. 3g did not exceed the upper limit. Based on\nthe above discussion, the RTESPA-525-30 tip can reflect the real morphology and\nmechanical properties at peaks and valleys in the crumpled structures.\n9. Especially in non-homogeneous microphase separated polymers, the tip size, type\nand cantilever properties are crucial for the result that should be expected and should\ntherefore be mentioned (see for instance M. Longo, et al., Polymer, 156 (2018) 22–29.\ndoi:10.1016/j. polymer.2018.09.043.\nReply: According to the RTESPA-525-30 tip, the tip and cantilever parameters are\npresented as follows. Tip parameters including tip height of 10-15 μm, end curvature\nradius of 30 nm; cantilever parameters including cantilever thickness of 5.75 μm,\ncantilever length of 125 μm, cantilever width of 40 μm, resonance frequency of 525\nkHz, spring constant of 200 N/m.\nThe tip size, type and cantilever properties have a significant impact on the surface\nmorphology, the damage to the sample and the accuracy of the test results. First of all,\nthe stiffness of the tip should match that of the sample, which is crucial for\nnanomechanical measurements. The selected tip with a large spring constant of 200\nN/m indicates a hardness property, which is beneficial to conducting a rapid scanning.\nMoreover, the cantilever is difficult to deform and can truly reflect the indentation depth;\nThe selected tip with a high resonance frequency of 525 kHz means reaching the\nequilibrium state quickly. Thus, for the crumpled structure with a large undulation,\nthe morphology can be rapidly detected, which was consistent with the SEM results,\nindicating that the crumpled structure is closely tightly on the polysulfone (PSf) support;\nThe selected tip with a curvature radius of 30 nm can avoid the damage of the sharp tip\nto the ultrathin sample surface, and the influence on the morphology and test results\ncaused by the contact between the tip side and the sample. The modifications are shown\nin line 431-446 in revised main text with yellow highlight.\n10. In this light, the conclusion in line 189-191 that Young’s modulus in the peaks is\nlower than that in the valleys may not be correct. The deformation measured in the\npeaks reflect both the indentation and the deformation of the entire thin film,\nwhereas the deformation in the valleys reflects only the indentation.\nReply: I’m sorry for the misunderstanding caused by the unclear description of Young’s\nmodulus testing methods. But, the lower Young’s modulus in the peaks than that in the\nvalleys is correct. In fact, the indentation depths at the peaks in the PT-1, PT-2 and PT-\n3 membranes, shown in Fig. 3h, were calculated by subtracting the corresponding\ncrumpled heights in Fig. 3d, which show a larger indentation at the peaks than valleys.\nMeanwhile, the applied force on the membrane surface via AFM tips is calculated as\nthe gas pressure of 0.15 GPa, which is much greater than the operation pressure. Hence,\nthe applied force via AFM tip is large enough to squeeze the peaks tightly on the mPSf\nsurface in the calculation of Young’s modulus. Consequently, the tested Young's\nmodulus of the peak, similar to the valley, was also obtained via pressing the peaks\ntightly on the mPSf membrane, which can eliminate the influence of morphology on\nthe test results. The modifications are shown in line 230-231 and 446-450 in revised\nmain text with yellow highlight.\n11. Gold nanoparticles are dispersed in the feed and the deposition on the surface is\ndiscussed as presumed evidence of the high low rate of the gas across the membrane.\nHowever, the dimensions of the nanoparticles are said to be 5 nm, whereas the smallest\nscale bar in Fig S27 is 200 nm. Thus, the particles are not visible at this scale. Figure\nd1-1 and d2-1 show an irregular morphology with small depressions between thin\n‘walls’. The changes seen from figure d1 to d1-1 and d2 to d2-1 are a different surface\nmorphology with features up to 50 nm and do not represent the 5 nm nanoparticles.\nReply: In Supplementary Fig. 35 (original Fig. 27), the deposited nanoparticles on the\nmembrane surface exist in an aggregated form rather than in a discrete form. TEM tests\nmainly reflected the difference in contrast between light and dark regions. The\naggregated nanoparticles are manifested as the dark regions in TEM images, while the\nlight regions indicate less coverage of gold nanoparticles. Image J software was used\nto analyze the changes from TEM images at the peaks and valleys respectively to\ndeduce the gas permeation across the crumpled membrane.\nThe TEM images in Supplementary Fig. 35 from d1 to d1-1 and d2 to d2-1 are the same\nmorphology in PT-4 membrane with smooth structure. The magnifications of d1 and\nd2 are different, resulting in the misunderstanding of different samples. We re-\ncharacterized the PT-4 membrane by TEM and the results were consistent with previous\nones.\nThe depressions and thin “walls”, shown in d2-1, mean the regions with high and low\ngas permeation rate respectively. We supplied the TEM images of PT-4 and PT-5\nmembrane, shown in Supplementary Fig. 35. All the results indicate the distribution of\ngold nanoparticles on the homogeneous membrane is random rather than uniform. The\nmodifications are shown in line 281 in revised main text with yellow highlight,\nSupplementary Figs. 35 and 36 in revised Supplementary Informantion.\n12. Furthermore, what is the linear perpendicular flow velocity of the gas on the\nmembrane? Is this sufficient to overcome gravity and act as the main driving force for\nparticle transport, rather than gravity or electrostatic interactions?\nReply: The linear perpendicular flow velocity of the gas molecules on the membrane\n(4.9 cm2) is about 1.2×10-4 m/s, which was tested by a soap-film flowmeter at the\npermeate side. However, in this work, we adopted a constant pressure (1.0 MPa) testing\nmethod to analyze the gas permeation, so the gold nanoparticles were in a constant\npressure environment. Hence, analyzing the force acting on gold nanoparticles from\ngas pressure can effectively determine whether they are affected by gravity.\nThe gravity of a gold nanoparticle with a diameter of 5 nm was calculated as follows.\nnanoparticle, and ρ is the density of gold nanoparticle.\nThe force of a gold nanoparticle under 1.0 MPa was calculated as follows.\nF=P×A\nWhere P represents the operation pressure, A is the surface area of a gold nanoparticle.\nThe calculated F (7.84×10−11 N) ≫W (1.24×10−20 N) indicates that the operation\npressure acts as the driving force for gold nanoparticles transport rather than gravity.\nMeanwhile, in the Supplementary Table 4, all the PT membranes and gold\nnanoparticles have negative charged, which shows the gold nanoparticles cannot be\nadsorbed on the membrane surface.\n13. Overall, the proof of the gas flow profile through the membrane, with preference\nfor the higher areas, seems insufficient on the one hand, but perhaps not particularly\nrelevant on the other hand. Proof of the collocation of the particles on the tops and\nnot on the valleys of the crumpled membrane surface requires the demonstration of the\ncross-sectional image of the membrane, appropriately made by embedding the surface\nin a resin (without moving the nanoparticles) and subsequent TEM analysis of a thin\nslice of this sample.\nReply: In this work, we adopt a pressure-constant testing method to analyze the gas\npermselectivity. Any position of the membrane surface shows the same probability to\ncontact with gas molecules, which is reflected as the deposited gold nanoparticles\nduring gas permeation process.\nThanks for your suggestion. We conducted FIB-TEM tests shown in Supplementary\nFig. 18 to observe the distribution of gold nanoparticles on the crumpled PA layer.\nHowever, it’s difficult to distinguish the locations of gold nanoparticles. We further\nanalyzed the distribution of Au element, but the results still cannot meet our\nrequirements. The reason is attributed to the dense arrangement of gold nanoparticles\nand the disruption of the original distribution of gold nanoparticles on the crumpled\nlayer via a FIB technology.\nTo avoid the movement of gold nanoparticles deposited on the membrane surface\nduring the sample preparation process, surface morphology characterizations were\nadopted in this work to further observe the distribution of gold nanoparticles on the\ncrumpled structure. Compared with TEM analyses in Supplementary Fig. 35, SEM\nsurface images provide a more intuitive and obvious observation for distinguishing the\ndistribution of gold nanoparticles. In Supplementary Fig. 37, the aggregated gold\nnanoparticles are mainly accumulated at the peaks, while they are rarely distributed at\nthe valleys, indicating the peaks as rapid gas transfer channels. The modifications are\nshown in Supplementary Figs. 18 and 37 in revised Supplementary Information.\n14.1 The transport model in Figure S28 does not have a strong scientific basis. The\norigin of the coefficients 2 and 3 is unclear and should be justified quantitatively.\nReply: We are very sorry for the confusion caused by the unscientific analysis in\ntransport model. Commonly, the gas transport resistance is inversely proportional to\nthe gas permeation. In our work, the gas permeability reflects the overall performance\nof the PT membrane, so the gas transport resistance also reflects the resistance of the\nentire structure and should not be divided into the resistance of peaks and valleys\nrespectively. The gas transport resistance of membranes is calculated as follow.\nAccording to Tripodi’s report (J Membrane Sci., 1981, 8, 233-246), the gas transport\nresistance can be calculated as follow. The permeation rate, or flux, for component i\nthrough a polymeric membrane can be described by:\nQ = P AΔc/l= BAΔc (1)\ni i i i i i i i\nwhere Qi is the permeation rate of component i, P is the intrinsic permeability of the\ni\npolymeric membrane to component i, B is the permeance of the polymeric membrane\ni\nto component i, A is the surface area of membrane, 1 is the membrane thickness, Δc\ni i i\nis the concentration difference of component i across the membrane (in the case of gas\npermeation, this is the partial pressure difference). Using the electrical analog, the\nabove relationship describing permeation through a polymer membrane is\nmathematically equivalent to Ohm’s law which describes current flow through a\nresistor:\nI = E/R (2)\nConceptually the current, I, can be equated with the permeation rate, Q. The driving\nforce for current flow, (i.e. the difference in electric potential E), is analogous to the\nconcentration gradient Δc. Hence, we can define, then, a resistance to permeate flow,\ni\nR, which is equivalent to the electrical resistance R:\ni\nR = l/PA=1/BA (3)\ni i i i i\nso that combining (1) and (3)\nQi = Δc/R (4)\ni i\nBased on equation (3) and schematic diagram shown in Supplementary Fig. 38, the gas\ntransport resistance of all the membranes is decided by the membrane thickness, surface\narea and gas permeability. In Supplementary Table 5, the results of R show that with\ni\nthe increase of operation pressure, the gas transport resistance of the homogeneous\nstructure increases rapidly, while that of the heterogeneous structure grows slowly,\nwhich further indicates the heterogeneous structure with a strong pressure-resistance.\nThe modifications are shown in line 303-316 in the main text, Supplementary Fig. 38,\nTable 5 in revised Supplementary Information with yellow highlight.\n14.2 The role of the individual components (PDMS and polyamide) should also be\ndiscussed in terms of more common models such as mixed matrix or resistances in series.\nReply: In the resistance model of membrane permeation (J Membrane Sci., 1981, 8,\n233-246), the total resistance is a function of the resistance in each layers including PA\nlayer, mPSf membrane. Meanwhile, the mPSf membrane, with a low resistance\ncompared with other membranes with PA layers, shows almost no effect on the overall\nresistance. Therefore, the resistance of the PT membrane is mainly concentrated in the\nPA layer.\n15. Line 246-247: please explain what is meant with “The cooperative effects of\nfunctional groups rearrangement at peaks and valleys, explain the heterogeneous\nmembranes with excellent gas separation performance”.\nReply: We modified this sentence as “The rearrangement of functional groups at peaks\nand valleys endow the crumpled membrane with independent and cooperative dual-\nfunction regions, which can improve the membrane performance from increased gas\ndiffusion and enhanced pressure resistance”.\nIn terms of gas diffusion, more amide groups are accumulated at peaks, remarkably\nincreasing the CO solubility and constructing rapid gas transfer channels; While the\n2\nphenyl groups in valleys maintain a high free volume due to the steric hindrance effects,\nwhich is beneficial to improving gas diffusion ability especially under high pressure.\nFrom the perspective of mechanical robustness, the cooperative effects of deformation\nat peaks and compaction-resistance ability at valleys, explain the heterogeneous\nmembrane with excellent mechanical property, which can effectively alleviate both the\nhorizontal and vertical stresses with stable structure and is critical to achieve high-\npressure separation. The modifications are shown in line 276-279 in revised main text.\n16. Commercial membranes for gas separation are normally produced by a continuous\nprocess and are often formed by hollow fibers as well as flat sheet membranes. A brief\ndiscussion on the feasibility of continuous production and the possible use of hollow\nfiber configuration should be added.\nReply: We thank for your positive suggestion. In this work, the microzone interfacial\npolymerization technology shows no special requirements for the membrane shape. For\nhollow fiber membranes, our design is to cover the hollow fiber membrane with a\nPDMS layer via a dip-coating technology at first, followed by immersing into one\nmonomer solution to construct micro areas, and then react with another monomer\nsolution to conduct interfacial polymerization reactions. Thus, a heterogeneous\ncrumpled membrane can be constructed on the outside of the hollow fiber membrane.\nIf the PDMS layer is coated on the inside of the hollow fibers, the heterogeneous\nstructure can also be obtained.\nMinor issues:\n17. Fig.7: the text in the IR spectra is too small to identify the peaks.\nReply: We have increased the font size of the texts in Supplementary Fig. 9 (original\nFig. 7).\n18. English language needs radical improvement.\nThe article is sometimes difficult to follow because of repetitions and not always logical\norder of the data and the discussion.\nReply: The language has been polished by a professional English editing policy, and\nwe further improved the logic of this manuscript in depth.\nOverall conclusion:\nThe manuscript may be suitable for publication, but the obvious mistakes must be\ncorrected and all weaknesses should be improved or properly justified. This will require\na major revision of the present manuscript.\nReply: We sincerely appreciate this reviewer for praising comments and detailed\nsuggestions regarding the improvement of our manuscript."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors answered all the questions and changed the manuscript accordingly. Therefore, I think that the manuscript can be accepted for publication.", "reviewer_2": "The experimental details are needed for determining the pore size in the PDMS layer. What instrument did the authors use to obtain Fig. S5? I cannot find any information in the experimental section.\nThe Raman depth profiling is also questionable. As far as I know, In confocal Raman imaging, the spatial resolution is typically about 200–500 nm, depending on the excitation wavelength and the numerical aperture (NA) of the objective lens. How could the authors obtain images with sub-100 nm resolution?\nThe authors still have not explained why TMC soaking led to pore formation in PDMS. Why did longer TMC soaking result in “damages the integrity of membrane structure”? Does this mean more pore structures formed or degradation to the PDMS polymer?\nThe authors did not understand my question about nanoindentation. What are the film thickness of the crumpled film at the valleys? If the film thickness at the valley is very small, the measurements are significantly affected by the substrate, which is widely acknowledged as the “substrate effect”. The other thing that the authors need to be aware of is that the tip radius is typically 20–100 nm. That means at indentation depths <10 nm, the measured response is dominated by the blunted tip apex rather than the designed geometry. This affects the contact area calculation which often leads to errors in hardness and modulus extraction. This is known as the “surface effect”.", "reviewer_3": "The authors made a great effort correct any shortcomings and to improve the quality of the manuscript in general.\nOnly few points for discussion remain:\nThe title seems to be inverted: Gas separation with Binary-cooperative heterogeneous membranes sounds more\nreasonable..\nResponse #3 point 5: Equation (1) is incorrect and must be D=l2/6Θ instead of D=l/6Θ2\nAlso the results do not seem to be correct. With a diffusion coefficient in the order of 10-5 cm2/s PDMS has a measurable time lag for a slab with a thickness of I mm. A film thickness of 100 micrometres would already be in the order of few seconds and membranes of 10 micrometers or less than 1 micrometre become unmeasurable short. Thus, if the authors have measured a measurable time lag, then this must have included the contribution of the porous support.\nThe authors made a great effort correct any shortcomings and to improve the quality of the manuscript in general. However, in some cases this opens new questions rather than answering the original questions. In other cases, the response is not satisfactory. Details are given below:\n1) The title seems to be inverted: Gas separation with Binary-cooperative heterogeneous membranes sounds more\nreasonable than Binary-cooperative heterogeneous membranes with gas separation.\n2) The authors have performed time lag measurements to determine the gas diffusion coefficient and indirectly the solubility\nof the gases (Response #3 point 5). However, equation (1) is incorrect and must be D=l2/6Θ instead of D=l/6Θ2. If they used\nindeed this equation, then all calculations are wrong and must be repeated with the correct equation.\nSecondly, regardless the equation used, time lag measurements seem impossible for the thin film membranes discussed in\nthis work. For instance, with a diffusion coefficient in the order of 10-5 cm2/s PDMS has a measurable time lag for a slab with\nhigh thickness: a rapid calculation reveals that a film thickness of 100 micrometres would already give a time lag in the order\nof few seconds. Instead, membranes of 100 nm, as reported in line 369 become unmeasurably short. Regarding the other\nmaterials, polysulfone and polyamide, both have such a low permeability that the permeance can be high only if a very thin\nfilm is obtained, and in this case the equation Θ=l2/6D leads again to unmeasurably short time lags.\nThus, the authors should report at least one representative original time lag measurement curve (permeate pressure vs\ntime). Thus, if the authors have measured a measurable time lag, then this must have included the contribution of the porous\nsupport. In any case, their equation (1) is wrong, and thus most likely also their calculations. Therefore, all calculations\nshould be checked, and some original time lag curves should be reported in the supplementary information to allow the\nreader to check the calculations and see if there are any anomalies in the original curves.\n3) What is the instrumental time lag of the measurement setup? How fast can valves be opened and how quickly can the\npressure be read?\nAs a test for the linearity of the time lag, I suggest calibrating the setup with neat PDMS films of 50, 100, 200 and 500\nmicrometres and plotting the time lag as a function of l2, extrapolating to l=0 to determine the instrumental time lag (see e.g.\nFig 4 and Fig. 8 in https://doi.org/10.1016/j.memsci.2018.04.029)\n4) The discussion on the mechanical tests remains unclear. The morphology has peaks and valleys but the force used in the\nmechanical tests is so high that it is supposed to squeeze the peaks onto the harder porous membrane support. Although\nthe authors attribute the difference in hardness between peaks and valleys to microphase separation it cannot be excluded\nthat it is simply a matter of thickness of the softer coating layer.\nAccording to line 230-231, the authors now calculate the indentation depths at the peaks by 230 subtracting the\ncorresponding crumpled heights in Fig. 3d. This is not fully clear. In any case it suggests that the samples are subjected to\nmuch larger deformations than licit for indentation measurements. Measurements of Young’s modulus should be carried out\nat low deformation in the elastic regime, not in the plastic regime. If it is necessary to press the thin layer of the crumpled\nmembrane onto the support before measuring its modulus, the measurement is clearly affected by the support, and thus not\nrepresentative for the film itself.\n5) In line 297-299 the authors state: “The rapid decrease in the CO2/N2 297 selectivity of the PT-4 and PT-5 membranes is\nattributed to the decreased free volume in the polymer network under pressure, which limits the solubility of gas molecules”.\nThis claim is in contrast with the results of the mechanical tests. Young’s modulus of these samples is in the order of GPa,\nwhereas the permeability measurements are carried out up to few MPa. It is more likely that pressure-dependence is related\nto the dual mode sorption mechanism, where the Langmuir sites are gradually saturated, but it is even more likely that the\npressure-dependence is a result of the ‘squeezing’ of the crumpled membrane onto the support (analogous to Fig. 3c).\nTherefore, it is essential that the authors report also the pressure needed to compress the crumpled areas of the membrane\n(See also the previous comment).\n6) Figure S18 (right photo) demonstrates that the PDMS also penetrates deep into the PSf layer. Thus, the representation of\na distinct PA layer on top of a distinct PDMS layer on top of a distinct PSf layer as the authors show in all schematic images\nis not completely correct. Which consequences does this have for the transport mechanism of these membranes?\n7) A clear cross-sectional SEM image must also be reported in the manuscript instead of just schematic drawings. This is the\nkey feature of the manuscript and should not be reported only in the SI.\n8) The authors overlook one important hypothesis regarding the high permeances of these membranes: The permeance of\nthin film composite membranes is proportional to the surface porosity: the lower the surface porosity, the smaller the ‘active’\narea is. This is the reason for the use of a highly permeable gutter layer in thin film composite gas separation membranes\nwith a low-permeable selective film. The present work appears to be rather similar to this situation, with PDMS coated onto\nPSf as the gutter layer for the selective PA film. However, air is the most permeable of all gutter materials and it seems that\nthis is confirmed by crumpling of the PA layer, which makes the film much more permeable. On the other hand, this does not\nexplain, how a porous PA can provide selectivity, and it seems that this could only be possible if the PA film is sealed by\nPDMS too. Nevertheless, the permeance is much higher than that reported for instance by Freeman et al.\n(https://doi.org/10.1016/j.memsci.2020.118009) where the membrane is prepared in the reverse order and PDMS is coated\nonto a PA reverse osmosis membrane and where the mechanism is explained on the basis of resistances in series/in\nparallel as discussed by Henis and Tripodi (https://doi.org/10.1016/S0376-7388(00)82312-1).\n9) Referring to the previous point: the authors should explain their results not only\nphenomenologically, but also using well known transport models for hybrid materials, such as the already mentioned model\nof Henis and Tripodi\n(https://doi.org/10.1016/S0376-7388(00)82312-1), the model for polymer blends by Robeson\n(http://dx.doi.org/10.1021/ie100153q), as well as the well-known Maxwell model.\n10) Typical RO membranes made by phase inversion have very low surface porosities, as low as 5%. If the surface porosity.\nIf the surface porosity of the PA membrane plays a role, for instance when closing the pores by pressing the PA film onto the\nsupport coating, then this has a much higher impact on the permeance than the surface area of the membrane (see Fig. S25\nand response to question #1, reviewer #3). In addition to the above models, the authors should consider the accessible\npores in their discussion and the gutter layer principle.\nMinor details:\nFigure S3: d) reads TEM surface image but should probably be SEM surface image"}, "author_response": "General reply: We sincerely appreciate this reviewer for praising comments and\ndetailed suggestions regarding the improvement of our manuscript. The following\ncontents are our point-by-point responses to the concerns raised by the reviewer.\n1. The experimental details are needed for determining the pore size in the PDMS layer.\nWhat instrument did the authors use to obtain Fig. S5? I cannot find any information in\nthe experimental section.\nReply: Thanks for your comments. N adsorption-desorption isotherms of the swelling\nthe pore size distribution of the PDMS layer was calculated based on the Barrett-Joyner-\nHalenda (BJH) model. The experimental details were shown in line 440-447 in Methods\nin revised main text with yellow highlight.\n2. The Raman depth profiling is also questionable. As far as I know, in confocal Raman\nimaging, the spatial resolution is typically about 200–500 nm, depending on the\nexcitation wavelength and the numerical aperture (NA) of the objective lens. How could\nthe authors obtain images with sub-100 nm resolution?\nReply: Thanks for the insightful question. We fully agree and acknowledge that the\noptical diffraction limit of our confocal Raman system (governed by the laser\nwavelength λ and the numerical aperture (NA) of the objective) defines its ultimate\nspatial resolution. For our configuration with a 532 nm laser and a NA of 1.4, the\ntheoretical spatial resolution is about 200-300 nm, and we cannot achieve direct optical\nresolution below this limit.\nHowever, the scale bar of 100 nm in Supplementary Fig.6a1 and a2 do not represent\nthe optical resolution. Instead, it indicates the sampling interval of the depth profiling.\nTo reconstruct a chemical profile, the sampling interval (in this case, 100 nm) should\nbe smaller than the optical resolution, which can effectively capture the shape of the\nTMC concentration gradient. Meanwhile, it can be discovered that the axis width of\nTMC signal areas in the Raman depth profiling is greater than that of an individual pore\nchannel on the PDMS layer, which is attributed to the scattering phenomenon of Raman\nlasers, caused by the overlap of TMC signals adjacent to the channels. We have added\nexplanations about the scale bar in the Supplementary Fig.6 with yellow highlights.\n3.1 The authors still have not explained why TMC soaking led to pore formation in\nPDMS.\nReply: In this work, the solvent (n-hexane) in TMC solution, with similar solubility\nparameter compared with PDMS, leads to the formation of pore structures in the PDMS\nlayer, which is explained by solvent-induced swelling mechanism and researched in\nprevious reports (J Membrane Sci., 2015, 475, 488). The detailed formation process of\npore structure in PDMS layer were shown in line 71-72 in the main text and\nSupplementary Fig.4 in revised Supplementary Information with yellow highlight.\n3.2 Why did longer TMC soaking result in “damages the integrity of membrane\nstructure”? Does this mean more pore structures formed or degradation to the PDMS\npolymer?\nReply: We agree with the reviewer’s comments. Longer TMC-solution soaking will\nintensify the swelling of the PDMS layer, which will further enlarge segment distance\nand produce more micropores based on solvent-induced swelling mechanism (see the\nresponse in Question 3.1). Excessive swelling will inevitably dissolve partial PDMS\nsegments, even cause microscopic cracks or complete rupture, resulting in a decrease\nof CO /N separation ability (Fig.R1).\n2 2\nFig. R1 The CO /N separation performance of mPSf membrane with soaking time. In the\n2 2\nfabrication of the crumpled membrane, the TMC-solution soaking time was controlled within 3 min.\n4. The authors did not understand my question about nanoindentation. What is the film\nthickness of the crumpled film at the valleys? If the film thickness at the valley is very\nsmall, the measurements are significantly affected by the substrate, which is widely\nacknowledged as the “substrate effect”. The other thing that the authors need to be\naware of is that the tip radius is typically 20–100 nm. That means at indentation depths\n<10 nm, the measured response is dominated by the blunted tip apex rather than the\ndesigned geometry. This affects the contact area calculation which often leads to errors\nin hardness and modulus extraction. This is known as the “surface effect”.\nReply: We fully agree with and sincerely thank the reviewer for these critical insights\nabout “substrate effect” and the “surface effect” in nanoindentation measurements.\nThe thickness of the valleys (~65 nm) is the same as that at the peaks. To minimize the\ninfluence of the substrate, the indentation depth should be less than 10~20% of the total\nthickness to avoid the “substrate effect” from previous reports (Nanoscale Res. Lett. 2011, 6, 270; J Mater. Res. 1992, 7, 1564; Langmuir 1999, 15, 5630). In this work, the\nmaximum indentation depth was still below 6 nm, which is less than 10% of the total\nthickness at valleys. Hence, this ensures that the measured modulus is dominated by\nthe properties of the valley.\nWe fully agree with the reviewer that the use of a nominal tip radius is insufficient,\nespecially at indentation depths (<10 nm) where the measured response is dominated\nby the blunted tip apex. In fact, we have noticed this issue you mentioned. Hence, both\nbefore and after testing, we have calibrated the tip radius and used the calibrated value\ninstead of nominal tip radius to measure the Young’s modulus of all the samples, which\ncan effectively eliminate the influence of tip blunting on the results. This calibrated tip\nradius (35±3 nm), which accounts for tip blunting, was used for all subsequent contact\narea calculations and modulus extractions from our samples. The details were shown in\nline 473-478 in Methods with yellow highlight.\nReviewer #3 (Remarks to the Author):\nThe authors made a great effort correct any shortcomings and to improve the quality of\nthe manuscript in general.\nOnly few points for discussion remain:\nThe title seems to be inverted: Gas separation with Binary-cooperative heterogeneous\nmembranes sounds more reasonable.\nResponse #3 point 5: Equation (1) is incorrect and must be D=l2/6Θ instead of D=l/6Θ2\nAlso the results do not seem to be correct. With a diffusion coefficient in the order of\n10-5 cm2/s PDMS has a measurable time lag for a slab with a thickness of 1 mm. A\nfilm thickness of 100 micrometres would already be in the order of few seconds and\nmembranes of 10 micrometers or less than 1 micrometre become unmeasurable short.\nThus, if the authors have measured a measurable time lag, then this must have included\nthe contribution of the porous support.\nThe authors made a great effort correct any shortcomings and to improve the quality of\nthe manuscript in general. However, in some cases this opens new questions rather than\nanswering the original questions. In other cases, the response is not satisfactory. Details\nare given below:\nGeneral reply: We sincerely appreciate this reviewer for praising comments and\ndetailed suggestions regarding the improvement of our manuscript. The following\ncontents are our point-by-point responses to the concerns raised by the reviewer.\n1. The title seems to be inverted: Gas separation with Binary-cooperative heterogeneous\nmembranes sounds more reasonable than Binary-cooperative heterogeneous\nmembranes with gas separation.\nReply: We fully agree with the reviewer’s suggestion. We have modified the title as\n“Gas separation with binary-cooperative heterogeneous membranes”.\n2. The authors have performed time lag measurements to determine the gas diffusion\ncoefficient and indirectly the solubility of the gases (Response #3 point 5). However,\nequation (1) is incorrect and must be D=l2/6Θ instead of D=l/6Θ2. If they used indeed\nthis equation, then all calculations are wrong and must be repeated with the correct\nequation.\nSecondly, regardless the equation used, time lag measurements seem impossible for the\nthin film membranes discussed in this work. For instance, with a diffusion coefficient\nin the order of 10-5 cm2/s PDMS has a measurable time lag for a slab with high\nthickness: a rapid calculation reveals that a film thickness of 100 micrometres would\nalready give a time lag in the order of few seconds. Instead, membranes of 100 nm, as\nreported in line 369 become unmeasurably short. Regarding the other materials,\npolysulfone and polyamide, both have such a low permeability that the permeance can\nbe high only if a very thin film is obtained, and in this case the equation Θ=l2/6D leads\nagain to unmeasurably short time lags.\nThus, the authors should report at least one representative original time lag\nmeasurement curve (permeate pressure vs time). Thus, if the authors have measured a\nmeasurable time lag, then this must have included the contribution of the porous support.\nIn any case, their equation (1) is wrong, and thus most likely also their calculations.\nTherefore, all calculations should be checked, and some original time lag curves should\nbe reported in the supplementary information to allow the reader to check the\ncalculations and see if there are any anomalies in the original curves.\nReply: We sincerely apologize for the wrong spelling and misunderstandings caused\nby the lack of description about testing process. Meanwhile, we have carefully checked\nall the calculations. In this work, we utilized the stacked PA layers, with a thickness of\nabout 40 μm, rather than composite membrane to perform the time-lag measurements,\nwhich can effectively eliminate the impact of porous support. The sample fabrication\nprocess of stacked PA layers was shown in line 498-511 with yellow highlight.\nOriginal time-lag curves of PT-3 membrane, as the representatives, were provided in\nSupplementary Fig.34 and time lags of other membranes were shown in Supplementary\nTable 2 in the Supplementary Information. Above discussions were mentioned in line\n268 in revised main text.\n3. What is the instrumental time lag of the measurement setup? How fast can valves be\nopened and how quickly can the pressure be read?\nAs a test for the linearity of the time lag, I suggest calibrating the setup with neat PDMS\nfilms of 50, 100, 200 and 500 micrometres and plotting the time lag as a function of l2,\nextrapolating to l=0 to determine the instrumental time lag (see e.g. Fig 4 and Fig. 8 in\nhttps://doi.org/10.1016/j.memsci.2018.04.029)\nReply: Thanks for your positive suggestion. All valves are automatically controlled,\nwhich can ensure extremely short response times. The feed pressure and permeate\npressure are continuously monitored and exported as an original time-lag curve to\nanalyze the diffusivity coefficient.\nThe instrumental time lag is negligible in calculation of diffusivity coefficient. In this\nwork, a fixed volume time-lag measurement was conducted, that is, the permeated gas\nmolecules through the samples to the downstream almost immediately contribute to the\ntotal pressure. Hence, the response time of gas flow from the membrane surface to the\npressure sensor is extremely fast (within milliseconds), which was also manifested in\nJansen’s work (Fig.5, J Membrane Sci. 2018, 561, 39). In Fig.R2, fitting the\nexperimental data of stacked PA layers from PT-3 membrane in a plot of the time lag\nas a function l2 yields shows almost no intercept on the Y-axis, and 1/6D as the slope\nof the curve, which also explains the negligible instrumental time lag. Additionally, the\ninstrumental time lag (θ ), discussed in Jansen’s work, is based on the mass\n0\nspectrometry measurement under sweeping gas or vacuum condition, where the feed\nstream is already flowing before switching this valve from the purge position to the test\nposition and reflected as the instrumental time lag.\nFig.R2 Determination of the diffusion coefficient for the PA layer in PT-3 membrane with different\nthicknesses according to D=l2/6θ.\nBased on above discussions, the time-lag measurements show no relationship with\nmPSf membrane (including PDMS and PSf) and instrumental time lag. Hence, we do\nnot analyze the instrumental time lag with neat PDMS films. We sincerely appreciate\nyour suggestions, which have deepened our understanding and recognition of time lag\nmeasurements.\n4. The discussion on the mechanical tests remains unclear. The morphology has peaks\nand valleys but the force used in the mechanical tests is so high that it is supposed to\nsqueeze the peaks onto the harder porous membrane support. Although the authors\nattribute the difference in hardness between peaks and valleys to microphase separation\nit cannot be excluded that it is simply a matter of thickness of the softer coating layer.\nAccording to line 230-231, the authors now calculate the indentation depths at the peaks\nby 230 subtracting the corresponding crumpled heights in Fig. 3d. This is not fully clear.\nIn any case it suggests that the samples are subjected to much larger deformations than\nlicit for indentation measurements. Measurements of Young’s modulus should be carried out\nat low deformation in the elastic regime, not in the plastic regime. If it is necessary to\npress the thin layer of the crumpled membrane onto the support before measuring its\nmodulus, the measurement is clearly affected by the support, and thus not\nrepresentative for the film itself.\nReply: We fully agree with and appreciate your opinions on the mechanical tests of the\ncrumpled structure. In this work, squeeze peaks onto the support under a high force can\nguarantee the test condition is consistent with that at valleys. Young’s modulus is a\nconstant to a certain material, which is independent of the material thickness and\nmorphology. Hence, the structural differences between the peaks and valleys, attributed\nto the microphase separation, mainly explains the differences in Young’s modulus.\nMeanwhile, the change of Young’s modulus of PA-type materials with structures has\nbeen confirmed by many researches (Int. J Solids Struct. 2022, 239, 111419; Compos.\nPart B-Eng. 2024, 286, 111809; Addit. Manuf., 2022, 51, 102576).\nThe reviewer rightly points out that indentation measurements on thin films must be\nconducted in the elastic regime where the substrate effect is negligible. To minimize\nthe influence of the substrate, the indentation depth should be less than 10~20% of the\ntotal thickness to avoid the “substrate effect” from previous reports (Nanoscale Res.\nLett. 2011, 6, 270; J Mater. Res. 1992, 7, 1564; Langmuir 1999, 15, 5630). In this work,\nthe maximum indentation depth was still below 6 nm, which is less than 10% of the\ntotal thickness at valleys. Hence, this ensures that the measured modulus is dominated\nby the properties of the valley. While, the indentation at peaks accounts for 50% of the\ntotal thickness, which seems to be plastic deformation. However, under PF-QNM mode\nin AFM mechanical tests, the Young's modulus is analyzed by extracting the linear part\nof the force-distance curve to ensure that the data points correspond to the elastic\nresponse.\nTo exclude the elastic deformation on the measurement of Young’s modulus at peaks,\nwe decreased the attached force on the AFM tip to re-evaluate the indentation depth\nand Young’s modulus, where the corresponding results shown at Fig.3h was obtained\nat the force setpoint of 7.8 μN. In Supplementary Fig.43a, the obtained Young’s\nmodulus is almost independent of the attached force, whether the indentation depth is\nless than 10% of the total thickness (unaffected by the substrate) or greater than 20%\n(plastic deformation). This result also manifests the Young’s modulus is calculated\nwithin the elastic response under PF-QNM mode. Hence, the indentation depth at the\npeaks, calculated by subtracting the crumpled height from the total vertical\ndisplacement of the probe, directly reflects the depth where the probe enters from the\nmembrane surface, which changes with the attached force. Above explanations were\nshown in line 214-216 in revised main text, and Supplementary Fig.43a in revised\nSupplementary Information with yellow highlight.\n5.1 In line 297-299 the authors state: “The rapid decrease in the CO /N selectivity of\n2 2\nthe PT-4 and PT-5 membranes is attributed to the decreased free volume in the polymer\nnetwork under pressure, which limits the solubility of gas molecules”. This claim is in\ncontrast with the results of the mechanical tests. Young’s modulus of these samples is\nin the order of GPa, whereas the permeability measurements are carried out up to few\nMPa.\nReply: We agree with the reviewer’s comments. In the PA layer, the transfer of CO\n2\nand N molecules follows solution-diffusion and facilitated transport mechanisms\n2\nsimultaneously. However, the rapid decrease of the CO /N selectivity is mainly\n2 2\nattributed to the facilitated transport mechanism, which is manifested by a rapid\ndecrease of CO permeance (Supplementary Fig.27b) and a slight decrease of N\n2 2\npermeance (Supplementary Fig.27d). The rapid decrease of CO permeance is mainly\n2\nattributed to the adsorption saturation of the amide groups as the Langmuir sites of CO\n2\nmolecules based on the facilitated transport mechanism. While, N permeance is almost\n2\nindependent of pressure based on solution-diffusion mechanism. We have modified the\ndescription in line 304-306 in revised main text.\n5.2 It is more likely that pressure-dependence is related to the dual mode sorption\nmechanism, where the Langmuir sites are gradually saturated, but it is even more likely\nthat the pressure-dependence is a result of the ‘squeezing’ of the crumpled membrane\nonto the support (analogous to Fig. 3c). Therefore, it is essential that the authors report\nalso the pressure needed to compress the crumpled areas of the membrane (See also the\nprevious comment).\nReply: Thanks for your comments. We first analyze whether the crumpled membrane\nis pressed onto the support under the operating pressure, which was conducted by\nchanging the attached tip force (F) to simulate the membrane under operation pressure.\nF can be determined from the operation pressure (P) and calibrated tip parameters (A)\nbased on the equation F=PA. In Supplementary Fig.43b, the attached force, changing\nfrom 16.8 to 41.6 nN, is to simulate the operation pressure from 1.0 to 3.0 MPa.\nCompared with original crumpled height (Supplementary Fig. 43c), the attached force\ncan only cause slight deformation, shown as slight decrease of crumpled height. The\nresult manifests the crumpled membrane cannot be squeezed onto the support with\noperation pressure. Hence, the decrease of CO permeance (Supplementary Fig.27a) is\n2\nattributed to the adsorption saturation of Langmuir sites (amide groups) in dual-mode\nsorption mechanism. The modifications were shown in line 268-270 in revised main\ntext, and Supplementary Fig.43b in revised Supplementary Information with yellow\nhighlight.\n6. Figure S18 (right photo) demonstrates that the PDMS also penetrates deep into the\nPSf layer. Thus, the representation of a distinct PA layer on top of a distinct PDMS layer\non top of a distinct PSf layer as the authors show in all schematic images is not\ncompletely correct. Which consequences does this have for the transport mechanism of\nthese membranes?\nReply: We agree with the reviewer’s opinion. In fact, in the fabrication of composite\nmembrane, the high fluidity of solution is inevitable to penetrate into the porous support,\nwhich is deemed as pore-penetration effect (Sep. Purif. Technol. 2019, 215, 670).\nGenerally, a spontaneous mutual diffusion process occurs at the interface of all\ncomposite materials, while the structural properties of the materials lead to differences\nin the diffusion layer thickness. If the diffusion layer shows no significance on the total\nperformance of composite materials, it is usually not reflected in the schematic diagram,\nwhich has been widely adopted in numerous composite membranes (Science 2024, 386,\n1037; Science 2023, 381, 1350).\nIn this work, after coating PDMS solution onto the PSf layer, partial PDMS segments\npenetrate into the PSf pores, presenting silicon signals shown in Supplementary Fig.18.\nThe pore penetration commonly occurs on the PSf surface with rapid solvent\nevaporation, combined with a high gas permeability of PDMS, which shows slight\nimpact on the gas permeability of the composite membrane (J Membrane Sci. 2022,\n658, 120763).\n7. A clear cross-sectional SEM image must also be reported in the manuscript instead\nof just schematic drawings. This is the key feature of the manuscript and should not be\nreported only in the SI.\nReply: Thanks for your insightful suggestion. We have added SEM cross-section image\nof the crumpled membrane in Fig.3c, line 198-199 in revised main text.\n8. The authors overlook one important hypothesis regarding the high permeances of\nthese membranes: The permeance of thin film composite membranes is proportional to\nthe surface porosity: the lower the surface porosity, the smaller the ‘active’ area is. This\nis the reason for the use of a highly permeable gutter layer in thin film composite gas separation membranes\nwith a low-permeable selective film. The present work appears to be rather similar to this situation, with PDMS coated onto\nPSf as the gutter layer for the selective PA film. However, air is the most permeable of all gutter materials and it seems that\nthis is confirmed by crumpling of the PA layer, which makes the film much more permeable. On the other hand, this does not\nexplain, how a porous PA can provide selectivity, and it seems that this could only be possible if the PA film is sealed by\nPDMS too. Nevertheless, the permeance is much higher than that reported for instance by Freeman et al.\n(https://doi.org/10.1016/j.memsci.2020.118009) where the membrane is prepared in the reverse order and PDMS is coated\nonto a PA reverse osmosis membrane and where the mechanism is explained on the basis of resistances in series/in\nparallel as discussed by Henis and Tripodi (https://doi.org/10.1016/S0376-7388(00)82312-1).\nReply: We thank for your valuable suggestions and in-depth thoughts on our work.\nWe have studied Freeman’s work (J Membrane Sci. 2020, 604, 118009) in the early stage,\nhowever, we contend that the distinctions between the two works extend beyond a mere\nreversal in the sequence of membrane fabrication, which is reflected from three aspects:\nmembrane structure, gas transfer mechanism, and functions of gutter layer. 1.\nMembrane structure. In our work, the selective layer (PA layer), fabricated with\nlonger IP reaction time (J. Mater. Chem. A, 2018, 6, 30) compared with that of\ncommercial PA membranes in Freeman’s work, shows a defect-free structure (almost\nno surface porosity observed from SEM images in Supplementary Fig. 15), which\nprovides gas selectivity for the composite membrane. We characterized the pure-gas\nselectivity of PA layer (Supplementary Table 7). As a result, the CO /N selectivity of\n2 2\nthe PA layer is remarkably higher than commercial PA membranes following Knudsen\ndiffusion. 2. Gas transfer mechanism. The gas permeance is inversely proportional to\nthe membrane thickness. In this work, the selective layer, with a thickness of about 60\nnm (only PA layer), explains a high CO permeance, while that (close to 1 μm) in\nMeanwhile, CO permeance of the mPSf membrane (PDMS coated PSf support) is\n2\nhigher than that in Freeman’s work (Table 4), which is attributed to different PDMS\nfabrication process and fabricated thickness. Additionally, the gas transfer process of\nPA layer in our work follows solution-diffusion mechanism with a dense structure,\nwhich demonstrates that the total performance of composite membrane is mainly\ndecided by the selective layer. While, the gas transfer process in Freeman’s work\nmainly follows Knudsen diffusion or viscous flow attributed to the porous structure,\nand separation performance depends on the PA layer coated with PDMS. 3. Functions\nof gutter layer. In our work, the gutter layer (PDMS layer) provides mechanical\nsupport for the PA layer and is deemed as the reaction sites to construct heterogeneous\nstructure, while that in Freeman’s work only aims at blocking the PA defects. The\nmodifications were shown in Supplementary Table 7 in revised Supplementary\nInformation with yellow highlight.\n9. Referring to the previous point: the authors should explain their results not only\nphenomenologically, but also using well known transport models for hybrid materials,\nsuch as the already mentioned model of Henis and Tripodi\n(https://doi.org/10.1016/S0376-7388(00)82312-1), the model for polymer blends by Robeson\n(http://dx.doi.org/10.1021/ie100153q), as well as the well-known Maxwell model.\nReply: Thanks for your insightful feedback, which enhances the understanding of this\nwork. Based on the discussion in Question 8, the series resistance model reported by\nHenis and Tripodi (J Membrane Sci. 1981, 8, 233) is suitable to illustrate the membrane\nwith high gas permeance, and detailed analysis process was shown in “Gas transport\nresistance model” in Supplementary information. In Supplementary Fig.40, from series\nresistance model, it can be inferred that heterogeneous PA layers in the composite\nmembranes show a higher CO permeance compared with that of homogeneous\n2\ncounterparts, indicating the heterogeneous structure endow the PA with enhanced gas\npermeation ability. The modifications were shown in line 319-326 in revised main text,\nSupplementary Fig.40 in revised Supplementary Information with yellow highlight.\nWe sincerely appreciate your proposal of utilizing gas transport models to analyze the\ngas permeation ability. However, due to the variability and complexity of\nheterogeneous crumpled structures, current transport models are insufficient to\neffectively analyze the structural advantages on gas permeation and selectivity in our\nwork. Therefore, we will discuss the gas transport mechanism of heterogeneous\ncrumpled structure in depth in another work. The innovation of our work is to construct\na new structure in ultrathin polymer membrane, which is shown as follows. 1) The first\nconstruction of independent and cooperative dual-function regions in the polymer\nmembrane. Peaks and valleys contribute individual values at structural stability and gas\ntransfer respectively. In terms of structure, peaks can effectively relieve external\nstresses through deformation behavior; while the valleys, composed of more rigid\ngroups, enhance the compactness resistance to maintain a high free volume. In terms of\ngas transfer, peaks with more amides form CO -philic channels which increase the CO\n2 2\npermeation, while the valleys maintain high CO diffusion ability. The cooperative\n2\neffects of dual-function regions in polymer membrane enhance the separation ability\nand structural stability simultaneously especially under high pressure. 2) In-situ\nmonitoring of the microphase separation. Based on AFM-IR scanning measurements,\nthe amide and phenyl groups are deduced to accumulate more at the peaks and valleys\nrespectively, while the microphase separation process was dynamically observed with\nin-situ Raman scanning technology via adjusting the Raman focusing mode. Hence, the\nheterogeneous structure can be mutual verified by choosing different focusing locations\nand detecting different functional groups in Raman scanning analyses. 3) The\nheterogeneous membrane provided a 300% increase in CO permeance and CO /N\n2 2 2\nselectivity compared to homogeneous counterparts, which also achieved one order of\nmagnitude higher than that of state-of-the-art membranes under high pressure. Specially,\nPT-3 membrane exhibits a minimum CO capture cost, which meets the US Department\n2\nof Energy (DOE) target, showing a good potential for CO capture in real flue gas.\n2 4\nperformance.\n10. Typical RO membranes made by phase inversion have very low surface porosities,\nas low as 5%. If the surface porosity of the PA membrane plays a role, for instance when\nclosing the pores by pressing the PA film onto the support coating, then this has a much\nhigher impact on the permeance than the surface area of the membrane (see Fig. S25\nand response to question #1, reviewer #3). In addition to the above models, the authors\nshould consider the accessible pores in their discussion and the gutter layer principle.\nReply: Thanks for your comments. Based on the discussions in Question 8 and 9, the\nfabricated PA layer, with a dense and defect-free structure, almost demonstrated no\nsurface microporosity. Hence, the transport model does not need to consider the\ninfluence of accessible pores on the membrane performance. In series resistance model,\nthe influence of dense PA layer and gutter layer on the total membrane performance\ncan be comprehensively considered. Hence, we deem that the series resistance model\ncan effectively explain the performance of the crumpled membrane. We sincerely thank\nfor your positive advice to explore the advantage of the crumpled structure, which\nmakes us aware that analyzing the transfer mechanism is crucial for realizing the\nstructure-activity relationship. Hence, we will further conduct in-depth research on the\ntransport mechanism based on the heterogeneous crumpled structure in the next work.\nMinor details:\n11. Figure S3: d) reads TEM surface image but should probably be SEM surface image.\nReply: Thanks for your suggestion. We have carefully checked and confirmed that\nSupplementary Fig.3d shows the TEM surface image of the crumpled membrane. In\nTEM images, image contrasts originate from the variations of the detecting thickness\n(not membrane thickness) caused by the peak and valley structures. The larger the\ndetecting thickness of a local region, the darker it appears on the TEM image as less\nelectrons are transmitted due to scattering. Therefore, in Supplementary Fig.3d, bright\nregions correspond to peak structures, while dark regions match valley structures\nbecause the crowded peaks cover parts of the valley structures (Supplementary Fig.13),\nresulting in the obstruction of electron transmission. Meanwhile, the bright regions also\nreflect the cavity structure in the peaks (Supplementary Fig.18). In SEM surface images\n(Supplementary Fig.15), the high locations on the surface (PA peaks) appear brighter\nas they generate more secondary electrons, while the low locations (the valleys) appear\nrelatively dark because fewer electrons are able to escape. Hence, although TEM and\nSEM images are similar, they both explain the crumpled morphology from different\naspects."}, {"round": 3, "reviewer_comments": {"reviewer_2": "The authors have addressed all my concerns. Now the paper can be recommended for publication.", "reviewer_3": "The authors have responded to the comments of the reviewers, but the new version of the manuscript is not convincing and\ntends to open more questions than it answers.\nFirst of all, the discussion on the depth resolution of the Raman profiling is misleading. A depth resolution that is higher than\nthe optical resolution cannot be not correct. The apparently high resolution is an illusion, because the observed signal is\neffectively a sort of moving average of the true resolution. Indeed, this allows observation of concentration profiles if there are\nalso differences at the scale of the optical resolution, but it is NOT the effective concentration gradient within the samples.\nSecondly, the nano-indenting experiments remain unclear. On the one hand, very large deformations are needed to\n‘squeeze’ the crumpled sections onto the support surface, and on the other hand the authors claim that only very small\ndeformations take place during the measurement.\nFinally, there seem to be discrepancies related to the diffusion coefficient measurements. D is measured on a sandwich of\nmany layers, treated with solvent and high temperature and pressure. This completely cancels the crumpled structure and\ndata are by no means comparable. In addition, the diffusion coefficient reported by the new procedure is about two orders of\nmagnitude lower than that reported for PDMS in the literature (Markov et al., Biomed Microdevices. 2014 Feb;16(1):91–96.\ndoi: 10.1007/s10544-013-9808-2; Monteleone et al., J. Membr. Sci. 648 (2022) 120356.\ndoi:10.1016/j.memsci.2022.120356.). If diffusion in PDMS is so much slower, it is difficult to understand how the composite\ncrumpled membrane can have such a high permeance.\nThe results are certainly worth to be published, I do not think that Nature Communications is the correct journal"}, "author_response": "General reply: We sincerely appreciate this reviewer for praising comments and detailed suggestions\nregarding the improvement of our manuscript. Your concerns mainly stem from our unclear description of\nthe details in the manuscript. The following contents are our point-by-point responses to your concerns.\n1. First of all, the discussion on the depth resolution of the Raman profiling is misleading. A depth\nresolution that is higher than the optical resolution cannot be not correct. The apparently high resolution is\nan illusion, because the observed signal is effectively a sort of moving average of the true resolution. Indeed,\nthis allows observation of concentration profiles if there are also differences at the scale of the\noptical resolution, but it is not the effective concentration gradient within the samples.\nReply: Thanks for your comments. Based on the official information of renishaw website\n(https://www.renishaw.com/en/overcoming-the-limitations-of-raman-spectroscopy--25811), the spatial\nresolution in a Raman image is a product of sophisticated system integration rather than a single optical\nparameter. The sampling interval, achievable with precision stages like Renishaw’s MS30 that provide step\nsizes down to 50 nm, creates a data grid finer than the laser spot itself. The combinations of spectrometer\nmagnification and the pixel size of the CCD detector determine the precision in distinguishing these closely\nspaced spectral data points. By applying advanced image reconstruction and deconvolution algorithms to\nthis oversampled and well-resolved dataset, the effective spatial resolution can be pushed beyond the\nconventional limits of optical microscopy. The spatial resolution of Raman imaging can be further\nenhanced to the nanoscale by coupling with other techniques. Meanwhile, it can be discovered that the\nRaman images, with a spatial resolution higher than the optical resolution, has been reported in many\nresearches (Nature, 2021, 590, 405; Chem. Soc. Rev., 2018, 47, 1822; Nat. Commun. 2018, 9, 2891; Nat.\nCommun. 2013, 4, 2592).\nIn our work, a high depth resolution refers to the high-precision mechanical control of the motorized\nstage (Renishaw MS30 encoded stage). The scale bar is the minimum increment that we can accurately\nreposition the sample in the Z-axis, which ensures sufficient collection of data points. The separate red\nregions (Fig.S6a) reflect a relatively high concentration of TMC monomers in the PDMS layer. Notably,\nin previous discussions, we also point out that the wide of red regions in Raman depth profiling is\nremarkably larger than that of an individual pore channel (~9 nm) in the swelling PDMS layer, which is\nattributed to the scattering phenomenon of Raman lasers, caused by the overlap of TMC signals adjacent\nto the channels. Hence, this method demonstrates a qualitative analysis of concentration gradient.\nAbove contents were mentioned on line 74 in main text and in Fig.S6 in Supplementary Information.\n1\n2. Secondly, the nano-indenting experiments remain unclear. On the one hand, very large deformations are\nneeded to ‘squeeze’ the crumpled sections onto the support surface, and on the other hand the authors claim\nthat only very small deformations take place during the measurement.\nReply: Thanks for your comments. The previous description about nanoindentation experiments conducted\nat peaks and valleys has led to your misunderstanding of this work. In this case, we deeply elaborate on the\ndifferences in testing methods at peaks and valleys respectively.\nIn the test of Young’s modulus, to minimize the influence of the substrate, the indentation depth should\nbe less than 10~20% of the sample thickness to avoid the “substrate effect” from previous reports\n(Nanoscale Res. Lett. 2011, 6, 270; J Mater. Res. 1992, 7, 1564; Langmuir 1999, 15, 5630). In terms of\nthe valley, the indentation depth is less than 10% of the membrane thickness, known as a “small\ndeformation”, resulting in an accurate Young's modulus without being affected by the substrate. While, for\npeaks, the measurement of the indentation depth is relatively complicated because of the crumpled\nmorphology. The reason is that we cannot obtain the actual indentation depth before the peaks were pressed\nonto the substrate, leading to the measurement error of Young’s modulus. Hence, a “large deformation”,\nresulting from the tip moving from the peak to the substrate, is crucial for accurately measuring Young’s\nmodulus of peaks. The detailed testing process and results at peaks and valleys were shown as follow\nrespectively.\n(1) Nanoindentation tests at peaks.\nIn Fig.R1a, the examples from Point 1 to Point 4, with different tip forces, are the representative testing\nstates, and corresponding results are shown in R1c. The tip displacement (D) increased from Point 1 to\nPoint 4 with the increased tip force, however the measured Young’s modulus at Point 1 and Point 2 is\nobvious lower than that at Point 3 and Point 4. The main reason is the inaccurate measurement of\nindentation depth, leading to a calculation error. Hence, the examples at other tip forces (>0.6 μN),\nincluding Point 3 and Point 4, are to squeeze the peaks onto the substrate, known as “large deformation”,\nwhich lead to a relatively accurate indentation depth calculated by subtracting the crumpled height (H)\nfrom tip displacement (D), and the measured results of Young’s modulus are almost the same. Meanwhile,\nit can be discovered that the calculated Young’s modulus is almost independent of indentation depths under\ndifferent tip forces (>0.6 μN), because Young’s modulus is analyzed by extracting the linear part of the\nforce-distance curve to ensure that the data points correspond to the elastic response in AFM tests (Bruker,\nDimension IconXR).\n(2) Nanoindentation tests at valleys.\nDifferent from the testing methods at peaks, in Fig.R1b, the tip displacement at valleys is equal to the\nindentation depth. In Fig.R1c, the indentation depth, tested under all the tip forces including Point 1 to\nPoint 4, is almost the same and remarkably lower than that at peaks because of more rigid groups\naccumulated at valleys. The slight changes of the measured Young’s modulus under different tip forces are\ndue to the elastic response with small deformations.\nTherefore, the differences in measuring Young’s modulus at peaks and valleys is to guarantee the\nmeasurement accuracy.\nAbove modifications were added in Fig.S43 in Supplementary Information and mentioned on line 216,\n471 in main text with yellow highlights.\nmodel. (c) The relationship between Young’s modulus, indentation depth, tip displacement and tip force. The\nindentation depth at the valley is equal to the tip displacement, while that at the peak is obtained by subtracting the\ncrumpled height from the tip displacement.\n3\n3.1 Finally, there seem to be discrepancies related to the diffusion coefficient measurements. D is measured\non a sandwich of many layers, treated with solvent and high temperature and pressure. This completely\ncancels the crumpled structure and data are by no means comparable. In addition, the diffusion coefficient reported by the new procedure is about two orders of\nmagnitude lower than that reported for PDMS in the literature (Markov et al., Biomed Microdevices. 2014\nFeb;16(1):91–96. doi: 10.1007/s10544-013-9808-2; Monteleone et al., J. Membr. Sci. 648 (2022) 120356.\ndoi:10.1016/j.memsci.2022.120356.). If diffusion in PDMS is so much slower, it is difficult to understand\nhow the composite crumpled membrane can have such a high permeance.\nReply: Thanks for your comments. The crumpled structures in our membrane are growth-derived, making\nthem resistant to flattening under squeezing. This fundamentally distinguishes them from the reversible\ncrumples caused by bending, which can be easily smoothed out (Fig. R2a and b). Meanwhile, the crumpled\nstructure is still maintained after a series of treatments (solvent, high temperature and pressure), as\nevidenced by the followings.\nThe crumpled structure was synthesized via interfacial polymerization under the solvent (hexane), and\ncorresponding SEM images shown in Fig. R2c and d (original Fig.S18) verified the crumple morphology.\nWe further characterized the cross-sectional morphology of stacked PA layers (Fig. R2e and f, added in\nFig.S34 in Supplementary Information and mentioned on line 268 in the main text), which also show\nobvious crumpled structure with that in Fig.R2c and d. Meanwhile, we have tested the performance of the\ncrumpled membranes at 120 ℃ for 4 h (Fig. R3, original Fig. S31) and 3.0 MPa (Fig. R4, original Fig.\nS33), which both shows stable gas separation performance, indicating a stable crumpled structure.\nMoreover, we simulated the crumpled structure treated at 3.0 MPa via adjusting the AFM tip force (Fig.\nR5, original Fig. S43d), and the results show that only slight deformation occurs.\ncross-section images of (c) PT-1 and (d) PT-2 membranes, (e) 5 and (f) 10 layers of stacked PA samples. The arrows\nrepresent the crumpled layers.\n2 2\nrepresent PT-3 membrane and the blue parts represent PT-5 membrane. The solid and hollow symbols mean the\nmembranes treated at 25 ℃ and 120 ℃, respectively. The CO /N separation performance of heterogeneous\n2 2\nmembrane (PT-3) is almost unchanged, while that of the homogeneous counterpart (PT-5) decrease.\nFig. R4 CO /CH separation performance of (a) CO permeance, (b) CO /CH selectivity, and CH /N separation\n2 4 2 2 4 4 2\nperformance of (c) CH permeance, (d) CH /N selectivity of PT-1, PT-2, PT-3, PT-4 and PT-5 membranes. Feed\n4 4 2\ngas: CO /CH mixed gas (10/90 by volume), CH /N mixed gas (50/50 by volume), 25 ℃. The PT-1 to PT-3\n2 4 4 2\nmembranes with crumpled morphology show high and stable separation performance within 3.0 MPa compared with\nthat of PT-4 and PT-5 membranes.\nto 41.6 nN, is to simulate the operation pressure from 1.0 to 3.0 MPa\n7\n3.2 In addition, the diffusion coefficient reported by the new procedure is about two orders of magnitude\nlower than that reported for PDMS in the literature (Markov et al., Biomed Microdevices. 2014\nFeb;16(1):91–96. doi: 10.1007/s10544-013-9808-2; Monteleone et al., J. Membr. Sci. 648 (2022) 120356.\ndoi:10.1016/j.memsci.2022.120356.). If diffusion in PDMS is so much slower, it is difficult to understand\nhow the composite crumpled membrane can have such a high permeance.\nReply: Thanks for your comments. As mentioned in Question 3.1, in the fabrication of stacked PA samples,\nthe PDMS layer was first peeled off from the composite membrane with solvent (n-hexane) treatment.\nHence, we only tested the diffusion coefficient of pure PA layers rather than that of PDMS. In our work,\nthe PA layer determines the total separation performance of the composite membrane based on previous\ndiscussions. Hence, the diffusion coefficient of the PA layer (Table R1, original Table S3) was tested to\nanalyze the CH /N separation performance (Fig. R4, original Fig. S33).\n4 2\nMeanwhile, the relationship between the diffusion coefficient (D) and the gas permeance (R) is not a\nsingle variable, which also involves the influence of film thickness (l) and solubility coefficient (S) based\non equations P=D*S (P represents the gas permeability) and R=P/l. Take the PA layer as an example\nshown in Table R1. The diffusion coefficient of PA layer is low but the solubility coefficient is relatively\nhigh. Combined with a thin film thickness (~65 nm), a relatively high gas permeance still can be obtained.\nTable R1 The solubility and diffusivity of CH and N of the PA layers from PT-1 to PT-5 membranes.\n4 2\nPermeability Solubilityb Diffusivityc Solubility Diffusivity\nSample selectivity selectivity\nCH N CH N CH N CH /N CH /N\n4 2 4 2 4 2 4 2 4 2\nPT-1 45.92 23.38 3.71 1.15 12.38 20.26 3.21 0.61\nPT-2 67.44 26.61 4.83 1.28 13.95 20.72 3.76 0.67\nPT-3 75.9 29.44 5.32 1.35 14.25 21.65 3.92 0.65\nPT-4 24.4 20.04 3.89 1.93 6.26 10.37 2.01 0.60\nPT-5 21.42 19.92 3.79 1.99 5.65 9.98 1.9 0.56\na Permeability, Barrer, 10-10 cm3 (STP) cm cm-2 s-1 cmHg-1\nb Solubility, 10-2 cm3 (STP) cm-3 cmHg-1\nc Diffusivity, 10-8 cm2 s-1\n8"}, {"round": 4, "reviewer_comments": {"reviewer_3": "The authors have responded satisfactorily and with plausible answers to the remaining questions of this reviewer.\nThis paper is now acceptable for publication."}, "author_response": "We thank the reviewer for noting the novelty and the significance of our work.\nWe also appreciate the reviewer’s suggestions and comments to help improve the\nquality of our manuscript."}]

Decision letter