Antigravity confined interfacial self-assembly approach for the synthesis and characterization of nanofilms

Domain: chemistry
Published: 2026-01-14
Editorial outcome: major_revision

Abstract
Gravitationally induced stratification during self-assembly often leads to density-driven vertical segregation, resulting in an inherent density gradient that severely limits the synthesis of metastable nanofilms requiring inverted architectures. Here we show an antigravity confined interfacial self-assembly approach based on a liquid-liquid interface formed between hydrophilic and hydrophobic porous membranes, where capillary forces suppress gravitational effects to enable precise molecular organization. Experimental data, supported by quantum chemistry, density functional theory, and Fick’s first law, demonstrate that capillary forces enhance local concentration and interaction probability, yielding highly ordered, stable nanofilms. Our approach achieves a 17-fold increase in film area than gravity-limited methods and a 109-fold improvement over unconfined techniques. These nanofilms exhibit the stability and mechanical property, showing promise for green enhanced oil recovery and multifunctional material development. Furthermore, our strategy offers a paradigm for nanofilm mechanical characterization, paving the way for future advances in the design and application of nanomaterials.

Introduction
Confined interfacial self-assembly is a materials synthesis process where molecular systems spontaneously organize into ordered structures at interfaces or surfaces under confined conditions1–3. This approach represents a versatile and powerful approach for designing and synthesizing materials with tailored functionalities, offering broad applications in nanotechnology, environmental science, and biomedical engineering4,5. In materials synthesis, it offers precise control over the formation of nanostructures, enabling the design of customized nanomaterials with specific properties. By utilizing confined spaces, this technique allows for the fine-tuning of the self-assembly process at the nanoscale, which is essential for creating functional materials, such as nanofilms.

However, the gravitationally induced stratification during self-assembly causes density-driven vertical segregation, typically accumulating heavier molecular components at the bottom and lighter ones at the top6,7. This inherent density gradient critically limits the synthesis of metastable nanofilms requiring inverted architectures where dense components must occupy upper layers to ensure structural integrity. Such forced positional inversion disrupts thermodynamic equilibrium, leading to localized stress concentration and ultimately destabilizes the interfacial assembly process for compromising the synthesis stability of the material8.

In this work, we show an antigravity confined interfacial self-assembly (ACIS) for synthesizing self-supporting nanofilms, overcoming above limitations by employing dominant capillary forces to counteract the macroscopic effects of gravity and achieve the inverted interface. Here we strategically selected a ubiquitous and critically important cyclodextrins (CDs) to validate the feasibility and practical applicability of our methodological approach, due to CDs, a prominent class of eco-friendly compounds, have captured significant attention in the research arena9,10. Their distinct molecular architecture bestows upon them a set of extraordinary properties, which in turn give rise to a broad spectrum of applications and exert a far-reaching influence across diverse scientific and industrial domains11.

The current synthesis of CD films typically hinges on a set of interactions and techniques: host-guest interactions, hydrogen bonding interactions, interface adsorption, and electrostatic interactions, alongside methods like self-assembly, interfacial polymerization, impregnation, chemical crosslinking, casting, and various coating approaches12–14. If the CD films are made even thinner, they will represent a critical frontier in material science due to their lightweight nature, self-healing property, fluidity, flexibility, maximize selectivity, and permeability7. The traditional strategy for thinning CD films primarily relies on composite synthesis using rigid supporting substrates15,16 or liquid-liquid interface self-assembly. However, the ultrathin thickness of the films formed through such heterogeneous structures cannot be considered as the intrinsic thickness of the films themselves, as these methods result in films that cannot be transferred independently and lack self-supporting capabilities after formation. Liquid-liquid interface self-assembly uses the interface to template molecules and stabilize properties, however, the droplet interface self-assembly uses the electrodes, and two-phase interface self-assembly depends on gravity17,18. These limitations are primarily affected by the phase density, which can hinder the selection of liquids in the self-assembly process (especially functional molecules in a phase with high phase density), large-scale synthesis of CD self-supporting nanofilms (CSNs), and the application of practical scenarios such as oil field, ultimately affecting the stability of the reaction interface, morphology, and structure of the nanofilms.

In this ACIS, the capillary force of the hydrophilic nylon and hydrophobic polytetrafluoroethylene (PTFE) membranes can effectively counteract the gravity effect to form a confined interface, which enables film formation under the same conditions where previous attempts failed(Fig.1a). It restricts the movement direction of CD and brings them into the reduced dimensionality, enhanced proximity, and increased diffusion to interface, thus increasing the host-guest interaction and hydrogen bonding between CDs and dodecane. This interaction results in the formation of surfactant-like compounds that possess the unique capability to congregate at the water-alkane interface, thereby facilitating directional self-assembly to form the stable and highly ordered CSNs. Multi-scale modeling, based on Fick’s first law to model the material diffusion process, combined with density functional theory calculation to analyze the interaction between molecules, to reveal the driving force and influencing factors of the diffusion process from different scales(Supplementary Figs.1–4).

At the oil-water interface formed by the alkane phase and the CD solution under the influence of gravity, the number of CD molecules in the lower layer is limited, resulting in fewer self-assembled molecules and weaker interfacial films. In contrast, at the antigravity confined interface, the CD solution infiltrated into the nylon membrane and the dodecane infiltrated in the PTFE membrane can overcome the phase gravitational constraints by the capillary force. Here, the CD molecules can form surface-active substances through host-guest interaction with dodecane at the interface, which subsequently self-assemble into the CSNs driven by hydrogen bond(Fig.1a, Left). Characterization of the CSNs, particularly after the removal of excess liquid, reveals a remarkably uniform and smooth surface morphology, as evidenced by Scanning Electron Microscopy (SEM) imaging. Notably, the CD nanofilms exhibit thickness in the sub-100 nm range, highlighting the effectiveness of this method for synthesizing nanofilms at the antigravity confined interface.

In terms of CSNs synthesis mechanism, the integration of a β-CD infused nylon membrane with a dodecane-saturated PTFE counterpart creates an antigravity confined interface(Fig.1b). This interface acts as a crucible where CD molecules migrate and engage in interactions with dodecane, leading to the formation of surface-active substances that mitigate interfacial tension. The diffusion rate of β-CD molecules to the interface and the amount of adsorption at the interface can be calculated by the interfacial tension(Supplementary Figs.5, 6, and Table 1). The relationship between the transmembrane pressure difference (ΔP), membrane pores (d), and the infiltrated liquid thickness (L) was calculated (Supplementary Fig. 7 and Tables 2–4). According to Laplace’s equation, Hagen-Poiseuille’s law, and Washburn equation, smaller membrane pores, characterized by low liquid surface curvature radius and high additional pressure, will produce significant resistance to the entry and passage of the liquid, eventually leading to greater liquid retention in the confined space between nylon and PTFE membranes. The congregated molecules, through a symphony of covalent and hydrogen bonding, orchestrate the synthesis of the CSNs. Quantum chemistry was employed to optimize the structure of β-CD-dodecane complexes, and the interaction region indicator (IRI) function can intuitively visualize the nature of the interactions. This approach not only realizes the synthesis of nanofilms, but also opens avenues for the development of nanofilm materials with tailored properties.

Results
Design, synthesis, and characterization of the CSNs
The synthesis of nanofilms at the liquid-liquid interface is widely recognized as a straightforward, efficient, and eco-friendly process for producing compact, robust, and easily controllable films6,8,19. By leveraging capillary forces, liquids can be confined within micro-structured porous solid matrices to form the confined interfaces20,21. Unlike current systems, the asymmetric hydrophilic–hydrophobic porous membranes employed here are designed to overcome gravitational limitations, significantly expanding their potential applications across diverse scientific fields22. Through the strategic arrangement of solid matrices with contrasting properties to encapsulate two immiscible liquids, a stable antigravity confined interface can be established. This interface is particularly susceptible to electrostatic interactions and van der Waals forces, providing an optimal environment for the synthesis of CD nanofilms.

Key factors influencing the properties of the self-assembled nanofilms include the pore size of the solid substrate and the composition of the liquids within the ACIS. In this study, substrates with pore sizes of 1 μm, 5 μm, and 8 μm were used, while the ACIS primarily consisted of CD solutions and alkanes(Fig.2a). CDs with biocompatible and biodegradable properties present a truncated cone shape with a central cavity, and they are widely utilized in pharmaceuticals, food industries, and biomedicine. The three natural forms (α-, β-, and γ-CD) possess hydrophobic cavity inner diameters of 4.7–5.3 Å, 6.0–6.5 Å, and 7.5–8.3 Å, respectively. Their amphiphilic nature, featuring a hydrophilic exterior and hydrophobic interior, enables host-guest interactions with hydrophobic molecules in aqueous environments23,24. As such, CDs serve as ideal hosts for alkanes, sheltering their hydrophobic moieties. Different alkanes may form different complexes with β-CD24,25.

Confocal microscopy (Supplementary Fig. 3) revealed that the confined space formed by infusing β-CD solution into a nylon membrane and dodecane into a PTFE membrane is approximately 4 μm wide. The aqueous phase, containing trace amounts of CD, has a density similar to water, while the oil phases, comprising octane, decane, dodecane, and hexadecane, exhibit lower densities.

Initial morphological characterization of films synthesized from water and CD solutions in dodecane was conducted via microscopy (Supplementary Fig.8). We further investigated the transmembrane behavior for the gas through the CSNs by measuring the critical pressure required for gas to penetrate interfacial films formed between water or CD solutions and dodecane(Fig.2b). Notably, the CSNs derived from β-CD and dodecane exhibited a higher critical pressure (~49.76 kPa) than those from other CDs, indicating greater mechanical stability and resistance to gas permeation.

We also examined β-CD behavior in alkanes with varying chain lengths(Supplementary Fig.9). Crystal formation was observed when β-CD solution was introduced into dodecane and hexadecane, attributable to the binding of one long-chain alkane molecule to two β-CD molecules25. The CSNs were fabricated by infusing β-CD solution into nylon membranes and different alkanes into PTFE membranes. Critical pressure measurements for gas transmission through these CSNs(Fig.2c) revealed that the system incorporating dodecane required the highest critical pressure (~49.76 kPa), underscoring the superior mechanical strength and stability of nanofilms self-assembled from β-CD-dodecane complexes.

The stability of the confined interface was quantified by measuring the critical transmembrane pressure required to rupture the liquid film and induce reconfiguration of the capillary-stabilized liquids26,27. In this system, a nylon membrane was used to confine the β-CD solution, while a PTFE membrane confined the dodecane (Supplementary Fig.10). The selection of appropriate pore sizes for each membrane proved crucial for successful nanofilm formation. As shown in Fig.2d, the critical pressures were evaluated for nanofilms formed using dodecane infiltrated into PTFE membranes (with 1 μm and 5 μm pores) and β-CD solution infused into nylon membranes (1 μm, 5 μm, and 8 μm pores). Following nanofilm synthesis, the critical transmembrane pressure increases across all pore sizes compared to the film-free system, indicating enhanced mechanical integrity of the interface.

The pore size of the nylon membrane had a greater impact on the critical pressure than that of the PTFE membrane, which we attribute to the diffusion of CDs through the nylon pores and the trajectory of gas pressure, which traverses the nylon membrane before the PTFE membrane. These membranes serve primarily to support the liquids in forming a stable antigravity interface. Smaller pores (e.g., 1 μm) require higher pressures to overcome capillary resistance, whereas larger pores (e.g., 8 μm) make the interface more susceptible to gravitational deformation due to the density contrast between the liquids. Among the configurations tested, the system combining a 5 μm PTFE membrane (dodecane) and a 5 μm nylon membrane (β-CD solution) proved optimal for fabricating and characterizing composite CSNs, based on the magnitude and consistency of pressure changes before and after film formation.

The ACIS establishes a liquid-liquid interface through capillary confinement of immiscible fluids within hydrophilic and hydrophobic porous matrices. The stability and antifouling properties of CSNs are critical for practical applications26,28. A common method to evaluate thin-film stability is Laplace pressure-driven film rupture29,30. Here, the marked increase in transmembrane pressure after CSN formation enables stability assessment via cyclic pressure loading and release (Supplementary Fig.11). As depicted in Fig.2e, CSNs derived from β-CD and dodecane exhibit exceptional stability: even after disruption at the critical pressure, the nanofilm reforms spontaneously upon pressure release, mediated by host-guest interactions and hydrogen bonding. This self-healing behavior ensures the long-term stability of the film as long as the β-CD/dodecane interface is maintained. Furthermore, no film residues were observed via SEM after rinsing (Supplementary Fig.12 and Tables 5–6), confirming the antifouling characteristics of the ACIS.

Compared with prior methods for synthesizing interfacial films, a key advantage of the ACIS is its capacity to form large-area interfaces with the same volume. The dimensions of the nanofilms are determined by the membrane area over which the β-CD solution and dodecane are distributed (Supplementary Fig.13). Using 6 μL of dodecane and 26 μL of β-CD solution infused into 25 mm-diameter membranes, the ACIS produces an interface congruent with the membrane area. In contrast, gravity interfacial self-assembly (GIS) yields an interface of only ~28 mm², and unconfined interfacial self-assembly (UIS) results merely in peripheral contact between the two liquids, leading to minimal film formation. As summarized in Fig.2f, the nanofilm area achieved via ACIS is approximately 17 times larger than that from GIS and 109 times greater than that from UIS, highlighting the efficiency of this approach for producing large-area nanofilms under equivalent volumetric conditions.

Condition and theoretical mechanism of the synthesis of the CSNs
Based on our previous investigations into the design of aqueous and alkane phases for the properties of the CSNs, we selected β-CD solution as the aqueous phase infused in a nylon membrane and dodecane as the alkane phase within a PTFE membrane. Figure 3a illustrates the molecular mechanism at the antigravity confined interface, where β-CD molecules eventually polymerize via hydrogen bonding. Initially, β-CD molecules dispersed in the aqueous phase diffuse toward the dodecane-water interface over time and with increasing concentration. At the interface, β-CD orients itself to encapsulate dodecane via host-guest interactions, forming a complex that reduces interfacial tension and drives the interfacial assembly. Subsequently, these complexes undergo interfacial polymerization through hydrogen bonding with β-CD molecules in the bulk phase, enhancing the stability and mechanical strength of the film.

The concentration of β-CD solution plays a critical role in the diffusion and interfacial binding of β-CD molecules, significantly influencing nanofilm formation. We characterized interfaces formed between dodecane and β-CD solutions at varying concentrations (Supplementary Fig.14). As shown in Fig.3b, we evaluated the critical transmembrane pressure required for gas to penetrate the CSNs synthesized with β-CD concentrations ranging from 0.001 to 0.005 mol/L. Compared to a pure water-dodecane interface, higher β-CD concentrations led to increased diffusion to the interface and correspondingly higher critical pressures, confirming enhanced mechanical strength due to molecular assembly. At 0.004 mol/L, a continuous nanofilm formed, effectively covering the nylon membrane pores (Supplementary Fig.15). Below this concentration, binding between β-CD and dodecane was insufficient for nanofilm formation. Film thickness increased with concentration, as evidenced by comparisons between 0.004 and 0.005 mol/L samples (Fig. 1a and Supplementary Fig.16).

Time-dependent diffusion and complex formation at the interface also affect film formation. β-CD molecules require time to diffuse, bind dodecane via host-guest interactions, and form hydrogen-bonded networks. As shown in Fig.3c, the critical pressure increased over time, indicating strengthening of the film. For instance, with 0.004 mol/L β-CD, the critical pressure rose from 44.35 kPa initially to 49.76 kPa after 2 h, indicating full nanofilm formation. Beyond this period, the interfacial molecular configuration saturated, and no further increase in pressure resistance was observed.

Interfacial tension measurements provide further insight into molecular behavior. We monitored dynamic interfacial tensions between dodecane and CD solutions (Fig. 3d and Supplementary Fig. 17). While β-CD and γ-CD solutions exhibited rapid interfacial tension reduction followed by stabilization, α-CD solution showed minimal change within 60 min, indicating β-CD and γ-CD molecules bind with the dodecanes to form the surface-active substances at the interface, and ineffective binding for α-CD31. The lowest equilibrium interfacial tension was observed with β-CD, confirming its superior ability to form amphiphilic complexes with dodecane.

We also examined β-CD interfacial behavior with alkanes of varying chain lengths (Fig. 3e and Supplementary Fig.18). Short- and medium-chain alkanes (octane, decane, dodecane) showed typical interfacial tension reduction curves, whereas hexadecane exhibited an initial rise followed by a decline, suggesting initial formation of non-amphiphilic complexes that later reorganize. Among these, the dodecane with medium-chain length yielded the lowest equilibrium interfacial tension with β-CD, indicating optimal complex stability.

Concentration-dependent interfacial tension profiles of β-CD solutions in dodecane are shown in Fig. 3f and Supplementary Fig.19. Concentrations up to 0.004 mol/L of β-CD solution exhibited classical amphiphile-like interfacial tension decay. At 0.005 mol/L, however, an initial interfacial tension increases suggested formation of non-amphiphilic complexes involving multiple β-CD molecules per dodecane, leading to less efficient interfacial tension reduction and altered film morphology. After all the dynamic interfacial tensions of β-CD solutions with different concentrations reach equilibrium values, we find that the interfacial tension of 0.004 mol/L of β-CD solution is the lowest, and the interfacial tension of 0.005 mol/L of β-CD solution is the highest. In a word, one β-CD molecule in 0.004 mol/L of β-CD solution and one dodecane molecule can form a strong amphiphilic complex. Those complexes at the interface will aggregate into a nanofilm with the interaction between β-CDs and dodecanes and the interaction between β-CDs31.

Given the density difference between CD solutions and alkanes, antigravity confinement promotes CD diffusion toward the underlying alkane phase. To elucidate the molecular basis of these observations, we performed quantum chemical calculations to characterize host-guest interactions between CDs and alkanes32. We used the XTB program for the configuration search to find the optimal structures for each CD-alkane complex. And the semiempirical quantum mechanical methods and the hybrid density functional B3LYP together with the basis set of 6-31G(d) are used to generate and optimize the complexes33,34. And then, the binding energies of the complexes with the lowest energy configurations were further calculated under B3LYP/6-311G(d) level using the Gaussian 16 program and revealed with IRI method35 using the software Multiwfn36. As shown in Fig. 3g, the binding energy for β-CD and dodecane was approximately −28 Kcal/Mol, significantly stronger than other CD-alkane complexes (all > −20 Kcal/Mol). Accordingly, the lowest energy configurations of CD and alkane are shown in Fig. 3h.

It is necessary to use quantum chemistry methods to optimize and search for the lowest potential energy surface to obtain the most stable conformation, and further analyze the intermolecular and intramolecular interactions. Further analysis of the lowest energy configuration revealed hydrogen bonding between adjacent β-CD molecules at the interface and with those in the bulk (Fig. 3i and Supplementary Fig.20). The interfacial β-CD molecules are oriented with their larger rim facing downward to engage with alkane molecules. Two predominant stacking modes were identified: small-ring to large-ring and small-ring to small-ring. Both configurations exhibited similar stability, suggesting their concurrent presence at the interface.

Applications
We further demonstrate the versatility of this method across multiple liquid-liquid systems, with potential applications in material science, emulsion processing, and the petroleum industry (Fig. 4a, Right). The morphology of the nanofilms is determined by the shape of the solid substrates used to confine the β-CD solution and dodecane. As illustrated in Fig. 4a, Left, employing nylon and PTFE membranes patterned as circles, hearts, triangles, five-pointed stars, and leaves enables the synthesis of correspondingly shaped CSNs via the ACIS. Comparisons between ACIS and GIS are showed in Fig. 4a, Right. As shown in gray, GIS in certain systems suffers from the formation of interfacial films with poor mechanical strength and limited area, and also exhibits significant limitations in practical applications. However, ACIS in these systems can effectively solve some limitations of GIS, as shown in pink. As shown in Fig. 4b and Supplementary Fig.21a, the temperature of dodecane under ACIS confinement remains 3 °C higher than that under GIS after 3 min, underscoring the potential of CSNs in insulation materials. A finding further validated in food insulation applications (Supplementary Fig.22).

The ACIS also facilitates unique emulsion behaviors. Unlike GIS, where alkane and CD solution rapidly separate into distinct layers, the ACIS allows the dispersion of CD solution droplets within the alkane phase (Fig. 4c). This emulsification process, stabilized by interfacial nanofilms, suggests promising applications in areas such as pesticide emulsifier formulation.

Aligned with global sustainable development goals, green petroleum extraction remains a critical endeavor. As a result, enhanced oil recovery has become an essential and indispensable part of this strategy37. The tertiary oil recovery technology based on oil-water interface behavior regulation has received widespread attention all along38,39, and the in-situ films formed by the ACIS are expected to have applications in green enhanced oil recovery (Supplementary Fig.23 and Table 7). A key challenge in chemical flooding for the Enhanced Oil Recovery (EOR) is the preferential flow of water through high-porosity and oil-depleted channels due to viscosity contrasts and pore heterogeneity. Without interfacial films, water flooding requires only low pressure (0.26 MPa) and primarily recovers oil from large pores. Following CD film formation, however, the required transmembrane pressure rises to 8.65 MPa, enabling displacement from smaller pores (Fig. 4d). The enhanced pressure tolerance and selective permeability offered by CSNs improve adaptability to subsurface heterogeneity39. Moreover, CDs are biocompatible and biodegradable, providing an ecologically superior alternative to conventional displacement agents such as synthetic surfactants and polymers38. This inherent advantage not only simplifies the displacement mechanism but also synergistically amplifies the displacement efficiency, ensuring an optimal synergy between the methodological approach and the material properties for maximized outcomes.

Characterizing the mechanical strength of ultrathin films remains a significant challenge40. There are some conventional methods to characterize the mechanical strength of ultrathin films including the SEM to directly observe the thickness of the film, the load-bearing method to place the weight above the film, the tensile method to test the stress-strain, and the Young’s modulus of the film, etc41–44. However, using the above methods is likely to destroy the CSNs during the moving and transferring processes of the films before the test operation, and it is difficult to detect and compare the mechanical strength of the films45. To address this, we developed a liquid clamp device based on ACIS for in-situ mechanical characterization via transmembrane pressure. In the initial state of the ACIS, opening the system requires a certain pressure (P1) generated by the compression of gas to overcome the capillary force of the gating liquid in the membrane channel. After the ultrathin film is synthesized, the pressure that would open the initial state of the ACIS will not open the film fabricating state of the ACIS (Fig. 4e). To open the film fabricating interface, the higher pressure (P2) is required. The critical pressure difference (ΔP) required to open the interface before and after ultrathin film formation serves as a direct measure of film mechanical strength (Fig. 4f).

We applied this method across several systems (Fig. 4g and Supplementary Fig.21b). The CSNs produced via ACIS exhibited a ~2 kPa higher ΔP than those from gravity confined interfaces, confirming superior mechanical integrity. For instance, millet porridge films showed greater strength than milk films.

In EOR contexts, the mechanical strength of interfacial films is critical in controlling the flow characteristics of oil-water mixtures: overly weak films permit premature water breakthrough, while excessively strong films may impede flow or elevate injection pressures. Tailoring film strength to specific reservoir conditions can promote fluid diversion and improve microscopic sweep efficiency40. Currently, few experimental methods exist for quantifying oil-water interfacial film mechanics. Our approach enables in-situ strength measurement and controlled self-assembly of interfacial films, offering a strategy for enhancing oil recovery in challenging reservoirs. For example, we tested the in-situ CSNs synthesized by the two types of petroleum, and the North three area oil exhibited a larger transmembrane pressure difference, indicating stronger films and better displacement performance.

Methods
Synthesis of the antigravity confined interfacial self-assembly
The water, 0.004 mol/L of α-CD, 0.001 mol/L of β-CD, 0.002 mol/L of β-CD, 0.003 mol/L of β-CD, 0.004 mol/L of β-CD, 0.005 mol/L of β-CD, and 0.004 mol/L of γ-CD solutions were used as the functional liquids infused to the nylon membrane used as the porous material in the upper layer of the ACIS. And in the lower layer of the ACIS, the octane, the decane, the dodecane, and the hexadecane were used as the functional liquids infused to the PTFE membrane used as the porous material. The ACIS was the overlap of the nylon membrane infused with the CD solution and the PTFE membrane infused with the alkanes to form the confined antigravity interface.

Characterizations of membranes
Microstructures and energy spectrum diagrams of the nylon membrane, the nylon membrane infused with the CD solution, the PTFE membrane, and the PTFE membrane infused with the alkanes in the ACIS were measured by using Field emission SEM (Zeiss GeminiSEM500).

Transmembrane critical pressure measurements
The CD solutions were infiltrated into the nylon membrane, and the alkanes were infiltrated into the PTFE membrane. And then, the gas was injected to pass through the overlapping the nylon membrane with CD solutions and PTFE membrane with the alkanes. Transmembrane critical pressures for gas passing through the ACIS system were measured by using the liquid gating intelligent tester and analyzer (GIFT-E1Pro) from Gating Inspired Future Technology Co., Ltd. (Xiamen, China). In all experiments, the gas flow pressures were produced by a syringe pump with a pressurization rate of 2 mL/min. Unless otherwise specified, the pore sizes of the nylon membranes and the PTFE membranes with diameter of 25 mm are 5 μm. All experiments were repeated at least three times.

Stability of film
The gas was injected to pass through overlapping the nylon membrane infiltrated with β-CD solution and PTFE membrane infiltrated with the dodecane. When gas passes through the system, the film is destroyed. After the gas input stops, the film continues to synthesize. After several times of gas injection and gas removal, the transmembrane pressure of the film is stable, indicating that if the liquid-liquid interface exists, the film will stably synthesize. Transmembrane critical pressures produced by the compression of the gas to pass through the CD self-supporting nanofilms (CSNs) were measured by using the liquid gating intelligent tester and analyzer (GIFT-E1A). In all experiments, the pressures were produced by the 2 mL/min of gas flow by a syringe pump. The pore sizes of the nylon membranes and the PTFE membranes with diameter of 25 mm are 5 μm. All experiments were repeated at least three times.

Characterization of film area
In this part, three methods are used to synthesize the films. By the ACIS, because the 26 μL of β-CD solution will infiltrate in the nylon membrane, and 6 μL of dodecane will infiltrate in the PTFE membrane, the area of film formed will be consistent with the area of the membranes. By the gravity interfacial self-assembly (GIS), 6 μL of the dodecane floats on 26 μL of the β-CD solution. By the unconfined interfacial self-assembly (UIS), when the 26 μL of β-CD solution touches the 6 μL of dodecane, it pushes the spread 6 μL of dodecane toward the edge, so that only the edge of the β-CD solution forms an interface with the dodecane. The areas of films are calculated using the radius measured by the ruler.

Interfacial tension measurements
The water, 0.004 mol/L of α-CD, 0.001 mol/L of β-CD, 0.002 mol/L of β-CD, 0.003 mol/L of β-CD, 0.004 mol/L of β-CD, 0.005 mol/L of β-CD, and 0.004 mol/L of γ-CD solutions were prepared by the deionized water. 10 μL of these solutions were injected into the alkanes to directly measure via the pendant drop method on the OCA100 system (Dataphysics, Germany) at room temperature. All experiments were repeated at least three times.

The binding energy calculations
Quantum Chemical (QC) methods were used to investigate non-covalent interactions, such as hydrogen bonds and van der Waals forces, which are essential for the stability of CD complexes. To investigate the host-guest interactions between CDs and alkane molecules, we adopted a multi-level computational strategy. Given the substantial size of CD complexes, the semiempirical quantum mechanical methods GFN1-xTB33 and GFN2-xTB34 were first applied for efficient conformational sampling. Then, the single point energies and binding energies based on the structure with the lowest energy were further calculated under B3LYP/6-311G(d) level using Gaussian 16 program, with Grimme’s D3BJ dispersion correction applied throughout to enhance accuracy. Solvation effects were incorporated via the Solvation Model based on Density (SMD) as an implicit solvent model. Finally, the binding natures in the studied complexes were revealed with IRI method35 using the software Multiwfn36, and binding energies were obtained based on the following equation:

Ebinding = Ecplx − (ECDopt + Eguestopt) (1)

All the visualization of molecular structures and contour surfaces were performed by VMD46. For the conformer search, the temperature is 298.15 K, and the energy window is 6 kcal mol⁻¹.

Visual analysis
The types of interactions that stabilize such complexes, including hydrogen bonding, van der Waals forces, and both hydrophobic and dipole-dipole interactions, typically cannot be modeled with the necessary accuracy using molecular mechanics methods. Graphical analysis of interactions is a useful way to examine chemical problems and visualize the type of interaction at a particular location in the system. The interaction area indicator (IRI) function35 is one of them, through its isolines, all types of interaction can be clearly grouped in a picture. IRI methods are excellent at revealing chemical bonds and weak interaction regions. Unlike Bader’s atoms in molecules (AIM) method, which is a method of calculating atomic charge based on real space segmentation, the IRI method more intuitively demonstrates the nature of the interaction. It is defined as follows:

IRI(r) = |∇ρ(r)| / [ρ(r)^a] (2)

Where ρ(r) is the electron density. If the iso-surface of IRI is blue, it indicates the van der Waals force. If the iso-surface is purple, it indicates that there is some steric hindrance. The yellow ones are covalent bonds. In addition to the intermolecular interactions, various intramolecular weak interactions can also be observed. And in this system of work, the weak interaction refers to hydrogen bonding.

Different shapes material synthesis
The nylon and PTFE membranes are cut into different shapes, including circles, hearts, triangles, pentagrams, and leaf shapes. The β-CD solution will infiltrate into the nylon membrane, and the dodecane will infiltrate in the PTFE membrane. After overlapping the two membrane systems for two hours, the corresponding shape of the films are synthesized. Dyes are soluble in alkanes and insoluble in water, and we found yellow dye on the hydrophilic nylon membrane, which further confirmed the synthesis of the film.

Insulation experiment
25 mL of the β-CD solution and the dodecane samples are heated to 85 °C and transferred to a beaker to observe the temperature change of the samples. In the GIS system, where the dodecane is on top, the dodecane dissipates heat faster. In the ACIS system, if the PTFE membrane and nylon membrane are fixed, the upper layer of the β-CD solution will not flow into the lower layer, and the system will slow heat dissipation. The sample without films cooled faster within 3 min.

Dispersion system preparation
There are two methods for dispersion system preparation. The GIS uses the dense β-CD solution phase as the dispersing phase and the dodecane as the dispersing substance. The ACIS uses the dense β-CD solution phase as the dispersing substance and the dodecane as the dispersing phase. The dispersing substance is placed into the syringe and dripped through the corresponding nylon and PTFE membranes with confined space to the dispersing phase.

Oil displacement experiment
A uniform Berea core with a gas permeability of 30×10⁻³ μm² was vacuumed for 4 h at room temperature and saturated with deionized water to calculate pore volume and porosity. The core was then heated for 12 h at a constant temperature of 25 °C. The original oil saturation of crude oil was calculated by using the oil to flush water. Next, the deionized water or β-CD solution was injected into the core. When the cumulative injection volume reached 2 PV, the water or β-CD solution was stopped. In this work, it is worth noting that we first injected 0.5 PV of the deionized water or β-CD solution, and then suspended for 2 h before further injected remaining 1.5 PV of liquid. Dynamic pressure and recovery were recorded during displacement. During the experiment, the injection rate was constant at 0.35 mL/min. A similar core is used when the injection liquid is changed. Each experiment was repeated three times.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "The manuscript explores an antigravity-confined interfacial self-assembly (ACIS) strategy for growing cyclodextrin–alkane nanofilms and compares it with conventional gravity-induced self-assembly (GIS). The topic is timely and potentially useful to the soft-matter community, and the abstract plus the opening half of the Introduction are clear and engaging. Unfortunately, the remainder of the paper lacks clarity, cohesion, and adequate evidence. The work does not warrant publication in Nature Communications.\n\nMajor issues:\nThe narrative quality declines sharply after the mid-Introduction. Organization becomes erratic, ideas are repeated, and awkward phrasing impedes comprehension. A careful, line-by-line edit is required to bring the latter sections up to the standard set by the opening pages.\n\nThe manuscript asserts that gravity fundamentally limits interfacial film formation, yet the key paragraph advancing this claim provides no citations. Please substantiate the argument with representative literature or supply systematic data showing that a broad range of interfacially assembled films fail under gravity. Without such evidence, the paper’s primary justification remains speculative.\n\nComparisons between GIS and ACIS are scattered throughout multiple sections. Consolidating these discussions—ideally in a single figure or a dedicated subsection—would clarify ACIS’s advantages and remove redundancy.\n\nThe mechanical and morphological improvements reported for ACIS films appear incremental when benchmarked against prior interfacial films. The manuscript should state more explicitly where the present approach surpasses earlier work, or adjust the claims to reflect a modest advance.\n\nNearly every data panel is accompanied by multiple schematic drawings. While cartoons can aid understanding, they currently overwhelm the actual measurements. Please reduce redundant schematics so that experimental evidence is more prominent.\n\nFigure 1 functions as an overview montage, yet panel 1c duplicates Figure 3i and other elements reappear later. Streamline Figure 1 to a concise concept graphic or remove duplicated content to avoid confusion.\n\nPage 3 contains a self-contradictory sentence claiming that the membrane “restricts CD mobility” while simultaneously “increasing diffusion.” Clarify whether confinement accelerates diffusion along the interface (reduced dimensionality) or slows overall transport.\n\nThe formation mechanism can likely be explained by classical nucleation and growth driven by host–guest enrichment at the interface. The quantum-mechanical calculations seem unnecessary unless they yield insights unattainable by simpler methods. Consider moving these computations to the Supporting Information or demonstrating explicitly how they alter the mechanistic picture.\n\nThe experimental setup is described almost verbatim three times on page 7, disrupting the narrative flow. Consolidate these repetitions and present each protocol only once.it is stated \"The CSNs are designed by infusing β-CD solutions into the nylon membrane and infusing octane, decane, dodecane, and hexadecane into the PTFE membrane.\"\"The antigravity confined interface is formed by infusing water or CD solutions into the nylon membrane and infusing alkane into the PTFE membrane\" \"In the system formed by infusing water or CD solutions into the nylon membrane and infusing dodecane into the PTFE membrane\" this is rather disturbing to read smoothly.", "reviewer_2": "This manuscript reports a self-assembly strategy that utilizes the oil-water interface to dimensionally localize the association between an n-alkane and a cyclodextrin, resulting in a self-supporting nanofilm. By sandwiching a water-infused, porous nylon membrane and an oil-infused, porous Teflon membrane, the authors create a capillary-force stabilized, gravity-inverting oil-water interface where cyclodextrin and dodecane assemble to produce the nanofilm. The authors demonstrate that the approach allows the formation of large-area film with markedly improved order and stability. They further illustrate the utility of the approach for applications across materials engineering, food processing, emulsion preparation, and oil displacement in petroleum recovery.\n\nThe approach presented is interesting, the findings insightful, and the applications promising. I recommend publication after the authors have considered the following minor questions, addressing which I believe will enhance the work's reach to the broader interdisciplinary readership of Nature Communications.\n\n1. The primary self-assembly strategy, which enables the interfacial synthesis in the present case mirrors previously reported approaches. These include the assembly at the low interfacial tension ATPS interface (Sproncken et al. DOI: 10.1038/s41586-024-07481-2) and droplet interface membranes (Huang et al. 10.1021/ja802089s, Holden et al. 10.1021/ja072292a). Although the authors cite Sponcken reference, the relevance needs to be more clearly articulated.\n\n2. The mechanism stabilizing the interfacial assembly is inadequately addressed. Why does dodecane fare better than other n-alkanes? Why b-CD? How the known cage-like and channel-like organization of alkane-conjugated cyclodextrin drive the interfacial assembly and stability needs to be better described.\n\n3. Here, the descriptions on pages 11 and 12 are needlessly repetitious and confusing. They can be consolidated into a simpler explanation.\n\n4. How are the films detached from the nylon and Teflon membranes? How does the inclusion geometry of cyclodextrin influence their functions?", "reviewer_3": "This manuscript reports a new molecular assemble approach for self-supporting nanofilms. The experimental approach is well documented and supported by theoretical studies. The samples are extensively characterized. The following minor revisions are recommended.\n\n- I have a few comments/questions regarding the computational part:\n*It is not clear which temperature and which energy window have been choosen for the conformer search.\n*Were the conformer calculated in vacuum or using a solvent shell?\n*The binding energy was calculated via E = E_cplx_opt – (E_CD_opt + E_guest_opt). Were single-point energies used for all three energies (E_cplx_opt, E_CD_opt and E_guest_opt)?\n- Will the diffusion of water into the hydrophilic membrane result in swelling of the membrane and thus change in transport properties? Or can it be neglected?\n- Is it possible to provide additional kinetic information on the film formation etc?\n- Is there some kind of temperature limit (for the diffusion)?\n- I have a few doubts about the term antigravity, because it does not neutralize gravitational force.\n- The applications are very promising. The up scaling of the process is demonstrated. Is this approach ready for industrial applications in its current form (industrial scale)? Or, if not, what is the current limitation?\n- There is no experiment on the long-term stability and no information on the limit of the fabricated films in general.\n- I miss some kind of short outlook in the conclusion, i.e. what are the next steps?\n\nSome small technical comments:\n- Some scale bars are missing in Fig. 4\n- The images of the molceules in Fig. 3h and 3i and Fig. 1c are very small. Is it possible to increase the size a little bit? It is very difficult to see details, e.g. the blue isosurfaces in Fig. 1c."}, "author_response": "Responses to the reviewer’s comments\nWe are grateful for the many thoughtful comments and suggestions that the reviewers have\nprovided. We really appreciate the effort they put into the reviewing process; the comments are\nsubstantive, helpful, and truly aimed at improving the manuscript.\nFor Reviewer 1:\nComment 1: “The manuscript explores an antigravity-confined interfacial self-assembly (ACIS) strategy for growing\ncyclodextrin–alkane nanofilms and compares it with conventional gravity-induced self-assembly (GIS). The topic is\ntimely and potentially useful to the soft-matter community, and the abstract plus the opening half of the Introduction are\nclear and engaging. Unfortunately, the remainder of the paper lacks clarity, cohesion, and adequate evidence. The work\ndoes not warrant publication in Nature Communications.”\nReply 1: We appreciate the reviewer’s positive evaluation of our work: “The topic is timely and\npotentially useful to the soft-matter community, and the abstract plus the opening half of the Introduction are clear and\nengaging.”. And we also thank the reviewer's professional comments. According to this comment,\nwe have revised the manuscript carefully to improve the clarity, cohesion, and adequate evidence\nof the manuscript. And please see the details in our revised manuscript highlighted in yellow.\nComment 2: “The narrative quality declines sharply after the mid-Introduction. Organization becomes erratic, ideas\nare repeated, and awkward phrasing impedes comprehension. A careful, line-by-line edit is required to bring the latter\nsections up to the standard set by the opening pages.”\nReply 2: We thank the reviewer’s suggestions on the organization and writing of this manuscript.\nAccording to this suggestion, we have reorganized the structure, eliminated redundancies,\nimproved the phrasing and revised the paper with a careful, line-by-line edit. For example, the\norganization of the paragraph “We demonstrate the method’s versatility with other liquid-liquid systems…have\npotential application in the preparation of pesticide emulsifiers” is divided into three sections for elaboration;\n“The antigravity confined interface is formed by infusing water or CD solutions into the nylon membrane…the film\ncovered with nylon membrane is thicker than that covered with PTFE membrane.” is moved to Supplementary\nInformation; the phrasing “As shown in Fig. 3b, we investigated the effect of the concentration of β-CD solution on\nthe critical pressures for the gas passing through the CSNs. The CSNs are synthesized by infusing 0.001 mol/L, 0.002\nmol/L, 0.003 mol/L, 0.004 mol/L, and 0.005 mol/L of β-CD solutions into the nylon membranes and infusing the dodecane\ninto the PTFE membranes.” is simplified to “As shown in Fig. 3b, we evaluated the critical transmembrane pressure\n1\nrequired for gas to penetrate the CSNs synthesized with β-CD concentrations ranging from 0.001 to 0.005 mol/L.”.\nPlease see more details in the revised manuscript highlighted in yellow.\nComment 3: “The manuscript asserts that gravity fundamentally limits interfacial film formation, yet the key\nparagraph advancing this claim provides no citations. Please substantiate the argument with representative literature\nor supply systematic data showing that a broad range of interfacially assembled films fail under gravity. Without such\nevidence, the paper’s primary justification remains speculative.”\nReply 3: We thank the reviewer’s suggestions on the citations of the gravity-limited interfacial film\nformation. According to this suggestion, we added the related references (J. Am. Chem. Soc. 144,\n11778-11787 (2022), Nature 630, 866-871 (2024), and J. Am. Chem. Soc. 144, 4853-4862 (2022))\nas ref. [6, 7, 8]. Yang et al. carried out the external polarization of the water/DCE interface by\ncyclic voltammetry to fabricate COF membranes, Lehane et al. reported the electrosynthesis of\nPEDOT thin films at a polarized liquid/liquid interface, and Sproncken et al. used the interface of\nan aqueous two-phase system to template and stabilize biomimetic block copolymer bilayers by an\nAg/AgCl wire electrode (Fig. R1). All these methods must be carried out under the distribution of\ndense (gravity effect) and needed electrodes to be fabricated into a film.\nFig. R1 | The interface film formation mechanism of gravitational distribution. (a)\nPhotographs of the glass cell before (top) and after 200 consecutive cyclic voltammetry scans\nshowing the formation of self-standing COF membrane at the interface (bottom). (b) Four-\nelectrode electrochemical cell after interfacial electrosynthesis. The acidic aqueous phase,\ncontaining the yellow Ce4+ oxidant, is on top and the more dense α, α, α-trifluorotoluene\n(TFT) organic solution containing the EDOT monomer is on the bottom. PEDOT forms\nexclusively as a thin blue film at the polarized liquid/liquid (L/L) interface. (c) Schematic\n2\nrepresentation of the self-healing test of the membrane. The density of the aqueous PEO\nphase is lower than that of the aqueous DEX phase.\nFurthermore, the controlled experiments were conducted to verify the situations where film\nformation is hindered due to gravitational distribution. The diffusion of CD molecules within the\nsystem, as well as the host-guest interactions at the interface, are governed by the system’s inherent\ndensity gradient. A comparative analysis reveals that successful film formation in the ACIS systems\ncorrelates with obviously higher resultant transmembrane pressures compared to the conventional\nGIS (non-film-forming) methods. This pronounced transmembrane pressure increase serves as a\ndistinctive characteristic and a potential indicator of the film formation process and its stability\nunder antigravity conditions. In practical applications such as oilfield recovery, where water\nflooding is employed for oil displacement, gravitational constraints prevent effective interfacial\nfilm assembly. The current experimental methodology allows for straightforward reproduction of\nthese findings, thereby validating our conclusion. Our additional comparative experiments further\ndemonstrate two key findings: firstly, that the transmembrane pressure differences in the ACIS\nsystem are obviously greater than those in the GIS system, and secondly, that this elevated pressure\nis an indicator of enhanced film stability (Table R1). According to this suggestion, in the\nIntroduction, the related references have been added in the manuscript “This inherent density gradient\ncritically limits the synthesis of metastable nanofilms requiring inverted architectures where dense components must\noccupy upper layers to ensure structural integrity.”. Please see the details in the revised manuscript\nhighlighted in yellow.\nTable R1. The interfacial films formed by the ACIS method and the GIS method.\nSystem β-CD/Dodecane β-CD/Middle east oil\nCondition Pore size: 5 μm; Gas flow: 2 mL/min; β-CD concentration: 0.004 mol/L.\nMethod ACIS GIS ACIS GIS\nFilm formation Yes No Yes No\n∆P (kPa) 2.37 1.35\nACIS-GIS\ndiscussions—ideally in a single figure or a dedicated subsection—would clarify ACIS’s advantages and remove\nredundancy.”\nReply 4: We thank the reviewer’s suggestion on the comparisons between GIS and ACIS.\nAccording to this suggestion, we have added a comparison chart in Fig. 4a to clarify ACIS’s\nadvantages. In the radar chart, we evaluated the two methods on a scale of relative performance for\nmechanical strength, area, and insulating efficacy.\nComment 5: “The mechanical and morphological improvements reported for ACIS films appear incremental when\nbenchmarked against prior interfacial films. The manuscript should state more explicitly where the present approach\nsurpasses earlier work, or adjust the claims to reflect a modest advance.”\nReply 5: We thank the reviewer’s comment on the mechanical and morphological improvements\nof ACIS films. It is noteworthy that the key advance of our work lies in achieving film formation\nunder the same conditions where previous attempts failed, not in improving the mechanical\nproperties of the film itself. We believe the core to improving the mechanical properties of films\nlies in the design and matching of film material feedstocks. Although under certain experimental\nconditions, we observed that the ACIS method can partially enhance film performance—an aspect\nthat is still under further investigation—we consider this to be subsequent research work of the\ncurrent study. According to this comment, we adjust the claims to reflect a modest advance as\nfollows: “In this ACIS, the capillary force of the hydrophilic nylon and hydrophobic polytetrafluoroethylene (PTFE)\nmembranes can effectively counteract the gravity effect to form a confined interface, which enables film formation under\nthe same conditions where previous attempts failed (Fig. 1a)...” and “Compared with prior methods for synthesizing\ninterfacial films, a key advantage of the ACIS is its capacity to form large-area interfaces with the same volume.”.\nPlease see the details in the revised manuscript highlighted in yellow.\nComment 6: “Nearly every data panel is accompanied by multiple schematic drawings. While cartoons can aid\nunderstanding, they currently overwhelm the actual measurements. Please reduce redundant schematics so that\nexperimental evidence is more prominent.”\nReply 6: We thank the reviewer’s professional suggestions on the schematic drawings of our\nmanuscript. According to this suggestion, we reduced schematics, and moved previous Fig. 2d to\nSupplementary Figure 10. Please see the details in the revised manuscript.\nreappear later. Streamline Figure 1 to a concise concept graphic or remove duplicated content to avoid confusion.”\nReply 7: We thank the reviewer’s suggestion on the Fig. 1 and Fig. 3. In fact, Fig. 1c and Fig. 3i\naddress different spatial interactions: Fig. 1c depicts the forces between CD at the interface and CD\nwithin the bulk system, whereas Fig. 3i focuses specifically on interactions between adjacent CDs\nlocalized at the interface. According to this suggestion, to avoid misunderstanding, we removed\nprevious Fig. 1c to Supplementary Figure 21 to avoid repetitive discussions in the maintext.\nComment 8: “Page 3 contains a self-contradictory sentence claiming that the membrane “restricts CD mobility”\nwhile simultaneously “increasing diffusion.” Clarify whether confinement accelerates diffusion along the interface\n(reduced dimensionality) or slows overall transport.”\nReply 8: We thank the reviewer’s comment on the diffusion expression of the manuscript. First of\nall, they are not contradictory. Because we intended to show that this confinement accelerates\ndiffusion of molecules from the bulk phase to the interface and slows the transport of molecules in\nother directions. According to this comment, in order to avoid this misunderstanding, we have\nrevised the “restricts CD mobility” as “restricts the movement direction of CD”, and revised “increasing diffusion”\nas “increased diffusion to interface” on Page 3.\nComment 9: “The formation mechanism can likely be explained by classical nucleation and growth driven by host–\nguest enrichment at the interface. The quantum-mechanical calculations seem unnecessary unless they yield insights\\unattainable by simpler methods. Consider moving these computations to the Supporting Information or demonstrating\nexplicitly how they alter the mechanistic picture.”\nReply 9: We thank the reviewer’s professional comment on the formation mechanism. We believe\nthat the analysis of quantum mechanics is still necessary. Classical nucleation occurs at\nmacroscopic liquid-droplet interfaces, whereas our system involves nucleation at microscopically\nconfined interfaces. Within such confined spaces, molecular aggregation is subject to geometric\nconstraints. Furthermore, while the interfacial tension in classical nucleation can be directly\nmeasured, it cannot be determined in real-time for our system. Consequently, the conditions within\nconfined spaces do not satisfy the prerequisites of classical nucleation theory.\nAccording to the assumptions of the classical theory (Crystal Growth & Design, 2016, 16(11):\n6663-6681), the nucleation free energy is calculated as follows:\n5\n−4𝜋𝑟3\n∆𝐺 = 𝐾𝑇𝑙𝑛𝑆+4𝜋𝑟2𝜎\n3𝜐\nOur system nucleates at the interface and can be regarded as heterogeneous nucleation, the\nmicroscopic nuclei in the classical nucleation theory can be regarded as macroscopic liquid droplets\nwith well-defined surfaces, and their free energy can be estimated using surface tension σ. However,\nour system nucleates at antigravity confined interface, and surface tension is difficult to real-time\nmeasure. Therefore, the quantum mechanics method provides a simple and effective approach. The\nhost-guest interaction is further stabilized by hydrogen bonds, π-π stacking, and cage-like\ninteractions, enhancing the orderliness and facilitating film formation. According to this comment,\nwe removed these computations to the Supporting Information (1.5 part).\nComment 10: “The experimental setup is described almost verbatim three times on page 7, disrupting the narrative\nflow. Consolidate these repetitions and present each protocol only once.it is stated \"The CSNs are designed by infusing\nβ-CD solutions into the nylon membrane and infusing octane, decane, dodecane, and hexadecane into the PTFE\nmembrane.\"\"The antigravity confined interface is formed by infusing water or CD solutions into the nylon membrane\nand infusing alkane into the PTFE membrane\" \"In the system formed by infusing water or CD solutions into the nylon\nmembrane and infusing dodecane into the PTFE membrane\" this is rather disturbing to read smoothly.”\nReply 10: We thank the reviewer’s careful suggestion on the description of our experimental setup.\nAccording to this comment, to avoid disrupting the narrative flow, we revised the “The CSNs are\ndesigned by infusing β-CD solutions into the nylon membrane and infusing octane, decane, dodecane, and hexadecane\ninto the PTFE membrane.” as “The CSNs were fabricated by infusing β-CD solution into nylon membranes and different\nalkanes into PTFE membranes.”. Furthermore, we have revised “The antigravity confined interface is formed by\ninfusing water or CD solutions into the nylon membrane and infusing alkane into the PTFE membrane” and “In the\nsystem formed by infusing water or CD solutions into the nylon membrane and infusing dodecane into the PTFE\nmembrane” as “An antigravity confined interface is constructed by infusing aqueous solutions—either water or CD\nsolutions—into the nylon membrane, while an alkane is introduced into the PTFE membrane.” and “When the system\ncontains water or CD solutions in the nylon membrane and dodecane in the PTFE membrane”, and removed them\nto Supplementary Information for explaining Supplementary Figure 10.\nIn summary, we thank the reviewer’s comments and suggestions, which are valuable in improving\nthe quality of the work. Thanks again!\nComment 1: “This manuscript reports a self-assembly strategy that utilizes the oil-water interface to dimensionally\nlocalize the association between an n-alkane and a cyclodextrin, resulting in a self-supporting nanofilm. By sandwiching\na water-infused, porous nylon membrane and an oil-infused, porous Teflon membrane, the authors create a capillary-\nforce stabilized, gravity-inverting oil-water interface where cyclodextrin and dodecane assemble to produce the nanofilm.\nThe authors demonstrate that the approach allows the formation of large-area film with markedly improved order and\nstability. They further illustrate the utility of the approach for applications across materials engineering, food processing,\nemulsion preparation, and oil displacement in petroleum recovery. The approach presented is interesting, the findings\ninsightful, and the applications promising. I recommend publication after the authors have considered the following\nminor questions, addressing which I believe will enhance the work's reach to the broader interdisciplinary readership of\nNature Communications.”\nReply 1: We appreciate the reviewer’s positive evaluation of our work: “The approach presented is\ninteresting, the findings insightful, and the applications promising.”. According to the professional comment\nand suggestion, we have carefully revised the manuscript. Please see the details in the revised\nmanuscript highlighted in yellow.\nComment 2: “1. The primary self-assembly strategy, which enables the interfacial synthesis in the present case\nmirrors previously reported approaches. These include the assembly at the low interfacial tension ATPS interface\n(Sproncken et al. DOI: 10.1038/s41586-024-07481-2) and droplet interface membranes (Huang et al. 10.1021/ja802089s,\nHolden et al. 10.1021/ja072292a). Although the authors cite Sponcken reference, the relevance needs to be more clearly\narticulated.”\nReply 2: We thank the reviewer’s professional suggestion on the relevance with previously\nreported approaches. According to this suggestion, we have cited those related references (J. Am.\nChem. Soc. 129, 8650-8655 (2007) and J. Am. Chem. Soc. 130, 5878-5879 (2008)) as ref. [17, 18].\nThe relevance is more clearly articulated in the Introduction as follows: “The traditional strategy for\nthinning CD films primarily relies on composite synthesis using rigid supporting substrates or liquid-liquid interface\nself-assembly” and “Liquid-liquid interface self-assembly uses the interface to template molecules and stabilize\nproperties, however, the droplet interface self-assembly uses the electrodes, and two-phase interface self-assembly\ndepends on gravity.” Please see the details in the revised manuscript highlighted in yellow.\nfare better than other n-alkanes? Why b-CD? How the known cage-like and channel-like organization of alkane-\nconjugated cyclodextrin drive the interfacial assembly and stability needs to be better described.”\nReply 3: We thank the reviewer’s professional question on the mechanism stabilizing of our\ninterfacial assembly. The reasons that “Why does dodecane fare better than other n-alkanes?” and “Why β-\nCD?” are the results of our previous exploratory experiments and theoretical calculations. We have\nmeasured the critical pressures, carbon contents, and dynamic interfacial tensions of the interfacial films\nsynthesized by CD solutions with dodecane (Fig. 2b and 4d) and β-CD solution with alkanes (Fig. 2c\nand 4e). In addition, we have calculated the binding energy and the lowest energy structure of the CD\nand the alkane (Fig. 3g and 3h). Therefore, for “How the known cage-like and channel-like organization of\nalkane-conjugated cyclodextrin drive the interfacial assembly and stability”, the experimental data and\ncalculations indicate that the dodecane with β-CD molecules will form complexes that have the maximal\nability to reduce the interfacial tension, enhance critical pressure and binding energy, which drives the\ninterfacial assembly and stability of the films. According to the comment and suggestion, we revised\nthe previous phrasing as follows: “Initially, β-CD molecules dispersed in the aqueous phase diffuse toward the\ndodecane-water interface over time and with increasing concentration. At the interface, β-CD orients itself to encapsulate\ndodecane via host-guest interactions, forming a complex that reduces interfacial tension and drives the interfacial\nassembly. Subsequently, these complexes undergo interfacial polymerization through hydrogen bonding with β-CD\nmolecules in the bulk phase, enhancing the stability and mechanical strength of the film.”. Please see the details in\nthe revised manuscript highlighted in yellow.\nComment 4: “3. Here, the descriptions on pages 11 and 12 are needlessly repetitious and confusing. They can be\nconsolidated into a simpler explanation.”\nReply 4: We thank the reviewer’s suggestion on the descriptions on Pages 11 and 12. According\nto this suggestion, to avoid previous repetition and confusion, we reorganized the structure,\neliminated redundancies, improved the phrasing and revised the paper with a careful, line-by-line\nedit to consolidate into a simpler explanation. For example, the previous maintext “Upon introduction\nof 0.004 mol/L β-CD into the system, a self-assembled nanofilm composed of β-CD and dodecane is formed to effectively\ncover the holes of the nylon membrane (Supplementary Fig. 14). When the concentration of β-CD solution is less than\n0.004 mol/L, the combination of β-CD molecules and dodecane molecules is not tight enough to form a nanofilm. We\nfurther measured the thickness of the films with 0.004 mol/L and 0.005 mol/L of β-CD solutions as shown in Fig. 1a and\nSupplementary Fig. 15, and the thickness of the CSN with 0.005 mol/L of β-CD solution was greater than that of 0.004\nmol/L of β-CD solution.” has been simplified to “At 0.004 mol/L, a continuous nanofilm formed, effectively covering\nthe nylon membrane pores (Supplementary Fig. 15). Below this concentration, binding between β-CD and dodecane was\ninsufficient for nanofilm formation. Film thickness increased with concentration, as evidenced by comparisons between\n8\n0.004 and 0.005 mol/L samples (Fig. 1a and Supplementary Fig. 16).”; the previous maintext “In the initial state\nof the CSN formed by 0.004 mol/L of β-CD solution and dodecane, the critical pressure for the gas to pass through the\nCSN system is about 44.35 kPa, and the critical pressure for the gas to pass through the CSN system is about 49.76 kPa\nafter 2 h. The results demonstrate that the nanofilm self-assembled by β-CD-dodecane complexes can be synthesized in\n0.004 mol/L of β-CD solution after 2h of the antigravity interface formation. In the absence of the influence of external\nforces, β-CD molecules diffuse towards the interface and bind with dodecane, and then self-assemble via hydrogen bonds\nto form a stable film, which takes approximately 2 h. After 2 h, the molecular configuration at the interface gradually\nbecame saturated, and the critical pressure did not increase any further, and a saturated film was formed.” has been\nconsolidated into a simpler explanation as follow: “For instance, with 0.004 mol/L β-CD, the critical pressure\nrose from 44.35 kPa initially to 49.76 kPa after 2 hours, indicating full nanofilm formation. Beyond this period, the\ninterfacial molecular configuration saturated, and no further increase in pressure resistance was observed.”. Please\nsee the details in the revised manuscript highlighted in yellow.\nComment 5: “4. How are the films detached from the nylon and Teflon membranes? How does the inclusion geometry\nof cyclodextrin influence their functions?”\nReply 5: We thank the reviewer’s professional question on the film detaching and cyclodextrin\nstructure influence. For the question about the film detaching, since the film is formed at the oil-\nwater interface, it is very convenient to separate one of the two membranes (the nylon / PTFE\nmembranes) separately, because there is a protective liquid layer around the film to maintain its\nintegrity. When considering the need to separate two membranes at the same time, some techniques\nare needed to avoid wrinkles. In practical applications, it is often necessary to determine whether a\nsingle or two simultaneous separation is required according to the application requirements. In most\ntesting processes, only a single separation is required to complete the testing and application of film\nperformance. For the question about the cyclodextrin structure influence, the inclusion geometry\nof cyclodextrin, featuring a hydrophilic exterior and hydrophobic interior, enables the host-guest\ninteractions with hydrophobic alkane molecules in aqueous environments. The above interactions\ndetermine the function of film formation.\nWe thank the reviewer’s comments, questions, and suggestions, which are valuable in improving\nthe quality of the work. Thanks again!\nComment 1: “This manuscript reports a new molecular assemble approach for self-supporting nanofilms. The\nexperimental approach is well documented and supported by theoretical studies. The samples are extensively\ncharacterized. The following minor revisions are recommended.”\nReply 1: We appreciate the reviewer’s positive evaluation of our work: “The experimental approach is\nwell documented and supported by theoretical studies. The samples are extensively characterized.”. According to\nthis comment, we have carefully revised computational part and technical comments of the\nmanuscript. Please see the details in the revised manuscript highlighted in yellow.\nComment 2: “It is not clear which temperature and which energy window have been choosen for the conformer\nsearch.”\nReply 2: We thank the reviewer’s professional comment on the temperature and energy window.\nIn this work, the temperature is 298.15 K and the energy window is 6 kcal·mol⁻¹ for the conformer\nsearch. According to this comment, we have added this information into the Methods.\nComment 3: “Were the conformer calculated in vacuum or using a solvent shell?”\nReply 3: We thank the reviewer’s question on the conformer calculation. The conformer was\ncalculated in vacuum.\nComment 4: “The binding energy was calculated via E = E_cplx_opt – (E_CD_opt + E_guest_opt). Were single-point energies used for all three energies (E_cplx_opt, E_CD_opt and E_guest_opt)?”\nReply 4: We thank the reviewer’s question on the binding energy. Yes, for all three energies\n(E , E and E ), we used single-point energies.\ncplx_opt CD_opt guest_opt\nComment 5: “Will the diffusion of water into the hydrophilic membrane result in swelling of the membrane and thus\nchange in transport properties? Or can it be neglected?”\nReply 5: We thank the reviewer’s question on the hydrophilic membrane and transport properties.\nAccording to this question, we did additional experiments. The transport properties of the\n10\nhydrophilic membrane have been tested in 1, 2, 4, 6, 12, and 24 h (Fig. R2). The results show that\nthe transport properties remained stable within 24 hours, and our tests in this work are conducted\naround 2 hours. Therefore, we think the diffusion of water can be neglected in this work.\nFig. R2 | The stability of the transmission properties of the hydrophilic membrane after\nbeing immersed in water.\nComment 6: “Is it possible to provide additional kinetic information on the film formation etc?”\nReply 6: We thank the reviewer’s question on the kinetic information of the film formation. At\npresent, we have already discussed the kinetic information in multiple sections of the manuscript,\nsuch as diffusion curves of β-CD solutions with different concentrations (Supplementary Figure 5),\ndynamic interfacial tensions of different systems with CD solution and alkane (Fig. 3d, 3e, and 3f),\nand critical pressures of the CSNs over time (Fig. 3c). We think that the above kinetic information\n(diffusion, interfacial assembly, and membrane strength) has already provided sufficient evidence\nto support the film formation.\nComment 7: “Is there some kind of temperature limit (for the diffusion)?”\nReply 7: We thank the reviewer’s professional question on the temperature limit. For the diffusion\nin liquids, the diffusion coefficient follows the Arrhenius equation: D = D exp(−\nE𝑎).\nD is a\n0 0\n𝑘𝑇\ntemperature-independent constant, E is the activation energy required for diffusion, k is the\na\nBoltzmann constant, and T is the absolute temperature. The above equation indicates that the\ndiffusion coefficient D increases exponentially with the rise of temperature T. In this work, the\nmain innovation of our work is to establish a stable antigravity liquid-liquid interface to form films.\nfilm formation, but the concentration diffusion is the key factor determining whether a film can be\nformed. Only when the temperature is extremely low, the thermal motion of molecules is weak,\nand the diffusion rate approaches zero (for example, water freezing temperature). Of course, if the\ntemperature is very high, for example, the rapid evaporation process of water system will also affect\nthe film forming conditions. In addition, considering the limitation of solute and membrane material\nstability, such as cyclodextrin molecules (< 80°C), and nylon membrane (< 60°C). Thus, the\nexperimental conditions and all calculations were carried out at the room temperature (298.15K).\nComment 8: “I have a few doubts about the term antigravity, because it does not neutralize gravitational force.”\nReply 8: We thank the reviewer’s professional comment on the term antigravity. In our work,\n“antigravity” is used as a descriptive, functional term within the context of materials science and\ninterfacial phenomena. It specifically denotes the effective suppression of gravitationally induced\nstratification by employing dominant capillary forces in a confined system. This usage is well-\nestablished in fields like biomechanics and soft matter physics, where it describes systems or\nmechanisms that counteract the macroscopic effects of gravity. We feel that 'antigravity' effectively\ncaptures the essence of our method. That is to say, our approach works by creating conditions where\ncapillary forces become dominant, thereby forming a liquid-liquid interface that opposes the\ninfluence of gravity. We acknowledge that the term 'antigravity' may be somewhat unconventional\nand have therefore evaluated potential alternatives. Options such as 'agravitropic' (limited to\nbotany), 'gravity-independent' (passive connotation), and 'gravity-defying' (lacking mechanistic\nspecificity) were all found inadequate. Thus, we currently employ 'antigravity' as the most intuitive\ndescriptor for the opposing force and resultant interface, and we sincerely welcome your\nperspective on this matter. Meanwhile, according to this comment, we have clarified this specific\nmeaning in the revised manuscript, “In this work, we show an antigravity confined interfacial self-assembly\n(ACIS) for synthesizing self-supporting nanofilms, overcoming above limitations by employing dominant capillary forces\nto counteract the macroscopic effects of gravity and achieve the inverted interface.”. Please see the details in the\nrevised manuscript highlighted in yellow.\nready for industrial applications in its current form (industrial scale)? Or, if not, what is the current limitation?”\nReply 9: We thank the reviewer’s professional question and positive evaluations on the potential\napplications. Yes, in fact, we are currently carrying out relevant industrial cooperation with the oil\ncompany to address the reservoir development issue in Enhanced Oil Recovery (EOR) process.\nComment 10: “There is no experiment on the long-term stability and no information on the limit of the fabricated\nfilms in general.”\nReply 10: We thank the reviewer’s comment on the long-term stability and the limit of the\nfabricated films. In our previous work, there was an experiment on the stability for 14 hours in Fig.\n2f. According to this comment, we did additional experiments about long-term stability of the film\n(Fig. R3). The results show that the fabricated film is stable within one week. For the information\nof the limitation, as mentioned above (the reply 7), our method is constrained by the temperature\nand the thermal stability of both the solute and the membrane materials.\nFig. R3 | The long-term stability of the fabricated films.\nComment 11: “I miss some kind of short outlook in the conclusion, i.e. what are the next steps?”\nReply 11: We thank the reviewer’s comment on the short outlook in the conclusion. As mentioned\nabove, we are currently carrying out relevant industrial cooperation with the oil company. Our\nresearch roadmap entails a dual-pronged strategy to address complex field conditions. First, we will\nendeavor to construct a robust materials database to guide the selection and optimization of\nchemistries for targeted applications. Second, we will enhance the diagnostic capabilities for\n13\nprobing confined oil-water interfaces under realistic temperature and pressure, facilitating the\napplication of this method to boost flooding efficacy in ultra-low permeability oil reservoirs.\nAccording to this comment, we added the outlook in the conclusion as follows: “Our future work will\npursue an integrated strategy to advance this method for complex field applications. This entails scaling up the synthesis\nand developing a comprehensive materials database to discover new ACIS-compatible functionalities and optimize\nchemistries. In parallel, we will advance diagnostic methods for characterizing interfaces under realistic temperature\nand pressure. The culmination of these efforts will be the validation of our method's performance in specific industrial\napplications, such as enhanced oil recovery in ultra-low permeability formations.”\nComment 12: “Some scale bars are missing in Fig. 4”\nReply 12: We thank the reviewer’s comment on the scale bar in Fig. 4. In the legend of the Fig. 4,\nwe have indicated the diameters of the bottles and cores, so there are no scale bars. According to\nthis comment, we have added scale bars in Fig. 4.\nComment 13: “The images of the molceules in Fig. 3h and 3i and Fig. 1c are very small. Is it possible to increase\nthe size a little bit? It is very difficult to see details, e.g. the blue isosurfaces in Fig. 1c.”\nReply 13: We thank the reviewer’s suggestion on the images of the molecules. According to this\nsuggestion, we have increased the size of the molecular structure in Fig. 1b, which is the original\nFig. 1c (from 10.62 cm ×8.74 cm to 15.2 cm ×12.51 cm) and Fig. 3h (from 5.67 cm ×6.84 cm to\n6.52 cm ×6.44 cm, 7 cm ×10.1 cm to 8.83 cm ×12.75 cm, 6.48 cm ×9.33 cm to 8.3 cm ×11.74 cm,\nand 7.89 cm ×10.52 cm to 8.97 cm ×11.67 cm) so that the details could be more clearly seen. For\nthe Fig. 3i, we have revised the illustration to enlarge the molecular structure from 3 cm ×7.1 cm\nto 4.4 cm ×9.5 cm.\nWe thank the reviewer’s comments, questions, and suggestions, which are valuable in improving\nthe quality of the work. Thanks again!\n14"}, {"round": 2, "reviewer_comments": {"reviewer_1": "I appreciate the authors' efforts to address my concerns and the extensive revisions undertaken. However, after careful consideration of the revised manuscript and rebuttal, I think further improvments are required.\n\nRegarding the evidence that gravity fundamentally limits interfacial film formation. The authors have misinterpreted my request. The three references they added (Yang, Lehane, and Sproncken) describe electrochemical methods that fail at ambient conditions because they require external polarization and electrodes, not because gravity prevents film formation. These papers do not demonstrate that gravity is the limiting factor—they demonstrate that electrochemical driving forces are necessary for those particular systems. Similarly, Table R1 shows only two examples from the authors' own CD-alkane system. This does not constitute evidence that a \"broad range of interfacially assembled films fail under gravity\" as I originally requested.\n\nThe authors provide an elaborate justification for why the quantum calculations are essential—arguing that classical nucleation theory is inappropriate for confined geometries and that interfacial tension cannot be measured in real-time.Yet classical nucleation theory has been successfully applied to confined systems (crystallization in nanopores, nucleation in microemulsions, etc.), and the inability to measure interfacial tension in real-time is an experimental limitation that does not automatically necessitate quantum mechanical calculations.\n\nRegarding the applications, I appreciate that the authors are pursuing industrial collaboration for enhanced oil recovery. However, this information should be integrated into the manuscript itself to strengthen the case for significance. If this methodology is indeed ready for industrial application as stated in Reply 9, the manuscript should discuss why density-inverted configurations are essential for EOR applications and why alternative approaches (microfluidics, electrochemical methods, etc.) are inadequate. This would substantially strengthen the justification for the work.", "reviewer_2": "The authors have adequately addressed all the queestions and concerns raised during the last round of review. I recommend publication.", "reviewer_3": "The authors have addressed all my concerns in the revised version of the manuscript.\nThe manuscript has improved and is now ready for publication."}, "author_response": "Responses to the reviewer’s comments\nWe are grateful for the comments and suggestions that the Reviewer 1 have provided. We really\nappreciate the effort Reviewer 2 and Reviewer 3 put into the reviewing process.\nFor Reviewer 1:\nComment 1: “Regarding the evidence that gravity fundamentally limits interfacial film formation. The authors have\nmisinterpreted my request. The three references they added (Yang, Lehane, and Sproncken) describe electrochemical\nmethods that fail at ambient conditions because they require external polarization and electrodes, not because gravity\nprevents film formation. These papers do not demonstrate that gravity is the limiting factor—they demonstrate that\nelectrochemical driving forces are necessary for those particular systems. Similarly, Table R1 shows only two examples\nfrom the authors' own CD-alkane system. This does not constitute evidence that a \"broad range of interfacially assembled\nfilms fail under gravity\" as I originally requested.”\nReply 1: We thank the reviewer’s comment on the citations of the gravity-limited interfacial film\nformation. Here, the cited examples (the three references) are not served to “gravity prevents film formation”,\nand they are used to illustrate the fundamental point: under gravitational conditions, the formation\nof stable liquid-liquid interfacial films often require additional energy input in many cases. In\ncomparison, our method enables autonomous antigravity organization without additional energy\ninput, facilitating film formation. For the comment “This does not constitute evidence that a \"broad range of\ninterfacially assembled films fail under gravity\" as I originally requested.”, we think there may be a\ndisagreement regarding the focus of our study. Our research does not aim to prove that gravity\nuniversally prevents interfacial film formation under all conditions, but rather demonstrates that\n“This inherent density gradient critically limits the synthesis of metastable nanofilms requiring inverted architectures\nwhere dense components must occupy upper layers to ensure structural integrity.”. Therefore, the significance of\nour work lies in highlighting a crucial mechanism—antigravity confined interfacial self-\nassembly—for film formation under specific conditions, rather than in establishing its generality.\nComment 2: “The authors provide an elaborate justification for why the quantum calculations are essential—arguing\nthat classical nucleation theory is inappropriate for confined geometries and that interfacial tension cannot be measured\nin real-time.Yet classical nucleation theory has been successfully applied to confined systems (crystallization in\nnanopores, nucleation in microemulsions, etc.), and the inability to measure interfacial tension in real-time is an\nexperimental limitation that does not automatically necessitate quantum mechanical calculations.”\ntheory. Regarding this comment, our previous response has already addressed the necessity of the\nquantum calculations. Although classical nucleation theory has been applied in nanopores, the\ncrystallization system discussed are relatively simple, while the specific confined system in our\nstudy is more complicated, involving dynamic molecular rearrangements and multiple competing\ninteractions. Therefore, we think it is better to use the quantum calculations to discuss the\nantigravity confined interfacial self-assembly process.\nComment 3: “Regarding the applications, I appreciate that the authors are pursuing industrial collaboration for\nenhanced oil recovery. However, this information should be integrated into the manuscript itself to strengthen the case\nfor significance. If this methodology is indeed ready for industrial application as stated in Reply 9, the manuscript should\ndiscuss why density-inverted configurations are essential for EOR applications and why alternative approaches\n(microfluidics, electrochemical methods, etc.) are inadequate. This would substantially strengthen the justification for\nthe work.”\nReply 3: We thank the reviewer’s interest in our applications. Yes, we are pursuing industrial\ncollaboration for enhanced oil recovery. Our collaboration needs to meet the requirements of the\nenterprise, and the specific experimental techniques involved are currently under development. Our\narticle mainly focuses on conducting research on the scientific issues involved. The technical issues\nare currently under investigation, and we think it is another story at present. According to this\ncomment, we added our perspective in the outlook section.\nAs for “why density-inverted configurations are essential for EOR applications”, we think in water-\nflooding EOR, the displacement process will emerge various multiphase interfaces including the\nantigravity interface. We think that the differences between antigravity interfaces and gravity\ninterfaces can be utilized to regulate the film formation behavior, thereby effectively increasing the\ninjection pressure and achieving the purpose of oil displacement from narrower pore throats. Of\ncourse, there are still many technical challenges involved. We are still working on it, and it is\nanother story at present.\nIn summary, we thank the reviewer’s comments, which are valuable in improving the quality of\nthe work. Thanks again!\n2"}, {"round": 3, "reviewer_comments": {"reviewer_1": "My concerns are addressed now."}, "author_response": ""}]

Decision letter