Borate driven heterogeneous networks for porous elastomers with improved tribological and mechanical performances

Domain: physics
Published: 2025-12-17
Editorial outcome: minor_revision

Abstract
Porous polydimethylsiloxane (PDMS) elastomers produced using conventional phase separation methods often suffer from limited tribological and mechanical properties. In this study, we present a general approach for the fabrication of porous elastomers with borate-driven heterogeneous networks, which leverage the borate at the two-phase boundary to stabilize the phases, without the need for additives such as surfactants. Pure porous elastomers are created by removing the alcoholysis phases, with precisely controllable pore structure and mechanical performance. Interestingly, under saltwater lubrication, an atypical corrosion–lubrication phenomenon occurs on the porous elastomers, reducing the friction coefficient and wear rate by over 95 and 90%, respectively. Additionally, unique mechanical advantages, such as 1250% of stretch, were predictively imparted to the elastomers by various boric acid functional groups. Our method is generally applicable to various PDMS systems and offers a novel approach for designing pure porous materials for water-lubricated components and flexible sensors.

Introduction
Double emulsions are formed via a phase separation, when two types of oils are sheared in specific proportions1. For example, beef soup exhibits oil-in-water phase separation between oil and water. Phase separation represents the transition from disorder to order in heterogeneous systems. To minimize free energy, colloids transform into two or more coexisting phases to achieve equilibrium2. The phase separation equilibrium is influenced by factors such as polymer–substrate interactions3, temperature4, pressure5,6, and composition ratio7,8. In a system with a constant amount of two substances a and b, the changes in the Gibbs free energies (G_a and G_b) per mole are described as follows9:

(∂G_a/∂T)_P dT + (∂G_a/∂P)_T dP = (∂G_b/∂T)_P dT + (∂G_b/∂P)_T dP (1)

where T and P represent the temperature and pressure of the system, respectively. By varying T, P, and the starting point of phase separation of components a and b, a controlled phase separation can be achieved. This principle also allows for the regulation of the liquid–liquid phase separation in polymer networks. In colloid systems, phase separation and polymerization typically occur simultaneously, enabling the control of the network structures of the polymer via adjustments in temperature, pressure, and the polymer ratio.

For centuries, corrosion has been regarded as one of the factors that exacerbate friction and wear. However, metal friction components, such as bearings, blades, and axes, have to be used in a corrosive environment10,11. Friction can destroy the passivation film on the metal surface and promote corrosion12. To avoid metal corrosion, non-metallic materials such as poly(ether-ether-ketone), epoxy resin, carbon composites, and polydimethylsiloxane (PDMS) have been used to replace metal in moving parts13,14. PDMS elastomers are critical base materials used in applications such as sensing15–18, anti-icing19–21, anti-fouling22,23, and anti-wear24. Hydrophobic PDMS has a coefficient of friction (COF) of 0.8–1.2 when used with water-based lubricants, and the high COF limits the use of PDMS25. Porous PDMS can reduce wear because their pores can capture the wear debris, thus reducing wear. However, conventional methods for preparing porous elastomers, including emulsion templates26,27, chemical foaming28, and particle template methods29, often face challenges in process control and compromise the frictional and mechanical performance of elastomers because of the numerous defects and impurities from surfactants and particle templates. An alternative approach involves fabricating porous elastomers using interpenetrating polymer networks (IPNs) by selectively degrading non-crosslinked subchains or extracting them from semi-IPNs or IPN precursors30–32. Existing studies on this method are limited and predominantly focus on composition ratio adjustments for pore structure control, ignoring the influence of pressure and temperature33,34. In addition to the PDMS network, another network in PDMS IPNs, such as poly(methyl methacrylate)33,35, has significantly distinct chemical characteristics compared to those of PDMS, which may result in a significant decrease in the mechanical properties of the elastomer when removed. Therefore, limited research has been conducted on the use of this method to regulate the mechanical properties. However, manipulating the degree of phase separation, fabricating highly pure porous polymer elastomers, and regulating their tribological and mechanical properties are theoretically feasible1,34–38.

This study presents a method for preparing heterogeneous-network porous PDMS (HNP-PDMS) elastomers, as shown in Fig. 1A. (For all abbreviations and their expansions, see Supplementary Table 1). Two networks were used: the first network consisted of D-PDMS with hydroxyl-terminated PDMS and boric acid (BA)39–41, whereas the second network was derived from Sylgard 184 PDMS components (vinyl-terminated PDMS, silica-hydrogen bonded PDMS, platinum catalyst42, and S-PDMS). The two networks, featuring similar main-chain properties, were driven by borate to achieve the heterogeneous phase separation. Prior to curing, the liquid mixture of Sylgard 184A + Sylgard 184B and dynamically crosslinked PDMS (S- and D-PDMS) was stirred to form multiple emulsions without any surfactants or solvents. Borates were incorporated into the PDMS network to stabilize the phase separation boundary to prepare the HNP-PDMS elastomers. HNP-PDMS@boric acid (BA) could spontaneously form the corrosion-induced self-lubrication effect in saltwater (3.5% of NaCl solution), changing the lubrication state from boundary lubrication to mixed lubrication (Fig. 1B, C). The COF and wear rate were as low as approximately 0.05 and 2.72 × 10−5 mm/Nm, respectively. Mechanical performance advantages could be imparted to the porous elastomers, such as a stretch percentage of 1250%, by controlling the temperature, pressure, and borate sites (Fig. 1C). Using a wide variety of BA derivatives and silicone materials, this study offers a new approach for designing specialized porous elastomers for enhanced water lubrication performance and preparing flexible sensors.

Results
In this study, we examined the blending state of the mixed S-PDMS and D-PDMS@BA prepolymer liquid (with a mass fraction of D-PDMS@BA of approximately 20%). To investigate the effect of the interactions between the two polymer chains on phase separation, molecular dynamics (MD) simulations were performed. We simplified the two polymer networks and established four molecular models (Supplementary Fig. 1). Figure 2A presents MD simulations snapshots showing the mutually repulsive positions of the two polymer chains at 300 K, at 0 and 100 ns. The solubility parameters are listed in Supplementary Table 2; the difference in the solubility parameters between S-PDMS and D-PDMS@BA is greater than 0.5, indicating that S-PDMS and D-PDMS@BA are incompatible. Therefore, mixing the two phases require additional energy; otherwise, phase separation occurs. In the phase-separation mixture, as shown in Supplementary Fig. 2, all hydroxyl groups of H-PDMS reacted after curing to obtain HN-PDMS@BA. Fourier transform infrared spectroscopy (FTIR) results show that the borate group of D-PDMS@BA can be considered the distinguishing characteristic, compared to S-PDMS (for detailed discussion, see Supplementary Information, Section 2.1). Consequently, we considered the interaction between borate ester and silicone oil as an important factor of incompatibility. The electrostatic potential of the repeating unit in D-PDMS@BA was calculated as shown in the Supplementary Fig. 3, to intuitively display the interactions of the borate bond with the siloxane backbone. The interactions suggest that the incompatibility is likely due to the repulsion between the B–O bonds and the oxygen in the Si–O backbone (for detailed discussion, see Supplementary Information, Section 2.1). Mean square displacement (MSD) results quantitatively showed that the system reached equilibrium at 95 ps (Fig. 2B). The boron atom exhibited a higher MSD than the D-PDMS@BA chain, which, combined with the electrostatic potential result, suggests that the borate increased the repulsion between the two chains. Consequently, we consider that increasing the D-PDMS@BA content (or the borate group content) intensifies the repulsion between D-PDMS@BA and S-PDMS, thereby enhancing the phase separation.

The initially polymerized D-PDMS@BA prepolymer was blended with the Sylgard 184 prepolymer and vacuumed in a drying oven to a pressure of −0.1 MPa, forming a transparent blend. As the pressure decreased, the solute precipitated and agglomerated through the spinodal decomposition mechanism, forming the microsphere and branched liquid phases (the phase separation is visible in Fig. 2C). According to the liquid–liquid phase separation mechanism9, ΔG_mix remains above 0 at air pressures of −0.1 and 0.0 MPa. The two phases are surrounded by borates, as shown in Fig. 1B. To better understand the molecular interactions involved in this process, additional MD simulations were performed with a mixed model of nine S-PDMS and nine D-PDMS@BA chains (Fig. 2E). During system relaxation, agglomeration of the D-PDMS@BA chains and entanglement of the S-PDMS chains occurred (Fig. 2E2, E3). A radial distribution function was used to study the aggregation of boron atoms (Supplementary Fig. 4). The appearance of a wide peak indicated that the boron atoms agglomerated within the 3–18 Å range (Fig. 2E2). The aggregation of boron atoms was hindered by the Si–O skeleton of S-PDMS or D-PDMS@BA during the agglomeration process, leading to the entanglement or encapsulation of D-PDMS@BA and S-PDMS (Supplementary Fig. 3 and Fig. 2E3). Because of the aforementioned state of the mixture, the prepolymer could be cured to obtain a heterogeneous network of PDMS with a smooth surface (Fig. 2D1). When the unstable D-PDMS@BA network was removed from HN-PDMS@BA using ethanol, owing to the alcoholysis of borate (Supplementary Fig. 5), an HNP-PDMS elastomer was obtained (Fig. 2D2). S-PDMS was encapsulated by a small amount of D-PDMS@BA, forming the polymer framework, and the reactions shown in Supplementary Fig. 6, facilitated this state (further discussion is provided in Supplementary Information, Section 2.1). The D-PDMS@BA phase was also surrounded by a small number of S-PDMS chains.

To understand the molecular orientations, phase structure, and microregions within the elastomers, small-angle X-ray scattering (SAXS) analyses were performed. The 2D SAXS patterns for S-PDMS, HN-PDMS@BA, and HNP-PDMS@BA under in situ stretching are shown in Fig. 3A, which illustrate the arrangement of the molecular chains. First, the SAXS results for elastomers at 0% stretch are discussed. As depicted in Supplementary Fig. 7, all samples displayed a characteristic peak at scattering vector q ≈ 0.08 nm−1, corresponding to a calculated periodicity of 78.5 nm for the microphase-separated domains. Porod curves for S-PDMS, HN-PDMS@BA, and HNP-PDMS@BA exhibited a positive deviation in the high-angle area (Fig. 3B1), suggesting the presence of a diffuse transition layer at the two-phase interface rather than an abrupt change in electron density. This phenomenon was attributed to the entanglement of the Si–O chains at the interface (Fig. 1B). Free volume fluctuations were observed within each phase of the soft–hard region, with no clear interface, suggesting the formation of a complex spatial distribution characterized by mutual wrapping and entangling43–45. Moreover, the elastomers displayed an initial parabolic peak in the low-angle region, followed by an increase (Supplementary Fig. 8), representing partial folding of the molecular chain in a spherical-random coil configuration46. Figures 3B2–4 show the Guinier curves of the natural logarithm of the scattered intensity (ln(I(q))) versus q. All Guinier curves displayed concave curved lines with rectilinear segments, indicating that the elastomers belonged to a spherical polydisperse system. The radius of gyration (R_g) of a scatter, which generally remains constant, quantitatively represents the molecular chain47,48. When qR_g < 1, R_g is determined by calculating the slope in the low-angle region. With the addition of D-PDMS@BA, the R_g decreased, indicating a shorter molecular chain length for D-PDMS@BA49. When D-PDMS@BA was removed using ethanol, the R_g of HNP-PDMS@BA exceeded that of S-PDMS, suggesting that the removed D-PDMS@BA network was entangled with short S-PDMS molecular chains. These findings aligned with our hypothesis regarding the multiple emulsion states of the HNP-PDMS@BA prepolymer. Based on the MD simulation results, phase separation analysis, SAXS results, and scanning electron microscopy (SEM) image shown in Fig. 2C, we inferred that the HN-PDMS possessed a heterogeneous network structure with interpenetrating networks at the phase boundaries (Fig. 1B). HNP-PDMS@BA featured not only a porous structure but also longer molecular chains compared to those of S-PDMS and HN-PDMS@BA.

We stretched the elastomers from 0 to 80% and observed the SAXS patterns during this process (Fig. 3A). As the stretch increased, the isotropy was disturbed, and the molecular chains became oriented toward the direction of stretching. Among the three kinds of samples (S-PDMS, HN-PDMS@BA, and HNP-PDMS@BA), the anisotropy of HNP-PDMS@BA was most pronounced. Studies have shown that the tensile strength and stiffness of polymers improve significantly when their molecular chains align along the stretching direction50, as this arrangement allows the chains to better resist the external stretching forces. The R_g values were fitted to a straight line, as shown in Fig. 3C–E, revealing a linear correlation between the radius of rotation and the stretching ratio during the stretching process. The introduction of the D-PDMS@BA network improved the linear fitting (R2=0.996), indicating that the D-PDMS@BA network promoted the alignment of the network toward the direction of the force during stretching. Notably, the slope values of the fitted lines for S- and HNP-PDMS are numerically similar to the tensile modulus (as discussed in Supplementary Information, Section 2.4), demonstrating that the slope values represent the strength and stiffness of the molecular chain.

The metastable state of the phase separation varied with increasing temperature and pressure (Fig. 4A). The diffusion coefficients of the two polymers changed depending on the temperature and pressure. MSD analysis was used to investigate the diffusion process of D-PDMS@BA, revealing that higher temperatures accelerated its diffusion, whereas the opposite was true for pressure (Supplementary Fig. 9 and Table 3). Consequently, by controlling the temperature and pressure, the entanglement and separation of the two chains can be regulated to achieve different network structures. Subsequently, the unstable D-PDMS@BA network in HN-PDMS@BA formed elastomers with diverse pore structures after undergoing alcoholysis. Supplementary Fig. 10 illustrates the mass change (△m) from HN-PDMS@BA to HNP-PDMS@BA as the curing temperature increases, showing that the reduction in mass diminishes with higher curing temperatures. The mass of dissolved D-PDMS@BA in S-PDMS was significantly lower than the mass of the first network (20 mg), suggesting that some D-PDMS@BA remained entangled with S-PDMS (further discussion is provided in Supplementary Information, Section 2.2).

Figure 4B shows the surface morphology of HNP-PDMS@BA elastomers synthesized at various temperatures. Fractal dimensions and pore roundness (θ) were quantified to investigate the phase separation using ImageJ software. As the temperature increased, the pores appeared denser (Supplementary Figs. 11 and 12), and θ progressively decreased (Supplementary Fig. 13), indicating that the pores became more irregular with increasing temperature. This phenomenon was attributed to the accelerated curing speed at higher temperatures, which disrupted the semi-stable state of the D-PDMS@BA sphere phase and drove the D-PDMS@BA chains to migrate toward the S-PDMS chains9. Conversely, when the pressure was improved (−0.1–0 MPa), the pores became smaller (5.16–1.16 μm) and sparser (Fig. 4C and Supplementary Fig. 14). This was because a higher pressure compressed D-PDMS@BA, making it difficult to diffuse, leading to a transition to a semi-stable state and smaller pores. These findings aligned with the results of our MD simulations. Supplementary Fig. 15 shows the SEM images of the different surfaces. Although some surfaces appeared smooth at high pressures and high temperatures, sparse pores were still seen in the SEM images (Supplementary Fig. 16A). The surfaces exhibited a ridge-like topography in three dimensions, at high pressure and high temperature, as seen in the confocal laser scanning microscopy images (Supplementary Fig. 17). As the temperature increased, the pores on the surfaces tended to shrink, eventually disappearing at 0 MPa. Under the same coordinate axis scale (objective lens 50×), the cross-sectional outline of HNP-PDMS@BA at 0 MPa approximated a straight line (Supplementary Fig. 18). The surface roughnesses of HNP-PDMS@BA elastomers, synthesized at various temperatures as shown in Fig. 4F, show a clear demarcation, providing a reference for designing friction surfaces. To investigate the oil-absorption capacity of the porous elastomers, methyl silicone oil was injected into HNP-PDMS@BA elastomers samples. An absorption map was obtained by calculating the porosity of HNP-PDMS@BA under 16 different conditions (Fig. 4E and Supplementary Eq. 12). The absorption percentage of HNP-PDMS@BA remained stable between 30 and 50% when the temperature and pressure were varied.

Subsequently, to investigate the internal microscopic pore structures of the porous elastomers, the internal morphology of the phases in HNP-PDMS@BA was observed using confocal laser scanning microscopy because of its transparency (Fig. 4D), revealing an internal interconnected and interpenetrating structure. For further investigations of the internal framework, the porous elastomer was cut diagonally and observed using SEM (Supplementary Fig. 16B). When the HNP-PDMS@BA elastomer, filled with silicone oil, was cut, the oil flowed out of the pores within 30 s (Supplementary Fig. 19). To investigate the smaller-scale features, the nanochannels in the elastomer were analyzed using transmission electron microscopy. These nanochannels, resembling cylindrical pipes with diameters less than 500 nm, extended through the elastomer (Supplementary Fig. 20). Additional pore details are shown in Supplementary Fig. 21. At an air pressure of −0.1 MPa, HNP-PDMS@BA primarily formed micron-sized pores (>0.5 μm) and mesopores (<50 nm), while at a pressure of 0.0 MPa, it formed more macropores (>50 nm). The absorption of silicone oil (30–50%) was significantly higher than that of mercury (porosity of approximately 10%), which may be attributed to the swelling of HNP-PDMS@BA owing to oil absorption23,51. These findings suggested that HNP-PDMS@BA featured a microsphere airspace and interconnected micro-nanochannels. To compare the pore structures of elastomers prepared using our method with those generated using conventional methods, we prepared porous samples with the same mass percentage as the first network. Supplementary Fig. 22 shows the SEM images of the surface morphology and cross-section of porous PDMS. The cross-sections of all samples were porous, and their surfaces were nonporous. The pores in the samples prepared by the particle template method were larger than those in the samples prepared by our emulsion method; larger pores were likely to lead to limited elongation at break and reduced toughness. This finding implied that our method not only imparted a unique porous structure to the elastomers (with adjustable surface pores and interconnected internal pores) but also laid the foundation for excellent tribological properties (as discussed in the next Section).

To investigate the ultra-low friction and wear behavior of HNP-PDMS@BA, we conducted ball-plate experiments under saltwater lubrication (Fig. 5A). In this section, P1 and P2 represent HNP-PDMS@BA-125/−0.1 MPa, and HNP-PDMS@BA-125/0 MPa, respectively, while G and S represent the GCr15 and Si3N4 balls, respectively. The morphology and wettability of the surfaces strongly affect the COF. In particular, if the surface wettability is improved and combined with appropriate surface structure, a transition of the lubrication regime can lead to a decrease in the COF52,53. We started the friction investigations by exploring the differences between the lubricating films on hydrophobic and hydrophilic surfaces during friction. Because the contact angle (CA) of saltwater is similar to that of pure water, pure water was used to simulate the wetting state of saltwater54. CAs for S-PDMS, P1, P1 after one friction test and P1 after three consecutive friction tests were measured as approximately 105, 101, 73, and 77°, respectively (Supplementary Fig. 23A–D). In the MD simulations, the CAs of the surfaces were set such that the error in each case was within 3°, compared to the experimental CAs (see the “Methods” section for the details). MD simulations were performed to investigate the differences in the water film on hydrophobic and hydrophilic surfaces (Supplementary Fig. 24 and Movies 1, 2). Results of the interactions between the ball, water, and the hydrophobic and hydrophilic surfaces at 10 ns are shown in Fig. 5B, and Supplementary Fig. 25. Compared to the hydrophobic surface, a complete water film was formed between the ball and the hydrophilic surface. Correspondingly, the water density distribution is shown in Fig. 5C. It shows that when only the wetting effect is considered, hydrophilic surfaces are more likely to cause water to accumulate at the bottom of the ball than hydrophobic surfaces. This hydrophilic shift is likely to lead to a COF close to that of previous studies25,55. Water was easily absorbed in the lower part of the ball and the water film density on the hydrophilic surface was more than twice that of the hydrophobic surface (Fig. 5C). As shown in Fig. 5D, the COF of P1-G and P2-G continually decreases sharply during the friction process and finally stabilizes. After stabilization, the average COF of S-PDMS-G, P1-G, P2-G, P1-S, and P2-S was 1.06, 0.17, 0.05, 1.17, and 1.13, respectively (Fig. 5E). By comparison, COF reduced by over 95% between S-PDMS-G/P1-Si/P2-Si and P2-G. As shown in Fig. 5F, P2-G wear volumes and rates reduced by over 90% between S-PDMS-G/P1-Si/P2-Si and P2-G. After friction, S-PDMS showed clear furrow wear, and P1 displayed nearly no wear marks (Fig. 5G, H). The other worn surfaces also showed fewer wear marks than S-PDMS, and the capture of wear debris by pores was observed on all surfaces (Supplementary Figs. 26 and 27).

When GCr15 was used as the friction pair, electrochemical corrosion continued to occur (Supplementary Fig. 28). We inferred that this electrochemical corrosion was beneficial to reduce the COF and wear, because the COF and wear rate were higher when Si3N4 was used as the friction pair. In the corrosion process, wear debris consisting of nanoclusters was produced in saltwater, which enhanced water adsorption under the influence of iron oxide (Supplementary Fig. 29). Meanwhile, the wear debris was captured by the pores (Supplementary Fig. 26), leading to the surface wetting change from hydrophobic to hydrophilic (Supplementary Fig. 23B, C), which in turn thickened the lubrication film. With the hydrophilic effect, pores store water easily, causing local dynamic pressure effects near the pores56. The Sq of P1 with large pores was 3.8 times higher than that of P2, as shown in Fig. 4F, increasing the initial wear and the wear debris capture ability (Supplementary Fig. 26D, E), which in turn thickened the lubrication film. Therefore, P1 exhibited faster friction reduction and a lower wear rate (Fig. 4B and D). Overall, when GCr15 and HNP-PDMS@BA (P1 and P2) were rubbed against each other, corrosion occurred and hydrophilic debris was produced, which led to hydrophilic HNP-PDMS@BA surfaces. The coordinated effect of the hydrophilic surface and the porous structure with stored liquid reduced abrasive and three-body wear, causing the boundary lubrication to transform into mixed lubrication, which in turn resulted in ultra-low friction and wear (Fig. 5I). The transformation is reflected by the shear stress and COF under a single reciprocating cycle (Supplementary Fig. 30). Compared to the unreduced state (Supplementary Fig. 30A–D), a clear sliding platform and a stable low COF appeared in the COF-reduced cycle (Supplementary Fig. 30E, F). At higher loads (4 N and 6 N), the sliding plateau disappeared, indicating that the friction was dominated by the elastic deformation of the surface57; however, the average COF continued to be low (Supplementary Fig. 31). Furthermore, the ability to improve the tribological properties was highly stable, as shown in Supplementary Figs. 32–39. P1 exhibited low friction and wear even after cyclic tensile, friction fatigue tests, or under heat and UV radiation (Supplementary Information, Section 2.3, for a detailed discussion).

The degree of macromolecular mixing and phase separation depended on the solubility of Sylgard 184A, Sylgard 184B, S-PDMS in D-PDMS, and the ability of D-PDMS to swell with Sylgard 184A and Sylgard 184B32. Based on our MD simulations and experiments, we inferred that the immiscibility of S-PDMS and D-PDMS prepolymers was closely related to the presence of borate. Consequently, we precisely controlled the mass of D-PDMS@BA to achieve different phase separations, resulting in elastomers with varying mechanical performances. As the proportion of S-PDMS was incrementally increased in D-PDMS, and when the mass percentage of D-PDMS was less than 20%, SEM analysis revealed the disappearance of the porous structure (Supplementary Fig. 40). This result was attributed to the complete dissolution of the D-PDMS@BA solute by the S-PDMS solvent, leading to a transition to a homogeneous network polymer. By investigating the changes in the mechanical performance during the transition, we determined that a lower amount of D-PDMS@BA led to higher toughness and breaking strength in HN-PDMS (Supplementary Fig. 41A; details are presented in Supplemental Discussion 2.4). This result implied that a porous elastomer with minimal D-PDMS could improve the mechanical performance. The tensile modulus of the HNP-PDMS@BA elastomer improved to nearly 1.6 MPa (Supplementary Fig. 41D), and was consistent with the R_g results from SAXS analyses. Generally, the compression modulus of PDMS is similar to its tensile modulus, and neither moduli are influenced by the curing pressure (Supplementary Fig. 42). However, the compression modulus of HNP-PDMS@BA could be adjusted from 0.25 to 1.25 MPa by changing the curing temperature and air pressure (Fig. 6A, B); the compression modulus negatively correlated with temperature and positively correlated with pressure. Overall, the results demonstrated the basic properties of a heterogeneous elastomer network when BA was used as the crosslinker and that the heterogeneous network was highly controllable and versatile.

Generally, pores tend to reduce the breaking elongation and modulus58. In this section, we demonstrate that this limitation can be avoided by introducing BA derivatives within a heterogeneous polymer network. The following networks were used: D-PDMS@methylboric acid (MBA), D-PDMS@phenylboric acid (PBA), D-PDMS@phenyldiboric acid (PdBA), and D-PDMS@biphenyl diboric acid (bPdBA). FTIR results confirmed the presence of D-PDMS in the new HNP-PDMS elastomers59 (Fig. 6C). Next, we evaluated the mechanical properties. As shown in Fig. 6D and E, the toughness and breaking strength significantly improved in the new HNP-PDMS elastomers. D-PDMS, D-PDMS@MBA, and D-PDMS@PBA exhibited a reduced tensile modulus, whereas D-PDMS@PdBA and D-PDMS@bPdBA showed an increased tensile modulus. Evidently, the introduction of the methyl and benzene rings enhanced the toughness of the HNP-PDMS elastomers. This improvement was attributed to the hydrophobic and π–π interactions of the benzene rings in the continuous phase of the heterogeneous polymer networks (Fig. 6F). Increasing the borate content also increased the tensile modulus of the porous elastomers. Therefore, the HNP-PDMS@PdBA and HNP-PDMS@bPdBA elastomers exhibited high tensile moduli (approximately 2 MPa), breaking strength (approximately 5.4 MPa), and toughness (approximately 8 MJ/m3) (Fig. 5E). Similarly, HNP-PDMS@bPdBA demonstrated controllability of the tensile modulus in the 0.15–2 MPa range, by adjusting the curing pressure and temperature (Fig. 6G and Supplementary Fig. 43B). Surprisingly, the stretch percentage could be improved to 1250%, which is attributed to the increase in the degree of viscous deformation of HNP-PDMS@bPdBA, as shown in Supplementary Fig. 44 (see Supplementary Information, Section 2.5, for more details). Additionally, the performance of HNP-PDMS@bPdBA was better than that of P-PDMS@Sugar (Fig. 6G). Subsequently, using six key parameters, we compared the mechanical performance of the HNP-PDMS elastomers with those of other methods and S-PDMS (Fig. 6H, I). The results highlighted the overall superior performance of HNP-PDMS elastomers, particularly stretch rate, toughness, and breaking strength. Theoretically, we could modify the continuous phase, introduce arbitrary functional groups, and endow porous elastomers with unique properties.

To validate our method on silicone-based materials, porous Ecoflex silicone@BA elastomers were prepared using commercial Ecoflex silicone with a composition similar to that of S-PDMS60. We could successfully apply our method to prepare the new porous silicone structures (Supplementary Fig. 45A, B). The breaking strength and toughness were significantly improved (Supplementary Fig. 45C, D). The introduction of D-PDMS@BA significantly delayed the fracture of the elastomer, and the toughness increased to 150%, despite the elastomer being porous. Furthermore, we successfully prepared new porous elastomers using three other PDMS materials (DC170, DC527, and RTV615), as shown in Supplementary Fig. 46. These porous elastomers also exhibited elongation improvement potential. These results proved that our method was applicable to the preparation of mechanically enhanced porous elastomers for all PDMS systems.

PDMS is inherently insulating; therefore, to prepare flexible sensors, conductive properties need to be introduced to PDMS materials. We used carbon fibers with a diameter of 7 μm and a length of 33.6 μm as the conductive material (Supplementary Fig. 47). To achieve conductivity in PDMS/silicone materials, rather than trying to form pathways by directly mixing PDMS with conductive materials (Supplementary Fig. 48A), the conductive material is usually connected within the polymer using a preparation method similar to that for preparing porous materials61,62. Therefore, based on the formation mechanism of HNP-PDMS@BA, we added carbon fibers to PDMS and successfully prepared conductive PDMS (HNP-PDMS@C, resistance <1 kΩ), without the need for additional surfactants or emulsions (Supplementary Fig. 48B, C). The mechanical performance of HNP-PDMS@C/−0.1 MPa is better than that of S-PDMS (Fig. 6J), likely owing to the dispersion of carbon fibers within the through-pores of the HNP-PDMS (Fig. 6K). This flexible conductive material can be used as the skin of bionic robot hands, for example, to sense force and identify materials (Fig. 6L). To demonstrate this application effect, HNP-PDMS@C/−0.1 MPa was encapsulated in S-PDMS, bent, and fixed on a robotic finger for contact detection (Supplementary Fig. 49A). The material acted as a strain and triboelectric sensor. As the contact force increased from 1 to 4 N, the change rate of resistance increased accordingly (Supplementary Fig. 49B). According to the peak value and width of the wave41, various materials can be distinguished as shown in Supplementary Fig. 49C, demonstrating practical potential applications. Overall, our method enables the emulsion-free formation of high-performance porous elastomers and flexible sensing materials.

Methods
Materials
HPDMS (average Mn ~550) was sourced from Sigma-Aldrich. A PDMS prepolymer (Sylgard 184, Sylgard 170, and Sylgard 527) and methyl silicone oil (100 cs) were purchased from Dow Corning (USA). Ecoflex 00–31 and RTV615 were obtained from Smooth-On (USA) and Momentive (USA). BA, MBA, PBA, PdBA, and bPdBA were obtained from Shanghai Macklin Biochemical Technology Co. Ltd. Ethanol (C2H6O), NaCl, and cane sugar salts were purchased from Tianjin Fuyu Fine Chemical Co. Ltd. Castor oil and glycerin were obtained from Sinopharm Chemical Reagent Co. Ltd. and Shanghai Acmec Biochemical Technology Co. Ltd, respectively. Baking soda was purchased from Tongbai Boyuan New Chemical Co. Ltd. Ecoflex 0031 silicone was obtained from Nantong Jingwei Biotechnology Co. All chemicals were used as received without further purification, and deionized water was used for all experiments and tests.

Fabrication of dynamically crosslinked polydimethylsiloxane
BA, MBA, PBA, PdBA, and bPdBA were dissolved in absolute ethanol and stirred. Subsequently, HPDMS and a BA or BA derivative solution were mixed in a vial, maintaining the molar ratio of Si–OH to B–OH at 1:1. A mixture of diol, BA, or BA derivative and ethanol was heated to 70 °C and stirred for 2 h in a closed environment to form the oligomeric products. Then, the reaction mixture was heated at 100 °C in an open environment to remove ethanol and water, further promoting the reaction to obtain D-PDMS.

Fabrication of heterogeneous-network porous polydimethylsiloxane elastomer
Sylgard 184A and Sylgard 184B were mixed in a mass ratio of 10:1. D-PDMS was added to the Sylgard 184 mixture at mass percentages of 8, 10, 11, 13, 16, and 20%. The mixture was stirred for 30 min, which in turn removed any bubbles by vacuuming. To facilitate the formation of the heterogeneous network, a final cure of HN-PDMS was performed at approximately 25, 125, 145, 165, or 185 °C under pressures of 0, −0.033, −0.066, or −0.1 MPa. Finally, the unstable D-PDMS network was removed by ultrasonic cleaning of the HN-PDMS elastomer with ethanol to obtain the HNP-PDMS elastomer.

Fabrication of control elastomers
S-PDMS was prepared by mixing Sylgard 184A and Sylgard 184B in a 10:1 ratio and curing the mixture. The sugar template, salt template, castor oil emulsion template, glycerine emulsion template, and baking soda foam were added to the Sylgard 184 mixture at a mass percentage of 20%. The mixture was stirred for 30 min, which in turn removed any bubbles by vacuuming. Then, the mixture was cured at 125 °C under −0.1 MPa to obtain porous PDMS. The sugar, salt, and baking soda foam templates were removed using deionized water. The castor oil emulsion template and glycerine emulsion were removed using ethanol. Ecoflex 0031 and porous Ecoflex silicone@BA were cured at 25 °C under atmospheric pressure for 12 h. The other preparation processes were the same as those used to prepare HNP-PDMS. The preparation processes of DC170@BA, DC527@BA, and RTV615@BA were the same as HNP-PDMS.

Fabrication of flexible sensor material
The preparation method of HNP-PDMS@C differs from that of HNP-PDMS@BA; the carbon fiber is added (25% of the total mass) during the mixing of the S-PDMS and the D-PDMS@BA prepolymers. Finally, the unstable D-PDMS@BA network was removed to obtain the HNP-PDMS@C by ultrasonic cleaning of the composite elastomer with ethanol. Two 1-mm thick S-PDMS sheets sandwiched a 1-mm thick HNP-PDMS@C to create the flexible sensor material.

Characterizations
The pores were obtained using mercury injection (mercury intrusion porosimetry, Micromeritics AutoPore V 9620, USA). The surface morphology of the elastomers was characterized using a tungsten filament SEM (ZEISS EVO 10, Germany). The chemical composition of the surface was obtained using an energy-dispersive spectrometer (EDS, OXFORD instruments, Abingdon, UK). The 3D topographic features of the polymer surfaces were examined using a laser scanning confocal microscope (Leica DCM8; Wetzlar, Germany). The roughness of every sample was estimated in the same scan sizes (objective lens 50×). An optical microscope (CX40M, Sunny Optical Technology Co. Ltd., Ningbo, China) equipped with a polaroid and warm white LED light (color temperature of 3000–3300k) was used to observe the liquid–liquid phase separation. The truncated face channels and diffraction of the elastomers were observed using transmission electron microscopy (Talos L120C G2). FTIR was performed on a Thermo Scientific Nicolet iS50 in the attenuated total reflectance mode. SAXS was conducted using a small-angle X-ray scatterer (Anton Paar SAXSpoint 2.0) to characterize the structural changes in the samples with different elastomers. Uniaxial tensile and compressive strain tests were performed using a universal tensile-compression tester (ZQ 990, China). Dynamic mechanical analysis (DMA) was performed using a DMA equipment (Netzsch, Germany, DMA 242) with a heating rate of 3 °C/min from −20 to 100 °C. An oscilloscope (Tektronix TBS2072B) was employed to capture and record the open circuit voltage. A LabVIEW-controlled digital source meter (Keithley 2400, America) recorded the resistance in real time.

Oil absorption capability
For the oil injection, all HN-PDMS@BA samples were cut into 10×10×1 mm pieces and weighed to obtain the initial mass (m). Then, the mass of each HNP-PDMS@BA elastomer (m_2) was weighed to be obtained. Each HNP-PDMS@BA elastomer was injected with methyl silicone oil in a vacuum environment. After oil injection, the surface oil was removed using oil blotting paper, and the mass of oiled HNP-PDMS@BA (m_1) was recorded (further details are presented in Section 2.2 of Supplementary Material). All experiments were repeated at least three times.

Molecular dynamics simulations for heterogeneous network
MD simulations were performed using an initial monomer, followed by crosslinking, geometry optimization, energy minimization, and dynamics. All simulations were implemented using the Materials Studio software package via the Amorphous Cell and Forcite modules. The Dreiding force field63 was used to determine atomistic interactions between polymer chains. Electrostatic interactions were computed using an Ewald representation, with temperature control achieved using a velocity-scale thermostat set to a relaxation time of 0.1 ps. Van der Waals interactions were calculated using an atom-based representation during model generation, equilibration, and subsequent production runs. The models were equilibrated at 300 K for 100 ps with a timestep of 1 fs in the NVT ensemble, followed by a restart at 300 K for an additional 100 ps in the NVE ensemble to finalize the cohesive energy density calculations. The cohesive energy density results for S-PDMS and D-PDMS@BA were obtained by repeating these simulation steps. For multiple-chain models, MD simulations were equilibrated at either 300 or 398 K for at least 100 ps in the NVT ensemble. The MSD and radial distribution function of D-PDMS@BA and B atoms were subsequently analyzed based on these simulations.

Molecular dynamics simulations for water wetting
All simulations were performed by LAMMPS. Water molecules were represented by the coarse-grained mW water molecules64. Water-solid interactions were described by 12–6 Lennard–Jones potential65,66, and the wettability of solid surfaces was controlled by the solid-water interaction parameter (ɛ), while the cutoff distance for water–solid interaction was set to 8 Å. All wetting simulations were performed for 10 ns in NVT ensemble, at 300 K. The temperature was controlled with the Nose–Hoover thermostat with a relaxation time of 0.5 ps, and periodic boundary conditions were set. To explore the interaction between GCr15, water, and hydrophobic or hydrophilic surface, a simplified model was established (Supplementary Fig. 50) and each ɛ was set (Supplementary Table 4). The Fe (001) plate model with a BCC lattice constant of 2.86 was built to simulate wetting the status of the steel (Supplementary Fig. 34), which shows approximately 78° of CA consistent with the previous study54. The hydrophobic or hydrophilic surface was built with an FCC lattice constant of 3.9, and the CA showed approximately 107° or 75° according to our previous study67. Images were visualized using the OVITO and Python packages in wetting simulation.

Density functional theory calculations
All density functional theory calculations were performed using the Vienna Ab initio Simulation Package (VASP, version 6.3.0)68. The Exchange–correlation interactions were treated within the generalized gradient approximation, employing the Perdew–Burke–Ernzerhof functional69. Ion–electron interactions were modeled using the projector augmented-wave method70. A plane-wave cutoff of 520 eV was used for all calculations. For isolated molecules, a vacuum spacing of at least 15 Å was applied along all directions, and Γ-point sampling was used for Brillouin zone integration. Geometries were optimized until the residual atomic forces were below 0.02 eV Å−1, with an electronic convergence criterion of 10−5 eV. Electrostatic potentials were evaluated using VASP’s default settings.

Friction performance test
Friction tests were performed using a friction testing machine (UMT-2, USA) at a relative humidity of 40–50% and a temperature of approximately 25 °C. The upper sample was a GCr15 or Si3N4 ball with a diameter of 9.5 mm. The lower sample was S-PDMS, P1, and P2 for the experiments. The loads of 2, 4, and 6 N were used; the reciprocating frequency was 4 Hz; The lubrication liquid was saltwater (3.5% of NaCl solution). The reciprocating stroke was 12 mm along the linear direction of the lower sample; hence, the average velocity was 48 mm/s. Before each friction test, the upper sample was ultrasonically cleaned with anhydrous ethanol for 5 min. Each combination was repeated at least thrice.

Mechanical performance tests
Uniaxial tensile and compression tests were conducted on all samples at velocities of 5 and 1 mm/min, respectively. Cyclic tensile and compression tests were performed under the same conditions. Samples were initially stretched or compressed to a specific stretching or compression ratio and then immediately unloaded. Two unloading conditions were adopted: nominal stress unloading to 0 Pa and displacement unloading to 0 mm. To minimize the Mullins effect71–73, the compression modulus was calculated within the linear region, ensuring a minimum stress of 0.015 MPa and linear fit with an R2 > 0.99. Each experiment was repeated at least three times.

Peer review rounds
[{"round": 1, "reviewer_comments": {"reviewer_1": "This article presents an innovative borate-driven approach for fabricating porous PDMS elastomers. By employing vacuum curing combined with controlled alcoholysis, the authors successfully achieve selective removal of one polymer network, resulting in interconnected porous structures with stabilized interfaces. The prepared materials demonstrate exceptionally low friction under saltwater lubrication conditions and enhanced mechanical strength, underscoring their significant potential for applications in water-lubricated components and flexible sensing devices. The authors thoroughly elucidate both the synthesis procedure and underlying mechanisms governing the material's formation. I believe this manuscript offers valuable contributions to the field and recommend its publication after the authors address the following questions.\n1. The paper repeatedly emphasizes the stabilizing role of borate groups at the interface but primarily relies on molecular dynamics simulations and macro-level performance tests. It lacks direct characterization to confirm how borate bonds interact with the siloxane backbone, including bond strength and dynamic reversibility.\n2. The conclusion section proposes potential applications in water-lubricated components and flexible sensors, which typically demand durability, fatigue life, and environmental stability. Have any relevant cyclic stretching or long-term wear tests (>10^5 cycles) been conducted to evaluate aging or performance degradation?\n3. Although ultra-low friction and wear are achieved under saltwater lubrication, the long-term interaction and durability of corrosion products (iron-oxide nanoclusters) within the pore structure remain underexplored. For instance, does the hydrophilicity and nanocluster trapping diminish after repeated friction or prolonged saltwater immersion?\n4. Following the previous point, how might this alter tribological behavior if corrosion products accumulate excessively or detach?\n5. The authors claim this method suits various PDMS systems and potentially non-silicone elastomers. However, only limited evidence (e.g., Ecoflex@BA) is provided, which seems insufficient to substantiate this claim.", "reviewer_2": "Title: Borate-Driven Heterogeneous Networks for Porous Elastomers with Enhanced Tribological and Mechanical Performances\nAuthor: Wu et al\nThe manuscript describes a method for making porous PDMS elastomer which have favorable tribological and mechanical properties. The method involves phase separation within the bulk of the crosslinkable mix and use of borate at the interface of the phases for stabilizing the two-phase system. Authors report also reduction in friction coefficient by over 95% in presence of salt water. Beside that, the porous material exhibits stretchability of 1250%. While the authors have presented in detail the method of making sample, they have not provided sufficient rational of several observations from the experiments. In other word, while the topic looks interesting, scientifically it does not appear very enriching yet. Furthermore, the manuscript is also not very easy to read. There are mix-up of tenses, long sentences, unnecessary adverbs, typographical errors. I have listed some of them below and have also written my comments and questions. Based on these observations I do not recommend acceptance of this manuscript for publication.\n(a) There are typographical errors and mixing of tenses.\nIn page 3 line 71, “… presented …” : why past tense?\nIn page 2 line 48, “Friction will destroy …” why future tense?\nIn page 4 line 81, “… rater …” : typo.\nIn page 4 line 81-83 “Unique advantages … borate sites”, not clear what the authors want to say here. What is “universal method”?\n(b) line 83-86: Author claims making “highly specialized …”. An interesting material has been made but it is not clear what is highly special about it. For example, pores do not appear interconnected here. Are they? Authors don’t even mention the pore diameter. Author has mentioned surface roughness attained at different temperature and pressure. But how was the roughness estimated? RMS roughness is expected to be different at different scan sizes. Furthermore, since the pores are not connected, is it fare to say that it is only the surface pores which could directly influence the friction coefficient; the pores that supposedly formed at the bulk of the material didn’t have any effect.\n(c) In fact, in figure 3C to E the symbols used for the data points are so small that it can not be see if there is any error bar there. Furthermore, it is not clear why the slopes of these lines are different and what exactly that signify. It is not clear also what the intercepts in these plots mean.\n(d) Page 5 line 108-109: “In the …S-PDMS”, Not clear what the author wants to say here.\n(e) Page 5 line 114: “…proposed …” Should it be past tense here?\n(f) Page 9 line 181-183 “As the stretch …pronounced” This sentence needs rewriting.\n(g) Page 12 line 264: “The particle …being isolated” This statement is not correct. It is possible to make network of inter-connected pores using particle templates. Secondly, the schematic of figure 4A and the SEM images of figure 4B that the authors have presented show that the pores are like vertical holes that spans from one cross-section to other but they do not appear to be interconnected.\n(h) Page 13 line 281: “Under certain …COF”: What are these “certain wetting conditions”? Why do circular textures (I understand presence of holes) at all reduce the COF?\n(i) Page 13 line 281: “Wetted surfaces … in methods)” What is the meaning of this statement? … particularly that of the word “guarantee”?\n(j) Page 14 line 293 “… water film density …” this phrase may have some meaning in MD solution, but practically it either doesn’t have meaning or it signifies some different parameter.\n(k) Page 14 line 297 “Amazingly, COF …” what is so “amazing” about it. Such adverbs are best avoided in a scientific document! Authors have rationalized this observation by attributing it to generation of debris because of “wear”. Authors have presented also debris volume for different cases. Shouldn’t the debris volume continue to increase with time during of the sliding experiment? Shouldn’t the debris volume vary with the speed of sliding? In fact, authors do not mention the sliding speed at all in the manuscript.\n(l) In figure 5D, authors have presented the COF as a function of reciprocal cycles. What is the significance of carrying out this experiment over 12000 cycles. Why the COF values for all cases become different after 4000 cycles. Secondly even in one cycle the normal load and shear load and consequently the COF should exhibit fluctuations. Authors do not make any mention of that. Secondly did the authors obtain shear load at different normal load?\n(m) Page 14 line 309: “…(Figure 22C)…”, There is no such figure!\n(n) The stretch percentage for some of the samples were found to be quite high, as high as 1250%. What leads to this increase, low crosllinking density, viscoelastic effect, smaller physical entanglement, what? Authors have not thrown any light on the possible mechanism that leads to this increase in extensibility.", "reviewer_3": "The authors report a novel, template-free emulsion method to create purely porous silicone elastomers by driving heterogeneous network formation using borate-based dynamic crosslinkers. By combining a borate-modified PDMS precursor with a commercial PDMS prepolymer and inducing spontaneous phase separation under controlled thermal and vacuum conditions, they generate an interconnected porous structure after selectively removing the sacrificial borate phase. The resulting materials exhibit remarkably low friction and wear under aqueous lubrication while retaining excellent stretchability and toughness. Furthermore, the approach allows precise tuning of pore morphology and mechanical properties through processing parameters and can be extended to other silicone elastomer systems, demonstrating broad potential for applications in low-friction, wear-resistant soft materials.\nHowever, the manuscript, in its current state, may not meet the standards for publication in Nature Communications, a journal known for its groundbreaking and influential contributions to the scientific community. The idea and concept of the paper are excellent and novel, but the available data on this particular aspect appears to be insufficient. Furthermore, there is a need for more comprehensive supporting evidence and data to bolster the proposed hypotheses.\nThe authors are encouraged to consider the following suggestions for enhancing the manuscript in preparation for future submissions.\nTo strengthen the manuscript, the authors should consider (Major):\n1. To fulfill the objectives proposed by the authors, additional stability and wear‐rate measurements under thermal, high‐temperature, UV, and aging conditions must be conducted.\n2. Beyond the current stability tests over several thousand cycles, experiments addressing a much longer fatigue life are required. Considering the applications the authors propose, stability over only a few thousand cycles is insufficient.\n3. The authors have validated their method in PDMS and Ecoflex. The claim that the fabrication approach applies to all polysiloxane systems is unsupported by evidence from only two examples; additional validation cases are needed to substantiate this assertion.\n4. The authors’ scientific novelty and extensive material analyses, including modeling, are highly commendable; demonstrating a practical application is necessary to better align with the scope of Nature Communications. Any example—such as the machinery, robots, bearings, or biological models—would be suitable."}, "author_response": "Thank you for the reviewers’ insightful comments and suggestions, which have been extremely helpful in improving our work. We have studied comments carefully and tried our best to made corrections to meet the approval. In addition, we have modified some formats and sentences to express the meaning clearly and accurately. Point-by-point responses to each of the Reviewer comments are listed in the following content.\n[Referees’ comments are in black; Author responses are in blue; The original texts are in purple; Revisions in the manuscript are highlighted.]\nReviewer #1 (Remarks to the Author):\nThis article presents an innovative borate-driven approach for fabricating porous PDMS elastomers. By employing vacuum curing combined with controlled alcoholysis, the authors successfully achieve selective removal of one polymer network, resulting in interconnected porous structures with stabilized interfaces. The prepared materials demonstrate exceptionally low friction under saltwater lubrication conditions and enhanced mechanical strength, underscoring their significant potential for applications in water-lubricated components and flexible sensing devices. The authors thoroughly elucidate both the synthesis procedure and underlying mechanisms governing the material's formation. I believe this manuscript offers valuable contributions to the field and recommend its publication after the authors address the following questions.\nResponse:\nWe highly appreciate Reviewer #1’s valuable and helpful comments. We have done our best to provide appropriate responses and the revised manuscript to address these questions.\n1. The paper repeatedly emphasizes the stabilizing role of borate groups at the interface but primarily relies on molecular dynamics simulations and macro-level performance tests. It lacks direct characterization to confirm how borate bonds interact with the siloxane backbone, including bond strength and dynamic reversibility.\nResponse:\nThank you for the valuable comment. To address your concern, we added Fourier transform infrared (FTIR) spectroscopy characterization, its analysis to confirm the bond strength and dynamic reversibility. As far as we know, direct characterization of molecular skeleton interactions is very difficult, but we have used density functional theory (DFT) calculations with higher accuracy than molecular dynamics simulations. We hope these meet your requirements. According to the previous study (Chem. Mater. 2014. 26. 12, 3781-3795), boroxine will be generated after the reaction between PDMS and boric acid, which is verfied by the result of FTIR as shown in Supplementary Fig. 2A. Boroxanes with multiple boronate esters support the speculation of B atom enriched at the two-phase boundary. Based on the wavelengths ( ) of Si-O and B-O displayed by FTIR, the force constant ( ) can be calculated according to the following formula:\n𝜈\n𝑘\n1 𝑘\n𝜈 = √\nand are speed of light and reduced ma2s𝜋s.𝑐 Su𝜇bstituting the wavelength values of Si-O and B-O measured by FTIR into the above eqution, we can get (677 N/m) >\n𝑐 𝜇\n(606 N/m). Using a repeating unit in D-PDMS@BA as a model, results of DFT\n𝑘𝐵−𝑂\ncalculation show that the bond dissociation energies of B-O and Si-O are 6.05 eV and\n𝑘𝑆𝑖−𝑂\n5.65 eV (BDE > BDE ), respectively. The bond dissociation energy results are\nB-O Si-O\nconsistent with the force stiffness results. Therefore, bond strength of B-O is more\nthan that of Si-O. Based on the above molecular model, we calculated the electrostatic\npotential of the molecule as shown in the Supplementary Fig. 3 to intuitively display\ninteractions of bonds with the siloxane backbone. When boric acid and HPDMS are\ncross-linked, a distinct repulsive region is formed. From the electrical potential values,\ncompared with the other groups, the silanol group is more likely to be closer to the boric\nacid; The non-polar methyl groups and polar hydroxyl groups are less likely to attract\neach other. To investigate the dynamic reversibility, we performed FTIR tests on D-\nPDMS@BA ethanol solution and D-PDMS@BA after evaporation of ethanol. FTIR\nresult in Supplementary Fig. 2B displays that the B-O and C-O peaks of D-PDMS\ndissolved in ethanol were broadened and shifted, respectively. The FTIR result of D-\nPDMS after evaporation of ethanol are consistent with that of D-PDMS not dissolved\nin ethanol. These results illustrate the dynamic reversibility of D-PDMS under the\ninfluence of ethanol. Besides, in our earlier study (ACS Applied Materials & Interfaces,\n2024, 16(43): 58980-58990), we demonstrated its force-triggered dynamic reversibility.\nRevised or added Figure:\nSupplementary Fig. 2. (A) Fourier transform infrared spectrum of S-PDMS, D-\nPDMS@BA, HN-PDMS@BA, and HNP-PDMS@BA. (B) Fourier transform infrared\nspectrum of ethanol, the mixture of D-PDMS@BA and ethanol, and D-PDMS@BA\nafter ethanol evaporated.\nSupplementary Fig. 3. Electrostatic potential map of a repeating unit in D-\nPDMS@BA\nRevised or added text (main text, page 5):\nIn the phase-separation mixture, as shown in Supplementary Fig. 2, all hydroxyl groups\nof H-PDMS reacted after curing to obtain HN-PDMS@BA. Fourier transform infrared\nspectroscopy (FTIR) results show that the borate group of D-PDMS@BA can be\nconsidered the distinguishing characteristic, compared to S-PDMS (for detailed\ndiscussion, see Supplementary Information, Section 2.1). Consequently, we considered\nthe interaction between borate ester and silicone oil as an important factor of\nincompatibility. The electrostatic potential of the repeating unit in D-PDMS@BA\nwas calculated as shown in the Supplementary Fig. 3, to intuitively display the\ninteractions of the borate bond with the siloxane backbone. The interactions suggest\nthat the incompatibility is likely due to the repulsion between the Si-O bonds and the\noxygen in the Si-O backbone (for detailed discussion, see Supplementary Information,\nSection 2.1).\nRevised or added text (Supplemental Information, Section 2.1):\nBased on the wavelengths ( ) of B-O and Si-O displayed by FTIR, the force constant\n( ) can be calculated according to the following formula:\n𝜈\n𝑘\n1 𝑘\n𝜈 = √ (S1)\nwhere and are speed of light and re2d𝜋uc𝑐ed 𝜇mass. Because of (677 N/m)>\n(606 N/m), bond strength of B-O is more than that of Si-O. Then, we evaluated\n𝑐 𝜇 𝑘𝐵−𝑂\nbond dissociation energies (BDEs) for two chemically distinct bonds within the target\n𝑘𝑆𝑖−𝑂\nmolecule, Si–O (siloxane bridge) and B–O (the terminal B–O–Si linkage). To avoid\nopen-shell radicals and ensure closed-shell fragments (Frag), we employed a\nhydrogenation (H -capping) scheme that conserves atom counts:\n,\nwhere each fragment is constructed by cleaving A–B and adding one H atom to A and\n𝑀+𝐻2 → 𝐹𝑟𝑎𝑔(𝐴−𝐻)+𝐹𝑟𝑎𝑔(𝐵−𝐻)\none H atom to B to satisfy valence. The bond dissociation energy is then\n(i) Si–O (siloxane) bond inside the chain)\n𝐸𝐵𝐷𝐸(𝐴−𝐵) = 𝐸[𝐹𝑟𝑎𝑔(𝐴−𝐻)]+𝐸[𝐹𝑟𝑎𝑔(𝐵−𝐻)]−𝐸[𝑀]−𝐸[𝐻2] (S2)\nCut the selected Si–O bridge in HO- [Si (CH ) –O-] –B(OH) , yielding two\n3 2 6 2\nfragments: the Si-terminated part is capped to –Si (CH ) –H, and the O-terminated part\n3 2\nis capped to –O–H (silanol). Apply Eq. (1):\n(ii) B–O (terminal B–O–Si linkage)\n𝐸𝐵𝐷𝐸(𝑆𝑖−𝑂) = 𝐸[𝐹𝑟𝑎𝑔 𝑤𝑖𝑡ℎ 𝑆𝑖 −𝐻]+𝐸[𝐹𝑟𝑎𝑔 𝑤𝑖𝑡ℎ 𝑂−𝐻]−𝐸[𝑀]−𝐸[𝐻2] (S3)\nCleaving the B–O bond that connects B(OH)₂ to the chain gives (a) the chain end\ncapped to –Si–O–H and (b) a boron fragment HB(OH)₂ (i.e., B gains one H). The\ncorresponding BDE is\nThis H₂-capping protocol yields closed-shell fragments and is robust for siloxane and\n𝐸𝐵𝐷𝐸(𝐵−𝑂) = 𝐸[𝑆𝑖 −𝑂−𝐻 𝑡𝑒𝑟𝑚𝑖𝑛𝑎𝑡𝑒𝑑 𝑐ℎ𝑎𝑖𝑛]+𝐸[𝐻𝐵(𝑂𝐻)2]−𝐸[𝑀]−𝐸[𝐻2](S4)\nboron–oxygen bonds. For nonequivalent Si–O bonds along the chain (e.g., near termini\nvs. interior), Eqs. S2 and 3 were applied to each distinct local environment. Based on\nthe above method, the calculation results by density functional theory show that the\nBDEs of B-O and Si-O are 6.05 eV and 5.65 eV, respectively (For more details on the\nmodifications to this section, see the Support Information ).\nRevised or added text (main text, Method, page 25):\nDensity functional theory calculations\nAll density functional theory (DFT) calculations were performed using the Vienna Ab\ninitio Simulation Package (VASP)61. Exchange–correlation interactions were described\nwithin the generalized gradient approximation using the Perdew–Burke–Ernzerhof\nfunctional62, and ion–electron interactions were treated with the projector augmented-\nwave method63. A plane-wave cutoff of 520 eV was used. For isolated molecules, a\nvacuum spacing of at least 15 Å was applied along all directions and Γ-point sampling\nwas adopted. Geometries were relaxed until the residual atomic forces were below 0.02\neV Å–1, with an electronic convergence threshold of 10–5 eV. Unless otherwise stated,\nelectrostatic potentials were evaluated using VASP’s default settings.\n2. The conclusion section proposes potential applications in water-lubricated\ncomponents and flexible sensors, which typically demand durability, fatigue life, and\nenvironmental stability. Have any relevant cyclic stretching or long-term wear tests\n(>10^5 cycles) been conducted to evaluate aging or performance degradation?\nResponse:\nThank you for the significant comment. We performed the long-term wear test\n(>1.2×10^5 cycles) for P1-G. With reciprocating cycles progressing and water\nevaporating, the COF increases, but the COF quickly decreases to a lower level after\nadding a little salt water (~0.1 mL) as shown in Supplementary Fig. 33. Besides, P1\nwas stretched for over 2000 cycles, with a stretch ratio of 20% in each cycle. Then,\nfriction testing of the sample after cyclic stretching revealed that it still exhibited low\nfriction, with the average COF less than 0.15 (Supplementary Fig. 35). Furthermore,\nafter 3 weeks of salt water immersion, UV irradiation, and heating treatment, P1 can\nstably reduce the COF. An increase in the COF at 60 °C after 10000 cycles, which is\ndue to the evaporation of water. However, the low COF state can be recovered after\nadding salt water (Supplementary Fig. 33). These indicate that this porous surface has\nthe potential for long-term service.\nRevised or added Figure:\nSupplementary Fig. 33. The COF–cycle curve of P1-G after 122400 reciprocating\ncycles (Yellow area: Lubrication deteriorated as the water evaporated; Blue area:\nLubrication improved after adding 0.1 mL of salt water).\nSupplementary Fig. 35. (A) The COF–cycle curve and (B) average COF of P1-G after\naging or degradation treatment.\n3. Although ultra-low friction and wear are achieved under saltwater lubrication, the\nlong-term interaction and durability of corrosion products (iron-oxide nanoclusters)\nwithin the pore structure remain underexplored. For instance, does the hydrophilicity\nand nanocluster trapping diminish after repeated friction or prolonged saltwater\nimmersion?\nResponse:\nThank you for the constructive suggestions. We repeated the friction test of P1-G three\ntimes in situ without processing and found that COF reduction still occurred\n(Supplementary Fig. 37). After repeated friction, the CA is still close to that after the\nfirst friction (Supplementary Figs. 23C and D). The corresponding SEM and EDS\nresults of the worn surface are shown in Supplementary Fig. 34B, which reveals the\npresence of wear debris and iron in the pores, indicating that the nanoclusters were still\ntrapped. Besides, combining the COF and SEM results of the surface subjected to\n122400 cycles in (Supplementary Fig. 34A), it can be seen that the function of surface\npores in capturing wear debris is still effective. Furthermore, the long-term NaCl\nimmersion (3 weeks) further reduces the COF (Supplementary Fig. 35).\nRevised or added Figure:\nSupplementary Fig. 37. After a 12000-cycle friction test, the friction test was repeated\nwithout any treatment.\nSupplementary Fig.23. The wetting status of water droplets on the (A) S-PDMS\nsurface, (B) P1 surface, (C) P1 surface after one friction experiment, and (D) P1 surface\nafter three repeated friction experiments.\nSupplementary Fig. 34. Results of SEM and EDS elemental analysis after (A) 122400\nreciprocating cycles and (B) three consecutive friction tests.\nSupplementary Fig. 35. (A) The COF–cycle curve and (B) average COF of P1-G after\naging or degradation treatment.\nRevised or added text (Supplemental Information, Section 2.3):\nTo investigate the stability of the low-friction transition and low-wear state, we perform\nfatigue and aging tests on the P1 (HNP-PDMS@BA-125/-0.1MPa). As shown in\nSupplementary Fig. 33, with reciprocating cycles progressing and water evaporating,\nthe COF increases, but the COF quickly decreases to a lower level after adding a little\n(~0.1 mL) salt water. SEM and EDS results show that the pores of P1 are always able\nto capture the wear debris during this process (Supplementary Fig. 34A). COF results\nof other tests are shown in Supplementary Fig. 35. Friction testing of the sample after\ncyclic stretching (over 2000 cycles, with a stretch ratio of 20% in each cycle) revealed\nthat it still exhibited low friction, with the average COF less than 0.15. Furthermore,\nafter 3 weeks of salt water immersion, UV irradiation (365 nm), and heating treatment\n(60 ℃), P1 can stably reduce the COF. An increase in the COF at 60 °C after 10000\ncycles, which is due to the evaporation of water. However, the low COF state can be\nrecovered after adding salt water. \n4. Following the previous point, how might this alter tribological behavior if corrosion\nproducts accumulate excessively or detach?\nResponse:\nWe are very grateful for the comments. Following the Response to 2, as shown in\nSupplementary Fig.33, the yellow area displays the change in COF when corrosion\nproducts accumulate by causing the water to evaporate almost completely. This shows\nthat excessive accumulation leads to an increase in COF, but the COF can drop rapidly\nwhen the products are diluted. The wear rate of the process is less than P1-G\n(Supplementary Fig.36). To study the effect of product detachment on friction, after the\nfirst friction test, the mixed liquid on the surface was wiped off by the dust-free fabric,\nand the new friction test was carried out. The COF dropped rapidly with almost no\nrunning-in period of thousands of cycles (Supplementary Fig.38). Compared with S-\nPDMS-G, P1-Si, and P2-Si, the COF of P1-Si still dropped by over 60%. We speculate\nthat the old ball with products still works. To verify that, we changed the new ball after\nthe mixed liquid on the surface was wiped off by the dust-free fabric and performed a\nfriction test. The friction results show that a running-in period of thousands of cycles is\nnecessary under this condition (Supplementary Fig.39).\nRevised or added Figure:\nSupplementary Fig. 33. The COF–cycle curve of P1-G after 122400 reciprocating\ncycles (Yellow area: Lubrication deteriorated as the water evaporated; Blue area:\nLubrication improved after adding 0.1 mL of salt water).\nSupplementary Fig. 36. P1-G-8.5h represents the sample after 122400 cycles of\nfriction.\nSupplementary Fig. 38. After the first friction test, wipe off the surface mixture\nwithout changing the ball: repeat the test.\nSupplementary Fig. 39. After the first friction test, wipe off the surface mixture and\nreplace the ball with a new one: repeat the test.\nRevised or added text (Supplemental Information, Section 2.3):\nIn any case, the wear rate of the aging sample (< 6.69×10-5 mm3/N·m) was reduced by\nover 75% compared with the wear rate of S-PDMS-G, as shown in Supplementary\nFig. 36. In particular, when the friction time was extended to 8.5 h (122400 cycles),\nthe wear rate was further reduced to as low as ~8.62×10-6 mm3/N·m. We repeated the\nfriction test of P1-G three times in situ without processing and found that COF\nreduction still occurred (Supplementary Fig. 37). After repeated friction tests, the CA\nis still close to that after the first friction test (Supplementary Figs. 23C and D). The\ncorresponding SEM and EDS results of the worn surface are shown in Supplementary\nFig. 34B, which reveals the presence of wear debris and iron in the pores, indicating\nthat the nanoclusters were still trapped. To study the effect of product detachment on\nfriction, after the first friction test, the mixed liquid on the surface was wiped off by\nthe dust-free fabric and the new friction test was carried out. The COF dropped\nrapidly with almost no running-in period of thousands of cycles (Supplementary\nFig.38). Compared to S-PDMS-G, P1-Si, and P2-Si, the COF of P1-Si still dropped\nby over 60%. We infer that the old ball with products still works. To verify that, we\nchanged the new ball after the mixed liquid on the surface was wiped off by the dust-\nfree fabric and performed a repeated friction test. The friction results show that a\nrunning-in period of thousands of cycles is necessary under this condition\n(Supplementary Fig.39). Overall, all these indicate that this porous surface has the\npotential for long-term service.\n5. The authors claim this method suits various PDMS systems and potentially non-\nsilicone elastomers. However, only limited evidence (e.g., Ecoflex@BA) is provided,\nwhich seems insufficient to substantiate this claim.\nResponse:\nThank you for pointing out the potential issue, and this is an important comment. To\naddress the issue, we added three other elastomer materials (DC170, DC527, and\nRTV615) for validation. Using the same preparation method as HNP-PDMS, we\nsuccessfully prepared new porous elastomers (DC170@BA, DC527@BA, and\nRTV615@BA) as shown in Supplementary Fig. 46. These porous elastomers have the\npotential to improve the elongation.\nRevised or added Figure:\nSupplementary Fig. 46. The surface SEM images of (A) DC170, (B) DC170@BA, (D)\nDC527, (E) DC527@BA, (G) RTV615, and (H) RTV 615@BA. Stress-stretch curves\nof (C) DC170 and DC170@BA, (F) DC527 and DC527@BA, (J)RTV615 and\nRTV615@BA.\nRevised or added text (main text, Section 2.6):\nThe introduction of D-PDMS@BA significantly delayed the fracture of the elastomer,\nand the toughness increased to 150 %, despite the elastomer being porous. Furthermore,\nwe successfully prepared new porous elastomers using three other PDMS materials\n(DC170, DC527, and RTV615), as shown in Supplementary Fig. 46. These porous\nelastomers also exhibited elongation improvement potential. These results proved that\nour method was applicable to the preparation of mechanically enhanced porous\nelastomers for all PDMS systems.\nReviewer #2 (Remarks to the Author):\nTitle: Borate-Driven Heterogeneous Networks for Porous Elastomers with Enhanced\nTribological and Mechanical Performances\nAuthor: Wu et al\nThe manuscript describes a method for making porous PDMS elastomer which have\nfavorable tribological and mechanical properties. The method involves phase\nseparation within the bulk of the crosslinkable mix and use of borate at the interface of\nthe phases for stabilizing the two-phase system. Authors report also reduction in friction\ncoefficient by over 95% in presence of salt water. Beside that, the porous material\nexhibits stretchability of 1250%. While the authors have presented in detail the method\nof making sample, they have not provided sufficient rational of several observations\nfrom the experiments. In other word, while the topic looks interesting, scientifically it\ndoes not appear very enriching yet. Furthermore, the manuscript is also not very easy\nto read. There are mix-up of tenses, long sentences, unnecessary adverbs, typographical\nerrors. I have listed some of them below and have also written my comments and\nquestions. Based on these observations I do not recommend acceptance of this\nmanuscript for publication.\nResponse:\nWe are very grateful to Reviewer #2 for the comments. Based on your comments and\nquestions, we have improved our manuscript. We hope that the readability and scientific\nquality of the revised manuscript have been sufficiently improved and meet your\nrequirements.\n(a) There are typographical errors and mixing of tenses.\nIn page 3 line 71, “… presented …” : why past tense?\nIn page 2 line 48, “Friction will destroy …” why future tense?\nIn page 4 line 81, “… rater …” : typo.\nIn page 4 line 81-83 “Unique advantages … borate sites”, not clear what the authors\nwant to say here. What is “universal method”?\nResponse:\nWe appreciate the reviewers' constructive comments and are deeply sorry for confusing\nyou. We reviewed the manuscript again and corrected the tense errors and typos. For\nthe final question, “Universal method” means that our method can be applied to a\nvariety of PDMS systems, and a variety of boric acid derivatives can work. The abrupt\nappearance here might be confusing, so we've changed the way this sentence is written.\nFor details on the changes, please see the revised text section below.\nRevised or added text (main text, page 3, line 71):\nThis study presents a method for preparing heterogeneous-network porous PDMS\n(HNP-PDMS) elastomers, as shown in Fig. 1A (For all abbreviations and their\nexpansions, see Supplementary Table S1).\nRevised or added text (main text, page 2 line 48):\nFriction can destroy the passivation film on the metal surface and promote corrosion.\nRevised or added text (main text, page 4, lines 81-83):\nMechanical performance advantages could be imparted to the porous elastomers, such\nas a stretch percentage of 1250%, by controlling the temperature, pressure, and borate\nsites (Fig. 1C). Using a wide variety of BA derivatives and silicone materials, this study\noffers a new approach for designing specialized porous elastomers for enhanced water\nlubrication performance and preparing flexible sensors.\n(b) line 83-86: Author claims making “highly specialized …”. An interesting material\nhas been made but it is not clear what is highly special about it. For example, pores do\nnot appear interconnected here. Are they? Authors don’t even mention the pore diameter.\nAuthor has mentioned surface roughness attained at different temperature and pressure.\nBut how was the roughness estimated? RMS roughness is expected to be different at\ndifferent scan sizes. Furthermore, since the pores are not connected, is it fare to say that\nit is only the surface pores which could directly influence the friction coefficient; the\npores that supposedly formed at the bulk of the material didn’t have any effect.\nResponse:\nWe are very grateful for your valuable suggestions. 1) In fact, the pores are\ninterconnected. As shown in Supplementary Fig. 19, the cross-section also has pores.\nAfter oil is injected, the oil can flow out of the cross-section. Additionally, the results\nof transmission electron microscopy (Supplementary Fig. 20) and laser confocal\nmicroscopy (Fig. 4D) suggest the presence of internally connected channels. These\nfurther confirmed the interconnected structure. In the previous manuscript, we\ndiscussed the surface pores on page 11, lines 221-226, and internal pores on page 12,\nlines 248-258. To avoid unclear expressions, we have modified the sentences (see the\nfollowing revised text). 2) The roughness (Rq/RMS) of each sample was estimated\nusing the same scan sizes (objective lens 50×) with laser confocal microscopy. The Sq\nin Fig. 4F is the average of 3 different samples cured at the same conditions. Sq also\ndescribes the surface porosity from another perspective. 3) In this study, the pores are\ninterconnected, but whether or not they are interconnected does not directly affect the\nCOF. The presence of internal pores may affect the modulus and, therefore, the COF.\nAs shown in Fig. 5D and Fig. 6B, although the moduli of P1(HNP-PDMS@BA/-0.1)\nand P2 (HNP-PDMS@BA/-0.0) vary significantly, the difference in their COF is not\nsignificant. However, the presence of GCr15 induces in-situ hydrophilic modification\nof the P1 and P2 surface under corrosion, reducing the COF. Therefore, the surface\npores contribute to the low COF (both by capturing wear debris, improving lubrication,\nand by accelerating corrosion under high roughness) rather than internal pores.\nRevised or added text (main text, page 11, lines 225-226)\nConversely, when the pressure was improved (–0.1 to 0 MPa), the pores became smaller\n(5.16 to 1.16 μm) and sparser (Fig. 4C and Supplementary Fig. 14).\nRevised or added text (main text, page 12, lines 248-258)\nSubsequently, to investigate the internal microscopic pore structures of the porous\nelastomers, the internal morphology of the phases in HNP-PDMS@BA was observed\nusing confocal laser scanning microscopy because of its transparency (Fig. 4D),\nrevealing an internal interconnected and interpenetrating structure. For further\ninvestigations of the internal framework, the porous elastomer was cut diagonally and\nobserved using SEM (Supplementary Fig. 16B). When the HNP-PDMS@BA elastomer,\nfilled with silicone oil, was cut, the oil flowed out of the pores within 30 s\n(Supplementary Fig. 19). To investigate the smaller-scale features, the nanochannels in\nthe elastomer were analyzed using transmission electron microscopy. These\nnanochannels, resembling cylindrical pipes with diameters less than 500 nm, extended\nthrough the elastomer (Supplementary Fig. 20). Additional pore details are shown in\nSupplementary Fig. 21. At an air pressure of –0.1 MPa, HNP-PDMS@BA primarily\nformed micron-sized pores (>0.5 μm) and mesopores (<50 nm), while at a pressure of\n0.0 MPa, it formed more macropores (>50 nm). The absorption of silicone oil (30–50%)\nwas significantly higher than that of mercury (porosity of approximately 10%), which\nmay be attributed to the swelling of HNP-PDMS@BA owing to oil absorption23,51.\nThese findings suggested that HNP-PDMS@BA featured a microsphere airspace and\ninterconnected micro–nano channels.\nRevised or added text (main text, page 22, lines 466-468)\nThe 3D topographic features of the polymer surfaces were examined using a laser\nscanning confocal microscope (Leica DCM8; Wetzlar, Germany). The roughness of\nevery sample was estimated in the same scan sizes (objective lens 50×).\nRevised or added text (Supplementary Discussion, Section 2.2)\nThe in the Fig. 4F is the average of 3 different samples cured under the same\nconditions.\n𝑆𝑞\n(c) In fact, in figure 3C to E the symbols used for the data points are so small that it can\nnot be see if there is any error bar there. Furthermore, it is not clear why the slopes of\nthese lines are different and what exactly that signify. It is not clear also what the\nintercepts in these plots mean.\nResponse:\nWe are very sorry that you feel confused. In fact, these points are the average radii of\ngyration (R ) calculated by Supplementary Eq. S10. We have added error bars. In this\ng\nstudy, we mainly utilized two types of PDMS networks. The introduction and partial\nexfoliation of D-PDMS caused changes in the molecular network, which in turn led to\ndifferent slopes. By calculating the tensile modulus, we found that the slope and\nmodulus are surprisingly consistent in value. Therefore, the slope can represent the\nstrength and stiffness of the molecular chain. The intercepts are the Rg of the elastomer\nat 0% stretching after fitting.\nRevised or added Figure:\nFig. 3. Gyration radius (R ) as a function of the stretching ratio for (C) S-PDMS,\ng\n(D) HN-PDMS@BA, and (E) HNP-PDMS@BA. The intercepts are the Rg of the elastomer\nat 0% stretching after fitting.\nRevised or added text (main text, page 9, lines 190-193):\nNotably, the slope values of the fitted lines for S- and HNP-PDMS are numerically\nsimilar to the tensile modulus (as discussed in Section 2.4), demonstrating that the slope\nvalues can represents the strength and stiffness of the molecular chain.\n(d) Page 5 line 108-109: “In the …S-PDMS”, Not clear what the author wants to say here.\n(e) Page 5 line 114: “…proposed …” Should it be past tense here?\n(f) Page 9 line 181-183 “As the stretch …pronounced” This sentence needs rewriting.\nTogether the response:\nWe appreciate the reviewer's careful reading and have revised the sentences accordingly.\nRevised or added text (main text, page 5, lines 108-109):\nIn the phase-separation mixture, as shown in Supplementary Fig. 2, all hydroxyl groups\nof H-PDMS reacted after curing to obtain HN-PDMS@BA. Fourier transform infrared\nspectroscopy (FTIR) results show that the borate group of D-PDMS@BA can be\nconsidered the distinguishing characteristic, compared to S-PDMS.\nRevised or added text (main text, page 5, line 114):\nConsequently, we consider that increasing the D-PDMS@BA content (or the borate\ngroup content) intensifies the repulsion between D-PDMS@BA and S-PDMS, thereby\nenhancing the phase separation.\nRevised or added text (main text, page 9, lines 181-183):\nWe stretched the elastomers from 0 to 80% and observed the SAXS patterns during this\nprocess (Fig. 3A). As the stretch increased, the isotropy was disturbed, and the\nmolecular chains became oriented toward the direction of stretching. Among the three\nkinds of samples (S-PDMS, HN-PDMS@BA, and HNP-PDMS@BA), the anisotropy\nof HNP-PDMS@BA was most pronounced.\n(g) Page 12 line 264: “The particle …being isolated” This statement is not correct. It is\npossible to make network of inter-connected pores using particle templates. Secondly, the\nschematic of figure 4A and the SEM images of figure 4B that the authors have\npresented show that the pores are like vertical holes that spans from one cross-section\nto other but they do not appear to be interconnected.\nResponse:\nThank you for the comments. 1) We agree with the reviewer's point. Adjusting the\nparticle concentration and dispersion allows for the network of interconnected pores.\nHowever, this can further degrade the material's mechanical properties. Our statement\nwas not accurate enough, so we have revised the sentence from the perspective of\nmechanical properties. The pores prepared by the particle template method are larger\nthan those prepared by the emulsion method, which may lead to limited elongation at\nbreak and toughness. 2) To avoid misunderstanding, we modified Fig. 4A as follows.\nFor detailed responses to interconnected pores, please refer to question (b).\nRevised or added Figure:\nFig. 4. (A) Schematic diagram illustrating the control of surface pore morphology. The\ninset optical images show HNP-PDMS@BA before and after oil absorption.\nRevised text (main text, page 12, lines 264-265):\nThe pores in the samples prepared by the particle template method were larger than\nthose in the samples prepared by our emulsion method; larger pores were likely to lead\nto limited elongation at break and reduced toughness.\n(h) Page 13 line 281: “Under certain …COF”: What are these “certain wetting\nconditions”? Why do circular textures (I understand presence of holes) at all reduce the\nCOF?\nResponse:\nThank you for the comments. 1) Generally, improving the hydrophilicity of the surface\ncan reduce the COF, which is attributed to reduced slip of the lubricating liquid, which\nin turn improves lubrication conditions. This hydrophilization can cause the lubrication\nstate to shift from boundary lubrication to mixed lubrication. 2) Surface texturing is a\ncommon method for reducing friction and wear. Over the past decade, our group has\nconducted extensive experiments and theoretical calculations to understand why\nsurface textures reduce COF. (Such as, Friction, 2025, 13(3). Tribology International,\n2025, 212: 110976. Tribology International, 2023, 180: 108310. Tribology\nInternational, 2020, 149: 105733. Applied Surface Science, 2013, 268: 79-86.) In fact,\ncircular textures do not necessarily reduce the COF. However, the circular texture is\nisotropic and easier to manufacture than other textures. It is generally believed that the\nreason for reducing the COF is that the structure can maintain a good lubrication state\nof the system, and hydrodynamic lubrication is formed near the pores. Once this\nlubrication is formed, it will be an effective means of reducing the COF. We apologize\nfor the lack of clarity in this sentence and have therefore rewritten it. Besides, to\nfacilitate the understanding of readers in multiple fields, we replace “texture” with\n“structure”.\nRevised text (main text, page 13, line 281):\nIn particular, if the surface wettability is improved and combined with an appropriate\nsurface structure, a transition of the lubrication regime can lead to a decrease in the\nCOF 52,53.\n(i) Page 13 line 286: “Wetted surfaces … in methods)” What is the meaning of this\nstatement? … particularly that of the word “guarantee”?\nResponse:\nWe appreciate the reviewer's comment and have rewritten the sentences accordingly.\nRevised text (main text, page 13, line 286):\nIn the MD simulations, the CAs of the surfaces were set such that the error in each case\nwas within 3°, compared to the experimental CAs (see the Methods section for the\ndetails).\n(j) Page 14 line 293 “… water film density …” this phrase may have some meaning in\nMD solution, but practically it either doesn’t have meaning or it signifies some different\nparameter.\nResponse:\nWe are deeply sorry that this sentence may have confused you. We have rewritten the\nsentence.\nRevised text (main text, page 14, line 293):\nCompared to the hydrophobic surface, a complete water film was formed between the\nball and the hydrophilic surface. Correspondingly, the water density distribution is shown\nin Fig. 5C. It shows that when only the wetting effect is considered, hydrophilic surfaces\nare more likely to cause water to accumulate at the bottom of the ball than hydrophobic\nsurfaces. This hydrophilic shift is likely to lead to a COF close to that of previous studies\n23,52.\n(k) Page 14 line 297 “Amazingly, COF …” what is so “amazing” about it. Such adverbs\nare best avoided in a scientific document! Authors have rationalized this observation by\nattributing it to generation of debris because of “wear”. Authors have presented also\ndebris volume for different cases. Shouldn’t the debris volume continue to increase with\ntime during of the sliding experiment? Shouldn’t the debris volume vary with the speed\nof sliding? In fact, authors do not mention the sliding speed at all in the manuscript.\nResponse:\nWe appreciate the comments. 1) We have revised the adverb that needs to be avoided.\n2) In the previous manuscript, we concluded that the decrease in COF was due to the\ntransformation of the boundary lubrication into mixed lubrication (Figure 5I). The\ntransformation is the reason for the decrease in the COF according to the Stribeck Curve.\n3) The one purpose of our study is to investigate the effects of lubrication state changes\ninduced by different friction pairs on wear rate and volume at low speeds. We don't\nseem to present debris volume, but rather wear volume and rate. The reviewer may be\nconcerned about the display of wear. Wear rate and volume are important indicators to\ncharacterize the wear resistance of materials (ASTM G133-22). Wear volume generally\ncontinues to increase with time, but wear volume is calculated based on the product of\nsliding distance and wear scar cross-sectional area. The sliding distance follows as:\n𝑋 = 0.002×𝑡×𝑓×𝐿\nwhere:\n𝑁 = 𝑡×𝑓\n= total sliding distance of the ball, m,\n= number of cycles in the test,\n𝑋\n= test time, s,\n𝑁\n= oscillating frequency, Hz (cycles/s), and\nt\n= length of stroke, mm.\n𝑓\nAccording to the Archard equation, at low speeds, speed changes have little effect on\n𝐿\nhardness and thus wear rate. Therefore, we believe that the current sliding speed can\ndemonstrate the potential application of our material, and we have also added the new\nresult of over 120000 cycles to support the potentiality (See Supplementary Fig.33). 4)\nWe mentioned another expression of sliding speed in the method: “The load of 2 N was\nexplored; the reciprocating frequency was 4 Hz; The lubrication liquid is the\nsaltwater (3.5% of NaCl solution). The reciprocating stroke is 12 mm along the\nlinear direction of the lower sample.” This frequency (Hz (cycles/s)) expression is\nused in standard experiments according to ASTM G133-22. We are grateful to the\nreviewer for reminding us of the sliding speed. We can convert the frequency into an\naverage velocity (48 mm/s) to facilitate the understanding of general readers.\nRevised text (main text, page 14, line 297):\nBy comparison, COF reduced by over 95% between S-PDMS-G/P1-Si/P2-Si and P2-\nG.\nRevised text (main text, page 24, lines 521-524):\nThe loads of 2, 4, and 6 N were used; the reciprocating frequency was 4 Hz; The\nlubrication liquid was saltwater (3.5% of NaCl solution). The reciprocating stroke was\n12 mm along the linear direction of the lower sample; hence, the average velocity was\n48 mm/s.\nRevised text (Supplementary Discussion, Section 2.3):\nWear volume generally continues to increase with time. Wear volume is calculated\nbased on the product of sliding distance and wear scar cross-sectional area. The sliding\ndistance follows as:\n𝑋 = 0.002×𝑡×𝑓×𝐿 (S19)\nwhere: 𝑁 = 𝑡×𝑓 (S20)\n= total sliding distance of the ball, m,\n= number of cycles in the test,\n𝑋\n= test time, s,\n𝑁\n= oscillating frequency, Hz (cycles/s), and\nt\n= length of stroke, mm.\n𝑓\n𝐿\n(l) In figure 5D, authors have presented the COF as a function of reciprocal cycles.\nWhat is the significance of carrying out this experiment over 12000 cycles. Why the\nCOF values for all cases become different after 4000 cycles. Secondly even in one cycle\nthe normal load and shear load and consequently the COF should exhibit fluctuations.\nAuthors do not make any mention of that. Secondly did the authors obtain shear load at\ndifferent normal load?\nResponse:\nWe appreciate the Reviewer’s comments. 1) According to ASTM G133-22, the number\nof cycles is one of the evaluation units in standard friction and wear tests (see the reply\nto (k)). When carrying out this experiment over 12000 cycles, the stable COF is\nachieved, allowing us to determine the friction status according to the Stribeck Curve.\nThere are many articles that follow the principles (such as Science Advances, 2025,\n11(4): eadr9834. Tribology International, 2023, 189: 108919.). 2) For the question of\nCOF values for all cases becoming different after 4000 cycles, what we understand is\nthe phenomenon that the COF is slightly reduced before 4000 cycles. In fact, all\nfrictions have a running-in process in the early stage. For S-PDMS-G, P1-Si, and P2-\nSi, the micro-peaks on the contact surfaces are smoothed, and the friction coefficient is\nslightly reduced. For P1-G and P2-G, the generation of nanoclusters improves surface\nwettability and thus significantly reduces the COF. 3) The reason why the force and\nCOF within one cycle are not mentioned is that, for practical applications, we are\nconcerned with the average COF over a long period of time. To study normal load (Fz),\nshear load (Fx), and consequently the COF of one cycle, we captured the cases at cycles\n481-484 (before rapid COF reduction) and 12001-12004 (after rapid COF reduction) as\nshown in Supplementary Fig. 30. All curves of normal load, shear load, and COF show\nstable periodicity. The normal load (Fz) fluctuates around 2 N. When the applied load\nis 2 N, Fx exhibits a high value and no sliding plateaus before rapid COF reduction\n(Supplementary Figs. 30A-D), indicating that that Fx is mainly dominated by the\nviscoelasticity of the polymer (Science 370.6514 (2020): 335-338). While obvious\nsliding platforms appear after rapid COF reduction (Supplementary Fig. 30E and F),\nindicating the friction process is caused by the combined action of viscoelasticity and\nsliding. Subsequently, we compared Fx under 4 cycles under different loads to obtain\nSupplementary Fig. 31, which showed that the increase in the applied load caused the\ndisappearance of the sliding platform. But the average COF decreases with increasing\napplied load (Supplementary Fig. 32).\nRevised or added Figure:\nSupplementary Fig. 30. Load status and the COF of (A) S-PDMS-G and (D) P1-G and\nin cycles 481-484. Load status and the COF of (B) S-PDMS-G, (C) P1-Si N , (E) P1-\n3 4\nG, and (F) P2-G in cycles 12001-12004.\nSupplementary Fig. 31. Changes in shear force under different applied loads\nSupplementary Fig. 32. (A) The COF–cycle curve and (B) average COF of P1-G\nunder different loads.\nRevised or added text (main text, page 15, line 320):\nThe coordinated effect of the hydrophilic surface and the porous structure with stored\nliquid reduced abrasive and three-body wear, causing the boundary lubrication to\ntransform into mixed lubrication, which in turn resulted in ultra-low friction and wear\n(Fig. 5I). The transformation is reflected by the shear stress and COF under a single\nreciprocating cycle (Supplementary Fig. 30). Compared to the unreduced state\n(Supplementary Figs. 30A–D), a clear sliding platform and a stable low COF appeared\nin the COF-reduced cycle (Figs. 30D and E). At higher loads (4N and 6N), the sliding\nplateau disappeared, indicating that the friction was dominated by the elastic\ndeformation of the surface57; however, the average COF continued to be low\n(Supplementary Fig. 31).\n(m) Page 14 line 309: “…(Figure 22C)…”, There is no such figure!\nResponse:\nWe are deeply sorry for missing the word “supplementary”. Due to the addition of a\nlarge number of figures, the numbering has changed. We have revised the main text.\nRevised or added text (main text, page 14, line 309):\nMeanwhile, the wear debris was captured by the pores (Supplementary Fig. 26),\nleading to the surface wetting change from hydrophobic to hydrophilic (Supplementary\nFig. 23B and C), which in turn thickened the lubrication film.\n(n) The stretch percentage for some of the samples were found to be quite high, as high\nas 1250%. What leads to this increase, low crosllinking density, viscoelastic effect,\nsmaller physical entanglement, what? Authors have not thrown any light on the possible\nmechanism that leads to this increase in extensibility.\nResponse:\nThank you for the valuable comment. As shown in Supplementary Fig. S43B, HNP-\nPDMS@bPdBA cured in -0.1MPa/25 ℃ shows the lowest tensile modulus. Low\nentanglement and crosslinking density generally result in low modulus and low\nelongation (Macromolecules. 2019. 52. 1, 121-134. Macro Materials & Eng. 2021. 306.\n12, 2100536). To investigate the cause of the high stretch, we performed dynamic\nmechanical analysis tests. Loss factor ( ), representing the degree of viscous\ndeformation, can be calculated according to the following formula:\n𝑡𝑎𝑛𝛿\nwhere and are storage modulus and l′′oss m′ odulus. Storage modulus and loss\n𝑡𝑎𝑛𝛿 = 𝑀 /𝑀\nmodulus ′represen′t′ viscosity and elasticity. The of HNP-PDMS@bPdBA cured\n𝑀 𝑀\nin -0.1MPa/25℃ is much larger than that of HNP-PDMS@bPdBA cured in -\n𝑡𝑎𝑛𝛿\n0.1MPa/125℃ and -0.0MPa/25℃ (Supplementary Fig. 44) Therefore, we believe that\nviscoelastic effect leads to the high stretch of HNP-PDMS@bPdBA cured in -\n0.1MPa/25℃. The stretch percentage could be improved to 1250%, which is attributed\nto the increase in the degree of viscous deformation of HNP-PDMS@bPdBA.\nRevised or added Figure:\nSupplementary Fig. 43. Changes in the of HNP-PDMS@bPdBA cured under\ndifferent conditions with temperature.\n𝑡𝑎𝑛𝛿\nRevised or added text (main text, page 18):\nSurprisingly, the stretch percentage could be improved by 1250%, which is attributed\nto the increase in the degree of viscous deformation of HNP-PDMS@bPdBA, as shown\nin Supplementary Fig. 44 (see Supplementary Information, Section 2.5, for more\ndetails). Additionally, the performance of HNP-PDMS@bPdBA was better than that of\nP-PDMS@Sugar (Fig. 6G).\nRevised or added text (Supplementary Discussion Section 2.4):\nAs shown in Supplementary Fig. S43B, HNP-PDMS@bPdBA cured in -0.1MPa/25 ℃\nshows lowest tensile modulus. Low entanglement and crosslinking density generally\nresult in low modulus and low elongation8,9. To investigate the cause of the high stretch,\nwe performed dynamic mechanical analysis tests. Loss factor ( ), representing the\n𝑡𝑎𝑛𝛿\ndegree of viscous deformation, can be calculated according to the following formula:\nwhere and are storage modulus and l′′oss m′ odulus. Storage modulus and loss\n𝑡𝑎𝑛𝛿 = 𝑀 /𝑀 (S21)\nmodulus ′represen′t′ viscosity and elasticity. The of HNP-PDMS@bPdBA cured\n𝑀 𝑀\nin -0.1MPa/25℃ is much larger than that of HNP-PDMS@bPdBA cured in -\n𝑡𝑎𝑛𝛿\n0.1MPa/125℃ and -0.0MPa/25℃ (Supplementary Fig. 44) Therefore, we believe that\nviscoelastic effect leads to the high stretch of HNP-PDMS@bPdBA cured in -\n0.1MPa/25℃. The stretch percentage could be improved to 1250%, which is attributed\nto the increase in the degree of viscous deformation of HNP-PDMS@bPdBA.\nRevised or added text (method, Characterizations):\nDynamic mechanical analysis (DMA) was performed using a DMA equipment\n(Netzsch, Germany, DMA242) with a heating rate of 3 °C/min from -20 °C to 100 °C.\nReviewer #3 (Remarks to the Author):\nThe authors report a novel, template-free emulsion method to create purely porous\nsilicone elastomers by driving heterogeneous network formation using borate-based\ndynamic crosslinkers. By combining a borate-modified PDMS precursor with a\ncommercial PDMS prepolymer and inducing spontaneous phase separation under\ncontrolled thermal and vacuum conditions, they generate an interconnected porous\nstructure after selectively removing the sacrificial borate phase. The resulting materials\nexhibit remarkably low friction and wear under aqueous lubrication while retaining\nexcellent stretchability and toughness. Furthermore, the approach allows precise tuning\nof pore morphology and mechanical properties through processing parameters and can\nbe extended to other silicone elastomer systems, demonstrating broad potential for\napplications in low-friction, wear-resistant soft materials. However, the manuscript,\nin its current state, may not meet the standards for publication in Nature Communications,\na journal known for its groundbreaking and influential contributions to the scientific\ncommunity. The idea and concept of the paper are excellent and novel, but the available\ndata on this particular aspect appears to be insufficient. Furthermore, there is a need for\nmore comprehensive supporting evidence and data to bolster the proposed hypotheses.\nThe authors are encouraged to consider the following suggestions for enhancing the\nmanuscript in preparation for future submissions.\nTo strengthen the manuscript, the authors should consider (Major):\n1. To fulfill the objectives proposed by the authors, additional stability and wear‐rate\nmeasurements under thermal, high‐temperature, UV, and aging conditions must be\nconducted.\nResponse:\nWe appreciate the Reviewer’s comments. We added additional stability tests, such as\nfriction under UV light and at 60 °C (which is high temperature relative to water), salt\nwater immersion for 3 weeks, and cyclic stretching for 2000 times to treat P1. Besides,\nwe performed 122400 cycles (test times: 8.5 h) and calculated the wear rate. As shown\nin Supplementary Fig. 35, regardless of the method used to treat the surface, a sharp\ndecrease in the COF always occurs. The average COF remains 0.03 ~ 0.2. An increase\nin the COF at 60 °C after 10000 cycles, which is due to the evaporation of water.\nHowever, the low COF state can be restored after adding salt water (see next response).\nIn any case, the wear rate of the aging sample (< 6.69×10-6 mm3/N·m) was reduced by\nover 75% compared with the wear rate of S-PDMS-G, as shown in Supplementary Fig.\n36. In particular, when the friction time was extended to 8.5 h (122400 cycles), the wear\nrate was further reduced to as low as ~8.62×10-6 mm3/N·m.\nRevised or added Figure:\nSupplementary Fig. 35. (A) The COF–cycle curve and (B) average COF of P1-G after\naging or degradation treatment.\nSupplementary Fig. 36. The wear rate of P1-G and its after aging or degradation\ntreatment.\n2. Beyond the current stability tests over several thousand cycles, experiments\naddressing a much longer fatigue life are required. Considering the applications the\nauthors propose, stability over only a few thousand cycles is insufficient.\nResponse:\nThank you for the significant comment. We performed the long-term wear test\n(>1.2×10^5 cycles) for P1-G. As reciprocating cycles progress and water evaporates,\ncausing the COF to increase, the COF quickly decreases to a lower level after adding a\nlittle water (~0.1 mL) as shown in Supplementary Fig. 33.\nRevised or added Figure:\nSupplementary Fig. 33. The COF–cycle curve of P1-G after 122400 reciprocating\ncycles (Yellow area: Lubrication deteriorated as the water evaporated; Blue area:\nLubrication improved after adding 0.1 mL of salt water).\nRevised or added text (Supplemental Information, Section 2.3):\nTo investigate the stability of the low-friction transition and low-wear state, we\nperform fatigue and aging tests on the P1 (HNP-PDMS@BA-125/-0.1MPa). As\nshown in Supplementary Fig. 33, with reciprocating cycles progressing and water\nevaporating, the COF increases, but the COF quickly decreases to a lower level after\nadding a little (~0.1 mL) salt water. SEM and EDS results show that the pores of P1\nare always able to capture the wear debris during this process (Supplementary Fig.\n34A). COF results of other tests are shown in Supplementary Fig. 35. Friction testing\nof the sample after cyclic stretching (over 2000 cycles, with a stretch ratio of 20% in\neach cycle) revealed that it still exhibited low friction, with the average COF less than\n0.15. Furthermore, after 3 weeks of salt water immersion, UV irradiation (365 nm),\nand heating treatment (60 ℃), P1 can stably reduce the COF. An increase in the COF\nat 60 °C after 10000 cycles, which is due to the evaporation of water. However, the\nlow COF state can be recovered after adding salt water. In any case, the wear rate of\nthe aging sample (< 6.69×10-5 mm3/N·m) was reduced by over 75% compared with\nthe wear rate of S-PDMS-G, as shown in Supplementary Fig. 36. In particular, when\nthe friction time was extended to 8.5 h (122400 cycles), the wear rate was further\nreduced to as low as ~8.62×10-6 mm3/N·m. We repeated the friction test of P1-G three\ntimes in situ without processing and found that COF reduction still occurred\n(Supplementary Fig. 37). After repeated friction tests, the CA is still close to that after\nthe first friction test (Supplementary Figs. 23C and D). The corresponding SEM and\nEDS results of the worn surface are shown in Supplementary Fig. 34B, which reveals\nthe presence of wear debris and iron in the pores, indicating that the nanoclusters were\nstill trapped. To study the effect of product detachment on friction, after the first\nfriction test, the mixed liquid on the surface was wiped off by the dust-free fabric and\nthe new friction test was carried out. The COF dropped rapidly with almost no\nrunning-in period of thousands of cycles (Supplementary Fig.38). Compared to S-\nPDMS-G, P1-Si, and P2-Si, the COF of P1-Si still dropped by over 60%. We infer\nthat the old ball with products still works. To verify that, we changed the new ball and\nperformed a repeated friction test. The friction results show that a running-in period of\nthousands of cycles is necessary under this condition (Supplementary Fig.39).\nOverall, all these indicate that this porous surface has the potential for long-term\nservice.\n3. The authors have validated their method in PDMS and Ecoflex. The claim that the\nfabrication approach applies to all polysiloxane systems is unsupported by evidence\nfrom only two examples; additional validation cases are needed to substantiate this\nassertion.\nResponse:\nThank you for pointing out the potential issue, and this is an important comment. To\naddress the issue, we added three other elastomer materials (DC170, DC527, and\nRTV615) for validation. Using the same preparation method as HNP-PDMS, we\nsuccessfully prepared new porous elastomers (DC170@BA, DC527@BA, and\nRTV615@BA) as shown in Supplementary Fig. 46. These porous elastomers have the\npotential to improve the elongation.\nRevised or added Figure:\nSupplementary Fig. 46. The surface SEM images of (A) DC170, (B) DC170@BA, (D)\nDC527, (E) DC527@BA, (G) RTV615, and (H) RTV615@BA. Stress-stretch curves\nof (C) DC170 and DC170@BA, (F) DC527 and DC527@BA, (J)RTV615 and\nRTV615@BA.\nRevised text (main text, Section 2.6):\nThe introduction of D-PDMS@BA significantly delayed the fracture of the elastomer,\nand the toughness increased to 150 %, despite the elastomer being porous. Furthermore,\nwe successfully prepared new porous elastomers using three other PDMS materials\n(DC170, DC527, and RTV615), as shown in Supplementary Fig. 46. These porous\nelastomers also exhibited elongation improvement potential. These results proved that\nour method was applicable to the preparation of mechanically enhanced porous\nelastomers for all PDMS systems.\n4. The authors’ scientific novelty and extensive material analyses, including modeling,\nare highly commendable; demonstrating a practical application is necessary to better\nalign with the scope of Nature Communications. Any example—such as the machinery,\nrobots, bearings, or biological models—would be suitable.\nResponse:\nWe are very grateful for your recognition and comments. In the previous manuscript,\nwe mentioned the potential application of our material in flexible sensors. In this\nrevised process, we performed a set of experiments to demonstrate the practical\napplication. To prepare flexible sensors, conductive properties need to be given to\nPDMS materials due to the insulating nature of PDMS. We used carbon fibers with a\ndiameter of 7 μm and a length of 33.6 μm as the conductive material (Supplementary\nFig. 47). It is difficult to form a pathway by directly mixing PDMS with conductive\nmaterials (Supplementary Fig. 48A). Based on HNP-PDMS@BA, however, we added\ncarbon fibers and successfully prepared conductive silicone (Resistance < 1kΩ) without\nthe need for additional surfactants (Supplementary Figs. 48B and C). Besides, the\nmechanical performance of HNP-PDMS@C/-0.1MPa is better than that of S-PDMS\n(Figure 6J). We attribute the improved performance of HNP-PDMS@C/-0.1MPa to the\ndispersion of carbon fibers within the through-pores of HNP-PDMS (Fig. 6K). This\nflexible conductive material can be used as the skin of the bionic robot hand to sense\nforce and identify materials (Fig. 6L). To demonstrate the application effect, HNP-\nPDMS@C/-0.1MPa is encapsulated in PDMS and then bent and fixed on the robotic\nfinger to contact the wall Supplementary Fig. 49A). In this case, our material can act as\nboth a strain sensor and a triboelectric sensor. As the contact force increases from 1N\nto 4N, the change rate of resistance also improves accordingly (Supplementary Fig.\n49B). According to the peak value and width of the wave, various materials can be\ndistinguished as shown in Supplementary Fig. 49C (ACS Appl. Mater. Interfaces. 2024.\n16. 43, 58980-58990). These demonstrate practical potential applications.\nRevised or added Figure:\nSupplementary Fig. 47. (A) Single carbon fiber (B) Distribution of carbon fiber length.\nSupplementary Fig. 48. Resistance of PDMS/C, HNP-PDMS@C/-0.0, and HNP-\nPDMS@C/-0.1 (Sample size: 10 mm×10 mm×1 mm).\nFig. 6. (J) Stress-stretch curves of PDMS, HNP-PDMS@C/-0.0, and HNP-PDMS@C/-\n0.1. (K) Cross-sectional SEM image of HNP-PDMS@C/-0.1. (L) Contact sensing\ndiagram.\nSupplementary Fig. 49. (A) Actual picture of the bionic robot hand contacting the\nmaterial. (B) Resistance changes under different forces (R and R are the initial\n0\nresistance and the resistance under pressure, contact speed: 50 mm/min). (C) Output\nvoltage (U) curves of 6 different materials under the same conditions (Contact speed:\n500 mm/min).\nRevised or added text (main text, Section 2.6):\nTo prepare flexible sensors, conductive properties need to be introduced to PDMS\nmaterials, as PDMS is inherently insulating. We used carbon fibers with a diameter of\n7 μm and a length of 33.6 μm as the conductive material (Supplementary Fig. 47). It is\ndifficult to form a pathway by directly mixing PDMS with conductive materials\n(Supplementary Fig. 48A). To achieve conductivity in PDMS/silicone materials, the\nconductive material is usually connected within the polymer using a similar preparation\nmethod as porous materials.58,59 Based on the formation mechanism of HNP-\nPDMS@BA, we added carbon fibers and successfully prepared conductive PDMS\n(Resistance < 1kΩ), again without the need for additional surfactants or emulsions\n(Supplementary Figs. 48B and C). Besides, the mechanical performance of HNP-\nPDMS@C/-0.1MPa is better than that of S-PDMS (Figure 6J). We attribute the\nimproved performance of HNP-PDMS@C/-0.1MPa to the dispersion of carbon fibers\nwithin the through-pores of HNP-PDMS (Figure 6K). This flexible conductive material\ncan be used as the skin of the bionic robot hand to sense force and identify materials\n(Figure 6L). To demonstrate the application effect, HNP-PDMS@C/-0.1MPa is\nencapsulated in PDMS and then bent and fixed on the robotic finger to contact the wall\n(Supplementary Fig. 49A). In this case, our material can act as both a strain sensor and\na triboelectric sensor. As the contact force increases from 1N to 4N, the change rate of\nresistance also improves accordingly (Supplementary Fig. 49B). According to the peak\nvalue and width of the wave39, various materials can be distinguished as shown in\nSupplementary Fig. 49C, demonstrating practical potential applications.\nRevised or added text (main text, method):\nFabrication of Flexible Sensor Material\nThe preparation method of HNP-PDMS@C differs from that of HNP-PDMS@BA;\nthe carbon fiber is added (25% of the total mass) during the mixing of the S-PDMS and the\nD-PDMS@BA prepolymers. Finally, the unstable D-PDMS@BA network was\nremoved to obtain the HNP-PDMS@C by ultrasonic cleaning of the composite\nelastomer with ethanol. Two 1-mm thick S-PDMS sheets sandwiched a 1-mm thick\nHNP-PDMS@C to create the flexible sensor material.\nCharacterizations\nDynamic mechanical analysis (DMA) was performed using a DMA equipment\n(Netzsch, Germany, DMA242) with a heating rate of 3 °C/min from -20 °C to 100 °C.\nAn oscilloscope (Tektronix TBS2072B) was employed to capture and record the open\ncircuit voltage. a LabVIEW-controlled digital source meter (Keithley 2400, America)\nrecorded the resistance in real time."}, {"round": 2, "reviewer_comments": {"reviewer_1": "The authors have fully addressed my concerns. I suggest the publication of the revised manuscript.", "reviewer_2": "[In correspondence with the editors, the referee expressed that the manuscript is ready for publication as-is.]", "reviewer_3": "The authors present their research in a logical and coherent manner, supported by robust experimental design, sound methodology, and convincing data analysis. The novelty of the work is evident in the way it bridges current knowledge gaps and provides new insights that are likely to stimulate further research and practical applications. I find no substantive weaknesses that would require revision, and I am pleased to recommend the manuscript for acceptance in its current form."}, "author_response": "Response Letter\nWe are grateful to the editor and reviewers for their comments on our article. [Referees’ comments are in black; Author responses are in blue]\nReviewer #1 (Remarks to the Author):\nThe authors have fully addressed my concerns. I suggest the publication of the revised\nmanuscript.\nResponse:\nWe appreciate the reviewer for the positive comments and recognition of our work. The\nmanuscript has greatly benefited from them.\nReviewer #2 (Remarks to the Author):\n[In correspondence with the editors, the referee expressed that the manuscript is ready\nfor publication as-is.]\nResponse:\nWe are very grateful to the reviewer for the comments and recognition of our work. The\nmanuscript has greatly benefited from them.\nReviewer #3 (Remarks to the Author):\nThe authors present their research in a logical and coherent manner, supported by robust\nexperimental design, sound methodology, and convincing data analysis. The novelty of\nthe work is evident in the way it bridges current knowledge gaps and provides new\ninsights that are likely to stimulate further research and practical applications. I find no\nsubstantive weaknesses that would require revision, and I am pleased to recommend\nthe manuscript for acceptance in its current form.\nResponse:\nWe appreciate the reviewer for the positive comments and recognition of our work. The\nmanuscript has been greatly improved."}]

Decision letter