Porous composite materials based on internal interface contact mechanism and their preparation methods, flexible pressure sensors

Abstract

This application discloses a porous composite material based on an internal interface contact mechanism, comprising a polymeric elastomer matrix with multiple micropores, and conductive fillers and nanofillers dispersed within the polymeric elastomer matrix; wherein the volume fraction of the conductive fillers is located within the percolation threshold neighborhood of the porous composite material; the porous composite material is further configured such that, under pressure, the micropores undergo reversible deformation and induce reversible contact between the conductive fillers, thereby achieving a change in the conductivity of the porous composite material. Furthermore, this application discloses a method for preparing the above-mentioned porous composite material and a flexible pressure sensor fabricated using the above-mentioned porous composite material. This application utilizes the internal interface contact conductivity mechanism induced by micropores to achieve high-sensitivity pressure response and high reliability in materials or devices, and is easy to process.

Description

Technical Field

[0001] This application relates to the field of flexible electronics and sensor technology, specifically to a porous composite material based on an internal interface contact mechanism and its preparation method, and an intrinsic resistive flexible pressure sensor. Background Technology

[0002] Flexible pressure sensors, as core components in flexible electronic systems, have significant application value in wearable health monitoring, electronic skin, human-computer interaction, and robotic tactile sensing. Currently, common flexible pressure sensors mainly include resistive, capacitive, piezoelectric, and isoelectric types. Among them, intrinsically resistive flexible pressure sensors have attracted widespread attention due to their simple structure and convenient signal reading.

[0003] Existing intrinsically resistive flexible pressure sensors typically use polymer-based conductive composite materials as the functional layer. Their pressure response mechanism mainly relies on the minute changes in the spacing between the conductive fillers or the resistance changes of existing conductive pathways during compression. However, because the conductive fillers are filled with an incompressible polymer matrix, it is difficult to form a new conductive network during compression, resulting in generally low sensitivity.

[0004] To improve sensitivity, existing technologies often enhance pressure response by introducing microstructures onto the material surface. However, this method still has significant drawbacks. On the one hand, surface microstructures are prone to collapse or fatigue failure under repeated loading, leading to decreased reliability. On the other hand, the fabrication process is complex, making it difficult to achieve large-area manufacturing or compatibility with advanced manufacturing processes such as 3D printing.

[0005] Therefore, there is an urgent need for an intrinsic resistive flexible pressure sensor that is highly sensitive, highly reliable, and easy to manufacture. Summary of the Invention

[0006] To address the aforementioned issues, this application proposes a porous composite material based on an internal interface contact mechanism, its preparation method, and a flexible pressure sensor. By utilizing the internal interface contact conductivity mechanism induced by micropores, the material or device achieves high-sensitivity pressure response and high reliability, and is easy to process.

[0007] The technical solution of this application includes: The first aspect of this application discloses a porous composite material based on an internal interface contact mechanism, comprising: A polymer elastomer matrix with multiple micropores, and Conductive fillers and nanofillers dispersed within a polymer elastomer matrix; Wherein, the volume fraction of the conductive filler is located within the percolation threshold neighborhood of the porous composite material; The electrical conductivity of the porous composite material changes in response to the reversible contact that occurs between the conductive fillers caused by the reversible deformation of the micropores when the porous composite material is under pressure.

[0008] As an optional option, the volume fraction of the conductive filler is 1% to 10%.

[0009] As an alternative, the conductive filler is one or more of nano-conductive indium tin oxide, carbon nanotubes, carbon black, and graphene; the polymer elastomer matrix is ​​a silicone rubber material, a polyurethane elastomer material, or a thermoplastic elastomer material; and the nanofiller is one or more of nanoscale aluminum oxide, calcium carbonate, and fumed silica.

[0010] As an alternative, the polymer elastomer matrix is ​​selected from polydimethylsiloxane, the conductive filler is selected from carbon nanotubes, and the nanofiller is selected from fumed silica.

[0011] As an alternative, the micropores are formed by the volatilization and removal of components in the porous composite material precursor by a volatile removable pore-forming agent; the volatile removable pore-forming agent is one or more of citrate ester plasticizers and fatty acid esters.

[0012] As an alternative, the micropores have a size of 1 to 50 micrometers.

[0013] A second aspect of this application discloses a preparation method for preparing the porous composite material based on an internal interface contact mechanism as described in the first aspect of this application or any alternative embodiment thereof; comprising: Selected nanofillers, conductive fillers, volatile removable pore-forming agents, and polymeric elastic matrices are mixed to obtain a precursor of a porous composite material; wherein, the content of the nanofillers is used to regulate the rheological properties of the precursor and the pore structure of the micropores. The precursor is coated onto the provided substrate to form a film of the target thickness; The film is cured in stages under multiple increasing temperature conditions, which causes the pore-forming agent to volatilize and form micropores at corresponding positions to obtain the porous composite material.

[0014] As an optional embodiment, the mass ratio of the polymer elastomer matrix, conductive filler, volatile removable pore-forming agent and nanofiller is 1 : 0.01~0.06 : 1~2 : 0.1~0.10.

[0015] As an optional approach, the film is cured in stages under multiple increasing temperature conditions, specifically including: first curing at 25~60℃ for 30~60 min; then curing at 80~100℃ for 30~90 min; and finally curing at 100~160℃ for 300~600 min.

[0016] A third aspect of this application discloses a flexible pressure sensor based on an internal interface contact mechanism, comprising: Electrode layer; and A functional sensitive layer stacked with the electrode layer; The functionally sensitive layer is made of a porous composite material based on an internal interface contact mechanism as described in the first aspect of this application or any alternative scheme thereof.

[0017] This application has the following beneficial effects: (1) The porous composite material based on the internal interface contact mechanism proposed in this application has a volume fraction of conductive filler within the percolation threshold neighborhood of the material. When the material is under pressure, the micropores formed inside are compressed, which induces the conductive fillers embedded in or attached to the pore wall to approach or rearrange themselves, generating new internal interface contact and realizing the reversible reconstruction of the conductive network. This can significantly amplify the change in conductivity and thus improve the pressure sensitivity.

[0018] (2) The porous composite material based on the internal interface contact mechanism proposed in this application transforms the pressure response carrier from the traditional surface microstructure deformation to the reversible reconstruction of the internal conductive network of the material. This not only significantly improves the pressure response sensitivity of the flexible pressure sensor made of this material, but also takes into account the structural stability and reliability of the device, and has cycle durability.

[0019] (3) The method for preparing porous composite materials proposed in this application uses a bulk composite system material composed of a polymer elastomer matrix, conductive filler, volatile removable pore-forming agent and nano-regulating components as a precursor. It can introduce a compressible microporous structure into the material in one step, which fundamentally avoids the complex micro-machining process of precision surface microstructure, significantly simplifies the process flow, and has a wide process window.

[0020] (4) The porous composite material preparation method proposed in this application uses a slurry-type composite material system with adjustable rheology as the material precursor. The rheological properties can be controlled by introducing nanofillers. Therefore, it can be used for simple film formation methods such as brush coating, blade coating, and casting, and is also compatible with existing sensor manufacturing processes such as screen printing, blade coating, and extrusion 3D printing. Furthermore, the shape, size, and porosity of the micropores can be adjusted by controlling the content of the nanofillers.

[0021] (5) The flexible pressure sensor based on the internal interface contact mechanism proposed in this application is suitable for wearable devices and curved surface conformal applications due to its flexibility and compressibility. Furthermore, it can also support planar arrays and curved surface 3D printing devices because it is easy to integrate with electrode layers and encapsulation layers. Attached Figure Description

[0022] Figure 1 : Schematic diagram of a flexible pressure sensor structure based on an internal interface contact mechanism (sandwich structure); In the figure: 100-flexible substrate layer, 200-lower electrode layer, 300-functional sensitive layer, 400-upper electrode layer, 500-top encapsulation layer.

[0023] Figure 2 : Schematic diagram of the internal structure of conductive composite material; In the diagram: 301 - micropores; 302 - conductive filler; 303 - polymer matrix.

[0024] Figure 3 Pressure response curve of a flexible pressure sensor based on internal interface contact mechanism.

[0025] Figure 4 : 25-hour drift performance test diagram of a flexible pressure sensor based on internal interface contact mechanism.

[0026] Figure 5 Response recovery speed of flexible pressure sensors based on internal interface contact mechanism.

[0027] Figure 6 Performance test of a flexible pressure sensor based on an internal interface contact mechanism after 10,000 long cycles.

[0028] Figure 7 : Interface toughness of flexible pressure sensors based on internal interface contact mechanism.

[0029] Figure 8 : Cross-sectional SEM images of the sample of Comparative Example F33, where (a) is a cross-sectional SEM image of the sample of Comparative Example F33 after being kept at 150 ℃ for 10 h; (b) is a magnified SEM image of the sample of Comparative Example F33 after being kept at 150 ℃ for 10 h.

[0030] Figure 9 The effect of different CNTS contents on pressure sensing performance.

[0031] Figure 10 The effects of different SiO2 contents on the mechanical properties and pressure sensing properties of composite materials, where: (a) is the stress-strain curve of composite materials with different SiO2 contents; (b) is the curve of relative conductivity of composite materials with different SiO2 contents as a function of pressure.

[0032] Figure 11 The effects of different PDMS:TBC ratios on the mechanical and pressure sensing properties of composite materials, where: (a) is the stress-strain curve of composite materials with different PDMS:TBC ratios; (b) is the curve of relative conductivity of composite materials with different PDMS:TBC ratios as a function of pressure.

[0033] Figure 12 The effects of different SiO2 and TBC contents and heat treatment conditions on the cross-sectional pore structure of ionomer rubber were investigated. (a) shows cross-sectional SEM images under different PDMS:TBC ratios and baking times; (b) shows cross-sectional SEM images under different SiO2 contents and baking times. Figure 12 All images in the figure were taken at the same magnification (500×), and the scale bar in the figure is 200 micrometers.

[0034] Figure 13 A flexible transparent pressure sensor array structure prepared by screen printing, wherein (a) is a front view and (b) is a back view.

[0035] Figure 14 : 3D modeling and 3D printing realization of the electrode layer of the curved conformal pressure sensor, wherein: (a) is the 3D structural model and electrode layout of the curved electrode layer in the modeling software; (b) is the physical image of the curved electrode layer 3D printed based on the model.

[0036] Figure 15 : 3D modeling and 3D printing realization of the functional layer of the curved conformal pressure sensor, wherein: (a) is a schematic diagram of the 3D structural model and electrode layout of the curved functional layer in the modeling software; (b) is a physical image of the curved functional layer 3D printed based on the model. Detailed Implementation

[0037] To address the problems of poor structural stability, reliance on surface microstructures leading to complex fabrication processes and insufficient durability in existing flexible pressure sensors, this application proposes a porous composite material based on an internal interface contact mechanism and its preparation method. This method introduces multiple compressible microporous structures (also known as "porous structures") within a conductive composite material in a one-step process, enabling reversible contact of the conductive filler within the micropores during compression. Using this material to fabricate intrinsically resistive flexible pressure sensors and other devices can significantly improve the pressure response sensitivity of the devices while maintaining both device stability and fabrication scalability.

[0038] The intrinsic resistive flexible pressure sensor (hereinafter referred to as "flexible pressure sensor") has a multi-layered structure, specifically a sandwich structure or a single-sided electrode structure. The sandwich structure includes, from bottom to top, a flexible substrate layer, a lower electrode layer, a functional sensitive layer, an upper electrode layer, and a top encapsulation layer. The single-sided electrode structure, also known as a single-layer interdigitated electrode structure, includes, from bottom to top, a flexible substrate layer, an interdigitated electrode layer, a functional sensitive layer, and a top encapsulation layer. The layers are tightly bonded together, forming a flexible overall structure. The functional sensitive layer is a porous composite material with multiple micropore structures, which is the key innovative part of this application.

[0039] The main components of the porous composite material proposed in this application include a polymer elastomer matrix and conductive fillers and nanofillers dispersed in the polymer elastomer matrix. The volume fraction of the conductive filler is located in the neighborhood of the percolation threshold of the porous composite material, and the electrical conductivity of the porous composite material changes in response to the reversible contact between the conductive fillers caused by the reversible deformation of the micropores when the porous composite material is under pressure.

[0040] Understandably, the percolation threshold is typically defined as the critical volume fraction of conductive filler required to form a continuous conductive network in the composite material system. The percolation threshold neighborhood—that is, slightly below, just above, or slightly above the percolation threshold—is typically 1% to 10%, preferably 2% to 3%.

[0041] The precursors for preparing porous composite materials mainly include the following components: a polymeric elastomer matrix, conductive fillers, volatile removable pore-forming agents, and regulating components (including pore structure regulation or rheological regulation). In the bulk composite system composed of the above components, the proportions of each component can be adjusted according to specific application requirements. The key is to ensure that the volume fraction of the conductive filler in the final material is within the percolation threshold range, thereby obtaining high pressure response sensitivity.

[0042] Regarding the selection of components in the precursor, it is particularly important to note that the selection of the polymer elastomer matrix (e.g., PDMS) and the pore-forming agent (e.g., TBC) should be synergistic to achieve a comprehensive effect of controllable pore formation, stable pore size distribution, and reversible reconstruction of the conductive network. Specifically, the following aspects should be considered: First, compatibility and dispersion morphology. Before removal, the pore-forming agent should form a stable dispersion morphology in the matrix, achieving uniform dissolution and micro-droplet dispersion to form a phase-separated network, enabling controllable pore formation and adjustable pore size, while also avoiding the structural fragility caused by macropore aggregation. Second, removal mechanism and temperature window. The removal method of the pore-forming agent is mainly volatilization. In terms of synergy, the conditions for pore-forming agent removal (mainly temperature and time) should match the matrix curing conditions to avoid instability before the matrix is ​​cured or inability to remove the agent after curing. Third, the reconfigurability of the conductive filler network. The pore structure should be able to deform under pressure, thereby triggering reversible contact in the conductive filler. This increases the number of contact points to reconstruct the conductive channels. For synergy, the matrix must possess appropriate elastic modulus and resilience, and the pore wall strength must be sufficient to withstand cyclic loading. Fourth, process adaptability is crucial. The rheological properties of the material system (such as viscosity and thixotropy) can be controlled by adding nanofillers to adapt to existing processes such as coating, screen printing, compression molding, and extrusion 3D printing. Typically, the addition of the pore-forming agent should not lead to severe oil seepage, uncontrollable phase separation, or printing collapse. Furthermore, this application also considers the safety and environmental friendliness of the material. The pore-forming agent should be non-toxic, non-irritating, recyclable, and easy to handle, and the removal process should not produce corrosive or highly hazardous byproducts. Furthermore, the resulting material should also be biocompatible for wearable / skin-contact applications.

[0043] Common polymer elastomer matrices can be made from silicone rubber, polyurethane elastomers, and thermoplastic elastomers, such as polydimethylsiloxane (PDMS), room temperature vulcanizing silicone rubber (RTV), addition-curing liquid silicone rubber (LSR), cast polyurethane elastomers (PU), thermoplastic polyurethane (TPU), and styrene-based thermoplastic elastomers (TPE / SEBS). However, it is important to note that, given the conductive mechanism of reversible micropore compression and internal interface contact reconstruction, and the need for multi-process adaptation, silicone rubber elastomers are typically the preferred choice for polymer elastomer matrices, such as the commonly used polydimethylsiloxane (PDMS). This is because silicone rubber elastomers possess high elastic recovery and fatigue stability, maintaining the integrity of the pore wall structure and achieving reversible pore deformation under cyclic loading, thus providing stable mechanical boundary conditions for the repeated generation and disappearance of conductive filler contact points. Simultaneously, their curing condition window is well-defined, facilitating coordinated matching with the pore-forming agent removal process, which is beneficial for obtaining porous elastomer structures with stable pore size distribution and controllable pore morphology.

[0044] The pore-forming agent can be a volatile, removable pore-forming component, such as citrate plasticizers (including but not limited to tributyl citrate, TBC, etc.), fatty acid esters, or other organic pore-forming components that can form a stable dispersed phase in the elastomer matrix during the curing stage and can be volatilized and removed under subsequent heating or vacuum conditions. However, it should be specifically noted that in the synergistic mechanism of "controllable micropore formation - stable pore size distribution - reversible reconstruction of conductive network" required in this application, the pore-forming agent removal method is preferably volatilization removal. This is because the volatilization removal process does not introduce additional steps such as liquid phase immersion or solvent exchange, which helps maintain the continuity and consistency of the pore structure and reduces the impact of residues on the stability of the conductive network. Simultaneously, in terms of synergy, the conditions for pore-forming agent removal should match the curing conditions of the elastomer matrix to avoid structural instability due to uncured matrix or difficulty in fully removing the pore-forming agent after curing. Furthermore, the pore-forming agent should also have appropriate compatibility with the polymer elastomer matrix, and be able to form a stable morphology of uniform dissolution or micro-droplet dispersion before removal, thus constituting a controllable phase separation network, thereby achieving controllable pore formation and adjustable pore size, and avoiding the structural fragility caused by the aggregation of large pores.

[0045] Common conductive fillers include nano-conductive indium tin oxide (ITO), carbon nanotubes (CNTS), carbon black (CB), and graphene (GN). However, it should be noted that carbon nanotubes are generally the preferred conductive filler in the internal interface contact conductivity mechanism adopted in this application. This is because the one-dimensional high aspect ratio structure of carbon nanotubes enables the formation of a conductive network close to the percolation threshold even with low filler content, and it is highly sensitive to minute changes in interface contact, thus significantly amplifying the pressure-induced conductive pathway reconstruction effect. That is, under external load, the microporous structure is compressed, causing new internal interface contacts to form between carbon nanotubes, resulting in a rapid increase in the number of conductive pathways and a reconstruction of the network topology. Compared to spherical carbon black, powdered nano-conductive indium tin oxide, or two-dimensional sheet graphene fillers, carbon nanotubes are more sensitive to minute changes in interface contact and possess good reversibility and cycle stability in elastomers, making them more suitable for achieving highly sensitive and stable piezoresistive pressure sensing.

[0046] Nanofillers can be selected from materials such as nanoscale alumina (Al2O3), calcium carbonate (CaCO3), and fumed silica (SiO2), with fumed silica being the preferred choice. When selecting nanofillers, both pore structure and rheological control need to be considered. Therefore, the selected nanofiller components should improve the low shear viscosity of the slurry and introduce appropriate yield stress to stabilize the microstructure during the pore-forming process, without significantly interfering with the formation of the conductive network. Due to its nanoscale size and high specific surface area, fumed silica can form a physical support network in an elastomer matrix, effectively inhibiting pore collapse and migration. It also possesses excellent shear-thinning properties, meaning it can flow smoothly under scraping or extrusion pressure, making it highly suitable for various manufacturing processes such as scraping, screen printing, and extrusion 3D printing.

[0047] Based on the above considerations, in an optional preferred embodiment, the polymer elastomer matrix is ​​selected as polydimethylsiloxane (PDMS), the pore-forming agent is selected as tributyl citrate (TBC), the conductive filler is selected as carbon nanotubes (CNTS), and the nanofiller is selected as fumed silica (SiO2).

[0048] In the above component ratio settings, the content of conductive filler is close to the percolation threshold of the composite material, so that the static operating point of the sensor falls within the region of highest sensitivity. The static operating point refers to the conductive state of the internal conductive network of the sensor in its initial state without external pressure (zero pressure), usually characterized by the initial resistance value. This setting is because too little conductive filler (below or far below the percolation threshold) will lead to poor conductive network connectivity, excessively high initial resistance, poor signal-to-noise ratio, and increased dispersion among different samples; too much conductive filler (far above the percolation threshold) will result in an overly dense network, reducing the relative increase in new contact points under pressure, leading to decreased sensitivity, increased slurry viscosity, difficulty in dispersion, and easy clogging of the screen or nozzle. Therefore, only when the conductive filler content is moderate, i.e., within the vicinity of the percolation threshold (slightly below, just reaching, or slightly above the percolation threshold), is the static operating point of the conductive composite material in a critical conductive network state.

[0049] Understandably, the critical conductive network state refers to the state in which the conductive network in the material is just connected but not yet stable when the content of conductive filler is just at or slightly above the percolation threshold. In this state, a small change in the filler (e.g., a change in spacing due to pressure) will cause a drastic change in resistance. Therefore, the pressure-induced increase in internal interface contact can significantly change the number of conductive pathways, thereby achieving high sensitivity.

[0050] The content of pore-forming agent mainly considers the balance between porosity, mechanical support, and stability. Too little pore-forming agent will result in insufficient porosity, limited increase in internal interface contact under pressure, and insignificant piezoresistive response. Too much pore-forming agent can easily lead to phase separation or migration before curing, resulting in coarsening of the pore structure, increased interconnected pores, and potentially reduced mechanical strength. Furthermore, it can cause increased pressure response hysteresis and unstable changes in baseline resistance (i.e., long-term drift) during cyclic loading and unloading. At a moderate pore-forming agent content, multiple uniformly distributed micropores can be formed, providing compressible space and promoting reversible contact of the conductive filler during the compression of the micropore walls, thereby improving sensitivity and expanding the working range.

[0051] The content of nanofillers is primarily determined by two factors: rheological support and pore structure stability. Generally, too few nanofillers result in insufficient yield stress, increased migration of pore-forming agents and pore coalescence, leading to uneven pore structure and decreased batch consistency. Too many nanofillers increase modulus and decrease compressibility, potentially weakening low-pressure sensitivity. Furthermore, excessively thick slurry can cause uneven coating, nozzle or screen clogging, and may even block conductive pathways. When the amount of nanofiller is appropriate, it not only forms a physical support network, stabilizing the slurry and pore structure and improving the shape retention of printing and 3D printing, but also does not significantly block conductive pathways. The pore structure includes structural characteristics such as porosity, pore shape, and size.

[0052] Taking a porous composite material precursor with PDMS as the polymeric elastomer matrix (i.e., component A), CNTS as the conductive filler (i.e., component B), TBC as the pore-forming agent (i.e., component C), and fumed SiO2 as the nanofiller (i.e., component D) as an example, with 100 parts by mass of component A, the addition amount of component B can be set to 1-6 parts by mass, preferably 2-4 parts by mass; the addition amount of component C can be set to 100-200 parts by mass, preferably 100-150 parts by mass; and the addition amount of component D can be set to 1-10 parts by mass, preferably 1-5 parts by mass. That is, the mass ratio of A, B, C, and D is 1: 0.01-0.06: 1-2: 0.01-0.10, and the preferred mass ratio is 1: 0.02-0.04: 1-1.5: 0.01-0.05.

[0053] This application enhances the sensitivity and structural stability of pressure sensors based on an internal interface contact mechanism. It shifts the primary carrier of the sensor's pressure response from traditional surface microstructure deformation to the reversible reconstruction of the conductive network within the material's internal micropores. Specifically, the flexible pressure sensor fabricated using the aforementioned porous composite material, based on the internal interface contact mechanism, undergoes reversible deformation of the micropores within its functional sensing layer under external load—that is, the pore walls are compressed. This induces the conductive fillers embedded within or attached to the pore walls to approach or rearrange themselves, resulting in reversible contact and the creation of new internal interface contacts. This process enables the conductive network to expand from few to many, and from discontinuous to nearly continuous, significantly amplifying changes in material conductivity and improving pressure sensitivity. Compared to solutions relying on fixed surface microstructure height and spacing, its sensitivity and linear range can be tuned through material composition, making it suitable for different pressure ranges and application scenarios.

[0054] Furthermore, by adjusting the porosity, pore size distribution, and volume fraction of conductive filler in the material, the static operating point of the conductive composite material can be made to be in a critical conductive network state. In this way, the contribution of the internal interface contact increment to the overall conductive network during the compression process is more significant, and the adjustability of the operating range is better.

[0055] Furthermore, the flexible pressure sensor based on an internal interface contact mechanism proposed in this application fundamentally improves the stability and reliability of the sensor structure. Micropores are distributed within the bulk phase of the conductive composite material used in the sensor's functional sensitive layer. The conductive network undergoes reversible contact and separation near the pore walls. The sensing mechanism primarily relies on the recoverable deformation of the elastomer matrix and the reversible reconstruction of the conductive filler network, rather than on fragile surface protrusions, micropillars, or fine patterns. This avoids the problems of easy wear, collapse, and fatigue of surface microstructures, fundamentally improving the sensor's structural stability. Under long-term cyclic loading, the sensor's surface geometry remains largely intact, and the pore wall structure is less prone to irreversible damage. This effectively suppresses sensitivity decay and baseline drift, significantly improving the device's stability and reliability during multiple cycles, overcoming the insufficient durability of existing flexible pressure sensors.

[0056] Taking a sandwich structure as an example, the flexible pressure sensor provided in this application is fabricated by building it layer by layer from bottom to top, mainly including the following steps: The preparation steps of the flexible substrate layer are as follows: the matrix material (e.g., liquid PDMS) is poured into a preset mold and cured to form a PDMS substrate layer with a certain thickness and flexibility, which is mainly used as a flexible support structure for sensors.

[0057] The preparation steps of the lower electrode layer are as follows: Conductive silver paste is coated onto the surface of the obtained substrate layer by means of screen printing, scraping, or spraying, and then cured to form the lower electrode layer. The lower electrode can be a continuous electrode or a patterned electrode structure.

[0058] The preparation steps of the functional sensitive layer are as follows: the polymer elastomer matrix, conductive filler, pore-forming agent and nanofiller are mixed and degassed in a predetermined ratio to obtain a uniformly dispersed functional sensitive layer precursor; then, the precursor is coated on the surface of the lower electrode layer by brushing or casting and cured; during the curing process, the pore-forming agent is volatilized and removed, forming a uniformly distributed microporous structure inside the functional sensitive layer material.

[0059] The fabrication steps of the upper electrode layer are as follows: Conductive silver paste is coated onto the surface of the functionally sensitive layer in the same or similar manner as the fabrication steps of the lower electrode layer described above, and then cured to form the upper electrode layer. The upper electrode can also be a continuous electrode or a patterned electrode structure. The upper electrode layer and the lower electrode layer are electrically connected through the functionally sensitive layer.

[0060] The top encapsulation layer is prepared by coating an encapsulation material (e.g., liquid PDMS) onto the surface of the upper electrode layer and curing it to form the top encapsulation layer. This layer is mainly used to protect the electrodes and the functional sensitive layer, and can also improve the overall stability and environmental adaptability of the sensor to a certain extent.

[0061] Thus, a flexible pressure sensor with micropores can be obtained.

[0062] Understandably, in this application, the core of the above process lies in the preparation step of the functional sensitive layer. Taking PDMS, multi-walled CNTS, TBC, and fumed SiO2 as the main components of the functional sensitive layer precursor as an example, this step will be further explained. Specifically, the preparation process of the functional sensitive layer precursor mainly includes the following steps: Step S1: Preparation of the matrix precursor. First, mix the two components of the polymeric elastic matrix (PDMS prepolymer and curing agent) according to the manufacturer's recommended ratio (e.g., 10:1 or 20:1) and stir for 1-3 minutes until homogeneous. Then, add the nanofiller (gas-phase SiO2) and the conductive filler (CNTS) to the pore-forming agent (TBC) in batches and stir at low speed for 3-10 minutes to ensure thorough mixing. Next, add the pre-mixed polymeric elastic matrix material and stir for another 3-10 minutes to form a stable and dispersed liquid-solid composite precursor. Finally, place the mixed liquid-solid composite precursor in a centrifugal degassing device for degassing for 2-10 minutes (preferably 3-5 minutes).

[0063] Step S2: Film Coating. The degassed precursor is coated onto the surface of the lower electrode layer. The coating method can be brush coating, blade coating, casting, screen printing, or extrusion 3D printing. The film thickness can be selected from 50μm to 1mm, preferably 200μm to 700μm, for example, 300μm, 400μm, 500μm, to match different range and sensitivity requirements.

[0064] Step S3: Curing and Pore Formation. The curing process can adopt a three-stage curing strategy: low-temperature pre-curing, medium-temperature curing, and high-temperature volatilization. Specifically, first, place the product in a forced-air drying oven and pre-cur it at 25~60 ℃ for 30~60 min to form an initial network, lock the dispersion state of each filler, and complete the initial cross-linking; then, cure it at 80~100 ℃ for 30~90 min to complete the cross-linking and structural shaping; finally, cure it at 100~160 ℃ for 300~600 min (preferably 120~150 ℃, 500~600 min) to ensure that the pore-forming agent TBC completely volatilizes and forms micropores. All of the above processes can be completed in the same forced-air drying oven, which can be achieved by using a pre-set temperature gradient.

[0065] It is worth noting that, to achieve large-scale manufacturing, the preparation process of the functionally sensitive layer precursor can adjust the rheological window according to process requirements to adapt to existing manufacturing processes (such as printing, 3D printing, etc.). The functionally sensitive layer precursor of this application can achieve multi-process compatibility under a unified process framework of first setting the rheological window and then curing and creating pores. For example, for screen printing, by adjusting the content of nanofiller (vaporized SiO2) to set the thixotropy and yield stress, the printed pattern can be quickly shaped after screen removal and maintain clear boundaries and consistent thickness; then, it is processed according to the above-mentioned curing and volatilization steps to form a microporous structure. As another example, for the blade coating / brush coating / casting process, by adjusting the system viscosity and flow parallelism to meet the requirements of large-area coating and multilayer stacking, the film layer is continuous and the thickness is controllable; then, it is processed according to the above-mentioned curing and volatilization steps to form a porous structure. For example, in extrusion 3D printing (layer-by-layer printing) processes, by constructing a rheological response with shear thinning and rapid thixotropic recovery, the material can be extruded within the nozzle, self-supporting after leaving the nozzle, and stacked layer by layer to form a shape. Subsequently, curing and removal of the pore-forming agent are performed after printing, thereby enabling the continuous manufacturing of conformal curved surface devices. Furthermore, the slurry-type composite material system used in this application, composed of a polymer elastomer matrix, conductive fillers, volatile removable pore-forming agents, and nano-controlled components, allows micropores to form naturally during film formation or curing, eliminating the need for complex foaming, template construction, or multi-step post-processing. It also eliminates the dependence on precise pore size distribution or regular pore arrays, greatly simplifying the pore-forming process and reducing pore-forming costs.

[0066] Based on the above description of the preparation process of the functional sensitive layer material, the principle of micropore formation is further explained as follows: Since TBC and PDMS are incompatible, in the liquid-solid bicontinuous phase composite material obtained by blending them, TBC is dispersed in solid PDMS as small spheres at the tens of micrometer scale. When an appropriate amount of gaseous SiO2 is added, because SiO2 is nanoscale and rich in polar groups on its surface, TBC adsorbs onto the surface of SiO2. The addition of gaseous SiO2 changes the dispersion state of TBC in PDMS, forming even smaller nanoscale aggregates. When the TBC liquid in the material evaporates at high temperature, pores are formed at the original locations of TBC, thus forming uniformly dispersed micropores inside the PDMS. The size of the formed micropores is related to the amount of gaseous SiO2 added, typically ranging from 1 to 50 micrometers. Furthermore, as the SiO2 content increases, the pore size decreases and the distribution becomes more uniform. Adding conductive fillers to this liquid-solid bicontinuous phase composite material precursor can form a conductive functional composite material. After TBC volatilizes, the remaining nanopores become spaces for reversible contact of the conductive filler, thus establishing a reversible conductive network.

[0067] This liquid-solid dual-continuous phase composite precursor, before curing into a film, contains both a continuously interconnected liquid network and a continuously interconnected solid network within the precursor slurry. These two networks are spatially interwoven rather than a simple point-like structure of "solid particles dispersed in a liquid." In this material system, the liquid phase consists of an elastomer matrix (PDMS) and a pore-forming agent (TBC), providing flowability and processability. The solid phase consists of nanofillers (vapor-phase SiO2) and synergistic conductive fillers (CNTS) forming a physically supporting framework network. This allows the slurry to exhibit yield stress and thixotropy under low shear to maintain its structure, while under high shear, it can shear thin to adapt to processes such as screen printing, blade coating, or extrusion 3D printing. It also rapidly recovers after shearing stops to support layer-by-layer forming. Simultaneously, this solid framework can inhibit microstructure migration and pore collapse during pore formation and curing, stabilizing pore size distribution and pore structure morphology. This provides a reliable structural basis for subsequent reversible pore compression triggering interfacial contact reconstruction within the conductive network.

[0068] This application introduces a microporous structure, enabling the conductive fillers to remain separated when not under pressure. Figure 2As shown, when external pressure is applied to the sensor, the micropores undergo reversible compressive deformation, causing the previously separated conductive fillers to come into contact within the material, forming a new conductive network and resulting in a significant reduction in the overall resistance of the material. This pressure response process mainly occurs within the material, thus belonging to an internal interface contact mechanism, which is significantly different from traditional pressure sensing methods that rely on surface microstructures or interface separation. Compared with existing technologies, the flexible pressure sensor proposed in this application achieves the establishment of a conductive network from scratch through an internal interface contact mechanism, significantly improving pressure sensitivity. Simultaneously, since the pressure response mainly occurs within the material, it also avoids the fatigue failure problem of surface microstructures, exhibiting good cycle stability and reliability. Furthermore, due to the good flexibility and high compressibility of the conductive composite material system forming the functional sensitive layer, it is also suitable for wearable and curved surface applications.

[0069] At the fabrication level, the flexible pressure sensor proposed in this application, based on an internal interface contact mechanism, eliminates the reliance on fine surface microstructures for its pressure response mechanism, thus fundamentally avoiding complex microfabrication processes. In contrast, many existing flexible pressure sensors rely on complex surface microstructures such as micropillar arrays and pyramid arrays, requiring precision processes like photolithography, etching, and micromolding, which are expensive, complex, and difficult to replicate on a large scale. The functional sensitive layer in this application employs a bulk composite system, spontaneously forming a microporous structure within the material through curing and the volatilization of pore-forming agents, rather than constructing fine morphologies on the surface. This fundamentally eliminates the dependence on fine surface microstructures and significantly simplifies the manufacturing process.

[0070] It is worth noting that this application utilizes a one-step method to fabricate the functional sensitive layer of a flexible pressure sensor. This method is simple, has a wide processing window, and is easily scaled up. As described above, the fabrication process begins with the mixing and dispersion of raw materials, followed by coating or printing to form a film, then curing and the evaporation and removal of the pore-forming agent, ultimately resulting in a functional sensitive layer with internal micropores. This process eliminates the need for multiple mask alignments, complex etching, or transfer operations, representing a simplified one-step pore-forming process. It offers a wide process parameter window, low dependence on equipment precision, and facilitates smooth scaling up between laboratory and industrial production.

[0071] In the preparation of the functional sensitive layer, the precursor is a tunable rheological slurry system. By introducing nanofillers, shear-thinning and thixotropic recovery properties are achieved, and viscosity and yield stress can be adjusted according to requirements. Therefore, it can be used for simple film formation methods such as brush coating, blade coating, and casting, and is also compatible with mature processes such as screen printing, blade coating, and extrusion 3D printing. Compared with solutions that rely on rigid substrate micromachining, this application is more conducive to the manufacturing of large areas, continuous processes, and programmable paths, which is beneficial for mass production and personalized customization, thereby effectively overcoming the problems of "complex processes and difficulty in large-scale preparation" in the prior art.

[0072] The solution and effects of this application will be further described below with reference to specific embodiments and accompanying drawings.

[0073] Example 1: An intrinsic piezoresistive flexible pressure sensor based on an internal interface contact mechanism was fabricated, and its performance was evaluated.

[0074] The flexible pressure sensor provided in Example 1 has a sandwich structure. From bottom to top, the device consists of a flexible substrate layer, a lower electrode layer, a functional sensitive layer, an upper electrode layer, and a top encapsulation layer. The functional sensitive layer uses PDMS as the polymer matrix, incorporates TBC as a pore-forming agent, multi-walled CNTS as a conductive filler, and fumed SiO2 as a nanofiller. Heat treatment causes the TBC to volatilize, forming a porous structure within the functional sensitive layer material, thereby constructing a pressure response network based on an internal interface contact mechanism.

[0075] In the functional sensitive layer, the proportions of PDMS, multi-walled CNTS, TBC, and vapor-phase SiO2 satisfy the following relationship (by mass fraction): PDMS:CNTS:TBC:SiO2=1:0.025:1:0.05.

[0076] That is, PDMS is 1 part, CNTS is 2.5% of the PDMS mass, TBC is 100% of the PDMS mass, and SiO2 is 5% of the PDMS mass. For example, in this embodiment, PDMS is 10g, CNTS is 0.25g, TBC is 10g, and SiO2 is 0.5g. In this embodiment, the preparation method of the functional sensitive layer is basically the same as the preparation method mentioned above, mainly including the following steps: Preparation of flexible substrate: A layer of PDMS with a thickness of about 500 μm was coated on the substrate using a blade coating process to form a flexible substrate; then it was placed in a forced-air drying oven and cured by heating at 60 ℃ for 1 h and 100 ℃ for 1 h in sequence to obtain the flexible substrate.

[0077] Preparation of the lower electrode layer: A PET film with a thickness of approximately 50 μm was cut using a laser cutter to obtain the desired electrode pattern; the treated PET film was attached to the surface of the flexible substrate as a mask; silver paste was applied to the surface of the flexible substrate using a scraper close to the mask, and then the PET mask was removed to form the lower electrode pattern; finally, it was placed in a forced-air drying oven and pretreated by slowly raising the temperature to 150 ℃ for 30 min to avoid the generation of bubbles during heating, and then kept at 150 ℃ for 30 min to complete the curing of the lower electrode layer.

[0078] Preparation of the functional sensitive layer: A PET film with a thickness of approximately 500 μm is cut using a laser cutter to obtain a mold that matches the size of the functional sensitive layer; the PET film is attached to the surface of the lower electrode layer as a mold; the precursor is filled into the mold using a scraper, and after filling, the mold is removed to obtain a film with a thickness of 500 μm; subsequently, the obtained film is post-processed according to the curing conditions of the aforementioned functional sensitive layer to obtain the functional sensitive layer.

[0079] Fabrication of the upper electrode layer: The fabrication method of the upper electrode layer is the same as that of the lower electrode layer, except that the flexible substrate layer is replaced by the pre-fabricated functional sensitive layer, and the upper electrode layer is formed on the surface of the functional sensitive layer.

[0080] Preparation of the top encapsulation layer: A layer of PDMS with a thickness of about 800 μm was coated on the surface of the upper electrode layer using a blade coating process as the top encapsulation layer; then it was placed in a forced-air drying oven and cured under conditions of heating at 60 ℃ for 1 h and heating at 100 ℃ for 1 h in sequence to complete the device encapsulation.

[0081] In the obtained flexible pressure sensor, the functional sensitive layer is disposed between the upper and lower electrode layers and forms electrical contact with the electrodes. When external pressure is applied to the sensor, the internal structure of the sensitive layer undergoes reversible deformation, thereby causing a change in its overall conductivity. Normal pressure is applied to the pressure sensor, and the pressure response characteristics and linearity of the flexible pressure sensor are tested to verify its electrical response behavior under different pressure loading conditions.

[0082] During the test, a pressure loading device was used to apply normal pressure to the pressure sensor, with a pressure loading range of 230-1500 kPa. Under constant test voltage conditions, the sensor's conductivity signal was acquired in real time. Using the initial conductivity value as a reference, the conductivity change was normalized to obtain... Figure 3 The pressure-conductivity response curve is shown.

[0083] like Figure 3 As shown, within the pressure range of 200–1500 kPa, the conductivity of this flexible pressure sensor exhibits an approximately linear increasing trend with increasing applied pressure. Linear fitting of the conductivity response curve within this pressure range yields the following result: sensitivity S = 0.045 kPa. -1 ; coefficient of determination R 2 ≈ 0.997. The results show that the sensor has good linear response characteristics in the medium and high voltage range.

[0084] As can be seen from Example 1, the flexible pressure sensor can maintain a stable and linear pressure response over a wide medium-to-high pressure range. Furthermore, the high linearity fitting results also indirectly indicate that the device response behavior is stable under the same process parameters, with minimal differences between devices, demonstrating good fabrication consistency. This effect is mainly attributed to the porous structure formed by TBC volatilization, resulting in a large number of initially separated conductive filler interfaces within the functional sensitive layer. Under external pressure, the micropores are gradually compressed, forming new internal interface contacts between the CNTS (Conductive, Non-Conductive, and Transformative) layers, thereby gradually establishing and enhancing conductive pathways within the material. Since the formation of conductive pathways mainly occurs at the internal interfaces of the material, rather than relying on surface microstructure deformation, good linearity and sensitivity can still be maintained under high pressure conditions. Therefore, this application overcomes the problem of saturation and linearity degradation under high pressure conditions in traditional piezoresistive flexible pressure sensors that rely on surface microstructures, making it suitable for medium-to-high pressure monitoring scenarios.

[0085] Furthermore, the flexible pressure sensor obtained in Example 1 was subjected to a long-term drift test under constant pressure to evaluate the stability and drift degree of its output signal under long-term constant pressure loading conditions, so as to verify the reliability of the sensor under continuous working conditions.

[0086] During the test, a constant normal pressure of 500 kPa was applied to the sensor surface. The test environment was room temperature (preferably 25±2℃), and the test duration was 25 hours. The sensor resistance value R was recorded in real time during the test.

[0087] The obtained data is processed as follows: the resistance value after reaching a stable state during the initial loading phase is used as the initial reference value R0, and the normalized output signal is calculated to obtain the relative resistance change rate. as follows: Where R is the real-time resistance value measured during the test.

[0088] like Figure 4 As shown, after applying a constant pressure of 500 kPa to the sensor, its normalized output signal... The sensor quickly reached a stable plateau within a short period. During the subsequent 25 hours of continuous loading, the output signal remained generally stable, without any significant or sustained upward or downward trend. Comparing the output values ​​at the start of the stable plateau with those at the end of the 25 hours, the relative change did not exceed 5%. After the test, the pressure was unloaded, and the sensor output signal essentially returned to its initial state, with no irreversible drift observed.

[0089] The above demonstrates that the flexible pressure sensor exhibits excellent long-term stability, with an output signal drift of no more than 5% after 25 hours of continuous operation under a constant pressure of 500 kPa. This verifies that the flexible pressure sensor provided in this application possesses good anti-drift capability and reliability under long-term constant load conditions. The low drift characteristic stems from the internal interface contact mechanism of this application; that is, under pressure, the conductive path is mainly dominated by the reversible change in the interface contact state within the porous structure of the material, avoiding signal instability caused by surface microstructure fatigue or creep. This long-term stability makes the sensor suitable for applications requiring continuous pressure or long-term monitoring, such as structural load monitoring, human body contact pressure monitoring, and long-term signal acquisition in wearable devices.

[0090] Furthermore, the response and recovery speed of the flexible pressure sensor obtained in Example 1 were tested to evaluate its dynamic response capability under transient loading and unloading conditions, that is, its response speed and recovery speed to rapid pressure changes.

[0091] During the test, instantaneous pressure was applied to the sensor and then unloaded, and the changes in the sensor's output electrical signal over time were recorded to obtain its response time and recovery time. Specifically, an instantaneous loading method was used, i.e., rapid loading and rapid unloading, with an applied pressure of 10 kPa. The sensor's output voltage signal was recorded in real time, with a sampling frequency meeting millisecond-level time resolution (512 Hz). The test environment was also room temperature (preferably 25±2 ℃).

[0092] like Figure 5 As shown, when a pressure of 10 kPa is applied to the sensor, its output voltage rises rapidly at the moment of loading and reaches a stable plateau within a short time; after the pressure is unloaded, the output signal quickly recovers to its initial state. Specifically, during the pressure loading process, the sensor's response time is approximately 2 ms; during the pressure unloading process, the sensor's recovery time is approximately 2 ms; during the load holding phase, the output signal remains stable without significant overshoot or oscillation. These results demonstrate that the sensor exhibits excellent dynamic response capability to rapid pressure changes.

[0093] The test results show that this flexible pressure sensor has millisecond-level response and recovery speeds, enabling it to quickly and accurately follow transient changes in external pressure. This rapid response characteristic also stems from the internal interface contact mechanism of this application: during pressure loading, the separated conductive fillers within the porous structure rapidly form interface contacts and establish conductive pathways; during unloading, these interface contacts quickly disengage, resulting in a rapid and reversible electrical response. Compared to piezoresistive sensors that rely on surface microstructures or macroscopic deformation, the changes in conductive pathways in this application primarily occur at the internal interface of the material, reducing structural hysteresis and recovery hysteresis, which is beneficial for achieving high-frequency, rapid dynamic pressure monitoring. Therefore, this flexible pressure sensor not only possesses good sensitivity and stability but also excellent dynamic response performance, making it suitable for applications requiring rapid pressure sensing.

[0094] Furthermore, the piezoresistive flexible pressure sensor obtained in Example 1 was subjected to cyclic loading stability testing, that is, long-term cyclic stability under repeated loading conditions, to verify its reliable working ability under repeated stress conditions.

[0095] Specifically, the fabricated flexible pressure sensor is placed in a pressure loading test system, with the upper and lower surfaces of the sensor fully in contact with the loading head and substrate. A cyclic loading-unloading method is used to apply a constant amplitude cyclic pressure to the sensor, with the cyclic loading pressure set at 300 kPa. The cyclic loading frequency remains constant, and the sensor undergoes 10,000 consecutive loading-unloading cycles. Throughout the cyclic loading process, the sensor's conductivity output signal is acquired and recorded in real time to evaluate its stability under long-term, repetitive stress conditions.

[0096] Test results are as follows Figure 6 As shown, the flexible pressure sensor underwent 10,000 load-unload cycles under a periodic loading condition of 300 kPa. Throughout the entire cyclic loading process, the sensor's output conductivity signal was continuously and stably acquired, without any output interruption, sudden failure, or significant noise amplification. The response waveform remained intact within each cycle, indicating that the sensor still possesses good operability under repeated stress conditions.

[0097] The above results demonstrate that the flexible pressure sensor based on the internal interface contact mechanism described in this application can withstand long-term repeated loading under moderate pressure conditions (300 kPa), and no structural or functional failures occurred during 10,000 cycles of loading. This indicates that the porous structure formed inside the sensing layer exhibits good structural stability during repeated compression-release processes; the internal interface contact between the conductive fillers maintains reversible changes during cyclic loading, preventing irreversible conductive pathways due to repeated loading. Compared to pressure sensors relying on surface microstructures, the internal interface contact mechanism of this application helps reduce the impact of cyclic fatigue on the functional stability of the device. Therefore, the flexible pressure sensor provided in this application is well-suited for applications requiring long-term repeated stress.

[0098] Example 2: A functional sensitive layer for fabricating a sensor was prepared, and the interfacial toughness between the PDMS flexible substrate and the functional sensitive layer was characterized to verify the interfacial bonding strength and stability between the functional sensitive layer and the PDMS flexible substrate. The interfacial toughness test specimen can be prepared according to the following steps: Preparation of PDMS flexible substrate: PDMS prepolymer and curing agent were mixed evenly at a mass ratio of 10:1 and degassed in a centrifugal degassing machine for 5 minutes; then, the degassed PDMS was coated onto a flat substrate with Teflon tape by a scraping method to facilitate subsequent demolding, and the film thickness was controlled to be about 0.5 mm; finally, the PDMS film was placed in an oven and cured at 60 ℃ for 1 hour and 100 ℃ for 1 hour. After cooling, it was not demolded to obtain the PDMS flexible substrate.

[0099] Cutting the specimen: Cut the obtained PDMS flexible substrate into strip specimens with a length of 40 mm and a width of 20 mm, and record the specimen width b (in meters).

[0100] Step B3: Set up the non-bonding area: Set up a double-sided release PET film as an isolation layer at one end of the PDMS flexible substrate. Both sides of the PET film are release coatings, with a length of 20 mm and a width slightly larger than the width of the sample. The area covered by the isolation layer forms the non-bonding area.

[0101] Formation of the functional sensitive layer: The conductive functional material is coated onto the surface of the PDMS substrate with the isolation layer, so that the functional sensitive layer covers the non-bonded area and the bonded area. The thickness of the functional sensitive layer is controlled at 500 μm, and it is cured under the curing conditions of the functional sensitive layer; after curing and cooling, the double-sided release PET film is removed to obtain an interfacial toughness test specimen with a free peeling crack initiation area at one end and the remaining area being the real interfacial bonded area.

[0102] Reinforcing peel arms are provided: A thin film of the same size is attached to both sides of the PDMS flexible substrate layer and the functionally sensitive layer as reinforcing peel arms. These reinforcing peel arms are selected from PET film, PI film, or other high-strength, flexible materials, and have a thickness of 50–100 μm. This is to prevent tearing of the functionally sensitive layer during the peeling process and ensure stable interfacial peeling.

[0103] The samples prepared in the above steps were subjected to a 180° peel test using a universal testing machine. The specific procedure was as follows: first, the free end of the PDMS flexible substrate was clamped in the lower fixture to keep it straight; then, the free end of the functional sensitive layer was clamped in the upper fixture, maintaining a peel angle of 180°±5°; then, peeling was performed using a displacement control mode, with a 500N sensor selected and a peel speed set to 50 mm / min. The peel force-displacement curve was recorded in real time during the test.

[0104] like Figure 7 As shown, in the initial stage of peeling, the peeling force increases rapidly with displacement, then enters a stable peeling stage. Within the stable peeling stage, the peeling force fluctuates less with displacement, exhibiting a distinct plateau region. Statistical analysis of the peeling force in the stable plateau section, normalized to the sample width b, yields an interfacial peeling force / width of approximately 320 N / m. This result indicates that a stable and continuous interfacial bond is formed between the functionally sensitive layer and the PDMS flexible substrate.

[0105] Based on the above test results, it can be seen that the functional sensitive layer and the PDMS flexible substrate layer of this application have high interfacial toughness, and the interface exhibits a stable peel force plateau under 180° peel conditions. No obvious overall tearing or instantaneous failure of the functional sensitive layer occurred during the peeling process, indicating high interfacial bonding strength and uniform force transmission. This interfacial toughness characteristic is beneficial for maintaining structural integrity and electrical performance stability under repeated loading, bending, or long-term service conditions of the sensor. Therefore, Example 2 verifies that the functional sensitive layer and the PDMS flexible substrate layer of this application have excellent interfacial toughness, providing support for the reliable application of pressure sensors in complex mechanical environments.

[0106] Example 3: The effect of CNTS content on the performance of a flexible pressure sensor based on an internal interface contact mechanism was investigated to verify the reasonable range of conductive filler content in this application and its effect on sensitivity and range control.

[0107] Similarly, the material system of the functional sensitive layer precursor is: PDMS (polymer matrix) + TBC (pore-forming agent) + CNTS (conductive filler) + SiO2 (nanofiller). The porous structure is formed by the volatilization and escape of TBC during the curing process.

[0108] With CNTS content as the variable, the other material types, proportions, and process conditions remained basically the same as in Example 1. Specifically, PDMS was 1 part, TBC was 100% of the PDMS mass, and SiO2 was 5% of the PDMS mass. Three comparative examples with CNTS content are shown below: Comparative Example F31: CNTS is 0% of the PDMS mass, i.e., PDMS:CNTS:TBC:SiO2 = 1:0:1:0.05; Comparative Example F32: CNTS is 2.5% of the mass of PDMS, i.e., PDMS:CNTS:TBC:SiO2 = 1:0.025:1:0.05; Comparative Example F33: CNTS is 5% of the PDMS mass, i.e., PDMS:CNTS:TBC:SiO2 = 1:0.05:1:0.05.

[0109] To evaluate the differences in pressure response amplitude and operating range of sensors with different CNTS contents, determine the influence of CNTS content on the formation of internal interface contact conductive pathways, and identify the optimal CNTS content range, a pressure loading device was used to apply normal pressure to the sensor, ranging from 0 to 3000 kPa. The conductivity signal output by the sensor was acquired under constant test voltage. To facilitate comparison between different samples, a normalized form was used to characterize the output change, resulting in a normalized response curve, which characterizes the relationship between the relative conductivity change and pressure. The relative conductivity change... It is expressed as follows: In the formula, The initial conductivity is given.

[0110] Based on clarifying the formation law of pore structure by TBC and SiO2, this application further characterizes the cross-sectional morphology of the complete and preferred material system. Figure 8 Figures (a) and (b) show the cross-sectional SEM images and magnified SEM images of Comparative Example F33, a sample with a PDMS:TBC mass ratio of 1:1 and CNTs and SiO2 contents of 5%, after being incubated at 150 ℃ for 10 h. It can be seen that after the introduction of CNTs, the sample still maintains a relatively obvious porous structure, with interconnected pore walls forming a continuous framework network. Combined with the magnified SEM images, it can be seen that the pore size distribution is relatively wide, but generally within the micrometer range, with typical pore sizes distributed between 1-50 μm. This indicates that in a complete material system, the droplet evaporation pore-forming process and the introduction of conductive fillers can work well together, thus forming a porous conductive composite system that combines a microporous structure and a conductive framework.

[0111] like Figure 9As shown, different CNTS contents have a significant impact on the sensor's pressure response, which is analyzed below: Comparative Example F31 (CNTS=0): In the range of 0~3000 kPa, the change in relative conductivity is close to zero, and the pressure response is not obvious, indicating that a conductive path cannot be formed without CNTS conductive filler, and the device cannot achieve pressure sensing output.

[0112] Comparative Example F32 (CNTS=0.025%): With increasing pressure, the change in relative conductivity increases significantly, showing a clear pressure response in the range of 0~3000 kPa, and the response amplitude is the largest. This indicates that the internal interface contact between conductive fillers is easily formed and continuously enhanced under pressure near this content, thus obtaining higher sensitivity and wider range.

[0113] Comparative Example F33 (CNTS=0.05): The relative change in conductivity was significantly lower than that of Group F32, and the pressure response was weakened. This indicates that the CNTS content was too high, the conductive network formed initial connectivity or tended to saturate, and the proportion of new internal interface contacts caused by pressure decreased, resulting in a significant decrease in electrical response.

[0114] The above comparative analysis shows that CNTS content is a key parameter affecting the performance of the flexible pressure sensor in this application, and can significantly control the pressure response amplitude and range. When the CNTS content is too low, it is difficult to form a conductive path, and the pressure stimulus cannot be effectively converted into an electrical signal output. When the CNTS content is within a suitable range (e.g., CNTS is 2.5% of the PDMS mass), there are a large number of internal interface contact points that can be activated by pressure. During the pressure loading process, the conductive path is gradually established from weak to strong, thereby obtaining a higher response and a wider working range. When the CNTS content is too high, the conductive network has been initially connected or rapidly saturated after compaction, and the gain of the internal interface contact mechanism is weakened, resulting in a decrease in sensitivity. Therefore, Example 3 demonstrates that this application can effectively control the sensor performance by optimizing the CNTS content, and provides experimental basis for determining the optimal CNTS content range.

[0115] Example 4: The effect of SiO2 content on the mechanical properties and pressure sensing properties of composite materials was investigated to determine the optimal addition range of SiO2 and achieve comprehensive optimization of device sensitivity, range and reliability.

[0116] Similarly, the material system of the functional sensitive layer precursor is: PDMS (polymer matrix) + TBC (pore-forming agent) + CNTS (conductive filler) + vapor phase SiO2 (nanofiller). The porous structure is formed by the volatilization and escape of TBC during the curing process.

[0117] Using the content of fumed SiO2 as the variable, except for the SiO2 content, the types, proportions, and preparation process conditions of other materials were basically the same as in Example 1 above. Specifically, PDMS was 1 part, TBC was 100% of the PDMS mass, CNTS was 5% of the PDMS mass, and the mass ratio of PDMS prepolymer to curing agent was 10:1. Five comparative examples of fumed SiO2 were set up as follows: Comparative Example F41: SiO2 is 0% of the mass of PDMS, i.e., PDMS:CNTS:TBC:SiO2 = 1:0.05:1:0; Example F42: SiO2 is 2.5% of the mass of PDMS, that is, PDMS:CNTS:TBC:SiO2 = 1:0.05:1:0.025; Example F43: SiO2 is 5% of the mass of PDMS, that is, PDMS:CNTS:TBC:SiO2 = 1:0.05:1:0.05; Example F44: SiO2 is 7.5% of the mass of PDMS, i.e., PDMS:CNTS:TBC:SiO2 = 1:0.05:1:0.075; Example F45: SiO2 is 10% of the mass of PDMS, that is, PDMS:CNTS:TBC:SiO2 = 1:0.05:1:0.1.

[0118] In this embodiment, mechanical property testing is performed. Specifically, the conductive composite materials with different SiO2 contents are added into a standard dumbbell-shaped mold and dried, and the sample dimensions are recorded. Then, a universal testing machine is used to perform uniaxial tensile testing to obtain stress-strain curves. The stress-strain curves are used to characterize the tensile strength, deformation capacity, and overall stiffness variation trend of the material.

[0119] On the other hand, pressure sensing performance tests were conducted. Specifically, conductive composite materials with different SiO2 contents in the gas phase were assembled into a sandwich-structured pressure device as the sensitive layer; a normal pressure was applied using a pressure loading device, with a pressure range of 0-2500 kPa; the output signal was acquired under constant test voltage / constant test circuit conditions, and the pressure response was characterized by the normalized index of relative conductivity change, resulting in a relative conductivity change-pressure curve.

[0120] Mechanical property results as follows Figure 10As shown in Figure (a), with the increase of fumed SiO2 content, the stress-strain curve of the composite material shifts upward overall, and the stress level increases under the same strain. This indicates that the fumed SiO2 nanofiller has a significant reinforcing effect on the PDMS matrix, improving the mechanical strength and load-bearing capacity of the material. Meanwhile, the material still maintains considerable deformation capacity within a certain strain range, indicating that this reinforcement does not lead to complete embrittlement of the material, thus meeting the deformability requirements of flexible sensors.

[0121] Pressure sensing results as follows Figure 10 As shown in Figure (b), there are significant differences in the change of relative conductivity of the composite material under different gaseous SiO2 contents. Specifically, when the gaseous SiO2 content is low (e.g., 0-2.5%), the change of relative conductivity is high. As the gaseous SiO2 content further increases (5-10%), the change of relative conductivity gradually decreases with the increase of pressure, that is, the pressure response sensitivity shows a downward trend. Under the condition of high gaseous SiO2 content (e.g., 10%), the response amplitude is the lowest, showing stronger stiffening or compression suppression characteristics.

[0122] As can be seen from Example 4, on the one hand, the vapor-phase SiO2 nanofiller can significantly improve the mechanical strength and load-bearing capacity of the composite material (the stress-strain curve shifts upward overall), which is beneficial for the sensor to maintain structural stability and deformation controllability under medium and high pressure conditions. On the other hand, the vapor-phase SiO2 content has a "strengthening-inhibition" trade-off relationship with the pressure sensing response. That is, an appropriate amount of vapor-phase SiO2 helps improve the stability of the material skeleton and the interfacial bonding, but when the vapor-phase SiO2 content is too high, the overall stiffness of the material increases and the pore compaction is restricted, resulting in a decrease in the amplitude of internal interface contact changes, thereby causing a decrease in the pressure response amplitude. Therefore, this application can achieve synergistic optimization of "mechanical reliability and sensing performance" by controlling the vapor-phase SiO2 content. Preferably, the vapor-phase SiO2 content is 5% of the PDMS mass to maintain a high pressure response while ensuring mechanical strength.

[0123] Example 5 characterizes the effect of the PDMS:TBC ratio (i.e., the amount of pore-forming agent TBC) on the pore structure formation, mechanical properties, and pressure sensing performance of the conductive composite material, in order to determine the optimal range of PDMS:TBC ratio and achieve comprehensive optimization of porosity, compressibility, sensitivity, and reliability.

[0124] Similarly, the precursor system of the functional sensitive layer is: PDMS (polymer matrix) + TBC (pore-forming agent) + CNTS (conductive filler) + SiO2 (nanofiller), and the porous structure is formed by the volatilization and escape of TBC during the curing process.

[0125] Using the PDMS:TBC ratio (i.e., mass ratio) as the variable, the types, contents, and process conditions of other materials remained basically the same as in Example 1. Specifically, PDMS was 1 part, CNTS was 5% of the PDMS mass, SiO2 was 5% of the PDMS mass, and the mass ratio of PDMS prepolymer to curing agent was 10:1. Five comparative examples of PDMS:TBC were set up as follows: Comparative Example F51: PDMS:TBC = 1:0; Example F52: PDMS:TBC = 1:0.5; Example F53: PDMS:TBC = 1:1; Example F54: PDMS:TBC = 1:1.5; Example F55: PDMS:TBC = 1:2.

[0126] In Example 5, mechanical property testing was conducted. First, conductive composite materials prepared with different PDMS:TBC ratios were added into a standard dumbbell-shaped mold and dried, and the sample size was recorded. Then, a universal testing machine was used to perform uniaxial tensile testing to obtain stress-strain curves, which were used to compare the changes in material strength and stiffness with the amount of pore-forming agent.

[0127] On the other hand, pressure sensing performance testing is carried out. First, materials with different PDMS:TBC ratios are used as functional sensitive layers to fabricate sandwich-structured sensor devices. Then, a normal pressure is applied using a pressure loading device, with a pressure range of 0~300 kPa. The output signal is acquired under constant test voltage / constant test circuit conditions, and the pressure response is characterized by the normalized index of relative conductance change, resulting in a relative conductance change-pressure curve.

[0128] Mechanical property results as follows Figure 11 As shown in Figure (a), with the increase of TBC content (i.e., the PDMS:TBC ratio changes from 1:0 to 1:2), the stress-strain curve of the composite material shifts downward overall, indicating a significant decrease in stress at the same strain. This suggests that increased porosity makes the material more compressible and reduces overall stiffness. Among them, the sample with PDMS:TBC=1:0 exhibits the highest stiffness, while the sample with PDMS:TBC=1:2 exhibits the lowest stiffness.

[0129] Pressure response results as follows Figure 11As shown in Figure (b), the pressure response of the materials varies significantly under different PDMS:TBC ratios. Specifically, when PDMS:TBC = 1:0 or 1:0.5, the change in relative conductivity with pressure is small and the response is not obvious. When PDMS:TBC = 1:1, 1:1.5, and 1:2, the change in relative conductivity with increasing pressure increases significantly, and the response amplitude is significantly improved. Among them, the 1:1 group has the highest overall response amplitude, showing better pressure sensing performance.

[0130] As can be seen from Example 5, the PDMS:TBC ratio is a key parameter for controlling pore structure and compressibility. Increasing the amount of TBC increases porosity, making the material more compressible (shifting the stress-strain curve downward), thereby changing the structural compaction behavior under pressure. An appropriate amount of TBC can significantly improve the pressure response amplitude. When the PDMS:TBC ratio is within a certain range (e.g., 1:1 to 1:2), the pore structure of the material gradually compacts during pressure loading, and the internal interface contact increases rapidly, resulting in a significant increase in the change of normalized output relative conductivity, thus obtaining a higher pressure response. When the TBC ratio is too low (e.g., 1:0 or 1:0.5), the pore structure is insufficient, the compressibility and the increase in internal interface contact are limited, resulting in a weaker sensing response. Therefore, this application achieves synergistic control of the material's mechanical properties and pressure sensing performance by selecting an appropriate PDMS:TBC ratio, with a preferred PDMS:TBC mass ratio of 1:1, to obtain a higher pressure response while ensuring structural stability.

[0131] Example 6 was used to characterize the pore structure regulation law of the porous composite material of this application. It examined the effects of the amount of pore-forming agent TBC, the content of inorganic nanofiller SiO2, and whether or not the material was heat-treated at 150 °C on the pore morphology, pore size and structural uniformity of the material cross section. This provides a structural basis for the formation of the "internal interface contact mechanism" of this application and provides experimental support for determining the optimal material ratio.

[0132] Similarly, the precursor system of the functional sensitive layer is: PDMS (polymer matrix) + TBC (pore-forming agent) + CNTS (conductive filler) + SiO2 (nanofiller), and the porous structure is formed by the volatilization and escape of TBC during the curing process.

[0133] This embodiment consists of two groups of experiments: Group 1: The effect of TBC dosage and whether or not heat treatment at 150 ℃ was performed on the pore structure. The PDMS:TBC mass ratios were 1:0, 1:0.5, 1:1, 1:1.5, and 1:2. The 150 ℃ heat treatment time was either 0 h or 10 h. The other material types, proportions, and preparation process conditions remained basically the same as in Example 1. Specifically, PDMS was 1 part, CNTS was 5% of the PDMS mass, and SiO2 was 5% of the PDMS mass.

[0134] Group 2: The effect of SiO2 content and whether or not heat treatment at 150 ℃ has been performed on the pore structure. The SiO2 mass fractions were 0%, 5%, 10%, and 15% (based on the PDMS matrix). The 150 ℃ heat treatment time was also divided into two types: 0 h and 10 h. The PDMS:TBC ratio was kept constant at 1:1, and other conditions remained basically the same.

[0135] Composite materials prepared under different ratios and conditions were filled into Teflon molds, dried, and then cut along the thickness direction of the sample to expose the cross-section. The cross-section of the sample was then subjected to gold / carbon spraying conductive treatment. The cross-section was then observed and images were acquired using a scanning electron microscope (SEM) to compare and analyze the characteristics such as pore size, pore shape, and pore distribution uniformity under different variable conditions.

[0136] like Figure 12 As shown in Figure (a), regarding the effect of the PDMS:TBC ratio and heat treatment time: under the condition of 0 h treatment at 150 ℃, TBC can be observed to exist in the form of droplets / dispersed phase inside the material, and the overall pores have not yet fully formed; under the condition of 10 h treatment at 150 ℃, TBC volatilizes and escapes, forming a distinct pore structure, indicating that heat treatment can effectively achieve volatilization and pore formation. This shows that as the TBC content increases (PDMS:TBC increases from 1:0.5 to 1:2), the pore volume fraction increases, the pore size increases and the morphology tends to be irregular, and the material structure gradually evolves from relatively dense to loose honeycomb structure. Under the condition of higher TBC content, the pores are highly aggregated, the interface roughness increases, the overall structure is more loose, and the stability decreases relatively.

[0137] like Figure 12As shown in (b), regarding the effect of SiO2 content on heat treatment time: before treatment at 150 °C (i.e., 0 h), TBC can be observed to exist in the PDMS matrix as dispersed droplets; after treatment at 150 °C for 10 h... After h, TBC volatilizes, leaving pores and forming a porous structure. With increasing SiO2 content (from 0% to 15%), the pore size decreases, the pore distribution becomes more uniform, and the pore structure becomes finer and more regular. This indicates that SiO2 nanofillers can regulate the stable dispersion and volatilization pore-forming process of the TBC phase, thereby achieving controllable pore size and pore distribution. Example 6 demonstrates that this application can form a repeatable porous structure through TBC volatilization pore formation, and the pore structure transforms from a dispersed phase / droplet state to a pore state with heat treatment time, indicating a clear pore-forming mechanism. The amount of TBC determines the porosity and pore size; increasing the TBC content can improve porosity and increase pore size, but excessive TBC can lead to irregular pores, aggregation, and a loose structure, thus reducing structural stability. An appropriate amount of SiO2 helps to obtain a smaller, more uniformly distributed pore structure, improving the material's framework stability and interface morphology consistency. Therefore, this application can obtain a porous structure with controllable pore size, controllable pore distribution, and controllable interface roughness by adjusting the TBC content, SiO2 content, and heat treatment time. This provides a structural basis for the generation and change of interface contact points inside the material under subsequent pressure loading, thereby supporting the improvement of sensor sensitivity, linearity, stability, and cycle reliability.

[0138] like Figure 13 As shown, the flexible pressure sensor of this application can be fabricated in a large area and multi-channel array using screen printing. In this array structure, the electrode layer and the functional sensitive layer are integrally integrated on a flexible transparent substrate, resulting in a regular and highly consistent device structure suitable for mass production. Furthermore, due to the sensor's excellent transparency and flexibility, real-time monitoring of multi-point pressure distribution can be achieved without obstructing the light path or visual information, making it suitable for applications such as wearable electronics, flexible displays, human-computer interfaces, and biomedical adhesive sensing.

[0139] like Figure 14 As shown in (a), this application first performs a three-dimensional structural modeling of the electrode layer of the conformal pressure sensor, designs the curvature topography and electrode arrangement in the modeling software, and directly forms the curved electrode layer through an extrusion 3D printing process. Figure 14 As shown in (b), the results show that by using silver paste as a conductive material, continuous and controllable electrode paths can be constructed on complex curved surfaces through extrusion 3D printing. This verifies the compatibility between the curved electrode layer structure and the extrusion 3D printing process, and provides a technological basis for the subsequent 3D printing of sensor functional layers under the same manufacturing path.

[0140] Based on this, combined Figure 15 As shown in (a) and (b), this application further demonstrates the 3D modeling and extrusion 3D printing fabrication of the functional sensitive layer of a conformal pressure sensor. The functional sensitive layer utilizes the conductive composite material proposed in this application, which, while maintaining pressure response performance, meets the requirements of extrusion 3D printing for rheological properties and forming stability. The results show that the conductive composite material of this application can not only be used in planar coating or printing processes, but also as a 3D printing paste, combined with 3D modeling and printing processes to achieve the direct construction of functional layers on complex curved surfaces.

[0141] As can be seen, this application verifies the compatibility of key structural layers of flexible pressure sensors with 3D printing technology by separately 3D modeling the curved electrode layer and the curved functional sensitive layer and fabricating them using extrusion 3D printing. This provides experimental evidence for the full 3D printing manufacturing of curved conformal pressure sensors. Compared with traditional flexible sensor fabrication methods that mainly rely on interlayer bonding or post-assembly, the 3D printing-based curved conformal manufacturing scheme proposed in this application helps reduce interface mismatch and adhesion failure between multi-layer structures, improving the structural integrity and service reliability of devices under complex curved surface conditions. Simultaneously, this scheme provides a new path for the rapid customized manufacturing of flexible pressure sensors on complex 3D structural surfaces, possessing significant engineering application value. Therefore, by combining the internal interface contact mechanism with extrusion 3D printing manufacturing technology, this application not only expands the application of flexible pressure sensors in the directions of arraying and curved conformal design but also verifies the feasibility of using conductive functional materials as 3D printing pastes, providing a technical solution with practical engineering significance for constructing fully 3D printed flexible pressure sensors. Therefore, at the product application level, the flexible pressure sensor proposed in this application possesses excellent material flexibility and high compressibility, making it suitable for wearable and conformal applications on curved surfaces. The polymer elastomer matrix and microporous structure employed together endow the functional sensitive layer with excellent flexibility and compressibility, maintaining stable output even under large bending radii and repeated bending conditions. Simultaneously, the internal pores provide compressible space, enabling the device to generate a significant electrical response even in low-pressure regions, balancing flexible fit with high-sensitivity detection. This makes it particularly suitable for applications such as wearable human body monitoring, robotic electronic skin, and complex curved surface devices.

[0142] Furthermore, this flexible pressure sensor is easily integrated with electrode and encapsulation layers, supporting planar arrays and curved surface 3D printed devices. Since the sensitive layer is formed as a slurry, it can be directly coated onto the flexible electrode, forming a bottom-up layered structure. Simultaneously, the material system is adaptable to curved surface 3D printing, enabling layer-by-layer deposition and co-forming on complex curved surfaces such as spheres and cylinders. Therefore, this application can not only construct planar array pressure sensors but also achieve conformal curved surface design, multi-channel arrays, and integrated packaging with other flexible devices, expanding the application scope of flexible pressure sensors in wearable health monitoring, human-computer interaction, and other fields.

[0143] In summary, this application improves structural stability and cycle durability at the product level by transforming the surface microstructure deformation commonly used in the background technology of sensor mechanism into the reversible reconstruction of the interface contact network in the bulk micropore. It also has high sensitivity and high reliability. At the process level, it avoids dependence on complex surface microstructures and precision micromachining processes, and realizes a simplified one-step, printable, and 3D printable manufacturing process. At the application level, it significantly improves applicability in wearable and complex curved surface scenarios through flexible, compressible, and conformal surface design.

[0144] Finally, it should be noted that although the embodiments of this application have been described above, this application is not limited to the specific embodiments and application fields described above. The specific embodiments described above are merely illustrative and instructive, not restrictive. Those skilled in the art, guided by this specification, can make many other forms without departing from the scope of protection of the claims of this application, and all of these are within the scope of protection of this application.

Claims

1. A porous composite material based on an internal interface contact mechanism, characterized in that, include: A polymer elastomer matrix with multiple micropores, and Conductive fillers and nanofillers dispersed within a polymer elastomer matrix; Wherein, the volume fraction of the conductive filler is located within the percolation threshold neighborhood of the porous composite material; The electrical conductivity of the porous composite material changes in response to the reversible contact that occurs between the conductive fillers caused by the reversible deformation of the micropores when the porous composite material is under pressure.

2. The porous composite material based on the internal interface contact mechanism according to claim 1, characterized in that, The volume fraction of the conductive filler is 1% to 10%.

3. The porous composite material based on the internal interface contact mechanism according to claim 1, characterized in that, The conductive filler is one or more of nano-conductive indium tin oxide, carbon nanotubes, carbon black, and graphene; the polymer elastomer matrix is ​​a silicone rubber material, a polyurethane elastomer material, or a thermoplastic elastomer material; the nanofiller is one or more of nanoscale aluminum oxide, calcium carbonate, and fumed silica.

4. The porous composite material based on the internal interface contact mechanism according to claim 1, characterized in that, The polymer elastomer matrix is ​​selected from polydimethylsiloxane, the conductive filler is selected from carbon nanotubes, and the nanofiller is selected from fumed silica.

5. The porous composite material based on the internal interface contact mechanism according to claim 1, characterized in that, The micropores are formed by the volatilization and removal of components in the porous composite material precursor by a volatile removable pore-forming agent; the volatile removable pore-forming agent is one or more of citrate ester plasticizers and fatty acid esters.

6. The porous composite material based on an internal interface contact mechanism according to any one of claims 1 to 5, characterized in that, The micropores have a size of 1 to 50 micrometers.

7. A preparation method, characterized in that, A method for preparing porous composite materials based on an internal interface contact mechanism as described in any one of claims 1 to 6; comprising: Selected nanofillers, conductive fillers, volatile removable pore-forming agents, and polymeric elastic matrices are mixed to obtain a precursor of a porous composite material; wherein, the content of the nanofillers is used to regulate the rheological properties of the precursor and the pore structure of the micropores. The precursor is coated onto the provided substrate to form a film of the target thickness; The film is cured in stages under multiple increasing temperature conditions, which causes the pore-forming agent to volatilize and form micropores at corresponding positions to obtain the porous composite material.

8. The preparation method according to claim 7, characterized in that, The mass ratio of the polymer elastomer matrix, conductive filler, volatile removable pore-forming agent and nanofiller is 1:0.01~0.06:1~2:0.1~0.

10.

9. The preparation method according to claim 7, characterized in that, The step of curing the film in stages under multiple increasing temperature conditions specifically includes: first curing at 25~60℃ for 30~60 min; then curing at 80~100℃ for 30~90 min; and finally curing at 100~160℃ for 300~600 min.

10. A flexible pressure sensor based on an internal interface contact mechanism, characterized in that, include: Electrode layer; as well as A functional sensitive layer stacked with the electrode layer; The functionally sensitive layer is made of a porous composite material based on an internal interface contact mechanism as described in any one of claims 1 to 6.

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