Ultrasensitive and highly repeatable resistive flexible pressure sensor with multi-interface enhanced structure

Abstract

The present invention discloses an ultra-sensitive, highly repeatable resistive flexible pressure sensor with a multi-interface enhancement structure. The sensor has a stacked structure, which includes an upper encapsulation layer, a high-conductivity layer, a low-conductivity layer, and a lower encapsulation layer from top to bottom. The encapsulation layer introduces a tension-compression conversion structure, which enables the flexible strain sensor to maintain its original sensitivity under pressure. The high-conductivity layer is coated on the low-conductivity layer, and a thiol-disulfide exchange reaction occurs between the high-conductivity layer and the low-conductivity layer through the principle of click chemistry, forming an extremely strong dynamic covalent bond, thereby enhancing the interface contact between the high-conductivity layer and the low-conductivity layer. The upper encapsulation layer and the high-conductivity layer, and the lower encapsulation layer and the low-conductivity layer are enhanced by an adhesive to achieve interface adhesion. The flexible pressure sensor prepared by the present invention has the characteristics of high repeatability, high sensitivity, high stability, etc., and can be well applied to the fields of human wearables, robot skin, etc.

Description

Technical Field

[0001] The present invention belongs to the field of sensors, and in particular relates to an ultra-sensitive high-repeatability resistive flexible pressure sensor with a multi-interface enhanced structure. Background Art

[0002] With the development of technologies such as the Internet of Things, intelligent robotics, and health monitoring, flexible sensors are attracting increasing attention as core components in wearable electronics and robotic electronic skin. Traditional strain gauge electronic sensors, due to material limitations, mostly have rigid substrates, making their flexibility and sensitivity difficult to achieve. Flexible pressure sensors overcome the shortcomings of rigidity and brittleness while offering significant advantages in flexibility and stretchability. Flexible pressure sensors play a crucial role in electronic skin, soft robotics, health monitoring, and other fields.

[0003] Currently, many high-performance flexible pressure sensors have been developed. These utilize flexible substrates and novel nanomaterials (MXene, carbon nanotubes) to demonstrate high sensitivity, rapid response, and a wide detection range. However, current sensor technology still has shortcomings in terms of high sensitivity and durability, which limits its development.

[0004] Patent application CN115931187A uses conductive fabric to prepare the electrode layer and the sensitive layer, and uses an adhesive layer to bond the electrode layer and the sensitive layer and perform the overall packaging of the sensor to produce a highly sensitive thin film flexible pressure sensor. The sensor can be triggered at a pressure as low as 10Pa. It has a simple structure and can be applied to smart touch products with strong practicality.

[0005] Patent application CN105783697A employs a method of pre-introducing microcrack structures within the conductive layer, resulting in a sensor with higher sensitivity during use. The addition of an encapsulation layer outside the conductive coating protects the crack structure within the conductive layer, significantly extending the service life of the crack strain sensor and significantly enhancing its stability. This flexible strain sensor is low-cost, easy to process, and suitable for mass production.

[0006] The upper and lower surfaces of the sensitive structural layer of the flexible pressure sensor in patent application CN112834087A respectively have a first micro-nano structure with a smaller height and a second micro-nano structure with a larger height. When the external force is small, the first micro-nano structure with a smaller height takes effect, causing a change in the electrical signal, thereby achieving high sensitivity of the flexible sensor; when the external force increases to a certain level, the second micro-nano structure with a larger height plays a major role, causing a change in the electrical signal, thereby achieving a wide range of the flexible sensor.

[0007] The flexible strain sensor described in patent application CN110823085A uses cutting or direct printing to create regular cracks, effectively controlling parameters such as crack shape, location, spacing, width, depth, and number. The mechanically sensitive layer of the flexible strain sensor is formed by bonding a highly conductive material layer and a semi-conductive material layer with regular cracks. This layer is fabricated and bonded layer by layer in a planar multilayer structure. The sensor exhibits high consistency, repeatability, sensitivity, and stretchability, while also being simple to manufacture, low-cost, and amenable to large-scale production.

[0008] Patent application CN109655180A employs a method of inverting a film to create a crack array structure and an inverse crack array structure on a PDMS surface. Two flexible substrates, each bearing a regular crack array structure and an inverse crack array structure, are placed opposite each other. The method utilizes the change in contact area between the crack array structure and the inverse crack array structure on the flexible substrate surface under external pressure to alter the resistance characteristics, thereby improving sensitivity and reliability. The fabrication method is simple, requiring no complex processes such as photolithography, resulting in low production costs and the ability to fabricate over large areas.

[0009] Patent application CN113701926A has prepared a flexible piezoresistive pressure sensor that combines a wrinkle structure with a crack structure. It has three modes to choose from: the first is a pressure sensor with a wrinkle structure dominant mode, with a sensitivity of up to 9.6kPa -1 , which can be used to detect extremely small signals such as sound waves; the second type is a pressure sensor with a dominant mode of both wrinkle structure and crack structure, which has moderate sensitivity and pressure detection range, sufficient to meet the detection of complex physiological signals of the human body; the third type of pressure sensor with a dominant mode of crack structure, its pressure detection range can be extended to 13MPa, breaking through the pressure detection limit of current flexible piezoresistive pressure sensors.

[0010] Although the research on flexible resistive pressure sensors has made great progress, the following problems still exist:

[0011] 1. Most resistive flexible pressure sensors contain only a single functional layer, resulting in a limited detection range. Most are only suitable for operation under low pressure conditions. This is because the functional layer of a single-functional-layer resistive pressure sensor deforms only under low pressure, causing a significant change in the front-to-back resistance, making the flexible strain sensor very sensitive. Under high pressure, however, there is no significant deformation of the functional layer, the conductive network hardly changes, the resistance value does not change significantly, and the sensor sensitivity is relatively low. To address the low sensitivity issue, many researchers have introduced crack-like microstructures into sensors. Compared to sensors with a single functional layer, this surface microstructure can increase the sensitivity of the sensor by dozens or even hundreds of times. However, sensors with single-layer crack structures generally have a narrow operating range. How to better combine high sensitivity and a wide operating range remains a major challenge in the development of flexible sensors.

[0012] To increase the operating range of resistive flexible pressure sensors, many researchers often employ layered and gradient designs. During loading and unloading, the mismatched interface between the conductive layer and the polymer substrate experiences cyclic shear stress, leading to fatigue failure and localized peeling / crack growth in the conductive layer. Flexible resistive pressure sensors exhibit significant differences in mechanical modulus and elongation at break between the functional layer and the substrate, and between different functional layers. Under repeated loading and unloading, the sensor's conductive functional layer is susceptible to peeling, shedding, or displacement, resulting in poor sensor stability.

[0013] 3. For resistive flexible pressure sensors based on crack structures, since the high-conductivity layer generally uses carbon-based materials and exhibits high brittleness, after an effective crack is generated in the high-conductivity layer, the contact parts on both sides of the crack in the high-conductivity layer are prone to fall off after repeated loading-unloading processes. After the unloading process is completed, it is difficult for the two sides to contact completely when the crack returns to its initial state, which makes the electrical stability of the contact on both sides of the crack in the high-conductivity layer worse, and the conductive path becomes extremely unstable, which ultimately deteriorates the electrical performance of the sensor.

[0014] 4. Flexible strain sensors are mainly used to measure the deformation of objects, which makes them outstanding in monitoring structural health, biomechanical signals and other fields. However, when it comes to scenarios where a wide range of pressure changes needs to be measured, strain sensors may not be able to provide a wide enough measurement range. The efficient operation of strain sensors usually depends on close contact with the object being measured to ensure accurate capture of deformation information. This requirement poses a major challenge in application scenarios where the object being measured has a complex shape or irregular surface. During the continuous loading-unloading process of the flexible strain sensor, the mismatched interface between the conductive layer and the polymer substrate is subjected to cyclic shear stress, resulting in an increased probability of fatigue failure of the conductive layer and local peeling / crack growth, and the bonding between the interfaces needs to be considered more complicated.

[0015] 5. For resistive flexible pressure sensors based on crack structures, the generation, location, and number of cracks are closely related to the sensitivity, stability, and repeatability of the flexible resistive pressure sensor. Controlling the generation, location, and number of cracks is a challenge. Inappropriate cracks can lead to unstable sensor performance, unpredictable resistance changes, and reduced service life. Designing a microstructure based on the crack microstructure to induce crack generation and control the location and number of cracks is particularly important.

[0016] 6. The high-conductivity layer of the resistive flexible pressure sensor often uses a composite conductive material, generally including a high molecular polymer and a conductive filler. The surface energy mismatch between the high molecular polymer and the conductive filler in the conductive layer, the unstable interface bonding, and the uneven dispersion lead to poor repeatability, stability, and consistency of the mechanical and electrical properties of the conductive layer, ultimately leading to poor durability and repeatability of the sensor. After a crack occurs in the high-conductivity layer of a flexible resistive pressure sensor based on a crack structure, it is possible that the crack will continue to extend downward into the low-conductivity layer, causing tiny cracks in the low-conductivity layer, weakening the fatigue resistance of the low-conductivity layer and deteriorating the repeatability and stability of the sensor. Due to the insufficient mechanical properties of the elastomer in the low-conductivity layer, these elastomers are prone to cracks, scratches, and fractures during the long-term use of the sensor, resulting in a decrease in the sensitivity, stability, and life of the sensor. Summary of the Invention

[0017] In response to the shortcomings of the existing technology, the present invention provides an ultra-sensitive and highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure and a preparation method thereof, which effectively improves the problem that flexible pressure sensors have difficulty in achieving both high sensitivity and high repeatability, and can be widely used in the fields of wearable electronics and electronic skin.

[0018] The resistive flexible pressure sensor provided by the present invention prepares a MXene film with good mechanical and electrical properties by mechanically and electrically modifying MXene respectively. At the same time, the structure of the low conductive layer and the high conductive layer of the sensor is designed, and the polymer surface of SR is modified by mercaptosilanization using MPTMS. A thiol-disulfide bond exchange reaction occurs between the low conductive layer and the high conductive layer, resulting in strong interfacial adhesion between the polymer substrate and the conductive layer, and between the low conductive layer and the high conductive layer.

[0019] In order to solve the above problems, the present invention adopts the following solutions:

[0020] An ultra-sensitive, highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure is characterized in that: the flexible pressure sensor has a stacked structure, consisting of an upper packaging layer, a high conductive layer, a low conductive layer, and a lower packaging layer from top to bottom; on the side where the upper packaging layer contacts the high conductive layer, a plurality of inner groove structures are arranged at intervals along the length direction of the sensor; each inner groove structure is connected along the width direction of the sensor; the high conductive layer is provided with a regular crack at a position below the inner groove structure, and the crack direction is along the width direction of the sensor; the low conductive layer has a planar structure; on the side where the lower packaging layer contacts the low conductive layer, a plurality of protrusion structures corresponding one to one to the inner groove structures and matching in size are arranged along the length direction of the sensor; each gap between the low conductive layer and the lower packaging layer is filled with an elastic pad that is consistent with the height of the protrusion structure.

[0021] Furthermore, the highly conductive layer is prepared by mixing a room-temperature vulcanized silicone rubber (K560-SR) hydrophilically modified with KH-560, bovine serum albumin (BSA), PEDOT:PSS, and a MXene electrically modified with KH-570 (K570-MXene). Furthermore, the weight percentages of PEDOT:PSS, MXene electrically modified with KH-570, room-temperature vulcanized silicone rubber hydrophilically modified with KH-560, and BSA in the highly conductive layer are as follows: 35-40% PEDOT:PSS, 35-40% KH-570 electrically modified MXene, 5-10% KH-560 hydrophilically modified room-temperature vulcanized silicone rubber, and the balance BSA. KH-560 hydrophilically modifies the room-temperature vulcanized silicone rubber (SR) and introduces epoxy groups into the SR, which can participate in the ring-opening reaction of epoxy compounds. This functional group can react with the active hydrogen atoms in PEDOT to form covalent bonds, or interact with the sulfonic acid groups in PSS through hydrogen bonds, enhancing compatibility. Adding an appropriate amount of K560-SR to the hybrid conductive ink of the high-conductivity layer, the physical interaction between PEDOT:PSS and MXene facilitates the construction of a network structure, forming a cross-linked network between K570-MXene and K560-SR. This improves the brittleness and easy shedding of the high-conductivity layer while maintaining its high conductivity. Ultimately, this improves the electrical stability of the contact between the two sides of the crack in the high-conductivity layer, further enhancing the stability of the sensor.

[0022] Furthermore, the thickness of the highly conductive layer is 200 μm to 300 μm, the conductivity is not less than 3500 S / cm, and the elongation at break is not greater than 10%. The sensitivity of a resistive pressure sensor is defined as the ratio of the change in sensor resistance to the initial resistance under unit pressure intensity. Different conductivities of the highly conductive layer and the low conductive layer result in different sensing performance for the entire sensor. The higher the conductivity of the highly conductive layer, the lower the initial resistance of the sensor's conductive path. The lower the conductivity of the low conductive layer, the greater the resistance change that can occur after the sensor is stretched and cracked, thereby increasing the sensitivity of the sensor.

[0023] Furthermore, the low-conductivity layer is prepared by mixing MPTMS-modified room-temperature vulcanizing silicone rubber (SR-MPTMS), ethyl silicate, and polysilazane-mechanically modified MXene. Furthermore, the weight percentages of polysilazane-mechanically modified MXene (PSZ-MXene), MPTMS-modified room-temperature vulcanizing silicone rubber, and ethyl silicate are as follows: 25-30% polysilazane-mechanically modified MXene, 60-65% MPTMS-modified room-temperature vulcanizing silicone rubber, and the balance ethyl silicate. Furthermore, during the preparation of the PSZ-MXene / SR composite material for the low-conductivity layer, the MXene reacts with chloroacetic acid to increase the number of –COOH groups on its surface. Water molecules adsorbed on the MXene surface promote the hydrolysis of hydrolysis-sensitive polysilazane, generating hydroxyl groups, which in turn leads to a condensation reaction between the polysilazane and MXene. These reactions promote the uniform dispersion of the PSZ-MXene in the SR matrix. When external forces act on the composite material, they are transferred through the filler, evenly distributing stress and avoiding stress concentration. Interfacial adhesion between PSZ-MXene and SR ensures effective load transfer, promotes the dispersion of fracture energy, and improves elongation at break. Polysilazane is grafted onto MXene via a condensation reaction, weakening the interaction between MXene and SR. The chemical interaction between the polysilazane-modified MXene and SR ensures uniform dispersion of the MXene within the SR matrix.

[0024] Furthermore, the thickness of the low-conductivity layer is 300-500μm, the conductivity is not higher than 15S / cm, the elongation at break is not less than 50%, and the tensile strength is 3-4Mpa. Furthermore, the flexible resistive pressure sensor greatly improves the sensitivity of the sensor by introducing a dual strain layer and a crack-type microstructure. When pressure is applied to the sensor, channel cracks are generated on the surface of the high-conductivity layer, the resistance value increases, and the tensile strength of the low-conductivity layer is higher, allowing the low-conductivity layer to continue to stretch. When a through crack is generated on the surface of the high-conductivity layer, the current is transmitted through the low-conductivity layer, and the sensor resistance will not be saturated immediately, thereby maintaining the high sensitivity of the sensor while improving the working range of the sensor.

[0025] Furthermore, the high conductive layer is coated on the low conductive layer, and a thiol-disulfide exchange reaction occurs between the high conductive layer and the low conductive layer through the principle of click chemistry to form an extremely strong dynamic covalent bond, thereby enhancing the interface contact between the high conductive layer and the low conductive layer. A mixed conductive ink of BSA, PEDOT:PSS and K570-MXene is coated on the surface of SR-MPTMS and dried at a constant temperature, and a thiol-disulfide exchange reaction occurs, forming a dynamic covalent bond between the mixed conductive ink and the SR-MPTMS surface, which promotes strong interfacial adhesion between the low conductive layer and the high conductive layer from the chemical bonding level, achieving the effect of enhanced bonding strength. Specifically, MPTMS in the low conductive layer modifies SR by thiol silanization of the polymer surface. The thiol (-SH) group in MPTMS is partially exposed on the surface of the silicone rubber. When the BSA with disulfide bonds in the high conductive layer contacts the thiol-modified silicone rubber surface, the disulfide bonds on the BSA molecules can react with the thiol groups of MPTMS. The thiol group of MPTMS will attack a sulfur atom in the BSA molecule, resulting in the cleavage of the disulfide bond and the formation of a new disulfide bond connecting MPTMS and BSA.

[0026] Furthermore, the upper and lower encapsulation layers are made of room-temperature vulcanized silicone rubber (SR), with a Shore A hardness of 40-80A. Furthermore, the resistive pressure sensor's encapsulation layer incorporates a tension-compression conversion structure (a combination of an internal groove and a protrusion), enabling the flexible strain sensor to maintain its original sensitivity under pressure. This structure also protects the sensor's internal high-conductivity and low-conductivity layers, making them less susceptible to damage from contact, friction, and other factors during use, thereby improving the sensor's reliability and environmental adaptability.

[0027] Furthermore, the cross-section of the inner groove structure of the upper packaging layer is a rectangular structure with chamfered corners, with a groove depth of 500-800μm and a width of 800-1000μm. The spacing between adjacent inner groove structures is 1000-1200μm. The raised structure of the lower packaging layer is arranged along the length of the sensor, corresponding one-to-one with the inner groove structure and matching its size. Furthermore, by adjusting the characteristic parameters of the inner groove structure of the upper packaging layer and the raised structure of the lower packaging layer, the pressure operating range of the sensor can be adjusted to varying degrees, achieving an organic combination of high sensitivity and a wide pressure operating range of the pressure sensor.

[0028] Furthermore, the elastic pad is made of porous silicone rubber with a porosity of 25-50%, a Shore hardness of 20-40A, and a tensile strength of 1-2MPa. The porous silicone rubber is prepared by mixing SR, azodicarbonamide, ZnO powder and polyphenylmethylsiloxane (PPMS). The mass percentages of SR, azodicarbonamide, ZnO powder and PPMS are: SR 45-55%, azodicarbonamide 5-10%, ZnO powder 1-2%, and the balance is PPMS. Furthermore, the elastic pad provides mechanical support for the upper low-conductivity layer, high-conductivity layer and upper packaging layer, and under the action of pressure, enables the upper packaging layer to continue to act downward, so that the high-conductivity layer and the low-conductivity layer can generate a lateral tensile force, thereby causing the high-conductivity layer to crack, so that the flexible strain sensor can maintain its original sensitivity under pressure.

[0029] The method for preparing the resistive flexible pressure sensor of the present invention comprises the following steps:

[0030] Step 1: Prepare a low conductive layer

[0031] MXene powder, chloroacetic acid, polysilazane and THF are placed in a beaker and magnetically stirred at room temperature to obtain MXene mechanically modified with polysilazane (PSZ-MXene); wherein the mass percentages of MXene powder, polysilazane and chloroacetic acid are: 55-60% MXene powder, 20-25% polysilazane, and the balance chloroacetic acid.

[0032] The room temperature vulcanized silicone rubber was repeatedly washed and dried with ethanol and distilled water. The cleaned substrate was treated with a plasma cleaner. The treated substrate was treated with a plasma cleaner at a concentration of 15 to 25 mg mL -1 The substrate is immersed in the silane coupling agent MPTMS for 2-3 hours, removed, washed with ethanol, and dried to obtain a room temperature vulcanized silicone rubber modified with MPTMS, wherein the mass percentage of the room temperature vulcanized silicone rubber and MPTMS is 95%-97%:5%-3%.

[0033] MXene mechanically modified by polysilazane and room temperature vulcanized silicone rubber modified by MPTMS are dissolved in THF, and then ethyl silicate as a curing agent is added and mixed evenly. The mixture is poured into a mold and cured at room temperature to form a low conductive layer. The mass percentages of MXene mechanically modified by polysilazane, room temperature vulcanized silicone rubber modified by MPTMS, and tetraethyl silicate are as follows: 25-30% of MXene mechanically modified by polysilazane, 60-65% of room temperature vulcanized silicone rubber modified by MPTMS, and the balance of ethyl silicate.

[0034] Step 2: Prepare a highly conductive layer

[0035] MXene is dispersed in deionized water, and then KH-570 is added dropwise. The mixture is allowed to stand at room temperature for 20-24 hours. The product is collected by centrifugation, washed multiple times with deionized water, and dried to obtain MXene electrically modified with KH-570; wherein the mass percentage of MXene and KH-570 is 95-97%:5%-3%.

[0036] Wash the room temperature vulcanized silicone rubber repeatedly in ethanol and distilled water to remove surface contaminants and grease. Air dry the silicone rubber surface. Treat the silicone rubber surface with a plasma cleaner to improve surface activity and cleanliness. Dissolve KH-560 in ethanol to a concentration of 15-25 mg mL. -1 The plasma-treated silicone rubber is immersed in the KH-560 solution for 2-3 hours. The silicone rubber is removed, the surface is washed with ethanol to remove excess KH-560 molecules, and then dried to obtain a room-temperature vulcanized silicone rubber hydrophilically modified with KH-560. The mass ratio of room-temperature vulcanized silicone rubber to KH-560 is 95-97%:5%-3%.

[0037] Room temperature vulcanized silicone rubber hydrophilically modified with KH-560, a PEDOT:PSS aqueous solution, and a MXene electrically modified with KH-570 are added to deionized water and stirred evenly, and bovine serum albumin is added and stirred evenly to obtain a highly conductive layer ink; wherein the mass percentages of PEDOT:PSS, MXene electrically modified with KH-570, room temperature vulcanized silicone rubber hydrophilically modified with KH-560, and bovine serum albumin are: PEDOT:PSS 35-40%, MXene electrically modified with KH-570 35-40%, room temperature vulcanized silicone rubber hydrophilically modified with KH-560 5-10%, and the balance is bovine serum albumin.

[0038] The high-conductivity layer ink is coated on one side of the low-conductivity layer and cured at room temperature to form a high-conductivity layer; an electrode is drawn out from both sides of the high-conductivity layer.

[0039] Step 3: Sensor assembly

[0040] The monomer and curing agent of the silicone rubber are mixed and molded into an upper packaging layer with an inner groove structure on the lower surface and a lower packaging layer with a convex structure on the upper surface respectively;

[0041] SR, azodicarbonamide, ZnO powder, and polyphenylmethylsiloxane (PPMS) were added to a beaker and stirred at room temperature on a magnetic stirrer to form a porous silicone rubber slurry. Azodicarbonamide served as a blowing agent, ZnO powder as a blowing catalyst, and PPMS as a solvent to adjust the viscosity of the prepared material. The weight percentages of SR, azodicarbonamide, ZnO powder, and PPMS were as follows: SR 45-55%, azodicarbonamide 5-10%, ZnO powder 1-2%, and the balance PPMS.

[0042] A porous silicone rubber slurry is poured onto the upper surface of the lower encapsulation layer, where the raised structure is not located. The slurry is then heated in a vacuum oven at 100-110°C for 2-3 hours to remove air bubbles. The foaming agent decomposes to generate gas, while the SR gradually solidifies, forming diffuse pores within the material. The porous composite material is then immersed in anhydrous ethanol and ultrasonically cleaned to remove any residual PPMS from the surface, forming elastic cushioning strips.

[0043] Fix the upper packaging layer above the high conductive layer with an adhesive, with the inner groove structure facing the high conductive layer; fix the lower packaging layer below the low conductive layer with an adhesive, with the protruding structure and the elastic pad facing the low conductive layer;

[0044] The assembled pressure sensor is placed in a tensile press and uniformly pressed (from top to bottom). Repeated loading and unloading cycles create cracks along the sensor's width, where the highly conductive layer lies below the groove structure within the upper packaging layer. This results in a resistive flexible pressure sensor.

[0045] Compared with the prior art, the beneficial effects of the present invention are embodied in:

[0046] 1. The resistive flexible pressure sensor proposed in this invention significantly improves its sensitivity by introducing a dual-strain layer and a cracked microstructure. When pressure is applied to the sensor, channel cracks form on the surface of the highly conductive layer, increasing its resistance. When through-cracks form on the surface of the highly conductive layer, current is transmitted through the less conductive layer, preventing the sensor's resistance from saturating immediately. This improves the sensor's operating range while maintaining high sensitivity.

[0047] 2. The resistive flexible pressure sensor proposed in this invention utilizes (3-mercaptopropyl)trimethoxysilane (MPTMS) to modify the polymer surface with mercaptosilane. A hybrid conductive ink composed of BSA, PEDOT:PSS, and K570-MXene is applied to the SR-MPTMS surface and dried at a constant temperature. This generates a thiol-disulfide exchange reaction, forming dynamic covalent bonds between the hybrid conductive ink and the SR-MPTMS surface. This chemically enhances interfacial adhesion between the low- and high-conductivity layers, ultimately enhancing bonding strength.

[0048] 3. The resistive flexible pressure sensor proposed in the present invention uses KH-560 to modify the hydrophilicity of SR and introduce epoxy groups into SR, which can participate in the ring-opening reaction of epoxy compounds. This functional group can react with the active hydrogen atoms in PEDOT to form covalent bonds, or interact with the sulfonic acid groups in PSS through hydrogen bonds to enhance compatibility. When an appropriate amount of K560-SR is added to the mixed conductive ink of the high conductive layer, the physical interaction between PEDOT:PSS and MXene contributes to the construction of the network structure, thereby forming a cross-linked network between K570-MXene and K560-SR. This improves the brittleness and easy falling off problem of the high conductive layer while maintaining the high conductivity of the high conductive layer, and ultimately improves the electrical stability of the contact on both sides of the crack in the high conductive layer, further improving the stability of the sensor.

[0049] 4. The resistive flexible pressure sensor proposed in the present invention introduces a tension-compression conversion structure into the packaging layer of the flexible strain sensor with a double-strain layer crack structure, so that the flexible strain sensor can maintain its original sensitivity under pressure action scenarios. At the same time, by adjusting the characteristic parameters of the inner groove structure of the upper packaging layer and the protrusion structure of the lower packaging layer, the pressure operating range of the sensor can be adjusted to different degrees, thereby realizing the organic unity of the high sensitivity and wide pressure operating range of the pressure sensor.

[0050] 5. The resistive flexible pressure sensor proposed in the present invention introduces a tension-compression conversion structure in the packaging layer. The upper packaging layer is fixed above the high-conductivity layer by an adhesive, and the inner groove structure faces the high-conductivity layer; the lower packaging layer is fixed below the low-conductivity layer by an adhesive, and the protrusion structure and the elastic pad face the low-conductivity layer; the upper packaging layer and the high-conductivity layer, as well as the lower packaging layer and the low-conductivity layer are tightly connected by adhesive. Since the inner groove structure of the upper packaging layer and the protrusion structure of the lower packaging layer are arranged in parallel, this structure enables the sensor to produce periodic stress concentration distribution under the repeated action of pressure, avoiding random cracks in the sensor, thereby obtaining high consistency of the sensor during the manufacturing process and high stability during use.

[0051] 6. In the resistive flexible pressure sensor proposed in the present invention, the negatively charged MXene nanosheets in the highly conductive layer typically aggregate and precipitate during the film formation process. KH570 was selected to functionalize the surface of the MXene nanosheets. The K570-MXene / PEDOT:PSS conductive ink maintains excellent stability, and the positively charged PEDOT molecules can electrostatically interact with the negatively charged surface of K570-MXene. The strong π-π interaction between PEDOT and K570-MXene effectively solves the problem of MXene nanosheet aggregation and precipitation. KH570 transforms the PEDOT chain from a benzene structure to a quinone structure, further improving the conductivity of the highly conductive layer. This further enhances the sensitivity of the sensor.

[0052] 7. In the resistive flexible pressure sensor proposed in the present invention, during the preparation of the PSZ-MXene / SR composite material for the low-conductivity layer, MXene reacts with chloroacetic acid to increase the number of –COOH groups on its surface. Water molecules adsorbed on the MXene surface promote the hydrolysis of hydrolysis-sensitive polysilazane, generating hydroxyl groups, which in turn cause a condensation reaction between the polysilazane and MXene. These reactions promote the uniform dispersion of PSZ-MXene in the SR matrix. When an external force acts on the composite material, the force can be transmitted through the filler, resulting in uniform stress distribution and avoiding stress concentration. The interfacial adhesion between PSZ-MXene and SR ensures effective load transfer, promotes the dispersion of fracture energy, and increases elongation at break, thereby improving the mechanical properties of the low-conductivity layer of the resistive flexible pressure sensor. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Figure 1 This is a schematic diagram of the appearance structure of the ultra-sensitive and highly repeatable resistive flexible pressure sensor with a multi-interface enhancement structure of the present invention.

[0054] Figure 2 This is a schematic diagram of the disassembled structure of the ultra-sensitive and highly repeatable resistive flexible pressure sensor with a multi-interface enhancement structure of the present invention.

[0055] Figure 3 This is a schematic diagram of the cross-sectional structure of the ultra-sensitive and highly repeatable resistive flexible pressure sensor with a multi-interface enhancement structure of the present invention.

[0056] Figure 1-3 The numbers in the figure are: 1 is the upper packaging layer, 1a is the inner groove structure, 2 is the high conductive layer, 3 is the low conductive layer, 4 is the lower packaging layer, 4a is the protruding structure, and 5 is the elastic pad.

[0057] Figure 4 Schematic diagram of the click chemistry principle at the interface between the low conductive layer and the high conductive layer in the present invention.

[0058] Figure 5 Schematic diagram of the principle of mechanical modification of MXene by polysilazane in the present invention.

[0059] Figure 6 Schematic diagram of the principle of electrically modifying MXene by KH570 and PEDOT:PSS in the present invention.

[0060] Figure 7 Schematic diagram of the sensing mechanism and local conductive path of the flexible pressure sensor of the present invention.

[0061] Figure 8 This is the pressure sensing characteristic curve of the flexible resistive pressure sensor of the present invention.

[0062] Figure 9 This is the frequency response characteristic curve of the flexible resistive pressure sensor of the present invention.

[0063] Figure 10 This is the step pressure characteristic curve of the flexible resistive pressure sensor of the present invention.

[0064] Figure 11 This is the electrical stability curve of the flexible resistive pressure sensor of the present invention. DETAILED DESCRIPTION

[0065] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following embodiments are implemented based on the technical solutions of the present invention, and provide detailed implementation methods and specific operating procedures. However, the protection scope of the present invention is not limited to the following embodiments.

[0066] Example 1

[0067] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. The following embodiments are implemented based on the technical solutions of the present invention, and provide detailed implementation methods and specific operating procedures. However, the protection scope of the present invention is not limited to the following embodiments.

[0068] like Figures 1 to 3The following are schematic diagrams of the external structure, disassembled structure, and cross-sectional structure of the resistive flexible pressure sensor provided in this embodiment. The flexible resistive pressure sensor provided in this embodiment comprises an upper packaging layer 1, a high-conductivity layer 2, a low-conductivity layer 3, a lower packaging layer 4, and an elastic pad 5. On the side of the upper packaging layer contacting the high-conductivity layer, a plurality of inner groove structures 1a are spaced apart along the length of the sensor; each inner groove structure extends across the width of the sensor; the high-conductivity layer has regular cracks formed below the inner groove structures, with the crack direction running along the width of the sensor; the low-conductivity layer is planar; on the side of the lower packaging layer contacting the low-conductivity layer, a plurality of protrusions 4a are provided along the length of the sensor, corresponding one-to-one to the inner groove structures and matching in size; and each gap between the low-conductivity layer and the lower packaging layer is filled with an elastic pad with the same height as the protrusion structure.

[0069] Specifically, the highly conductive layer is made from a mixture of room-temperature vulcanized silicone rubber hydrophilically modified with KH-560, bovine serum albumin, PEDOT:PSS, and MXene electrically modified with KH-570. The less conductive layer is made from a mixture of room-temperature vulcanized silicone rubber modified with MPTMS, ethyl silicate, and MXene mechanically modified with polysilazane. The highly conductive layer is coated on top of the less conductive layer, and click chemistry creates a thiol-disulfide exchange reaction between the two layers, forming a strong dynamic covalent bond and enhancing the interfacial contact between them.

[0070] The resistive flexible pressure sensor of this embodiment is manufactured according to the following steps:

[0071] Step 1: Prepare a low conductive layer

[0072] 1.2 g of MXene powder, 0.4 g of chloroacetic acid, 0.4 g of polysilazane and 10 mL of THF were placed in a beaker, stirred on a magnetic stirrer at room temperature for 3 hours, and dried at room temperature for 2 hours to obtain MXene mechanically modified with polysilazane (PSZ-MXene).

[0073] Take 4.8g of room temperature vulcanized silicone rubber and wash and dry it 5 times with ethanol and distilled water alternately. The cleaned substrate is treated with a plasma cleaner for 10 minutes. The treated substrate is then added to 10mL of 20mg mL -1 The substrate was immersed in the silane coupling agent MPTMS for 2 hours, and the substrate was taken out, washed with ethanol, and dried to obtain the room temperature vulcanized silicone rubber modified by MPTMS.

[0074] 1.5g of polysilazane-modified MXene, 3g of MPTMS-modified room-temperature vulcanized silicone rubber, and 20mL of THF were placed in a beaker and magnetically stirred at room temperature for 1 hour. Then, 0.5g of ethyl silicate curing agent was added and stirred for another 3 hours. The mixture was poured into a mold and cured at room temperature to form a low-conductivity layer. The low-conductivity layer had a thickness of 300μm, a conductivity of 10S / cm, an elongation at break of 61.3%, and a tensile strength of 3.4MPa.

[0075] Step 2: Prepare a highly conductive layer

[0076] 0.95 g of MXene powder was dispersed in 20 mL of deionized water, and then 1 mL of 50 mg mL -1 The KH-570 was placed at room temperature for 24 hours, and the product was collected by centrifugation, washed with deionized water and dried 5 times to obtain MXene electrically modified with KH-570.

[0077] Take 3.8g of room temperature vulcanized silicone rubber and wash it alternately in ethanol and distilled water five times to remove surface contaminants and grease. Air dry the silicone rubber surface at room temperature for 3 hours. Use a plasma cleaner to treat the silicone rubber surface for 20 minutes to improve surface activity and cleanliness. Dissolve 0.2g of KH-560 in 10mL of ethanol to a concentration of 20mg·mL -1 The plasma-treated silicone rubber was immersed in the KH-560 solution for 2 hours. The silicone rubber was removed, the surface was washed with ethanol, and dried to obtain a room temperature vulcanized silicone rubber hydrophilically modified with KH-560.

[0078] Take 0.2g of room temperature vulcanized silicone rubber hydrophilically modified by KH-560, PEDOT:PSS aqueous solution (containing 0.8g PEDOT:PSS), and 0.8g of MXene electrically modified by KH-570, add them to 20mL of deionized water and stir at 60°C for 2 hours. Add 0.2g of bovine serum albumin and continue stirring for 2 hours to obtain a highly conductive layer ink.

[0079] A highly conductive layer ink was applied to one side of the low-conductive layer and cured at room temperature for 5 hours to form a highly conductive layer. An electrode was drawn from each side of the highly conductive layer. The highly conductive layer had a thickness of 200 μm, a conductivity of 3600 S / cm, and an elongation at break of 5.2%.

[0080] Step 3: Sensor assembly

[0081] 5g of SR and 0.5g of curing agent were mixed and stirred at room temperature for 1 hour. The resulting layers were then molded to form an upper encapsulation layer with an inner groove structure on the lower surface and a lower encapsulation layer with a raised structure on the upper surface. The inner groove structure had a chamfered rectangular cross-section, with a groove depth of 600μm and a width of 800μm. The spacing between adjacent inner groove structures was 1000μm.

[0082] 4 g of SR, 0.48 g of azodicarbonamide, 0.12 g of ZnO powder, and 3.4 g of PPMS were added to a beaker and stirred on a magnetic stirrer at room temperature for 30 minutes to obtain a porous silicone rubber slurry.

[0083] A porous silicone rubber slurry was poured onto the upper surface of the lower encapsulation layer in areas where the raised structures were not present. The slurry was heated in a vacuum oven at 110°C for 2 hours to remove air bubbles. The slurry was then immersed in anhydrous ethanol and ultrasonically cleaned for 10 minutes to form an elastic gasket. The gasket had a porosity of 40%, a hardness of 30 Shore A, and a tensile strength of 1.5 MPa.

[0084] Fix the upper packaging layer above the high conductive layer with an adhesive, with the inner groove structure facing the high conductive layer; fix the lower packaging layer below the low conductive layer with an adhesive, with the protruding structure and the elastic pad facing the low conductive layer;

[0085] The assembled pressure sensor was subjected to a uniform force of 5N under a tensile press. After 30 cycles of loading and unloading, a crack formed along the width of the sensor at a location in the highly conductive layer below the groove structure within the upper packaging layer. This resulted in a resistive flexible pressure sensor.

[0086] Figure 4 This is a schematic diagram of the click chemistry principle at the interface between the low-conductivity layer and the high-conductivity layer in this example. The disulfide bonds on the BSA in the conductive ink can react with the sulfhydryl groups on the substrate through an exchange reaction, forming new disulfide bonds between the conductive layer and the substrate, ensuring strong interfacial adhesion.

[0087] Figure 5 Figure 1 is a schematic diagram of the principle behind the mechanical modification of MXene with polysilazane in this example. MXene reacts with chloroacetic acid to increase the number of –COOH groups on its surface. Water molecules adsorbed on the MXene surface promote the hydrolysis of hydrolysis-sensitive polysilazane, generating hydroxyl groups, which in turn induce a condensation reaction between the polysilazane and MXene. These reactions promote the uniform dispersion of PSZ-MXene in the SR matrix. The interfacial adhesion between PSZ-MXene and SR ensures efficient load transfer, promotes the dispersion of fracture energy, and increases elongation at break, thereby enhancing the mechanical properties of the sensor's low-conductivity layer.

[0088] Figure 6The schematic diagram shows the principle of electrically modifying MXene with KH570 and PEDOT:PSS in this example. KH570 functionalizes the surface of the MXene nanosheets. The K570-MXene / PEDOT:PSS conductive ink maintains excellent stability, with the positively charged PEDOT molecules electrostatically interacting with the negatively charged surface of the K570-MXene. The strong π-π interaction between PEDOT and K570-MXene effectively addresses the aggregation and precipitation of MXene nanosheets. KH570 transforms the PEDOT chains from a benzene structure to a quinone structure, lowering the energy barrier for carrier transport and further improving the conductivity of the high-conductivity layer.

[0089] Figure 7 The sensing mechanism and local conductive path schematic diagram of the resistive flexible pressure sensor provided in this embodiment. Due to the difference in elongation at break between the high conductive layer and the low conductive layer and the restriction of the encapsulation layer on the stretching of the high conductive layer area, cracks will be generated in the high conductive layer. The transmission path of electrons at the crack is from the high conductive layer to the low conductive layer, bypassing the crack and then returning to the high conductive layer, and so on. This is equivalent to connecting several low-resistance high conductive layers and high-resistance low conductive layers in series. Therefore, when the sensor is subjected to pressure, the sensor resistance increases rapidly, the sensor sensitivity is high, and when a through crack is generated in the high conductive layer, the electron transmission channel is not disconnected, and the sensor can still respond to resistance changes under greater pressure. Therefore, the sensor maintains high sensitivity while having a larger sensing range. In the figure, R is the equivalent resistance of the high conductive layer, R1 and R2 are the equivalent resistances after the high conductive layer is cracked, and R' is the equivalent resistance of the conductive path through the low conductive layer.

[0090] Figure 8 The pressure sensing characteristic curve of the resistive flexible pressure sensor provided in this embodiment. In the pressure working range of 0-20kPa, the sensor sensitivity is about 52.3kPa -1 .

[0091] Figure 9 The frequency response characteristic curves of the resistive flexible pressure sensor provided in this embodiment are shown. The resistance change characteristic curves from a cyclic loading experiment under 20 kPa pressure at loading frequencies of 1 Hz, 5 Hz, and 10 Hz show that the sensor output resistance does not shift significantly, indicating that the sensor can operate at different frequencies of 1 Hz, 5 Hz, and 10 Hz. The sensor maintains high stability at different frequencies.

[0092] Figure 10 The step pressure characteristic curve of the resistive flexible pressure sensor provided in this embodiment is shown in FIG. The flexible resistive pressure sensor prepared in this embodiment was subjected to a step test, and the results showed that it can work stably under pressures of 0-40 kPa.

[0093] Figure 11 This is the electrical stability curve of the resistive flexible pressure sensor provided in this example. The flexible resistive pressure sensor prepared in this example was subjected to 6000 cycles of loading / unloading (with a pressure range of 0-20 kPa) to test its electrical stability and repeatability. The sensor exhibited stable electrical characteristics after 6000 cycles, demonstrating good consistency.

[0094] The above-described embodiments merely illustrate several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person skilled in the art would be able to make numerous modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. An ultra-sensitive, highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure, characterized by: The flexible pressure sensor has a stacked structure, which comprises, from top to bottom, an upper packaging layer, a high conductive layer, a low conductive layer, and a lower packaging layer; On the side of the upper packaging layer contacting the high conductive layer, a plurality of inner groove structures are arranged at intervals along the length direction of the sensor; each inner groove structure is continuous along the width direction of the sensor; A regular crack is formed on the highly conductive layer below the inner groove structure, and the crack direction is along the width direction of the sensor; The low conductive layer has a planar structure; A plurality of protrusion structures corresponding to the inner groove structures and having matching sizes are provided along the length direction of the sensor on the side of the lower packaging layer contacting the low conductive layer; Each gap between the low-conductivity layer and the lower packaging layer is filled with an elastic pad having the same height as the protruding structure.

2. The ultra-sensitive, highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure according to claim 1, characterized in that: The highly conductive layer is prepared by mixing room temperature vulcanized silicone rubber hydrophilically modified with KH-560, bovine serum albumin, PEDOT:PSS and MXene electrically modified with KH-570.

3. The ultra-sensitive, highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure according to claim 1 or 2, characterized in that: The thickness of the highly conductive layer is 200-300 μm, the conductivity is not less than 3500 S / cm, and the elongation at break is not higher than 10%.

4. The ultra-sensitive, highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure according to claim 1, characterized in that: The low-conductivity layer is prepared by mixing room-temperature vulcanized silicone rubber modified by MPTMS, ethyl silicate, and MXene mechanically modified by polysilazane.

5. The ultra-sensitive and highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure according to claim 4, characterized in that: The low-conductive layer has a thickness of 300-500 μm, a conductivity of no more than 15 S / cm, an elongation at break of no less than 50%, and a tensile strength of 3-4 MPa.

6. The ultra-sensitive, highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure according to claim 2 or 4, characterized in that: The high conductive layer is coated on the low conductive layer, and a thiol-disulfide bond exchange reaction occurs between the high conductive layer and the low conductive layer through the principle of click chemistry to form an extremely strong dynamic covalent bond, thereby enhancing the interface contact between the high conductive layer and the low conductive layer.

7. The ultra-sensitive, highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure according to claim 1, characterized in that: The upper packaging layer and the lower packaging layer are made of room temperature vulcanized silicone rubber, and the hardness of the packaging layer is Shore hardness 40-80A.

8. The ultra-sensitive and highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure according to claim 1, characterized in that: The cross section of the inner groove structure is a rectangular structure with chamfers, the groove depth is 500-800 μm, the width is 800-1000 μm, and the spacing between adjacent inner groove structures is 1000-1200 μm.

9. The ultra-sensitive and highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure according to claim 1, characterized in that: The elastic pad is made of porous silicone rubber with a porosity of 25-50%, a hardness of 20-40A Shore A hardness, and a tensile strength of 1-2 MPa.

10. A method for preparing an ultra-sensitive and highly repeatable resistive flexible pressure sensor with a multi-interface enhanced structure according to any one of claims 1 to 9, characterized in that: The steps include: Step 1: Prepare a low conductive layer MXene powder, chloroacetic acid, polysilazane, and THF are placed in a beaker and magnetically stirred at room temperature to obtain a MXene mechanically modified with polysilazane; wherein the mass percentages of MXene powder, polysilazane, and chloroacetic acid are: 55-60% MXene powder, 20-25% polysilazane, and the balance chloroacetic acid; After cleaning the room temperature vulcanized silicone rubber, -1 The obtained product is immersed in the silane coupling agent MPTMS for 2-3 hours, taken out, washed with ethanol, and dried to obtain a room temperature vulcanized silicone rubber modified with MPTMS, wherein the mass ratio of the room temperature vulcanized silicone rubber to MPTMS is 95%-97%:5%-3%; Dissolving polysilazane-mechanically modified MXene and MPTMS-modified room-temperature vulcanized silicone rubber in THF, then adding ethyl silicate as a curing agent and mixing thoroughly, pouring the mixture into a mold and curing it at room temperature to form a low-conductivity layer. The weight percentages of polysilazane-mechanically modified MXene, MPTMS-modified room-temperature vulcanized silicone rubber, and ethyl silicate are as follows: 25-30% polysilazane-mechanically modified MXene, 60-65% MPTMS-modified room-temperature vulcanized silicone rubber, and the balance ethyl silicate. Step 2: Prepare a highly conductive layer Disperse MXene in deionized water, then add KH-570 dropwise, and allow to stand at room temperature for 20-24 hours. Collect the product by centrifugation, wash it with deionized water multiple times, and dry it to obtain MXene electrically modified with KH-570; wherein the mass percentage of MXene and KH-570 is 95-97%:5%-3%; Dissolve KH-560 in ethanol to a concentration of 15-25 mg mL -1 The cleaned room temperature vulcanized silicone rubber was immersed in a KH-560 solution for 2-3 hours; taken out and washed with ethanol and dried to obtain a room temperature vulcanized silicone rubber hydrophilically modified with KH-560, wherein the mass percentage of the room temperature vulcanized silicone rubber and KH-560 was 95-97%: 5%-3%; Adding a room temperature vulcanized silicone rubber hydrophilically modified with KH-560, a PEDOT:PSS aqueous solution, and a MXene electrically modified with KH-570 to deionized water and stirring uniformly, adding bovine serum albumin and stirring uniformly to obtain a highly conductive layer ink; wherein the mass percentages of PEDOT:PSS, MXene electrically modified with KH-570, room temperature vulcanized silicone rubber hydrophilically modified with KH-560, and bovine serum albumin are as follows: 35-40% PEDOT:PSS, 35-40% MXene electrically modified with KH-570, 5-10% room temperature vulcanized silicone rubber hydrophilically modified with KH-560, and the balance being bovine serum albumin; The high conductive layer ink is coated on one side of the low conductive layer and cured at room temperature to form a high conductive layer; an electrode is drawn out on both sides of the high conductive layer; Step 3: Sensor assembly The monomer and curing agent of the silicone rubber are mixed and molded into an upper packaging layer with an inner groove structure on the lower surface and a lower packaging layer with a convex structure on the upper surface respectively; Room temperature vulcanized silicone rubber, azodicarbonamide, ZnO powder and polyphenylmethylsiloxane are mixed and stirred uniformly to obtain a porous silicone rubber slurry; wherein the mass percentages of room temperature vulcanized silicone rubber, azodicarbonamide, ZnO powder and polyphenylmethylsiloxane are: room temperature vulcanized silicone rubber 45-55%, azodicarbonamide 5-10%, ZnO powder 1-2%, and the balance polyphenylmethylsiloxane. Pouring a porous silicone rubber slurry on the upper surface of the lower packaging layer where no protruding structure is provided, heating the slurry at 100-110° C. in a vacuum oven for 2-3 hours to remove bubbles, and ultrasonically cleaning the slurry in anhydrous ethanol to form an elastic gasket strip; Fixing the upper packaging layer on the high conductive layer by adhesive, with the inner groove structure facing the high conductive layer; Fixing the lower packaging layer below the low-conductivity layer by adhesive, with the protruding structure and the elastic pad facing the low-conductivity layer; The assembled pressure sensor is uniformly pressurized under a tensile press. During repeated loading and unloading, a crack is formed along the width of the sensor at the position where the highly conductive layer is located below the groove structure in the upper packaging layer, thus forming a resistive flexible pressure sensor.

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