Ultrasensitive and fatigue-resistant flexible pressure sensor array based on Poisson's ratio anisotropic regulation

Abstract

The present invention belongs to the field of sensor technology, and discloses an ultra-sensitive and fatigue-resistant flexible pressure sensor array based on Poisson's ratio anisotropic regulation, including upper and lower sensor array units, each sensor array unit including a base layer, a low-conductivity layer, a high-conductivity layer and an adhesive layer stacked in sequence vertically, the side of the base layer opposite to the low-conductivity layer is designed to be meshed with a rack shape, and the high-conductivity layer is designed to include a plurality of long high-conductivity strips, and the stress is concentrated by mismatching the elastic modulus of the base layer and the low-conductivity layer, so that the high-conductivity strips preferentially generate cracks at the stress concentration point, i.e., at the position corresponding to the plurality of tooth tops of the tooth surface of the base layer, so that the array can be highly integrated. The flexible pressure sensor array provided by the present invention has high sensitivity, a wide working range, a high fatigue threshold and good stability.

Description

Technical Field

[0001] The invention belongs to the technical field of sensors, and specifically relates to an ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation. Background Art

[0002] Flexible resistive sensors have a wide range of applications as core potential components of wearable electronic devices due to their simple structure, low cost, high linearity, and excellent sensing performance. Flexible resistive sensors based on crack structures have attracted much attention due to their simple preparation, high sensitivity, and fast response. However, the narrow sensing range, insensitivity to pressure and strain, and deformation and fracture of the substrate due to fatigue lead to changes in the crack structure and failure, which greatly limits the practical application and service life of such sensors.

[0003] In recent years, people have done a lot of research on ultra-sensitive and fatigue-resistant flexible resistive sensors:

[0004] The academic paper "A stretchable strain sensor based on a metal nanoparticle thin film for human motion detection (J. Lee, S. Kim, J. Lee, D. Yang, BC Park, S. Ryu, I. Park, A stretchable strain sensor based on a metal nanoparticle thin film for human motion detection Nanoscale 2014, 6, 11932.) proposed a new type of stretchable strain sensor. By building a stress-sensitive unit with a bridge structure between two PDMS substrates to expand the crack expansion under pressure, the sensor has high sensitivity not only to tensile but also to compressive strain. However, this structure requires a tough interface bonding and is prone to breakage in practical applications.

[0005] The academic paper "Channel Crack-Designed Gold@PU Sponge for Highly ElasticPiezoresistive Sensor with Excellent Detectability" (Yun.hui Wu, Hai-zhou Liu, Song Chen, Xu-chu Dong, Ping-ping Wang, Shu-qi Liu, Yong Lin, Yong Wei, and Lan Liu. Channel Crack-Designed Gold@PU Sponge for Highly ElasticPiezoresistive Sensor with Excellent Detectability ACS Applied Materials&Interfaces20179(23), 20098-20105) proposed the successful preparation of an elastic three-dimensional conductive network using gold ion sputtering, and cleverly designed channel cracks on the three-dimensional sponge skeleton to achieve a dual enhancement of sensor sensitivity and response range, meeting the needs of monitoring the full range of human motion. However, due to the large structural differences between different sponge skeletons, the sensor consistency is poor.

[0006] The academic paper "An Anti-Fatigue Design Strategy for 3D Ribbon-Shaped Flexible Electronics (Cheng X, Zhang F, Bo R, et al. An anti-fatigue design strategy for 3D ribbon-shaped flexible electronics. Adv Mater. 2021; (): 2102684.) proposes to convert metal-dominated failure into the desired polymer-dominated failure, by adding an ultra-thin polymer layer (such as polyimide, PI and PDMS, etc.) on top of the metal layer (such as copper, gold and silver, etc.), significantly extending the fatigue life of 3D ribbon-shaped flexible electronic devices. The demonstrated 3D resistive sensor can be used in 10 5 Long-term vibration measurements during 10 loading cycles.

[0007] In the patent text with publication number CN115678132B, a method for preparing anti-fatigue rubber is proposed. The invention introduces multi-dimensional nanofillers into the rubber base material, namely spherical carbon black, tubular nanofiller carbon nanotubes, and flaky nanofiller graphene oxide. The filler network structure formed by these fillers in the rubber base is strong, which limits the mobility of the rubber molecular chain and causes the crack tip morphology to evolve continuously during the expansion, resulting in new morphologies such as passivation, deflection, and branching, thereby reducing the crack propagation rate.

[0008] In the patent document with publication number CN109655180A, a crack array structure and a crack array anti-structure are generated on the PDMS surface by inverting the film, two flexible substrates with regular crack array structures and crack array anti-structures are arranged opposite to each other, and the contact area change between the crack array structure and the crack array anti-structure on the surface of the flexible substrate under the action of external pressure is used to change the characteristics of the resistor, thereby improving sensitivity and reliability. The preparation method is simple, does not require complex processes such as photolithography, has low production costs, and can be prepared on a large area.

[0009] In the patent text with publication number CN118641068A, by introducing glycerol and hygroscopic ionic salts into the ion gel, the ion gel has both high moisturizing effect and strong moisture absorption capacity, thereby improving the durability and reliability of the capacitive sensor based on the ion gel. However, it cannot fundamentally solve the problem of decreased sensor sensitivity caused by the easy water loss of ion gel-based sensors.

[0010] Although some progress has been made in the research on the stability and consistency of flexible pressure sensors, the current flexible pressure sensors still have the following shortcomings:

[0011] 1. Under the action of alternating loads, the high strain area of ​​the flexible pressure sensor is prone to fatigue damage. The damage continues to develop at the microscopic level to form macroscopic fine cracks, which begin to slip and expand on different planes near the crack tip. When the remaining cross-section of the object is insufficient to resist the external load, the sensor will physically break or electrically fail, affecting the normal use of the sensor.

[0012] 2. Many composite materials are composed of an elastomer matrix and nanoparticles of hard materials. Such composite materials usually have superior performance and good fatigue resistance and are widely used. However, embedding nanoparticles into elastomers usually requires strong shear forces, using machines such as extruders and roll mills, which cut polymer chains and reduce performance.

[0013] 3. In order to improve the performance of flexible pressure sensors, crack-like surface microstructures are introduced into the stress-sensitive elements of the sensors. Although crack-based pressure sensing arrays show great potential in wearable applications due to their extraordinary sensitivity, there are structural limitations. Since vertically applied stress does not cause obvious crack opening in an effective manner, the sensor is insensitive to vertical stress.

[0014] 4. Flexible sensors based on single-layer crack structures cannot have both high sensitivity and wide working range. When the stress-sensitive element forms a channel crack structure, the conductive path of the sensor is quickly cut off under small deformation, making the sensor have ultra-high sensitivity but a narrow working range; when the stress-sensitive element forms a network crack structure, the crack direction is randomly distributed and the length is short. Due to the reduced crack propagation efficiency, the sensor has a wide working range but low sensitivity.

[0015] 5. Based on the flexible pressure sensor with crack structure, stress sensitive elements are mostly made by adding conductive fillers such as metal nanowires and carbon fillers into polymers. However, such fillers are poorly bonded to polymers, unevenly dispersed in polymers and easily precipitated, which results in obvious hysteresis and poor stability of the sensor. Another method for preparing stress sensitive elements is to use conductive polymers to prepare stress sensitive elements. Among them, PEDOT:PSS is widely used due to its excellent electrochemical properties and biocompatibility. However, wearable devices require good air permeability. PEDOT:PSS is easy to absorb moisture and has poor wettability. It will absorb human sweat and moisture in the air and decompose and fail. In addition, PEDOT:PSS has poor intrinsic conductivity and is difficult to meet the requirements of sensor sensitivity.

[0016] 6. The flexible pressure sensor has different mechanical moduli and elongation at break between the conductive layer and the substrate, and between different strain layers. The bonding between the layers is purely based on van der Waals force, and the interface adhesion is weak and the compatibility is poor. Since the flexible pressure sensor needs to deform repeatedly during operation, it may cause peeling, falling off or displacement between the layers, resulting in poor stability and durability of the sensor.

[0017] 7. When the sensor is used in robot skin, the more tactile array units there are per unit area, the higher the measurement accuracy. The information detected by a single flexible pressure sensor is very limited and cannot meet the needs of high-precision measurement. Summary of the invention

[0018] The purpose of the present invention is to overcome the shortcomings of the prior art and provide an ultra-sensitive and fatigue-resistant flexible pressure sensor array based on anisotropic regulation of Poisson's ratio. The sensitivity is increased by deterministically distributing the sensing direction through a substrate with an anisotropic Poisson's ratio, and the fatigue resistance of the flexible sensor is increased based on a multi-scale stress dispersion mechanism. The problems existing in the above-mentioned prior art are effectively solved, and the invention can be widely used in the fields of wearable electronics and electronic skin.

[0019] The present invention is achieved through the following technical solutions:

[0020] The present invention firstly discloses an ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation, comprising upper and lower two sensor array units;

[0021] Each sensor array unit includes a base layer, a low-conductivity layer, a high-conductivity layer and an adhesive layer which are stacked in sequence in the vertical direction; the base layer and the side opposite to the low-conductivity layer are both in the shape of a rack and the tooth surfaces of the two are meshed, and the elastic modulus of the low-conductivity layer is greater than the elastic modulus of the base layer; the high-conductivity layer includes a plurality of long high-conductivity strips, the plurality of high-conductivity strips are coated on the surface of the low-conductivity layer and are arranged at intervals along the width direction of the high-conductivity strips, the length extension direction of the high-conductivity strips is perpendicular to the tooth top extension direction of the tooth surface of the base layer, each high-conductivity strip is provided with cracks at the positions corresponding to the plurality of tooth tops of the tooth surface of the base layer, and the plurality of cracks divide the high-conductivity strips into a plurality of sections;

[0022] The upper and lower sensor array units are bonded together by an adhesive layer, and the tooth top extension directions of the tooth surfaces of the base layers of the upper and lower sensor array units are perpendicular to each other.

[0023] As a preferred solution of the above-mentioned pressure sensing array, the cross-sectional shape of the tooth grooves of the tooth surface of the base layer is a triangle.

[0024] As a preferred solution of the above pressure sensing array, the base layer and the adhesive layer are both made of polyethyl acrylate and polymethyl methacrylate.

[0025] As a preferred solution of the above pressure sensing array, the low conductive layer is made of polyethyl acrylate, polymethyl methacrylate and PEDOT:PSS.

[0026] As a preferred solution of the above pressure sensing array, the highly conductive layer is made of polyethyl acrylate, PEDOT:PSS and ethylene glycol.

[0027] As a preferred solution of the above pressure sensing array, the conductivity of the low conductive layer material is not higher than 50S / cm, and the elongation at break is not lower than 150%.

[0028] As a preferred solution of the above pressure sensing array, the conductivity of the highly conductive layer is not less than 2000 S / cm, and the elongation at break is not greater than 8%.

[0029] As a preferred solution of the above pressure sensing array, in each of the sensor array units, the tooth top height of the tooth surface of the base layer is greater than 40% of the overall height of the base layer and the low conductive layer.

[0030] The present invention also discloses a method for preparing the above-mentioned ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation, comprising the following steps:

[0031] Step 1: Prepare base layer and bonding layer slurry:

[0032] Preparation of polyethyl acrylate (PEA) emulsion: ethyl acrylate (EA) and silane coupling agent (3-(trimethoxysilyl)propyl methacrylate (TMSPMA)) were ultrasonically mixed, surfactant (sodium dodecyl sulfate (SDS), thermal initiator (ammonium persulfate (APS)) and distilled water were added, nitrogen was flushed into the mixture and stirred at 300 rpm for 10 min, and then sealed with a septum plug; a syringe needle connected to the balloon was inserted into the septum plug, and the reaction container was placed in an oil bath at 70-85°C and heated and stirred for 8-10 h to obtain a PEA emulsion; wherein the molar ratio of the silane coupling agent to EA was 10 -4 ~10 -3 : 1, the molar ratio of the surfactant to EA is 2×10 -3 ~4×10 -3 : 1, the molar ratio of the thermal initiator to EA is 10 -4 ~10 -3 :1, the mass ratio of distilled water to EA is 2-4:1;

[0033] Preparation of polymethyl methacrylate (PMMA) emulsion: MMA and silane coupling agent 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) were ultrasonically mixed, surfactant sodium dodecyl sulfate (SDS), thermal initiator ammonium persulfate (APS) and distilled water were added, nitrogen was flushed into the mixture and stirred at 300 rpm for 10 min, and then sealed with a septum plug; a syringe needle connected to the balloon was inserted into the septum plug, and the reaction container was placed in an oil bath at 70-85°C and heated and stirred for 8-10 h to obtain PMMA emulsion; wherein the molar ratio of the silane coupling agent to MMA was 10 -3 ~10 -2 : 1, the molar ratio of the surfactant to MMA is 2×10 -3 ~4×10 -3 : 1, the molar ratio of the thermal initiator to MMA is 10 -3 ~10-2 :1; the mass ratio of the distilled water to the MMA is 2-4:1;

[0034] The PEA emulsion, the PMMA emulsion and distilled water are mixed and stirred uniformly at a volume ratio of 1:0.2-0.4:1.2-1.4 to obtain a base layer and an adhesive layer slurry;

[0035] Step 2: Prepare low conductive layer slurry:

[0036] After mixing the PEA emulsion and the PMMA emulsion prepared in step 1, the PEDOT:PSS emulsion is added and vortexed to mix evenly to obtain a low conductive layer slurry; wherein the volume ratio of the PEA emulsion, the PMMA emulsion and the PEDOT:PSS emulsion is 1:0.4~0.55:0.008~0.01;

[0037] Step 3: Prepare high conductive layer slurry:

[0038] The PEA emulsion, PEDOT:PSS emulsion and ethylene glycol prepared in step 1 are vortex-mixed uniformly in a volume ratio of 1:30-40:3-4 to obtain a highly conductive layer slurry;

[0039] Step 4: Prepare the sensor array unit by using a spin coating process combined with mold forming:

[0040] Spraying a silicone release agent on the surface of a mold for making a base layer and drying it; injecting the base layer and the adhesive layer slurry into the mold, first heating it on a 40-50° C. hot plate for 10-15 minutes, and then heating it in a 60-70° C. oven for 5-6 hours to shape it, and making a base layer with a rack-shaped surface;

[0041] Inject low-conductivity layer slurry into the tooth grooves of the base layer and make the low-conductivity layer slurry completely cover the surface of the base layer, heat it on a 40-50°C hot plate for 10-15 minutes, and then heat it in a 130-150°C oven for 10-12 hours to solidify the low-conductivity layer and the base layer into one; repeatedly press the obtained low-conductivity layer / base layer combined structure under a pressure of 15kpa-30kpa for 2000-3000 times to stabilize the microstructure; then use a screen printing method to scrape the high-conductivity layer slurry on the surface of the low-conductivity layer, heat it on a 40-50°C hot plate for 10-15 minutes, and shape the high-conductivity layer slurry into a plurality of long high-conductivity strips; spin-coat the base layer and the bonding layer slurry on the side where the high-conductivity strips are formed to form a bonding layer, so as to obtain a sensor array unit;

[0042] Step 5: Assemble the flexible pressure sensing array:

[0043] Repeat steps 1 to 4 to obtain two sensor array units; then align the upper and lower sensor array units, and make the extension directions of the tooth tops of the base layer tooth surfaces of the two sensor array units perpendicular to each other; heat the device on a 40-50°C hot plate for 10-15 minutes, and then heat it in a 130-150°C oven for 10-12 hours, so that the devices are bonded together through the adhesive layer; finally, press the device repeatedly at a pressure of 10-30KPa for 50-100 times, so that each highly conductive strip forms cracks at the positions of multiple tooth tops of the corresponding base layer tooth surface, and multiple cracks divide the highly conductive strip into several sections, thus completing the preparation of an ultra-sensitive, fatigue-resistant, flexible pressure sensor array based on anisotropic regulation of Poisson's ratio.

[0044] Compared with the prior art, the present invention has the following advantages:

[0045] 1. The present invention provides an ultra-sensitive, fatigue-resistant, flexible pressure sensing array based on anisotropic regulation of Poisson's ratio, which comprises an upper and lower sensor array unit, each of which comprises a base layer, a low-conductivity layer, a high-conductivity layer and an adhesive layer stacked in sequence in a vertical direction, wherein the side of the base layer opposite to the low-conductivity layer is designed to be meshing rack-shaped, and the high-conductivity layer is designed to include a plurality of long high-conductivity strips, and stress is concentrated by mismatching the elastic modulus of the base layer and the low-conductivity layer, so that cracks are preferentially generated in the high-conductivity strips at the stress concentration point, i.e., at the position corresponding to the plurality of tooth tops of the tooth surface of the base layer, so that the array can be highly integrated and provide sufficient sensing arrays within a unit area; in addition, the tooth top extension directions of the base layer tooth surfaces of the upper and lower sensor array units are designed to be perpendicular to each other, so that the upper and lower sensor array units can accurately locate the pressure point by cross-intersection, thereby being able to more accurately sense and obtain pressure information.

[0046] 2. The present invention provides an ultra-sensitive, fatigue-resistant flexible pressure sensor array based on anisotropic regulation of Poisson's ratio, in which each sensor array unit is formed by bonding a low-conductivity layer and a high-conductivity layer to form a strain sensitive element of the sensor array, thereby enabling the sensor array to have high sensitivity and a wide working strain range.

[0047] 3. The ultra-sensitive anti-fatigue flexible pressure sensing array based on anisotropic regulation of Poisson's ratio provided by the present invention has a good anti-fatigue effect due to the selection of various materials for the base layer, low-conductivity layer, high-conductivity layer and adhesive layer, and can form strong adhesion between layers.

[0048] 4. The ultra-sensitive and fatigue-resistant flexible pressure sensing array based on anisotropic regulation of Poisson's ratio proposed in the present invention plays a multi-scale stress dispersion role through the cross-linking structure of PEA polymer emulsion and PMMA glassy polymer emulsion and silane coupling agent in the base layer and the low conductive layer, so that the device has a high fatigue threshold and good stability.

[0049] 5. The ultra-sensitive anti-fatigue flexible pressure sensing array based on Poisson's ratio anisotropic regulation proposed by the present invention adopts a method of directly mixing different emulsions in aqueous solution, which only requires simple stirring. As the water evaporates, the silane coupling agent in the solution can cross-link different polymer chains and glassy particles, which can avoid chain breaks caused by high-intensity processes (such as extrusion and rolling mills), which is simple and convenient to operate and can ensure the high performance of the material.

[0050] 6. The ultra-sensitive and fatigue-resistant flexible pressure sensor array based on Poisson's ratio anisotropic regulation proposed in the present invention has a high conductive layer made of a mixture of PEDOT:PSS emulsion and PEA emulsion. The coating has high conductivity and can remain stable in water.

[0051] 7. The ultra-sensitive and fatigue-resistant flexible pressure sensing array based on anisotropic regulation of Poisson's ratio proposed in the present invention has the following characteristics: when each layer of slurry is coated on the surface of the base layer, the silane groups of the silane coupling agent in the emulsion are condensed into siloxane bonds, and the siloxane bonds are cross-linked with the silanol groups on the PEA polymer chain to form a strong adhesion force, thereby making the various layers of the device tightly combined. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] Figure 1 is a stereogram of the flexible pressure sensing array of the present invention.

[0053] Figure 2 It is a three-dimensional exploded view of the flexible pressure sensing array of the present invention.

[0054] Figure 3 It is a longitudinal cross-sectional view of the flexible pressure sensing array of the present invention.

[0055] Figure 4 It is a cross-sectional view of the lower sensor array unit of the present invention before and after pre-compression.

[0056] Figure 5 It is a three-dimensional structural schematic diagram of the lower sensor array unit of the present invention in a state where the cracks in the highly conductive layer are opened after pre-compression.

[0057] Figure 6 This is a schematic diagram of the principle of amplifying the fatigue threshold of the base layer in the flexible pressure sensing array of the present invention.

[0058] Figure 7 It is a schematic diagram of the principle of stable conductivity in water after the high conductive layer PEDOT:PSS emulsion and silane grafted PEA emulsion in the flexible pressure sensing array of the present invention are mixed.

[0059] Figure 8 This is a schematic diagram of the principle of forming siloxane bonds between layers in the flexible pressure sensing array of the present invention.

[0060] Fig. 9 A schematic diagram of a mold used to make the base layer of the flexible pressure sensing array of the present invention.

[0061] Fig.10 FIG. 1 is a pressure-sensitivity characteristic curve of a high conductive strip in an upper sensor array unit of the flexible pressure sensing array manufactured in the embodiment.

[0062] Fig.11 The frequency response characteristic of a high conductive strip in the upper sensor array unit of the flexible pressure sensing array manufactured in the embodiment.

[0063] Fig.12 It is a step response characteristic curve of a high conductive strip in the upper sensor array unit of the flexible pressure sensing array manufactured in the embodiment.

[0064] Fig.13 This is a repeatability test curve of a high conductive strip in the upper sensor array unit of the flexible pressure sensing array manufactured in the embodiment.

[0065] Numbers in the figure: 1 upper sensor array unit, 2 lower sensor array unit, 3 base layer, 4 low conductive layer, 5 high conductive layer, 6 adhesive layer, 7 high conductive strip, 8 tooth top, 9 crack, 10 wire.

[0066] Figures 10 to 13 In the figure, △R / R0 represents the sensitivity of the sensor, R0 is the initial resistance of the sensor, and △R is the difference between the resistance of the sensor under pressure and the initial resistance. DETAILED DESCRIPTION

[0067] See also Figures 1 to 5The present invention discloses an ultra-sensitive, fatigue-resistant, flexible pressure sensing array based on Poisson's ratio anisotropic regulation, including two upper and lower sensor array units, the two sensor array units are an upper sensor array unit 1 and a lower sensor array unit 2. Each sensor array unit includes a base layer 3, a low-conductivity layer 4, a high-conductivity layer 5, and an adhesive layer 6 stacked in sequence along the vertical direction. The sides opposite to the base layer 3 and the low-conductivity layer 4 are both rack-shaped and the tooth surfaces of the two are meshed, and the elastic modulus of the low-conductivity layer 4 is greater than the elastic modulus of the base layer 3. In each sensor array unit, the height of the tooth top 8 of the tooth surface of the base layer 3 is greater than 40% of the overall height of the base layer 3 and the low-conductivity layer 4. The high conductive layer 5 includes a plurality of long strip-shaped high conductive strips 7, which are coated on the surface of the low conductive layer 4 and arranged at intervals along the width direction of the high conductive strips 7. The length extension direction of the high conductive strips 7 is perpendicular to the extension direction of the tooth tops 8 of the tooth surface of the base layer 3. Each high conductive strip 7 is provided with cracks 9 at the positions corresponding to the plurality of tooth tops 8 of the tooth surface of the base layer 3, and the plurality of cracks 9 divide the high conductive strips 7 into several sections; the two ends of the plurality of high conductive strips 7 of the high conductive layer 5 are externally connected to the wires 10. The upper and lower sensor array units are bonded together by the bonding layer 6, and the extension directions of the tooth tops 8 of the tooth surface of the base layer 3 of the upper and lower sensor array units are perpendicular.

[0068] The cross-sectional shape of the tooth groove of the tooth surface of the base layer 3 is a triangle. In each sensor array unit, the rack-shaped meshing structure between the low conductive layer 4 and the base layer 3 has an anisotropic Poisson's ratio. If the Z-axis direction represents the direction of the vertical stress, the X-axis direction represents the direction of the length extension of the tooth top 8 along the base layer 3, and the Y-axis direction represents the direction of the length extension of the high conductive strip 7, the Poisson's ratio during compression can be defined as:

[0069] (1)

[0070] (2)

[0071] In formula (1) and formula (2), ε x represents the strain in the X direction, ε y represents the strain in the Y direction, ε z represents the strain in the Z direction, υ zx Indicates the Poisson's ratio in the X direction when the material is subjected to pressure in the Z direction, υ zy It represents the Poisson's ratio in the Y direction when the material is subjected to pressure in the Z direction. z is a negative value, so Poisson's ratio is proportional to the strain in the corresponding direction.

[0072] When compressive stress is applied to the sensor in the Z direction, if the material with isotropic Poisson's ratio is deformed in a uniform direction in all directions, the crack 9 of the high conductive layer 5 cannot be effectively opened. In each sensor array unit of the present invention, a rack-like meshing structure is adopted between the low conductive layer 4 and the base layer 3. The periodic teeth in the Y direction promote deformation in the Y direction, while there is no such structural release in the X direction, making deformation more likely to occur in the Y direction. At the same time, the low conductive layer 4 with a smaller elastic modulus is more easily deformed than the base layer 3 with a larger elastic modulus, which amplifies the deformation trend in the Y direction. That is, when the sensor array unit of the present invention is subjected to Z-direction pressure, its Poisson's ratio v in the Y direction is zy Greater than Poisson's ratio in the X direction zx , which exhibits an anisotropic Poisson's ratio. Based on the anisotropic regulation of this Poisson's ratio, the crack 9 of the high conductive strip 7 can be effectively opened under pressure, so that the sensor has a significant resistance change under pressure.

[0073] See also Figure 4 , which is a cross-sectional view of the lower sensor array unit 2 prepared in this embodiment before and after pre-compression, and it also illustrates the sensing mechanism and the local conductive path. It can be seen that the main transmission path of the current before pre-compression is the high conductive layer 5 of the sensor. After the sensor is pre-compressed, due to the mismatch between the tooth top 8 of the tooth surface of the base layer 3 and the elastic modulus of the low conductive layer 4, the stress is concentrated, and cracks 9 are generated in the high conductive layer 5 at the stress concentration point. The high conductive strip 7 is divided into several sections by multiple cracks 9. At this time, the current transmission path is from the high conductive layer 5 to the low conductive layer 4, and so on, which is equivalent to connecting several low-resistance high conductive layers 5 and high-resistance low conductive layers 4 in series. Therefore, when the sensor is compressed, the gap of the crack 9 increases, resulting in an increase in the sensor resistance, which effectively improves the sensing performance of the sensor. Figure 4 R represents the resistance of the high conductive layer 5 when not compressed, R' refers to the resistance of the low conductive layer 4 when not compressed, and R is much smaller than R'; R1 and R2 represent the resistance of each section separated by the crack 9 in the high conductive layer 5 after the crack 9 is generated, and R" refers to the resistance of the current transmitted through the low conductive layer 4 at the crack 9 of the high conductive strip 7 after the crack 9 is generated in the high conductive strip 7.

[0074] The base layer 3 and the adhesive layer 6 are both made of polyethyl acrylate (PEA) and polymethyl methacrylate (PMMA). The rubber-glass nanocomposite is prepared by mixing a PEA aqueous emulsion and a PMMA aqueous emulsion, each of which is prepared separately with a single type of polymer chain, and each polymer chain is copolymerized with a small amount of a silane coupling agent. When the two emulsions are mixed, PMMA is in the form of glass particles and PEA is in the form of rubber particles. Figure 6As shown, when the emulsion of the base layer 3 and the low conductive layer 4 is dried, the PMMA glass particles maintain their shape, but the PEA rubber particles change their shape to form a continuous matrix. Subsequently, the silane groups of the silane coupling agent condense into siloxane bonds, which crosslink the PEA rubber chains and crosslink the PEA rubber chains with the PMMA glass particles. When the base layer 3 material is subjected to stress, first, through the covalent interconnection between the particles and the polymer, the strong adhesion between the polymer and the particles through covalent bonds allows the high stress to be transferred from the polymer to the particles. In this way, the stress can be dispersed in many interparticle gaps in the particle cluster, and when one gap is broken, the energy stored in multiple gaps will be dissipated. Secondly, the presence of long polymer chains in the composite material helps to disperse stress. When the crack 9 hits the particle cluster, the rigid particles disperse the stress into multiple gaps in the particle cluster. The rupture of a single gap releases the energy stored in multiple gaps, resulting in stress dispersion at the polymer and particle scales. When the sensor generates macro cracks 9 due to fatigue accumulation during repeated loading and unloading, when cracks 9 hit the PEA polymer strands, high tension is transmitted to other strands of the strands that are cross-linked, and the rigid PMMA particles can further disperse the stress beyond the single-layer polymer chain. Cracks 9 become blunt and bifurcate, and the bifurcated cracks 9 run in a direction perpendicular to the pre-cracks 9, greatly delaying the expansion of cracks 9. This multi-scale stress dispersion greatly increases the fatigue threshold.

[0075] The low conductive layer 4 is made of polyethyl acrylate, polymethyl methacrylate and PEDOT:PSS. The conductivity of the low conductive layer 4 can be adjusted by adjusting the amount of PEDOT:PSS within a limited range as required, and the elastic modulus of the low conductive layer 4 material can be adjusted by adjusting the amount of polymethyl methacrylate within a limited range as required.

[0076] The highly conductive layer 5 is made of polyethyl acrylate, PEDOT:PSS and ethylene glycol. PEDOT:PSS is known as the most outstanding conductive polymer, with good film-forming properties, high transparency, adjustable conductivity and excellent thermal stability. However, PEDOT:PSS exhibits strong acidity, is easy to absorb moisture and has poor wettability, which will reduce the efficiency and stability of the device. The present invention improves the shortcomings of PEDOT:PSS by mixing a silane coupling agent grafted PEA emulsion and a conductive polymer PEDOT:PSS emulsion. As the water evaporates, the emulsion particles fuse into a continuous solid, in which PEDOT:PSS and PEA split into two domains, and the characteristic size of these two domains is about microns. Figure 7As shown, in the dried coating, PSS is a glassy polymer, PEDOT is a crystalline polymer, PEA is a rubbery polymer, PEDOT:PSS forms one continuous domain, PEA forms another continuous domain, and PEDOT chains are stacked into percolation nanocrystals. The PSS chains are not cross-linked but continuous. The PEDOT nanocrystals embedded in PSS are much smaller than the latex particles. Therefore, the PEDOT nanocrystals in the coating prepared from the mixed emulsion can form a percolation network, just like in the coating prepared from pure PEDOT:PSS. The formation of percolation nanocrystals of PEDOT is not interfered by the hydrophobic and rubbery PEA chains, so the coating has high conductivity. Moreover, the PEA network prevents PSS from over-swelling and falling off from the substrate, making the coating stable in water.

[0077] The conductivity of the low conductive layer 4 material is not higher than 50 S / cm, and the conductivity of the high conductive layer 5 is not lower than 2000 S / cm. The sensitivity of the sensor is defined as the rate of change of the resistance of the sensor under unit pressure. Therefore, the conductivity of the high conductive layer 5 and the low conductive layer 4 are different, and the sensing performance of the entire sensor device is also different. The high conductivity of the high conductive layer 5 makes the initial resistance of the sensor small enough, and the low conductivity of the low conductive layer 4 prevents electrical failure of the sensor under large compression, so that the sensor has the characteristics of a wide sensing range. The sensitivity of the sensor prepared according to the above conductivity reaches 2000kPa. -1 above.

[0078] The elongation at break of the low conductive layer 4 material is not less than 150%. The elongation at break of the high conductive layer 5 is not greater than 8%. When the elongations at break of the low conductive layer 4 and the high conductive layer 5 are different, under compression, since the mechanical properties of the low conductive layer 4 are better than those of the high conductive layer 5, under compression, the deformation of the high conductive layer 5 of the sensor will first reach the elongation at break and generate cracks 9.

[0079] like Figure 8 As shown, when each layer of slurry is coated on the surface of the base layer 3, the water gradually evaporates with heating, and the silane groups of the silane coupling agent 3-(trimethoxysilyl)propyl methacrylate in the emulsion condense into siloxane bonds, which cross-link with the silanol groups on the PEA polymer chain to form a strong adhesion force, thereby tightly combining the various layers of the device.

[0080] The following is a detailed description of an embodiment of the present invention. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0081] Ethyl acrylate used in the following examples was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. (AR 99%);

[0082] The methyl methacrylate used in the following examples was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. (AR 99%);

[0083] 3-(Trimethoxysilyl)propyl methacrylate used in the following examples was purchased from Sigma-Aldrich (AR 98%);

[0084] The sodium dodecyl sulfate used in the following examples was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. (AR ≥ 99%);

[0085] The ammonium persulfate used in the following examples was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. (AR 98.5%);

[0086] The PEDOT:PSS emulsion used in the following examples was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. (solid content 1.5%);

[0087] The ethylene glycol used in the following examples was purchased from Shanghai MacLean Biochemical Technology Co., Ltd. (AR 98%). Example 1

[0088] In this embodiment, the above-mentioned ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation is prepared according to the following steps:

[0089] Step 1: Prepare base layer and bonding layer slurry:

[0090] Preparation of PEA emulsion: 72 g EA and 17.1 μL TMSPMA were mixed and sonicated for 5 min to remove dissolved oxygen. The mixture of EA and TMSPMA was added to a 500 mL round-bottom flask, and 0.415 g SDS, 0.016 g APS and 168 g distilled water were added. Nitrogen was flushed into the mixture and stirred at 300 rpm for 10 min, and then sealed with a septum plug. The syringe needle connected to the balloon was inserted into the septum plug to balance the additional pressure of the exothermic polymerization process. The flask was placed in an oil bath at 65 ° C and stirred in a magnetic stirrer at 300 rpm for 8 h to obtain a PEA emulsion. The prepared emulsion was stored in a plastic jar made of high-density polyethylene (VWR, 16125-810) at room temperature.

[0091] Preparation of PMMA emulsion: 73.1 g of MMA and 171 μL of TMSPMA were mixed and sonicated for 5 min to remove dissolved oxygen. The mixture of MMA and TMSPMA was added to a 500 mL round-bottom flask, and 0.415 g of SDS, 0.16 g of APS, and 168 g of distilled water were added. Nitrogen was flushed into the mixture and stirred at 300 rpm for 10 min, and then sealed with a septum plug. A syringe needle connected to a balloon was inserted into the septum plug to balance the additional pressure of the exothermic heat during the polymerization process. The flask was placed in an oil bath at 65 ° C and stirred in a magnetic stirrer at 300 rpm for 8 hours to prepare the PMMA emulsion. The prepared emulsion was stored in a plastic jar made of high-density polyethylene (VWR, 16125-810) at room temperature.

[0092] 5 mL of PEA mixed emulsion and 1 mL of PMMA mixed emulsion were introduced into a beaker, and then 6 mL of distilled water was added to dilute them, and stirred evenly with a glass rod to obtain base layer and adhesive layer slurry.

[0093] Step 2: Prepare low conductive layer slurry:

[0094] 5 mL of the PEA emulsion prepared in step 1 and 2.4 mL of the PMMA emulsion were mixed, and then 0.04 mL of the PEDOT:PSS emulsion was added and mixed evenly on a vortex mixer to obtain a low conductive layer slurry.

[0095] Step 3: Prepare high conductive layer slurry:

[0096] 0.18 mL of the PEA emulsion prepared in step 1 was mixed with 6 mL of the PEDOT:PSS emulsion and 0.6 mL of the ethylene glycol solution, and mixed evenly on a vortex mixer to obtain a highly conductive layer slurry.

[0097] Step 4: Prepare the sensor by using a spin coating process combined with mold forming:

[0098] A silicone release agent is sprayed on the glass mold (whose structure is as shown in FIG. Fig. 9 The base layer and adhesive layer slurry were injected into the mold, and then heated on a 45°C hot plate for 15 minutes (to evaporate water from the emulsion to ensure that no steam bubbles are formed in the coating), and then placed in a 65°C oven for further heating for 6 hours to solidify and shape, to produce a base layer 3 with a rack-shaped surface.

[0099] The low-conductivity layer slurry is injected into the tooth groove of the base layer 3 so that the low-conductivity layer slurry completely covers the surface of the base layer 3, and then heated on a 45°C hot plate for 15 minutes, and then placed in a 140°C oven for 12 hours to solidify the low-conductivity layer 4 and the base layer 3 into one; the obtained low-conductivity layer 4 / base layer 3 combined structure is repeatedly pressed 3000 times under a pressure of 20KPa to stabilize the microstructure; then the high-conductivity layer slurry is scraped on the surface of the low-conductivity layer 4 by screen printing, and heated on a 45°C hot plate for 15 minutes to shape the high-conductivity layer slurry into a plurality of long high-conductivity strips 7; the base layer and the bonding layer slurry are spin-coated on the side where the high-conductivity strips 7 are formed to form a bonding layer 6, and a sensor array unit is obtained;

[0100] Step 5: Assemble the flexible pressure sensing array:

[0101] Repeat steps 1 to 4 to obtain two sensor array units; then align the upper and lower sensor array units, and make the extension directions of the tooth tops 8 of the tooth surface of the base layer 3 of the two sensor array units perpendicular to each other; place the device on a 45°C hot plate for 15 minutes, and then place it in a 140°C oven for 12 hours, so that the device is bonded together through the bonding layer 6 (the bonding layer and the silane groups on the surface of the high conductive layer 5 condense into siloxane bonds, and the siloxane bonds cross-link the PEA chains to form a tight fit). The two ends of the multiple high conductive strips 7 of the high conductive layer 5 are externally connected to the wires 10. Finally, the device is repeatedly pressed 80 times under a pressure of 20KPa, so that each high conductive strip 7 forms cracks 9 at the positions of the multiple tooth tops 8 on the tooth surface of the corresponding base layer 3, and the multiple cracks 9 divide the high conductive strip 7 into several sections, that is, the preparation of the ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation is completed.

[0102] Fig.10 This is the pressure sensing characteristic curve of a high conductive strip 7 in the upper sensor array unit 1 of the flexible pressure sensing array of this embodiment. In the working pressure range of 0~10kPa, the sensor sensitivity is about 1500kPa -1 The isotropic Poisson's ratio device used as a comparison in the figure replaces the low-conductivity layer 4 / base layer 3 combination structure of the device in this embodiment with a planar low-conductivity layer 4 / planar base layer 3 structure without a rack structure, and the raw material dosage in the low-conductivity layer slurry is 5mL of PEA emulsion, 2.4mL of PMMA emulsion, and 0.04mL of PEDOT:PSS emulsion, so that the elastic modulus of the base layer 3 and the low-conductivity layer 4 are the same. Within the working pressure range of 0~5kPa, the sensitivity of the isotropic Poisson's ratio device is only 120kPa -1 .

[0103] Fig.11This is the frequency response characteristic curve of a high conductive strip 7 in the upper sensor array unit 1 of the flexible pressure sensor array of this embodiment. From the resistance change characteristic curve of the cyclic loading experiment under the loading frequency of 0.5 Hz, 1 Hz, 2 Hz, and 4 Hz and the pressure of 8 kPa, it can be seen that the output resistance of the sensor does not deviate significantly, indicating that the sensor can be applied to different frequencies of 0.5 Hz, 1 Hz, 2 Hz, and 4 Hz, and the sensor has high stability at different frequencies.

[0104] Fig.12 The step pressure characteristic curve of a high conductive strip 7 in the upper sensor array unit 1 of the flexible resistive pressure sensor array of this embodiment is shown in Figure 1. The strain sensor prepared in this embodiment is subjected to a step test, and the result shows that it can work stably under the pressure of 0-30 kPa.

[0105] Fig.13 This is the electrical stability curve of a high conductive strip 7 in the upper sensor array unit 1 of the flexible resistive pressure sensor array of this embodiment. The flexible resistive pressure sensor array prepared in this embodiment was subjected to 3500 cycles of loading / unloading (pressure application range of 0-3 kPa) to test the electrical stability and repeatability of the sensor. It can be seen that after 3500 cycles of testing, the sensor has stable electrical characteristics, thus proving that the sensor has good consistency.

[0106] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. An ultra-sensitive, fatigue-resistant flexible pressure sensor array based on Poisson's ratio anisotropic regulation, characterized by: It includes upper and lower sensor array units; Each sensor array unit includes a base layer, a low-conductivity layer, a high-conductivity layer and an adhesive layer which are stacked in sequence in the vertical direction; the base layer and the side opposite to the low-conductivity layer are both in the shape of a rack and the tooth surfaces of the two are meshed, and the elastic modulus of the low-conductivity layer is greater than the elastic modulus of the base layer; the high-conductivity layer includes a plurality of long high-conductivity strips, the plurality of high-conductivity strips are coated on the surface of the low-conductivity layer and are arranged at intervals along the width direction of the high-conductivity strips, the length extension direction of the high-conductivity strips is perpendicular to the tooth top extension direction of the tooth surface of the base layer, each high-conductivity strip is provided with cracks at the positions corresponding to the plurality of tooth tops of the tooth surface of the base layer, and the plurality of cracks divide the high-conductivity strips into a plurality of sections; The upper and lower sensor array units are bonded together by an adhesive layer, and the tooth top extension directions of the tooth surfaces of the base layers of the upper and lower sensor array units are perpendicular to each other.

2. The ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation according to claim 1, characterized in that: The tooth groove cross-section of the base layer tooth surface is in a triangular shape.

3. The ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation according to claim 1, characterized in that: The base layer and the adhesive layer are both prepared from polyethyl acrylate and polymethyl methacrylate.

4. The ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation according to claim 1, characterized in that: The low conductive layer is prepared from polyethyl acrylate, polymethyl methacrylate and PEDOT:PSS.

5. The ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation according to claim 1, characterized in that: The high conductive layer is prepared from polyethyl acrylate, PEDOT:PSS and ethylene glycol.

6. The ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation according to claim 1, characterized in that: The electrical conductivity of the low-conductive layer material is not higher than 50S / cm, and the elongation at break is not lower than 150%.

7. The ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation according to claim 1, characterized in that: The electrical conductivity of the highly conductive layer is not less than 2000 S / cm, and the elongation at break is not greater than 8%.

8. The ultra-sensitive anti-fatigue flexible pressure sensor array based on Poisson's ratio anisotropic regulation according to claim 1, characterized in that: In each of the sensor array units, a tooth top height of a tooth surface of the base layer is greater than 40% of a total height of the base layer and the low conductive layer.

9. A method for preparing an ultra-sensitive and fatigue-resistant flexible pressure sensor array based on Poisson's ratio anisotropic regulation according to any one of claims 1 to 8, characterized in that: The steps include: Step 1: Prepare base layer and bonding layer slurry: Preparation of polyethyl acrylate (PEA) emulsion: ethyl acrylate (EA) and silane coupling agent (3-(trimethoxysilyl)propyl methacrylate (TMSPMA)) were ultrasonically mixed, surfactant (sodium dodecyl sulfate (SDS), thermal initiator (ammonium persulfate (APS)) and distilled water were added, nitrogen was flushed into the mixture and stirred at 300 rpm for 10 min, and then sealed with a septum plug; a syringe needle connected to the balloon was inserted into the septum plug, and the reaction container was placed in an oil bath at 70-85°C and heated and stirred for 8-10 h to obtain a PEA emulsion; wherein the molar ratio of the silane coupling agent to EA was 10 -4 ~10 -3 : 1, the molar ratio of the surfactant to EA is 2×10 -3 ~4×10 -3 : 1, the molar ratio of the thermal initiator to EA is 10 -4 ~10 -3 :1, the mass ratio of distilled water to EA is 2-4:1; Preparation of polymethyl methacrylate (PMMA) emulsion: MMA and silane coupling agent 3-(trimethoxysilyl)propyl methacrylate (TMSPMA) were ultrasonically mixed, surfactant sodium dodecyl sulfate (SDS), thermal initiator ammonium persulfate (APS) and distilled water were added, nitrogen was flushed into the mixture and stirred at 300 rpm for 10 min, and then sealed with a septum plug; a syringe needle connected to the balloon was inserted into the septum plug, and the reaction container was placed in an oil bath at 70-85°C and heated and stirred for 8-10 h to obtain PMMA emulsion; wherein the molar ratio of the silane coupling agent to MMA was 10 -3 ~10 -2 : 1, the molar ratio of the surfactant to MMA is 2×10 -3 ~4×10 -3 : 1, the molar ratio of the thermal initiator to MMA is 10 --3 ~10 -2 :1; the mass ratio of the distilled water to the MMA is 2-4:1; The PEA emulsion, the PMMA emulsion and distilled water are mixed and stirred uniformly at a volume ratio of 1:0.2-0.4:1.2-1.4 to obtain a base layer and an adhesive layer slurry; Step 2: Prepare low conductive layer slurry: After mixing the PEA emulsion and the PMMA emulsion prepared in step 1, the PEDOT:PSS emulsion is added and vortexed to mix evenly to obtain a low conductive layer slurry; wherein the volume ratio of the PEA emulsion, the PMMA emulsion and the PEDOT:PSS emulsion is 1:0.4~0.55:0.008~0.01; Step 3: Prepare high conductive layer slurry: The PEA emulsion, PEDOT:PSS emulsion and ethylene glycol prepared in step 1 are vortex-mixed uniformly in a volume ratio of 1:30-40:3-4 to obtain a highly conductive layer slurry; Step 4: Prepare the sensor array unit by using a spin coating process combined with mold forming: Spraying a silicone release agent on the surface of a mold for making a base layer and drying it; injecting the base layer and the adhesive layer slurry into the mold, first heating it on a 40-50° C. hot plate for 10-15 minutes, and then heating it in a 60-70° C. oven for 5-6 hours to shape it, and making a base layer with a rack-shaped surface; Inject low-conductivity layer slurry into the tooth grooves of the base layer and make the low-conductivity layer slurry completely cover the surface of the base layer, heat it on a 40-50°C hot plate for 10-15 minutes, and then heat it in a 130-150°C oven for 10-12 hours to solidify the low-conductivity layer and the base layer into one; repeatedly press the obtained low-conductivity layer / base layer combined structure under a pressure of 15kpa-30kpa for 2000-3000 times to stabilize the microstructure; then use a screen printing method to scrape the high-conductivity layer slurry on the surface of the low-conductivity layer, heat it on a 40-50°C hot plate for 10-15 minutes, and shape the high-conductivity layer slurry into a plurality of long high-conductivity strips; spin-coat the base layer and the bonding layer slurry on the side where the high-conductivity strips are formed to form a bonding layer, so as to obtain a sensor array unit; Step 5: Assemble the flexible pressure sensing array: Repeat steps 1 to 4 to obtain two sensor array units; then align the upper and lower sensor array units, and make the extension directions of the tooth tops of the base layer tooth surfaces of the two sensor array units perpendicular to each other; heat the device on a 40-50°C hot plate for 10-15 minutes, and then heat it in a 130-150°C oven for 10-12 hours, so that the devices are bonded together through the adhesive layer; finally, press the device repeatedly at a pressure of 10-30KPa for 50-100 times, so that each highly conductive strip forms cracks at the positions of multiple tooth tops of the corresponding base layer tooth surface, and multiple cracks divide the highly conductive strip into several sections, thus completing the preparation of an ultra-sensitive, fatigue-resistant, flexible pressure sensor array based on anisotropic regulation of Poisson's ratio.

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