Gel film of pressure sensor, preparation method of gel film and sensor

Abstract

The invention belongs to the field of sensors, and particularly relates to a gel film of a pressure sensor, a preparation method thereof and the sensor. A base material of the gel film comprises polymer ionic liquid gel, first nano-particles are doped in the gel film, each first nano-particle comprises an inner core and a coating layer coating the surface of the inner core, the inner core comprises Fe3O4, and the coating layer comprises polyaniline; in the thickness direction of the gel thin film, the elasticity modulus of the gel thin film changes in a gradient mode, the concentration of the first nano-particles changes in a gradient mode, and the elasticity modulus gradient change direction is consistent with the concentration gradient change direction; the sensitivity can be obviously improved, and the measuring range of the sensor is widened.

Description

Technical Field

[0001] The present invention belongs to the field of sensors, and in particular relates to a gel film of a pressure sensor, a preparation method thereof, and a sensor. Background Art

[0002] Body weight, muscle strength and coordination, movement patterns and posture, activity level and intensity, joint structure and alignment, external loads, and ground reaction forces all contribute to stress on the knee joint. The knee is one of the most complex and heaviest-bearing joints in the human body. Excessive stress on the knee can easily lead to pain, strain (such as patellar tendinitis and pes anserinus bursitis), and cartilage wear (osteoarthritis). Effectively monitoring knee stress is crucial for injury prevention, rehabilitation guidance, performance optimization, osteoarthritis management, and postoperative recovery.

[0003] Flexible wearable pressure sensors can be used in fields such as knee joint pressure monitoring, but the sensitivity and sensing range of existing sensors are limited.

[0004] It should be noted that this part of the present invention only provides background technology related to the present invention and does not necessarily constitute prior art or public known technology. Summary of the Invention

[0005] The purpose of the present invention is to overcome the defects of limited sensitivity and sensing range of existing pressure sensors when monitoring knee joint pressure, etc., and to provide a gel film of a pressure sensor, a preparation method thereof, and a sensor, which can significantly improve the sensitivity while widening the sensing range.

[0006] To achieve the above objectives, in a first aspect, the present invention provides a gel film for a pressure sensor, wherein the substrate of the gel film comprises a polymer ionic liquid gel, the gel film is doped with first nanoparticles, the first nanoparticles comprising a core and a coating layer coated on the surface of the core, the core comprising Fe3O4, and the coating layer comprising polyaniline; Along the thickness direction of the gel film, the elastic modulus of the gel film changes gradiently and the concentration of the first nanoparticles changes gradiently, and the direction of the elastic modulus gradient change is consistent with the direction of the concentration gradient change.

[0007] In some preferred embodiments, along the thickness direction of the gel film, the area ratio of the first nanoparticles in the cross-section of the gel film changes gradually, and the direction of the area ratio gradient change is consistent with the direction of the elastic modulus gradient change, and the area ratio changes gradually in the range of 7%~13% to 85%~95%.

[0008] In some preferred embodiments, along the direction of the gradient increase of the elastic modulus, the cross-linking density of the gel film increases gradiently.

[0009] In some preferred embodiments, the thickness of the gel film is 200 μm to 800 μm.

[0010] In some preferred embodiments, the ratio of the radius of the core of the first nanoparticle to the thickness of the coating layer is 2 to 4; and the particle size of the first nanoparticle is 15 nm to 30 nm.

[0011] In some preferred embodiments, in the polymer ionic liquid gel, the cation of the ionic liquid includes at least one of a 1-ethyl-3-methylimidazolium cation, a 1-butyl-3-methylimidazolium cation, a 1-hexyl-3-methylimidazolium cation, and a 1-allyl-3-methylimidazolium cation, and the anion of the ionic liquid includes at least one of a bis(trifluoromethylsulfonyl)imide anion, a tetrafluoroborate anion, and a hexafluorophosphate anion.

[0012] In some preferred embodiments, in the polymer ionic liquid gel, the polymer includes at least one of acrylamide-butyl acrylate copolymer, acrylic acid-ethyl acrylate copolymer, acrylic acid-methyl acrylate copolymer, and acrylic acid-acrylamide copolymer.

[0013] In a second aspect, the present invention provides a method for preparing the gel film described in the first aspect, comprising: dispersing nanoparticles in a polymer ionic liquid gel matrix liquid, adding a photoinitiator to the matrix liquid, mixing uniformly to obtain a mixed liquid, injecting the mixed liquid into a mold, placing the mold containing the mixed liquid on a UV exposure table, applying a magnetic field along the thickness direction of the mixed liquid, and inducing a curing reaction by UV irradiation to obtain the gel film; the nanoparticles include first nanoparticles and second nanoparticles, the first nanoparticles and the second nanoparticles respectively including a core and a coating layer coated on the surface of the core, the cores of the first nanoparticles and the second nanoparticles both include Fe3O4, the coating layer of the first nanoparticle includes polyaniline, the coating layer of the second nanoparticle includes a crosslinking agent, the matrix liquid includes an ionic liquid and an organic monomer, and under UV irradiation conditions, the crosslinking agent causes the organic monomer to undergo a polymerization and crosslinking reaction.

[0014] In some preferred embodiments, the organic monomers include acrylamide monomers and acrylic acid monomers.

[0015] Preferably, the preparation of the second nanoparticles comprises: coating SiO2 on the surface of Fe3O4 particles, performing amino modification on the surface of the SiO2 coating layer to obtain precursor nanoparticles, and coating methacrylic anhydride on the surface of the precursor nanoparticles.

[0016] Preferably, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, the content of acrylamide monomer in the organic monomer is 10wt%~50wt% and the content of acrylic acid monomer is 50wt%~90wt%, the matrix liquid further comprises a solvent, and the solvent is anhydrous ethanol; the composition of the matrix liquid includes: the ratio of the mass of the ionic liquid to the mass of the organic monomer is 0.3~0.7, the ratio of the mass of the solvent to the mass of the organic monomer is 0.15~0.25; the photoinitiator The initiator is LAP photoinitiator (lithium phenyl (2,4,6-trimethylbenzoyl) phosphonate), and the composition of the mixed solution includes: the ratio of the mass of the first nanoparticles to the mass of the organic monomer is 0.001-0.005, the ratio of the mass of the second nanoparticles to the mass of the organic monomer is 0.005-0.02, and the ratio of the mass of the photoinitiator to the mass of the organic monomer is 0.003-0.007; the magnetic induction intensity of the magnetic field is 0.15T-0.9T.

[0017] In a third aspect, the present invention provides a pressure sensor, comprising: a plate comprising a first plate and a second plate stacked together; The sensitive layer is stacked between the first electrode plate and the second electrode plate, and comprises the gel film described in the first aspect or the gel film prepared by the preparation method of the gel film described in the second aspect.

[0018] In a fourth aspect, the present invention provides a pressure sensor for a knee joint, which is the pressure sensor described in the third aspect.

[0019] The gel film of the present invention has a gradient change in elastic modulus along the thickness direction of the gel film. When the pressure is low, the side of the gel film with the lower elastic modulus deforms significantly, which can improve the signal strength in the low-pressure area of ​​the pressure sensor and improve the low-pressure sensitivity. Since the elastic modulus on one side of the gel film is higher, the upper limit of the sensor's sensing range can be widened. When the pressure is high, the elastic modulus on one side of the gel film is higher, and the deformation of the gel film is relatively small. On the side of the gel film with the higher elastic modulus, the concentration of first nanoparticles having a conductive polyaniline coating is also relatively high. Due to the higher elastic modulus on one side of the gel film and the higher concentration of the first nanoparticles, the signal strength in the high-pressure area of ​​the sensor can be improved while widening the upper limit of the sensor's sensing range, thereby improving the high-pressure sensitivity. Because the gel film is doped with nanoparticles with a core of Fe3O4, Fe3O4 has magnetic properties. By applying an external magnetic field, the magnetic properties of Fe3O4 trigger the redistribution of the nanoparticles, and the distribution density of the nanoparticles is dynamically adjusted in real time. This can regulate the elastic modulus distribution of the gel film and make the sensor stiffness distribution adaptively change with the movement state of the knee joint, thereby preventing the sensor from being unable to withstand strong pressure and exceeding the sensing range.

[0020] During the preparation of the gel film of the present invention, a mixed liquid contains first nanoparticles and second nanoparticles, both of which have cores including Fe3O4. A magnetic field is applied along the thickness direction of the mixed liquid, that is, a magnet is set on one side of the thickness direction of the mixed liquid. Under the action of the magnetic field, the first nanoparticles and the second nanoparticles migrate, and a concentration gradient exists between the first nanoparticles and the second nanoparticles. The concentration of the nanoparticles is higher on the side close to the magnet and lower on the side away from the magnet. During the ultraviolet light irradiation and curing process, a concentration gradient of the first nanoparticles and a concentration gradient of the second nanoparticles are formed in the gel film. Due to the inclusion of the second nanoparticles, the concentration gradient of the first nanoparticles and the second nanoparticles is increased. The coating includes a crosslinking agent, which simultaneously forms a concentration gradient of the crosslinking agent while forming a concentration gradient of the second nanoparticles. UV light irradiation is used for UV curing, causing organic monomers in the matrix liquid to undergo a polymerization and crosslinking reaction, thereby fixing the concentration gradients of the first and second nanoparticles and simultaneously forming a concentration gradient of crosslink density. A greater crosslink density of the polymer increases the elastic modulus, and a greater nanoparticle concentration increases the elastic modulus. By forming the concentration gradients of the first and second nanoparticles, as well as the crosslink density, a gel film is prepared, which exhibits a gradient of elastic modulus along the thickness of the gel film. The present invention can simultaneously form a nanoparticle concentration gradient and a crosslink density concentration gradient simply by applying a magnetic field along the thickness of the mixed solution. The elastic modulus gradient is formed through the synergistic action of the nanoparticle concentration gradient and the crosslink density concentration gradient. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other relevant drawings can be obtained based on these drawings without paying any creative work.

[0022] Figure 1 is a cross-sectional view of a pressure sensor of the present invention; Figure 2 This is a physical picture of the gel film of the present invention; Figure 3 This is the microstructure diagram of the gel film of the present invention.

[0023] Description of reference numerals: 1. Upper electrode; 11. Flexible base layer; 12. Polymer layer containing hydrogen bonds; 2. Lower electrode; 3. Gel film sensitive layer. DETAILED DESCRIPTION

[0024] The endpoints of the ranges and any values ​​disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoints of each range, the endpoints of each range and individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered to be specifically disclosed herein.

[0025] The inventors of the present invention have found that the sensitivity and sensing range of existing pressure sensors are limited when monitoring knee joint pressure, etc.

[0026] In this regard, in a first aspect, the present invention provides a gel film for a pressure sensor, wherein the substrate of the gel film comprises a polymer ionic liquid gel, the gel film is doped with first nanoparticles, the first nanoparticles comprising a core and a coating layer coated on the surface of the core, the core comprising Fe3O4, and the coating layer comprising polyaniline; Along the thickness direction of the gel film, the elastic modulus of the gel film changes gradiently and the concentration of the first nanoparticles changes gradiently, and the direction of the elastic modulus gradient change is consistent with the direction of the concentration gradient change.

[0027] The gel film of the present invention comprises a polymer ionic liquid gel. The coating layer of the first nanoparticles doped in the gel film comprises polyaniline. The polyaniline coating acts as a "conductor network" to form a conductive path within the gel film, enabling the gel film to function as a pressure-sensitive layer of a pressure sensor. When used as the pressure-sensitive layer of a pressure sensor, the elastic modulus of the gel film varies gradiently along its thickness. When pressure is low, the side of the gel film with the lower elastic modulus deforms significantly, thereby increasing signal strength in the low-pressure region of the pressure sensor and improving low-pressure sensitivity. The higher elastic modulus on one side of the gel film widens the upper limit of the sensor's sensing range. At higher pressures, the higher elastic modulus on the side of the gel film results in relatively less deformation of the gel film. Furthermore, the side of the gel film with the higher elastic modulus also has a relatively higher concentration of the first nanoparticles having the conductive polyaniline coating. The higher elastic modulus on one side of the gel film and the higher concentration of the first nanoparticles enhance the sensor's signal strength in the high-pressure region and improve its high-pressure sensitivity while widening the upper limit of the sensor's sensing range.

[0028] Because the gel film is doped with nanoparticles containing Fe3O4 as the core, Fe3O4 exhibits magnetization properties. Applying an external magnetic field triggers the redistribution of the nanoparticles, allowing for real-time dynamic adjustment of the nanoparticle distribution density. This allows for the regulation of the elastic modulus distribution of the gel film, enabling the sensor's stiffness distribution to adapt to changes in the knee joint's motion state, preventing the sensor from overcoming the pressure and exceeding its sensing range when subjected to strong pressure. The polyaniline coating on the surface of the nanoparticles also prevents agglomeration of the nanoparticles when the external magnetic field induces redistribution.

[0029] The present invention does not limit the method for characterizing the concentration of the first nanoparticles. For example, a scanning electron microscope is used to measure and calculate the area ratio of the first nanoparticles in the cross section perpendicular to the thickness direction of the gel film, and to measure and calculate the area ratio of the first nanoparticles on the surfaces on both sides of the gel film in the thickness direction.

[0030] In some preferred embodiments, the area ratio of the first nanoparticles in the cross-section of the gel film varies gradually along the thickness direction of the gel film, and the direction of the area ratio gradient variation is consistent with the direction of the elastic modulus gradient variation, and the area ratio gradient varies within a range of 7%-13% to 85%-95%. Under this preferred embodiment, regulating the concentration of the first nanoparticles on the side of the gel film with a higher elastic modulus is more conducive to improving the signal strength in the high-voltage region of the sensor and improving high-voltage sensitivity. The area ratio of the first nanoparticles in the cross-section of the gel film can be obtained, for example, by scanning electron microscopy. The area ratio of the first nanoparticles in the cross-section of the gel film is on both sides of the thickness direction of the gel film, which is reflected as the area ratio of the first nanoparticles on the surfaces of both sides of the gel film.

[0031] In some preferred embodiments, along the direction of the gradient increase of the elastic modulus, the cross-linking density of the gel film increases gradiently.

[0032] In some preferred embodiments, the gel film has a thickness of 200 μm to 800 μm. In this preferred embodiment, the gel film has a thickness of no less than 200 μm, resulting in a wider modulus gradient, which is more conducive to improving low-pressure sensitivity and expanding the upper limit of the sensor's sensing range. The gel film thickness is preferably 350 μm to 650 μm, and more preferably 400 μm to 600 μm.

[0033] In some preferred embodiments, the ratio of the radius of the first nanoparticle's core to the thickness of the coating is 2 to 4; the particle size of the first nanoparticle is 15 nm to 30 nm. In this preferred embodiment, the ratio of the radius of the first nanoparticle's core to the thickness of the coating is no greater than 4, which is more conducive to improving the signal strength in the high-voltage area of ​​the sensor and improving high-voltage sensitivity. A ratio of no less than 2 is more conducive to dynamically adjusting the distribution density of the nanoparticles in real time by applying a magnetic field, regulating the elastic modulus distribution of the gel film, and adaptively changing the sensor stiffness distribution with the motion state of the knee joint, etc. The particle size of the first nanoparticle is 15 nm to 30 nm, which is more conducive to preventing nanoparticle sedimentation or agglomeration during the application of an external magnetic field, effectively regulating the distribution density of the nanoparticles, effectively regulating the elastic modulus distribution of the gel film, and adaptively changing the sensor stiffness distribution with the motion state of the knee joint, etc. The ratio of the radius of the first nanoparticle's core to the thickness of the coating is, for example, 2, 2.5, 3, 3.5, and 4, and the particle size of the first nanoparticle is, for example, 15 nm, 20 nm, 25 nm, and 30 nm.

[0034] In some preferred embodiments, in the polymer ionic liquid gel, the cation of the ionic liquid includes at least one of a 1-ethyl-3-methylimidazolium cation, a 1-butyl-3-methylimidazolium cation, a 1-hexyl-3-methylimidazolium cation, and a 1-allyl-3-methylimidazolium cation, and the anion of the ionic liquid includes at least one of a bis(trifluoromethylsulfonyl)imide anion, a tetrafluoroborate anion, and a hexafluorophosphate anion.

[0035] In some preferred embodiments, the polymer in the polymer ionic liquid gel includes at least one of acrylamide-butyl acrylate copolymer, acrylic acid-ethyl acrylate copolymer, acrylic acid-methyl acrylate copolymer, and acrylic acid-acrylamide copolymer. More preferably, the polymer is an acrylic acid-acrylamide copolymer. On the one hand, the concentration of the first nanoparticles coated with a conductive polyaniline layer is relatively high on the side of the gel film with a higher elastic modulus. This preferred embodiment further enhances the high-voltage sensitivity of the sensor. Furthermore, the polymer ionic liquid gel formed by the acrylic acid-acrylamide copolymer is more stable, facilitating accurate pressure sensing and improved sensor sensitivity.

[0036] In a second aspect, the present invention provides a method for preparing the gel film described in the first aspect, comprising: dispersing nanoparticles in a polymer ionic liquid gel matrix liquid, adding a photoinitiator to the matrix liquid, mixing uniformly to obtain a mixed liquid, injecting the mixed liquid into a mold, placing the mold containing the mixed liquid on a UV exposure table, applying a magnetic field along the thickness direction of the mixed liquid, and inducing a curing reaction by UV irradiation to obtain the gel film; the nanoparticles include first nanoparticles and second nanoparticles, the first nanoparticles and the second nanoparticles respectively including a core and a coating layer coated on the surface of the core, the cores of the first nanoparticles and the second nanoparticles both include Fe3O4, the coating layer of the first nanoparticle includes polyaniline, the coating layer of the second nanoparticle includes a crosslinking agent, the matrix liquid includes an ionic liquid and an organic monomer, and under UV irradiation conditions, the crosslinking agent causes the organic monomer to undergo a polymerization and crosslinking reaction.

[0037] During the preparation of the gel film of the present invention, a mixed liquid contains first nanoparticles and second nanoparticles, both of which have cores including Fe3O4. A magnetic field is applied along the thickness direction of the mixed liquid, that is, a magnet is set on one side of the thickness direction of the mixed liquid. Under the action of the magnetic field, the first nanoparticles and the second nanoparticles migrate. There is a concentration gradient between the first nanoparticles and the second nanoparticles. The concentration of the nanoparticles is higher on the side close to the magnet and lower on the side away from the magnet. During the ultraviolet light irradiation and curing process, a concentration gradient of the first nanoparticles and a concentration gradient of the second nanoparticles are formed in the gel film. Due to the inclusion of the second nanoparticles, the concentration of the first nanoparticles and the second nanoparticles is lower. The coating includes a crosslinking agent, which forms a concentration gradient of the crosslinking agent while forming a concentration gradient of the second nanoparticles. UV light irradiation is used for UV curing, and the organic monomers in the matrix liquid undergo a polymerization and crosslinking reaction. While fixing the concentration gradient of the first nanoparticles and the concentration gradient of the second nanoparticles, a concentration gradient of crosslink density is formed. The greater the polymer crosslinking density, the greater the elastic modulus. The greater the nanoparticle concentration, the greater the elastic modulus. By forming the concentration gradient of the first nanoparticles, the concentration gradient of the second nanoparticles, and the concentration gradient of the crosslink density, the prepared gel film has an elastic modulus gradient along the thickness direction of the gel film. The present invention can simultaneously form a concentration gradient of the nanoparticles and a concentration gradient of the crosslink density by simply applying a magnetic field along the thickness direction of the mixed liquid. The elastic modulus gradient is formed by the synergistic action of the concentration gradient of the nanoparticles and the concentration gradient of the crosslink density. It can be understood that the thickness direction of the mixed liquid corresponds to the thickness direction of the gel film formed by the curing reaction.

[0038] The present invention does not limit the preparation method of the first nanoparticles; wet coating methods, etc., can be used. Preparation in an aqueous system is preferred. Fe3O4 interacts with water, equivalent to hydration, and the Fe3O4 surface contains hydroxyl groups (-OH). These hydroxyl groups (-OH) form coordination bonds with amine groups (-NH-) in polyaniline. This improves the interfacial stability between the core of the first nanoparticle and the coating layer, further preventing separation of the Fe3O4 and polyaniline during use of the pressure sensor, thereby ensuring stable operation of the sensor. The present invention does not limit the formation of the Fe3O4 core; for example, the Fe3O4 core can be obtained by reacting FeCl3·6H2O and NaAc in an ethylene glycol solvent.

[0039] In some preferred embodiments, the organic monomers include acrylamide monomers and acrylic acid monomers.

[0040] Preferably, the preparation of the second nanoparticles includes: coating Fe3O4 particles with SiO2, performing amino modification on the surface of the SiO2 coating to obtain precursor nanoparticles, and coating the precursor nanoparticles with methacrylic anhydride. This preferred embodiment facilitates stable coating of the Fe3O4 core with the methacrylic anhydride crosslinker during gel film preparation, and forms a concentration gradient of crosslinking degree by applying a magnetic field. The amino modification method of the present invention, for example, involves reacting Fe3O4 particles coated with a SiO2 layer with γ-aminopropyltriethoxysilane (APTES) in an aqueous system. The methacrylic anhydride coating method of the present invention, for example, utilizes a wet coating process in an aqueous system.

[0041] Preferably, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, the content of acrylamide monomer in the organic monomer is 10wt%~50wt% and the content of acrylic acid monomer is 50wt%~90wt%, the matrix liquid also includes a solvent, and the solvent is anhydrous ethanol; the composition of the matrix liquid includes: the ratio of the mass of the ionic liquid to the mass of the organic monomer is 0.3~0.7, and the ratio of the mass of the solvent to the mass of the organic monomer is 0.15~0.25; the photoinitiator is a LAP photoinitiator, and the composition of the mixed liquid includes: the ratio of the mass of the first nanoparticles to the mass of the organic monomer is 0.001~0.005, the ratio of the mass of the second nanoparticles to the mass of the organic monomer is 0.005~0.02, and the ratio of the mass of the photoinitiator to the mass of the organic monomer is 0.003~0.007; the magnetic induction intensity of the magnetic field is 0.15T~0.9T. Under this preferred embodiment, by controlling the type of ionic liquid, the type and composition of the organic monomer, the type of solvent, the composition of the matrix liquid, the composition of the mixed liquid, the content of the first nanoparticles, the content of the second nanoparticles, and the magnetic induction intensity of the magnetic field, it is more conducive to making the area ratio of the first nanoparticles in the cross-section of the gel film along the thickness direction of the gel film gradually change within the range of 7%~13% to 85%~95%.

[0042] Further preferably, the ratio of the radius of the core of the first nanoparticle to the thickness of the coating layer is 2 to 4, the particle size of the first nanoparticle is 15 nm to 30 nm, the ratio of the radius of the core of the second nanoparticle, the thickness of the SiO2 coating layer, and the thickness of the methacrylic anhydride coating layer is 1:0.2 to 0.4:0.1 to 0.15, the particle size of the second nanoparticle is 16 nm to 37 nm, and the conditions for the ultraviolet light curing reaction include: the ultraviolet light wavelength is 365 nm, the ultraviolet light intensity is 40 mW / cm 2 ~50 mW / cm 2 , and the UV irradiation time is 2 minutes to 6 minutes. Under this preferred embodiment, by further controlling the nanoparticle size, the ratio of the core to the coating thickness, and the conditions of the UV curing reaction, it is more conducive to improving the low-pressure sensitivity of the sensor, broadening the upper limit of the sensor's sensing range, while increasing the signal strength in the sensor's high-pressure region and improving high-pressure sensitivity. Controlling the particle size of the first nanoparticles to 15 nm to 30 nm and the particle size of the second nanoparticles to 16 nm to 37 nm prevents nanoparticle agglomeration and sedimentation, and also facilitates the formation of a concentration gradient of the first nanoparticles and a concentration gradient of the second nanoparticles by applying a magnetic field.

[0043] In a third aspect, the present invention provides a pressure sensor, comprising: a plate comprising a first plate and a second plate stacked together; The sensitive layer is stacked between the first electrode plate and the second electrode plate, and comprises the gel film described in the first aspect or the gel film prepared by the preparation method of the gel film described in the second aspect.

[0044] The gel film serving as the sensitive layer in the pressure sensor of the present invention has a gradient change in elastic modulus along the thickness direction of the gel film. When the pressure is low, the side of the gel film with the lower elastic modulus deforms significantly, thereby increasing the signal strength in the low-pressure region of the pressure sensor and improving the low-pressure sensitivity. Since the elastic modulus on one side of the gel film is higher, the upper limit of the sensor's sensing range can be widened. To widen the sensing range, the concentration of first nanoparticles having a conductive polyaniline coating on the side of the gel film with the higher elastic modulus is also relatively higher. Due to the higher elastic modulus on one side of the gel film and the higher concentration of the first nanoparticles, the signal strength in the high-pressure region of the sensor can be increased while widening the upper limit of the sensor's sensing range, thereby improving the high-pressure sensitivity.

[0045] In a fourth aspect, the present invention provides a pressure sensor for a knee joint, which is the pressure sensor described in the third aspect.

[0046] In a fifth aspect, the present invention provides a pressure sensor, referring to Figure 1 , including an upper electrode plate 1, a lower electrode plate 2 and a gel film sensitive layer 3 stacked between the upper electrode plate 1 and the lower electrode plate 2 ( Figure 2 This is a physical picture of the gel film of the present invention. Figure 3 is a microstructure diagram of the gel film of the present invention); The upper electrode plate 1 includes a stacked flexible substrate layer 11 and a hydrogen-bonded polymer layer 12. The side of the hydrogen-bonded polymer layer 12 facing away from the flexible substrate layer 11 has a directional crack network, and the cracks in the directional crack network have a consistent direction. The upper electrode plate 1 also includes an electrode layer (not shown in the figure), which is continuously attached to the side of the hydrogen-bonded polymer layer 12 where the directional crack network is located. The electrode layer is attached to the inner surface of the crack and the surface of the crack edge. The gel film sensitive layer 3 includes a gel film, the substrate of which includes a polymer ionic liquid gel, and the gel film is doped with first nanoparticles (not shown in the figure). The first nanoparticles include a core and a coating coated on the surface of the core. The core includes Fe3O4, and the coating includes polyaniline. Along the thickness direction of the gel film, the elastic modulus of the gel film changes gradiently and the concentration of the first nanoparticles changes gradiently. The direction of the elastic modulus gradient change is consistent with the direction of the concentration gradient change. The side of the gel film with a lower elastic modulus is located near the upper electrode 1. The lower electrode plate 2 includes a polymer film and an electrode layer. One side surface of the polymer film has a protrusion array. The protrusion is arched, and the modulus of the arched protrusion increases gradually from the bottom to the top. The electrode layer is attached to the side of the polymer film where the protrusion array is located.

[0047] The material of the electrode layer of the upper plate of the present invention is preferably a conductive polymer / silver nanowire composite material layer, and the conductive polymer is further preferably a conductive polymer composed of poly(3,4-ethylenedioxythiophene) / poly(p-styrene sulfonic acid). The present invention does not limit the material of the electrode layer of the lower plate, for example, it can be a Ti / Au electrode, and the thickness of the electrode layer is also not limited, for example, it can be 80nm to 120nm. The pressure sensor of the present invention can, for example, connect each electrode to the edge processing module through a serpentine metal wire, and the material of the serpentine metal wire is, for example, a eutectic gallium-indium alloy, EGaIn.

[0048] The upper electrode plate of the pressure sensor of the present invention has a directional crack network on the side of the polymer layer containing hydrogen bonds facing away from the flexible base layer. The cracks in the directional crack network have a consistent direction. When the pressure sensor is subjected to pressure, the cracks open and deform, and the area of ​​the electrode plate in contact with the sensitive layer becomes larger, generating a pressure-capacitive signal, which can improve the response sensitivity of the pressure sensor when subjected to relatively small pressure. When the pressure sensor is subjected to relatively large or more frequent pressure, the cracks are prone to break, which is manifested as fine cracks extending around the directional cracks, affecting the sensing accuracy and sensor life. When the pressure sensor is subjected to relatively small pressure for a period of time, the width of the extended small cracks is shortened to the molecular force spacing. Through hydrogen bond self-repair, the extended small cracks can be eliminated and the broken cracks can be repaired, which can improve the sensing accuracy and sensor life.

[0049] The lower electrode plate of the pressure sensor of the present invention has a protrusion array on one side surface of the polymer film, and the protrusions are arched. The electrode layer is attached to the side of the polymer film where the protrusion array is located. When the arch is under pressure, the contact area changes, and the top of the arch is coupled with the sensitive layer to generate a capacitance signal. The arch electrode and the electrode on the other side of the sensitive layer constitute an interface capacitance. When the arch is under pressure, the interface capacitance changes to generate an ionization signal, which can improve the response sensitivity of the sensor when it is subjected to greater pressure. The modulus of the arch protrusion increases gradually from the bottom to the top, which can further improve the response sensitivity of the pressure sensor when it is subjected to greater pressure.

[0050] In a sixth aspect, the present invention provides a pressure sensor for a knee joint, which is the pressure sensor described in the fifth aspect.

[0051] The present invention will be further described in detail below with reference to specific embodiments.

[0052] Example 1 A pressure sensor includes: a plate, which includes a first plate and a second plate stacked together; a sensitive layer stacked between the first plate and the second plate; the sensitive layer includes a gel film, the substrate of the gel film includes a polymer ionic liquid gel, the polymer is an acrylic acid-acrylamide copolymer, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, the gel film is doped with first nanoparticles, the first nanoparticles include a core and a coating layer coated on the surface of the core, the core is Fe3O4, the coating layer is polyaniline, the ratio of the radius of the core of the first nanoparticle to the thickness of the coating layer is about 3, and the first nanoparticles are doped with first nanoparticles. The particle size of the rice particles is about 22 nm. Along the thickness direction of the gel film, the crosslinking density of the gel film changes gradiently, the concentration of the first nanoparticles changes gradiently, and the elastic modulus of the gel film changes gradiently. The direction of the crosslinking density gradient change, the direction of the first nanoparticle concentration gradient change, and the direction of the elastic modulus gradient change are consistent. Along the thickness direction of the gel film, the area ratio of the first nanoparticles in the cross-section of the gel film changes gradiently, and the direction of the area ratio gradient change is consistent with the direction of the elastic modulus gradient change. The area ratio changes gradiently in the range of 10% to 90%. The thickness of the gel film is about 500 μm.

[0053] A method for preparing the aforementioned gel film comprises: Step 1: preparing second nanoparticles, coating SiO2 on the surface of Fe3O4 particles, performing amino modification on the surface of the SiO2 coating layer to obtain precursor nanoparticles, coating the surface of the precursor nanoparticles with methacrylic anhydride (cross-linking agent) to obtain second nanoparticles, wherein the ratio of the radius of the core of the second nanoparticles, the thickness of the SiO2 coating layer, and the thickness of the methacrylic anhydride coating layer is 1:0.2:0.15, and the particle size of the second nanoparticles is approximately 20 nm; preparing first nanoparticles by wet coating in an aqueous system, wherein the ratio of the radius of the core of the first nanoparticles to the thickness of the coating layer is approximately 3, and the particle size of the first nanoparticles is approximately 22 nm; Step 2: dispersing the first nanoparticles and the second nanoparticles in a polymer ionic liquid gel matrix liquid, adding a photoinitiator to the matrix liquid, mixing uniformly to obtain a mixed liquid, and injecting the mixed liquid into a mold; the matrix liquid includes 1-ethyl-3-methylimidazole bis(trifluoromethylsulfonyl)imide (ionic liquid), acrylamide monomer / acrylic acid monomer (organic monomer), and anhydrous ethanol, wherein the content of acrylamide monomer in the organic monomer is 30wt% and the content of acrylic acid monomer is 70wt%, the composition of the matrix liquid is that the ratio of the mass of the ionic liquid to the mass of the organic monomer is 0.5, the ratio of the mass of the solvent to the mass of the organic monomer is 0.22, the photoinitiator is LAP photoinitiator, the composition of the mixed liquid is that the ratio of the mass of the first nanoparticle to the mass of the organic monomer is 0.003, the ratio of the mass of the second nanoparticle to the mass of the organic monomer is 0.012, and the ratio of the mass of the photoinitiator to the mass of the organic monomer is 0.005; Step 3: Place the mold containing the mixed solution on a UV exposure table, apply a magnetic field along the thickness direction of the mixed solution, and after UV irradiation to induce a curing reaction, remove the magnetic field and dry at 60°C to obtain the gel film; the magnetic induction intensity of the magnetic field is 0.5T, and the conditions for the UV irradiation curing reaction include: UV wavelength of 365 nm, UV intensity of 40 mW / cm 2 , the UV irradiation time is 5min.

[0054] Example 2 The preparation method of the gel film is carried out in accordance with Example 1, except that in step 3, the magnetic field intensity is 0.1 T. The pressure sensor is prepared in accordance with Example 1, except that the area ratio of the first nanoparticles in the cross section of the gel film is gradually changed within a range of 40% to 60%.

[0055] Example 3 The preparation method of the gel film was similar to that of Example 1, except that in step 2, the ratio of the mass of the first nanoparticles to the mass of the organic monomer in the mixed solution was 0.0007. The pressure sensor was similar to that of Example 1, except that the area percentage of the first nanoparticles in the cross-section of the gel film varied gradually within a range of 6% to 83%.

[0056] Example 4 The preparation method of the gel film was carried out with reference to Example 1, except that in step 1, the ratio of the radius of the core of the second nanoparticle, the thickness of the SiO2 coating layer, and the thickness of the methacrylic anhydride coating layer was 1:0.2:0.3.

[0057] Example 5 Referring to the gel film of Example 1, the difference is that in step 1, the ratio of the radius of the inner core of the first nanoparticle to the thickness of the coating layer is 5.

[0058] Comparative Example 1 The gel film of Example 1 is referred to, except that the first nanoparticles do not have a coating layer of polyaniline.

[0059] Test Case The pressure sensors obtained from the above embodiments and comparative examples were subjected to low-pressure sensitivity and high-pressure sensitivity tests. The low-pressure sensitivity test method is to start from 0 MPa and load the pressure step by step at 5 points of 0.1 MPa, 0.2 MPa, 0.3 MPa, and 0.4 MPa; maintain the pressure at each point for 60 seconds and record the positive stroke output value; unload in the reverse direction to 0 MPa and record the reverse stroke output value, completing 3 cycles; calculate the slope of the working straight line in the low-pressure area. The high-pressure sensitivity test method is to start from 0.6 MPa and load at 5 points of 0.7 MPa, 0.8 MPa, 0.9 MPa, and 1.0 MPa; maintain the pressure at each point for 60 seconds and record the positive stroke output; maintain the pressure at 1.0 MPa for 1 minute and detect the overload stability; calculate the high-pressure sensitivity slope. The test results are shown in Table 1.

[0060] Table 1

[0061] Compared with the embodiment and comparative example 1, the surface of the first nanoparticles has a polyaniline coating layer, which can significantly improve the high-pressure sensitivity of the sensor.

[0062] Comparing Example 1 with Example 2, the magnetic induction intensity of the magnetic field is not less than 0.15T, which is more conducive to making the minimum value of the gradient change range of the area ratio of the first nanoparticles in the cross section of the gel film along the thickness direction of the gel film not more than 13%, and the maximum value not less than 85%, thereby improving the high-pressure sensitivity and low-pressure sensitivity of the sensor; Comparing Example 1 with Example 3, in the mixed solution, the ratio of the mass of the first nanoparticles to the mass of the organic monomer is not less than 0.001, which is more conducive to making the area ratio of the first nanoparticles in the cross section of the gel film along the thickness direction of the gel film The minimum value of the degree of change range is not less than 7%, and the maximum value is not less than 85%, thereby improving the high-pressure sensitivity and low-pressure sensitivity of the sensor; comparing Example 1 with Example 4, the ratio of the radius of the inner core of the second nanoparticle, the thickness of the SiO2 coating layer, and the thickness of the methacrylic anhydride coating layer is 1:0.2~0.4:0.1~0.15, which is more conducive to improving the low-pressure sensitivity and high-pressure sensitivity of the sensor; comparing Example 1 with Example 5, the ratio of the radius of the inner core of the first nanoparticle to the thickness of the coating layer is 2~4, which is more conducive to improving the low-pressure sensitivity and high-pressure sensitivity of the sensor.

[0063] The preferred embodiments of the present invention have been described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, various simple variations of the technical solution of the present invention may be made, including combining the various technical features in any other appropriate manner. These simple variations and combinations should also be regarded as disclosed in the present invention and fall within the scope of protection of the present invention.

Claims

1. A gel film for a pressure sensor, characterized in that: The substrate of the gel film includes a polymer ionic liquid gel, the gel film is doped with first nanoparticles, the first nanoparticles include a core and a coating layer coated on the surface of the core, the core includes Fe3O4, and the coating layer includes polyaniline; Along the thickness direction of the gel film, the elastic modulus of the gel film changes gradiently and the concentration of the first nanoparticles changes gradiently, and the direction of the elastic modulus gradient change is consistent with the direction of the concentration gradient change.

2. The gel film according to claim 1, wherein Along the thickness direction of the gel film, the area ratio of the first nanoparticles in the cross-section of the gel film changes gradually, and the direction of the area ratio gradient change is consistent with the direction of the elastic modulus gradient change, and the area ratio changes gradually in the range of 7%~13% to 85%~95%.

3. The gel film according to claim 1, wherein Along the direction of the gradient increase of the elastic modulus, the cross-linking density of the gel film increases gradiently.

4. The gel film according to claim 1, wherein The thickness of the gel film is 200 μm to 800 μm.

5. The gel film according to claim 1, wherein The ratio of the radius of the core of the first nanoparticle to the thickness of the coating layer is 2 to 4; the particle size of the first nanoparticle is 15 nm to 30 nm.

6. The gel film according to claim 1, wherein In the polymer ionic liquid gel, the cation of the ionic liquid includes at least one of 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-allyl-3-methylimidazolium cation, and the anion of the ionic liquid includes at least one of bis(trifluoromethylsulfonyl)imide anion, tetrafluoroborate anion, and hexafluorophosphate anion.

7. The gel film according to claim 1, wherein In the polymer ionic liquid gel, the polymer includes at least one of acrylamide-butyl acrylate copolymer, acrylic acid-ethyl acrylate copolymer, acrylic acid-methyl acrylate copolymer, and acrylic acid-acrylamide copolymer.

8. The method for preparing a gel film according to any one of claims 1 to 7, characterized in that: include: Nanoparticles are dispersed in a polymer ionic liquid gel matrix liquid, and a photoinitiator is added to the matrix liquid, mixed evenly to obtain a mixed liquid, the mixed liquid is injected into a mold, the mold containing the mixed liquid is placed on a UV exposure table, a magnetic field is applied along the thickness direction of the mixed liquid, and a curing reaction is initiated by UV irradiation to obtain the gel film; the nanoparticles include first nanoparticles and second nanoparticles, the first nanoparticles and the second nanoparticles respectively include a core and a coating layer coated on the surface of the core, the cores of the first nanoparticles and the second nanoparticles both include Fe3O4, the coating layer of the first nanoparticles includes polyaniline, the coating layer of the second nanoparticles includes a crosslinking agent, the matrix liquid includes an ionic liquid and an organic monomer, and under UV irradiation conditions, the crosslinking agent causes the organic monomer to undergo a polymerization and crosslinking reaction.

9. The method for preparing a gel film according to claim 8, wherein: The organic monomers include acrylamide monomers and acrylic acid monomers.

10. The method for preparing a gel film according to claim 9, wherein: The preparation of the second nanoparticles includes: coating SiO2 on the surface of Fe3O4 particles, performing amino modification on the surface of the SiO2 coating layer to obtain precursor nanoparticles, and coating methacrylic anhydride on the surface of the precursor nanoparticles.

11. The method for preparing a gel film according to claim 9, wherein: The ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, the content of acrylamide monomer in the organic monomer is 10wt% to 50wt% and the content of acrylic acid monomer is 50wt% to 90wt%, and the matrix liquid further includes a solvent, which is anhydrous ethanol; The composition of the matrix liquid includes: the ratio of the mass of the ionic liquid to the mass of the organic monomer is 0.3~0.7, and the ratio of the mass of the solvent to the mass of the organic monomer is 0.15~0.25; the photoinitiator is a LAP photoinitiator, and the composition of the mixed liquid includes: the ratio of the mass of the first nanoparticles to the mass of the organic monomer is 0.001~0.005, the ratio of the mass of the second nanoparticles to the mass of the organic monomer is 0.005~0.02, and the ratio of the mass of the photoinitiator to the mass of the organic monomer is 0.003~0.007; the magnetic induction intensity of the magnetic field is 0.15T~0.9T.

12. A pressure sensor, characterized in that: include: The electrode plate comprises a first electrode plate and a second electrode plate stacked together; The sensitive layer is stacked between the first electrode plate and the second electrode plate, and comprises the gel film according to any one of claims 1 to 7 or the gel film prepared by the method for preparing the gel film according to any one of claims 8 to 11.

13. A pressure sensor for a knee joint, characterized in that: This is the pressure sensor according to claim 12.

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