Gel film for pressure sensor and method for manufacturing the same and sensor

Abstract

The present application belongs to the field of sensor, and particularly relates to a gel film of pressure sensor and a preparation method thereof and a sensor. The base material of the gel film comprises a polymer ionic liquid gel, and the gel film is doped with first nanoparticles, the first nanoparticles comprise a core and a coating layer coated on the surface of the core, the core comprises Fe3O4, and the coating layer comprises polyaniline; along the thickness direction of the gel film, the elastic modulus of the gel film changes in a gradient manner and the concentration of the first nanoparticles changes in a gradient manner, the direction of the elastic modulus gradient change is consistent with the direction of the concentration gradient change; the sensitivity can be significantly improved, and the range of the sensor can be widened.

Description

TECHNICAL FIELD

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

[0002] Body weight, muscle strength and coordination, movement patterns and posture, activity volume and intensity, joint structure and alignment, external load, and ground reaction force, etc. will bring pressure to the knee joint of the human body. The knee joint is one of the most complex and largest weight-bearing joints in the human body. Excessive pressure on the knee joint is easy to cause pain, strain (such as patellar tendonitis and bursitis), and cartilage wear (osteoarthritis). Effective monitoring of knee joint pressure is crucial for preventing injuries, guiding rehabilitation, optimizing athletic performance, osteoarthritis management, postoperative recovery, etc.

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

[0004] It should be noted that this part of the present application only provides background technology related to the present application, and does not necessarily constitute prior art or common knowledge. SUMMARY

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

[0006] In order to achieve the above-mentioned purpose, in a first aspect, the present application provides a gel film of a pressure sensor, the base material of the gel film comprises a polymer ionic liquid gel, the gel film is doped with first nanoparticles, the first nanoparticles comprise a core and a coating layer coated on the surface of the core, the core comprises Fe3O4, and the coating layer comprises polyaniline.

[0007] 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 gradient change of the elastic modulus is consistent with the direction of the gradient change of the concentration.

[0008] 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 gradiently, the direction of the gradient change of the area ratio is consistent with the direction of the gradient change of the elastic modulus, and the area ratio changes gradiently in the range of 7%~13% to 85%~95%.

[0009] In some preferred embodiments, along the direction of the gradient increase of the elastic modulus, the crosslinking density of the gel film increases gradiently.

[0010] In some preferred embodiments, the thickness of the gel film is 200 μm to 800 μm.

[0011] In some preferred embodiments, the ratio of the radius of the inner 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.

[0012] In some preferred embodiments, in the polymeric ionic liquid gel, the cation of the ionic liquid comprises 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 comprises at least one of bis(trifluoromethylsulfonyl)imide anion, tetrafluoroborate anion, and hexafluorophosphate anion.

[0013] In some preferred embodiments, in the polymeric ionic liquid gel, the polymer comprises at least one of acrylamide-butyl acrylate copolymer, acrylic acid-ethyl acrylate copolymer, acrylic acid-methyl acrylate copolymer, and acrylic acid-acrylamide copolymer.

[0014] In a second aspect, the present application provides a preparation method of the gel film according to the first aspect, comprising: dispersing nanoparticles in a polymeric ionic liquid gel base liquid, adding a photoinitiator to the base liquid, mixing uniformly to obtain a mixed liquid, injecting the mixed liquid into a mold, placing the mold containing the mixed liquid on an ultraviolet exposure platform, applying a magnetic field along the thickness direction of the mixed liquid, and irradiating ultraviolet light to initiate a curing reaction, thereby obtaining the gel film; wherein the nanoparticles comprise first nanoparticles and second nanoparticles, the first nanoparticles and the second nanoparticles each comprise an inner core and a coating layer coated on the surface of the inner core, the inner core of the first nanoparticles and the second nanoparticles each comprises Fe3O4, the coating layer of the first nanoparticles comprises polyaniline, and the coating layer of the second nanoparticles comprises a crosslinking agent; and the base liquid comprises an ionic liquid and an organic monomer, and under the condition of ultraviolet light irradiation, the crosslinking agent causes the organic monomer to undergo a polymerization and crosslinking reaction.

[0015] In some preferred embodiments, the organic monomer comprises acrylamide monomer and acrylic acid monomer.

[0016] Preferably, the preparation of the second nanoparticles comprises: coating SiO2 on the surface of Fe3O4 particles, performing an amination modification on the surface of the SiO2 coating layer to obtain precursor nanoparticles, and coating methacrylic anhydride on the surface of the precursor nanoparticles.

[0017] 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 base solution further comprises a solvent, and the solvent is anhydrous ethanol; the composition of the base solution comprises: 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 (lithium phenyl(2,4,6-trimethylbenzoyl)phosphinate), and the composition of the mixed solution comprises: 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.

[0018] In a third aspect, the present application provides a pressure sensor, comprising: a polar plate comprising a first polar plate and a second polar plate stacked together;

[0019] a sensitive layer stacked between the first polar plate and the second polar plate, comprising the gel film prepared by the preparation method of the gel film according to the first aspect or the second aspect.

[0020] In a fourth aspect, the present application provides a pressure sensor for a knee joint, which is the pressure sensor according to the third aspect.

[0021] The gel film of the present application, along the thickness direction of the gel film, the elastic modulus of the gel film changes in gradient, when the pressure is low, the side of the gel film with lower elastic modulus deforms obviously, which can improve the signal intensity of the low pressure area of the pressure sensor and improve the low pressure sensitivity, because the elastic modulus of one side of the gel film is higher, the upper limit of the sensor sensing range can be expanded, the sensing range is widened, when the pressure is higher, the elastic modulus of one side of the gel film is higher, the deformation of the gel film is relatively small, and the concentration of the first nanoparticles with conductive polyaniline coating layer on the side of the gel film with higher elastic modulus is also relatively high, through the higher elastic modulus of one side of the gel film and the higher concentration of the first nanoparticles, the signal intensity of the high pressure area of the sensor can be improved while the upper limit of the sensor sensing range is expanded, and the high pressure sensitivity is improved. Because the nanoparticles with Fe3O4 as the core are doped in the gel film, Fe3O4 has magnetization characteristics, by applying an external magnetic field, the magnetization characteristics of Fe3O4 cause the redistribution of the nanoparticles, the distribution density of the nanoparticles is dynamically adjusted in real time, which can regulate the elastic modulus distribution of the gel film, so that the stiffness distribution of the sensor changes adaptively with the motion state of the knee joint and the like, thereby preventing the sensor from being unable to resist the pressure and exceeding the sensing range when the sensor is subjected to strong pressure.

[0022] In the preparation process of the gel film of the present application, the mixed solution contains the first nanoparticles and the second nanoparticles with Fe3O4 as the core, a magnetic field is applied along the thickness direction of the mixed solution, i.e. a magnet is arranged on one side of the mixed solution in the thickness direction, under the action of the magnetic field, the first nanoparticles and the second nanoparticles migrate, the first nanoparticles and the second nanoparticles exist in concentration gradient, the concentration of the nanoparticles on the side close to the magnet is higher, and the concentration of the nanoparticles on the side far from the magnet is lower, during the ultraviolet light irradiation and curing process, the concentration gradient of the first nanoparticles and the concentration gradient of the second nanoparticles are formed in the gel film, because the coating layer of the second nanoparticles includes a crosslinking agent, the concentration gradient of the crosslinking agent is formed at the same time as the concentration gradient of the second nanoparticles, the ultraviolet light irradiation is carried out for ultraviolet light curing, the organic monomers in the base solution undergo polymerization and crosslinking reaction, the concentration gradient of the crosslinking density is formed at the same time as the concentration gradient of the first nanoparticles and the concentration gradient of the second nanoparticles, the greater the crosslinking density of the polymer, the greater the elastic modulus, the greater the concentration of the nanoparticles, the greater the elastic modulus, through the formation of the concentration gradient of the first nanoparticles, the concentration gradient of the second nanoparticles and the concentration gradient of the crosslinking density, the prepared gel film has elastic modulus gradient along the thickness direction of the gel film. The present application can form the concentration gradient of the nanoparticles and the concentration gradient of the crosslinking density at the same time only by applying a magnetic field along the thickness direction of the mixed solution, and the elastic modulus gradient is formed through the synergistic effect of the concentration gradient of the nanoparticles and the concentration gradient of the crosslinking density. BRIEF DESCRIPTION OF DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the present application, and therefore should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0024] Figure 1 A cross-sectional view of a pressure sensor of the present application;

[0025] Figure 2 A physical diagram of a gel film of the present application;

[0026] Figure 3 A microstructure diagram of a gel film of the present application.

[0027] Explanation of reference signs:

[0028] 1, upper electrode plate; 11, flexible substrate layer; 12, hydrogen-bonded polymer layer; 2, lower electrode plate; 3, gel film sensitive layer. DETAILED DESCRIPTION

[0029] The endpoints of the ranges and any values disclosed herein are not limited to the precise values recited as the exact dimensions are not considered critical for the present application. The endpoints of the ranges and any values are provided as approximations only and are understood to encompass values approximately the same as the endpoints. Any numerical range recited is intended to include all sub-ranges subsumed therein. For ranges including an approximate value, the approximate value is intended to mean + / - 1% of the value. In some embodiments, the number of significant digits conveys neither limitations on discemability nor on accuracy, for the purposes of this application. All numerical values are understood to be modified in all instances by the term "about" to permit for variations in estimation, measurement, and / or transmission of the value, either inherent in the measurement process or arising from the statistics of a sampling or measuring process.

[0030] The inventor of the present application has found that the existing pressure sensor has limited sensitivity and sensing range when monitoring the pressure of the knee joint.

[0031] To this end, in a first aspect, the present application provides a gel film of a pressure sensor, the base material of the gel film comprising a polymer ionic liquid gel, the gel film being 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.

[0032] Along the thickness direction of the gel film, the elastic modulus of the gel film changes in a gradient manner and the concentration of the first nanoparticles changes in a gradient manner, and the direction of the gradient change of the elastic modulus is consistent with the direction of the gradient change of the concentration.

[0033] The substrate of the gel film of the present application comprises a polymer ionic liquid gel, and the coating layer of the first nanoparticles doped in the gel film comprises polyaniline. The polyaniline coating layer forms a conductive path in the gel film as a "wire network", so that the gel film can be used as a pressure-sensitive layer of a pressure sensor. When used as a pressure-sensitive layer of a pressure sensor, the elastic modulus of the gel film changes in a gradient along the thickness direction of the gel film. When the pressure is low, the side of the gel film with a lower elastic modulus deforms significantly, which can improve the signal intensity in the low pressure area of the pressure sensor and improve the low pressure sensitivity. Since the elastic modulus of one side of the gel film is higher, the upper limit of the sensing range of the sensor can be widened. When the pressure is high, the side of the gel film with a higher elastic modulus deforms relatively less, while the side of the gel film with a higher elastic modulus has a relatively higher concentration of the first nanoparticles with a conductive polyaniline coating layer. By increasing the elastic modulus of one side of the gel film and the concentration of the first nanoparticles, the signal intensity in the high pressure area of the sensor can be improved while the upper limit of the sensing range of the sensor is widened, and the high pressure sensitivity is improved.

[0034] Since the gel film is doped with nanoparticles with Fe3O4 as the core, Fe3O4 has magnetization characteristics. By applying an external magnetic field, the magnetization characteristics of Fe3O4 can cause the redistribution of the nanoparticles, dynamically adjust the distribution density of the nanoparticles in real time, and control the elastic modulus distribution of the gel film, so that the stiffness distribution of the sensor can adaptively change with the motion state of the knee joint, etc. Thus, when the sensor is subjected to strong pressure, the sensor can resist the pressure and not exceed the sensing range. The surface of the nanoparticles of the present application is coated with polyaniline, which can also prevent the nanoparticles from agglomerating when the first nanoparticles are redistributed by applying an external magnetic field.

[0035] The present application does not limit the method for characterizing the concentration of the first nanoparticles. For example, a scanning electron microscope can be 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 the area ratio of the first nanoparticles on the two surfaces of the gel film in the thickness direction.

[0036] In some preferred embodiments, the area ratio of the first nanoparticles in the cross section of the gel film changes in a gradient along the thickness direction of the gel film, and the direction of the gradient change of the area ratio is consistent with the direction of the gradient change of the elastic modulus. The area ratio changes in a gradient in the range of 7% to 13% to 85% to 95%. In this preferred scheme, controlling 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 intensity in the high pressure area of the sensor and improving the high pressure sensitivity. The area ratio of the first nanoparticles in the cross section of the gel film is obtained by a scanning electron microscope, and the area ratio of the first nanoparticles on the two surfaces of the gel film in the thickness direction is represented by the area ratio of the first nanoparticles on the two surfaces of the gel film.

[0037] In some preferred embodiments, the cross-linking density of the gel thin film increases along the direction of the gradient increase of the elastic modulus.

[0038] In some preferred embodiments, the thickness of the gel thin film is 200 μm to 800 μm. In this preferred scheme, the thickness of the gel thin film is not less than 200 μm, and the modulus gradient is wider, which is more conducive to improving the low-pressure sensitivity and widening the upper limit of the sensor sensing range. The thickness of the gel thin film is preferably 350 μm to 650 μm, and more preferably 400 μm to 600 μm.

[0039] 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. In this preferred scheme, the ratio of the radius of the core of the first nanoparticle to the thickness of the coating layer is not higher than 4, which is more conducive to improving the signal intensity in the high-pressure region of the sensor and improving the high-pressure sensitivity. The ratio is not less than 2, which 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 thin film, and making the stiffness distribution of the sensor adaptively change 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 the nanoparticles from settling or agglomerating during the application of an external magnetic field, effectively adjusting the distribution density of the nanoparticles, effectively regulating the elastic modulus distribution of the gel thin film, and making the stiffness distribution of the sensor adaptively change with the motion state of the knee joint, etc. The ratio of the radius of the core of the first nanoparticle to the thickness of the coating layer 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.

[0040] In some preferred embodiments, in the polymeric ionic liquid gel, the cation of the ionic liquid comprises at least one of 1-ethyl-3-methylimidazole cation, 1-butyl-3-methylimidazole cation, 1-hexyl-3-methylimidazole cation, and 1-allyl-3-methylimidazole cation, and the anion of the ionic liquid comprises at least one of bis(trifluoromethylsulfonyl)imide anion, tetrafluoroborate anion, and hexafluorophosphate anion.

[0041] In some preferred embodiments, the polymer in the polymer ionic liquid gel comprises at least one of acrylamide-butyl acrylate copolymer, acrylic acid-ethyl acrylate copolymer, acrylic acid-methyl acrylate copolymer, and acrylic acid-acrylamide copolymer. The polymer is further preferably acrylic acid-acrylamide copolymer, on the one hand, the concentration of the first nanoparticles with the polyaniline coating layer is relatively high on the side with higher elastic modulus of the gel thin film, which is more conducive to improving the high pressure sensitivity of the sensor under this preferred scheme, on the other hand, the polymer ionic liquid gel formed by the acrylic acid-acrylamide copolymer is more stable, which is more conducive to accurately sensing pressure and improving sensing sensitivity.

[0042] In a second aspect, the present application provides a preparation method of the gel thin film of the first aspect, comprising: dispersing nanoparticles in a polymer ionic liquid gel base liquid, adding a photoinitiator to the base liquid, mixing uniformly to obtain a mixed liquid, injecting the mixed liquid into a mold, placing the mold containing the mixed liquid on an ultraviolet exposure platform, applying a magnetic field along the thickness direction of the mixed liquid, and irradiating ultraviolet light to initiate a curing reaction to obtain the gel thin film; the nanoparticles comprise first nanoparticles and second nanoparticles, the first nanoparticles and the second nanoparticles each comprise a core and a coating layer coated on the surface of the core, the core of the first nanoparticles and the second nanoparticles each comprises Fe3O4, the coating layer of the first nanoparticles comprises polyaniline, and the coating layer of the second nanoparticles comprises a crosslinking agent; the base liquid comprises an ionic liquid and an organic monomer, and under the condition of ultraviolet light irradiation, the crosslinking agent causes the organic monomer to undergo a polymerization and crosslinking reaction.

[0043] In the preparation process of the gel film, the mixed solution contains the first nanoparticles and the second nanoparticles, both of which include Fe3O4, and a magnetic field is applied along the thickness direction of the mixed solution, i.e., a magnet is arranged on one side in the thickness direction of the mixed solution. Under the action of the magnetic field, the first nanoparticles and the second nanoparticles migrate, and the first nanoparticles and the second nanoparticles have a concentration gradient. On the side close to the magnet, the concentration of the nanoparticles is relatively high, and on the side far from the magnet, the concentration of the nanoparticles is relatively low. During the ultraviolet light irradiation and curing process, the concentration gradient of the first nanoparticles and the concentration gradient of the second nanoparticles are formed in the gel film. Since the coating layer of the second nanoparticles includes a crosslinking agent, the concentration gradient of the crosslinking agent is formed at the same time as the concentration gradient of the second nanoparticles. During the ultraviolet light irradiation and curing process, the organic monomers in the base solution undergo polymerization and crosslinking reactions, and at the same time, the concentration gradient of the crosslinking density is formed. The greater the crosslinking density of the polymer, the greater the elastic modulus. The greater the concentration of the nanoparticles, the greater the elastic modulus. Through the formation of the concentration gradient of the first nanoparticles, the concentration gradient of the second nanoparticles, and the concentration gradient of the crosslinking density, the elastic modulus gradient changes along the thickness direction of the gel film. According to the present application, only by applying a magnetic field along the thickness direction of the mixed solution, the concentration gradient of the nanoparticles and the concentration gradient of the crosslinking density can be formed at the same time. The elastic modulus gradient is formed through the synergistic effect of the concentration gradient of the nanoparticles and the concentration gradient of the crosslinking density. It can be understood that the thickness direction of the mixed solution corresponds to the thickness direction of the gel film formed by the curing reaction.

[0044] The present application does not limit the preparation method of the first nanoparticles, which can be coated by wet method, etc., and is preferably prepared in a water system. Fe3O4 and water have certain interaction, which is equivalent to hydration. The surface of Fe3O4 contains hydroxyl groups (-OH), and the hydroxyl groups (-OH) on the surface of Fe3O4 form coordinate bonds with the amine groups (-NH-) in polyaniline. The interface stability of the core and the coating layer of the first nanoparticles is improved, which is more conducive to preventing the separation of Fe3O4 and polyaniline during the use of the pressure sensor, thereby ensuring the stable use of the sensor. The present application does not limit the formation of the Fe3O4 core, for example, FeCl3·6H2O and NaAc are reacted in an ethylene glycol solvent to obtain the Fe3O4 core.

[0045] In some preferred embodiments, the organic monomers include acrylamide monomers and acrylic acid monomers.

[0046] Preferably, the preparation of the second nanoparticles comprises: coating the surface of Fe3O4 particles with SiO2, modifying the surface of the SiO2 coating layer with amino groups to obtain precursor nanoparticles, and coating the surface of the precursor nanoparticles with methacrylic anhydride. In this preferred scheme, the methacrylic anhydride crosslinking agent is more stably coated on the surface of the Fe3O4 core during the preparation of the gel film, and a concentration gradient of crosslinking degree is formed by applying a magnetic field. The amino modification method of the present application, for example, reacts Fe3O4 particles coated with a SiO2 layer with γ-aminopropyltriethoxysilane (APTES) in a water system. The methacrylic anhydride coating method of the present application, for example, uses wet coating in a water system.

[0047] Preferably, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, the content of acrylamide monomers in the organic monomers is 10wt%-50wt%, and the content of acrylic acid monomers is 50wt%-90wt%, the base solution further comprises a solvent, and the solvent is anhydrous ethanol; the composition of the base solution comprises: the ratio of the mass of the ionic liquid to the mass of the organic monomers is 0.3-0.7, and the ratio of the mass of the solvent to the mass of the organic monomers is 0.15-0.25; the photoinitiator is a LAP photoinitiator, and the composition of the mixed solution comprises: the ratio of the mass of the first nanoparticles to the mass of the organic monomers is 0.001-0.005, the ratio of the mass of the second nanoparticles to the mass of the organic monomers is 0.005-0.02, and the ratio of the mass of the photoinitiator to the mass of the organic monomers is 0.003-0.007; the magnetic induction intensity of the magnetic field is 0.15T-0.9T. In this preferred scheme, by controlling the type of ionic liquid, the type and composition of organic monomers, the type of solvent, the composition of the base solution, the composition of the mixed solution, 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 change in the range of 7%-13% to 85%-95%.

[0048] Further preferably, the ratio of the radius of the core of the first nanoparticles to the thickness of the coating layer is 2-4, the particle size of the first nanoparticles is 15 nm-30 nm, the ratio of the radius of the core of the second nanoparticles to the thickness of the SiO2 coating layer to the thickness of the methacrylic anhydride coating layer is 1:0.2-0.4:0.1-0.15, the particle size of the second nanoparticles is 16 nm-37 nm, and the ultraviolet light irradiation curing reaction conditions comprise: the wavelength of the ultraviolet light is 365 nm, the ultraviolet light intensity is 40 mW / cm 2 ~50 mW / cm 2, the ultraviolet light irradiation time is 2 min~6 min. Under this preferred scheme, by further controlling the particle size of the nanoparticles, the ratio of the core and the coating layer thickness, and the ultraviolet light curing reaction conditions, the low pressure sensitivity of the sensor is improved, the upper limit of the sensor sensing range is widened, and the signal intensity in the high pressure region of the sensor is improved, and the high pressure sensitivity is improved. The particle size of the first nanoparticles is controlled to be 15 nm~30 nm, and the particle size of the second nanoparticles is controlled to be 16 nm~37 nm, so as to prevent the nanoparticles from agglomerating and settling, and also to facilitate the formation of the concentration gradient of the first nanoparticles and the concentration gradient of the second nanoparticles by applying a magnetic field.

[0049] In a third aspect, the present application provides a pressure sensor, comprising: a polar plate, comprising a first polar plate and a second polar plate stacked;

[0050] a sensitive layer, which is stacked between the first polar plate and the second polar plate, comprises the gel film of the first aspect or the gel film prepared by the preparation method of the second aspect.

[0051] The gel film as the sensitive layer in the pressure sensor of the present application changes in the gradient of the elastic modulus of the gel film in the thickness direction of the gel film. When the pressure is low, the side of the gel film with lower elastic modulus deforms significantly, which can improve the signal intensity in the low pressure region of the pressure sensor and improve the low pressure sensitivity. Since the side of the gel film with higher elastic modulus can widen the upper limit of the sensor sensing range, the gel film with higher elastic modulus has a higher concentration of the first nanoparticles with the polyaniline coating layer. By the higher elastic modulus of the side of the gel film and the higher concentration of the first nanoparticles, the signal intensity in the high pressure region of the sensor can be improved while widening the upper limit of the sensor sensing range, and the high pressure sensitivity can be improved.

[0052] In a fourth aspect, the present application provides a pressure sensor for a knee joint, which is the pressure sensor of the third aspect.

[0053] In a fifth aspect, the present application provides a pressure sensor, referring to Figure 1 , comprising an upper polar plate 1, a lower polar plate 2, and a gel film sensitive layer 3 stacked between the upper polar plate 1 and the lower polar plate 2 in sequence Figure 2 is a physical map of the gel film of the present application, Figure 3 is a microstructure map of the gel film of the present application;

[0054] The upper electrode plate 1 comprises a flexible substrate layer 11 and a hydrogen-bond-containing polymer layer 12 stacked together, the hydrogen-bond-containing polymer layer 12 has a directional crack network on the side away from the flexible substrate layer 11, the cracks in the directional crack network have a consistent direction, and further comprises an electrode layer (not shown in the figure) continuously attached to the side of the hydrogen-bond-containing polymer layer 12 where the directional crack network is located, the electrode layer is attached to the inner surface of the cracks and the surface of the crack edges.

[0055] The gel film sensitive layer 3 comprises a gel film, the base material of the gel film comprises a polymer ionic liquid gel, the gel film is doped with first nanoparticles (not shown in the figure), the first nanoparticles comprise a core and a coating layer covering the surface of the core, the core comprises Fe3O4, and the coating layer comprises polyaniline, the elastic modulus of the gel film changes in a gradient along the thickness direction of the gel film, the concentration of the first nanoparticles changes in a gradient along the thickness direction of the gel film, the direction of the gradient change of the elastic modulus is consistent with the direction of the gradient change of the concentration, and the side of the gel film with a lower elastic modulus is arranged close to the upper electrode plate 1.

[0056] The lower electrode plate 2 comprises a polymer film and an electrode layer, the side surface of the polymer film has an array of protrusions, the protrusions are in the shape of arches, the modulus of the arch-shaped protrusions increases in a gradient from the bottom to the top, and the electrode layer is attached to the side of the polymer film where the array of protrusions is located.

[0057] The material of the electrode layer of the upper electrode plate of the present application is preferably a conductive polymer / silver nanowire composite layer, and the conductive polymer is further preferably a conductive polymer composed of poly(3,4-ethylenedioxythiophene) / poly-p-phenylene sulfonic acid, the material of the electrode layer of the lower electrode plate of the present application is not limited, for example, it is a Ti / Au electrode, and the thickness of the electrode layer is also not limited, for example, it is 80-120 nm. The pressure sensor of the present application can be connected to an edge processing module through a serpentine metal wire, and the material of the serpentine metal wire is, for example, eutectic gallium-indium alloy, EGaIn.

[0058] The upper electrode plate of the pressure sensor of the present application, the side of the hydrogen-bond-containing polymer layer away from the flexible substrate layer has a directional crack network, the cracks in the directional crack network have a consistent direction, when the pressure sensor is subjected to pressure, the cracks are deformed by opening, the area of the electrode plate in contact with the sensitive layer increases, a pressure capacitance signal is generated, and the response sensitivity of the pressure sensor under smaller pressure can be improved, wherein when the pressure sensor is subjected to larger or more frequent pressure, the cracks are prone to breakage, which is manifested as small cracks extending out around the directional cracks, affecting the sensing accuracy and the service life of the sensor, when the pressure sensor is subjected to smaller pressure for a period of time, the width of the small cracks extending out is shortened to the distance between molecular forces, and through hydrogen bonding self-repairing, the small cracks extending out can be eliminated, the broken cracks can be repaired, the sensing accuracy and the service life of the sensor can be improved.

[0059] The lower plate of the pressure sensor of the present application has a convex array on one side surface of a polymer film, the convexes are in the shape of arches, an electrode layer is attached to the side of the polymer film where the convex array is located, the contact area of the arches changes when the arches are pressed, the top of the arches is coupled with the sensitive layer to generate a capacitive signal, the arches and the electrodes on the other side of the sensitive layer form an interfacial capacitor, the interfacial capacitor changes when the arches are pressed to generate an off-electric signal, the response sensitivity of the pressure sensor under a larger pressure can be improved, the modulus of the arches increases in a gradient from the bottom to the top, and the response sensitivity of the pressure sensor under a larger pressure can be further improved.

[0060] In a sixth aspect, the present application provides a pressure sensor for a knee joint, which is the pressure sensor of the fifth aspect.

[0061] The present application will be further described in detail below with reference to specific embodiments.

[0062] Embodiment 1

[0063] A pressure sensor, comprising: a plate, comprising a first plate and a second plate stacked; a sensitive layer, stacked between the first plate and the second plate; the sensitive layer comprises a gel film, the substrate of the gel film comprises a polymer ionic liquid gel, the polymer is an acrylic-acrylamide copolymer, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide, the gel film is doped with first nanoparticles, the first nanoparticles comprise 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 nanoparticles to the thickness of the coating layer is about 3, the particle size of the first nanoparticles is about 22 nm, along the thickness direction of the gel film, the crosslinking density of the gel film changes in a gradient, the concentration of the first nanoparticles changes in a gradient, the elastic modulus of the gel film changes in a gradient, the direction of the crosslinking density gradient, the direction of the concentration gradient of the first nanoparticles, and the direction of the elastic modulus gradient 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 in a gradient, the direction of the area ratio gradient is consistent with the direction of the elastic modulus gradient, and the area ratio changes in a gradient in the range of 10% to 90%; the thickness of the gel film is about 500 μm.

[0064] A preparation method of the aforementioned gel film, comprising:

[0065] Step one: preparing the second nanoparticles, coating the surface of Fe3O4 particles with SiO2, modifying the surface of the SiO2 coating layer with amino, obtaining the precursor nanoparticles, coating the surface of the precursor nanoparticles with methacrylate (crosslinking agent), obtaining the second nanoparticles, the ratio of the radius of the core of the second nanoparticles, the thickness of the SiO2 coating layer, and the thickness of the methacrylate coating layer is 1:0.2:0.15, the particle size of the second nanoparticles is about 20 nm, the first nanoparticles are prepared by wet coating in a water system, the ratio of the radius of the core of the first nanoparticles to the thickness of the coating layer is about 3, and the particle size of the first nanoparticles is about 22 nm;

[0066] Step two: dispersing the first nanoparticles and the second nanoparticles in a polymer ionic liquid gel matrix liquid, adding a photoinitiator to the matrix liquid, and uniformly mixing to obtain a mixed liquid, and injecting the mixed liquid into a mold; the matrix liquid comprises 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide (ionic liquid), acrylamide monomer / acrylic acid monomer (organic monomer), anhydrous ethanol, the content of acrylamide monomer in the organic monomer is 30 wt%, the content of acrylic acid monomer is 70 wt%, the mass ratio of the ionic liquid to the organic monomer in the matrix liquid is 0.5, the mass ratio of the solvent to the organic monomer is 0.22, the photoinitiator is LAP photoinitiator, the mass ratio of the first nanoparticles to the organic monomer in the mixed liquid is 0.003, the mass ratio of the second nanoparticles to the organic monomer is 0.012, and the mass ratio of the photoinitiator to the organic monomer is 0.005;

[0067] Step three: placing the mold containing the mixed liquid on a UV exposure platform, applying a magnetic field along the thickness direction of the mixed liquid, and after the UV light irradiation initiates the curing reaction, removing the magnetic field and drying at 60°C, to obtain the gel film; the magnetic induction intensity of the magnetic field is 0.5T, and the UV light irradiation curing reaction conditions include: the UV light wavelength is 365 nm, the UV light intensity is 40 mW / cm 2 , and the UV light irradiation time is 5 min.

[0068] Example 2

[0069] The preparation method of the gel film of Reference Example 1 is referred to, except that in Step three, the magnetic induction intensity of the magnetic field is 0.1T. The pressure sensor of Reference Example 1 is referred to, except that the area ratio of the first nanoparticles in the cross-section of the gel film is gradiently changed in the range of 40% to 60%.

[0070] Example 3

[0071] The preparation method of the gel film of Comparative Example 1 was followed, except that in step two, 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 of Comparative Example 1 was followed, except that the area ratio of the first nanoparticles in the cross section of the gel film was gradiently changed in the range of 6% to 83%.

[0072] Example 4

[0073] The preparation method of the gel film of Comparative Example 1 was followed, except that in step one, the ratio of the radius of the core of the second nanoparticles to the thickness of the SiO2coating layer to the thickness of the methacrylic anhydride coating layer was 1:0.2:0.3.

[0074] Example 5

[0075] The gel film of Comparative Example 1 was followed, except that in step one, the ratio of the radius of the core of the first nanoparticles to the thickness of the coating layer was 5.

[0076] Comparative Example 1

[0077] The gel film of Comparative Example 1 was followed, except that the first nanoparticles did not have a coating layer of polyaniline.

[0078] Test Example

[0079] The pressure sensors obtained in the above examples and comparative examples were tested for low pressure sensitivity and high pressure sensitivity. The testing method for low pressure sensitivity was to load pressure in steps of 0.1 MPa, 0.2 MPa, 0.3 MPa, 0.4 MPa from 0 MPa in 5 points; each point was kept for 60 seconds, and the positive stroke output value was recorded; the reverse unloading was to 0 MPa, and the reverse stroke output value was recorded, and 3 cycles were completed; and the working straight line slope in the low pressure area was calculated. The testing method for high pressure sensitivity was to load in 5 points of 0.7 MPa, 0.8 MPa, 0.9 MPa, and 1.0 MPa from 0.6 MPa; each point was kept for 60 seconds, and the positive stroke output was recorded; the overloading stability was detected at 1.0 MPa for 1 minute; and the high pressure sensitivity slope was calculated. The test results are shown in Table 1.

[0080] Table 1

[0081]

[0082] Comparing the comparative example and Comparative Example 1, the surface of the first nanoparticles has a coating layer of polyaniline, which can significantly improve the high pressure sensitivity of the sensor.

[0083] Compared with the comparative example 1 and the 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 area ratio gradient change range 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 the low pressure sensitivity of the sensor; compared with the comparative example 1 and the example 3, the ratio of the mass of the first nanoparticles to the mass of the organic monomer in the mixed solution is not less than 0.001, which is more conducive to making the minimum value of the area ratio gradient change range of the first nanoparticles in the cross section of the gel film along the thickness direction of the gel film not less than 7% and the maximum value not less than 85%, thereby improving the high pressure sensitivity and the low pressure sensitivity of the sensor; compared with the comparative example 1 and the example 4, the ratio of the radius of the core of the second nanoparticles to the thickness of the SiO2 coating layer to 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 the high pressure sensitivity of the sensor; compared with the comparative example 1 and the example 5, the ratio of the radius of the core of the first nanoparticles to the thickness of the coating layer is 2~4, which is more conducive to improving the low pressure sensitivity and the high pressure sensitivity of the sensor.

[0084] The above describes the preferred embodiments of the present application in detail, but the present application is not limited thereto. Within the technical concept of the present application, various simple modifications can be made to the technical solutions of the present application, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be considered as the disclosed content of the present application and belong to the protection scope of the present application.

Claims

1. A gel film for a pressure sensor, characterized by, The substrate of the gel film comprises a polymeric ionic liquid gel, the gel film is doped with first nanoparticles, the first nanoparticles comprise a core and a coating layer coated on the surface of the core, the core comprises Fe3O4, and the coating layer comprises polyaniline; The elastic modulus of the gel film changes in a gradient along the thickness direction of the gel film, and the concentration of the first nanoparticles changes in a gradient along the thickness direction of the gel film, the direction of the gradient change of the elastic modulus is consistent with the direction of the gradient change of the concentration.

2. The gel film according to claim 1, wherein The area proportion of the first nanoparticles in the cross section of the gel film changes in a gradient along the thickness direction of the gel film, the direction of the gradient change of the area proportion is consistent with the direction of the gradient change of the elastic modulus, and the area proportion changes in a gradient from 7% to 13% to 85% to 95%.

3. The gel film of claim 1, wherein The crosslinking density of the gel film increases in a gradient along the direction of the gradient increase of the elastic modulus.

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

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

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

7. The gel film of claim 1, wherein In the polymeric ionic liquid gel, the polymer comprises 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 of producing a gel film according to any one of claims 1 to 7, characterized by, Comprise: The nanoparticles are dispersed in a polymeric ionic liquid gel matrix liquid, a photoinitiator is added to the matrix liquid, and the mixture is uniformly mixed to obtain a mixed liquid, the mixed liquid is injected into a mold, the mold containing the mixed liquid is placed on an ultraviolet exposure platform, a magnetic field is applied along the thickness direction of the mixed liquid, ultraviolet light irradiation initiates a curing reaction, and the gel film is obtained; the nanoparticles comprise first nanoparticles and second nanoparticles, the first nanoparticles and the second nanoparticles each comprise a core and a coating layer coated on the surface of the core, the core of the first nanoparticles and the second nanoparticles each comprises Fe3O4, the coating layer of the first nanoparticles comprises polyaniline, and the coating layer of the second nanoparticles comprises a crosslinking agent; the matrix liquid comprises an ionic liquid and an organic monomer, and under ultraviolet light irradiation conditions, the crosslinking agent causes the organic monomer to undergo a polymerization and crosslinking reaction.

9. The method of claim 8, wherein the gel film is prepared by the steps of: The organic monomer comprises an acrylamide monomer and an acrylic acid monomer.

10. The method of claim 9, wherein the gel film is prepared by the steps of: 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.

11. The method of claim 9, wherein the gel film is prepared by the steps of: The ionic liquid is 1-ethyl-3-methyl imidazole bis(trifluoromethyl sulfonyl) imide, the content of acrylamide monomer in the organic monomer is 10wt%-50wt% and the content of acrylic acid monomer is 50wt%-90wt%, the base solution further comprises a solvent, and the solvent is anhydrous ethanol; The composition of the base solution comprises: 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, the composition of the mixed solution comprises: 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 by Comprise: a polar plate comprising a first polar plate and a second polar plate stacked together; a sensitive layer stacked between the first polar plate and the second polar plate, comprising the gel film of any one of claims 1-7 or the gel film prepared by the method of any one of claims 8-11.

13. A pressure sensor for a knee joint, characterized by It is the pressure sensor of claim 12. It is the pressure sensor of claim 12.

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