Polymer ion gel film for capacitive sensor, preparation method and capacitive sensor

Abstract

This invention belongs to the field of sensors, and relates to a polymer ionogel membrane for capacitive sensors, its preparation method, and the capacitive sensor itself. One side of the membrane has a layer of spontaneously crystallized polymer ionogel particles. The gel particles have a spherical or near-spherical structure, and the gel particle layer forms an uneven structure on one side surface of the membrane. Each gel particle includes a porous polymer backbone and an ionic liquid located within the pores. The polymer backbone includes an enriched first PVDF-based polymer. Adjacent polymer ionogel particles are mainly connected by a second PVDF-based polymer. The composition of the polymer ionogel membrane includes a PVDF-based polymer to ionic liquid mass ratio of 1:2 to 2:1. Based on the mass of the PVDF-based polymer, the content of the first PVDF-based polymer is 80wt% to 95wt%, and the content of the second PVDF-based polymer is 5wt% to 20wt%. When used in a capacitive sensor, the gel membrane can improve detection sensitivity.

Description

Technical Field

[0001] The present invention belongs to the field of sensors, and in particular, relates to a polymer ion gel membrane for a capacitive sensor, a preparation method and a capacitive sensor. Background Art

[0002] A thin film capacitive sensor is a sensor that uses changes in the mechanical properties of a thin film to detect external force or strain. The basic principle is to use the property that the capacitance of a thin film material changes when it is subjected to force or strain, and convert the capacitance change into an electrical signal through a circuit, thereby realizing the detection of force or strain. The thin film capacitive sensor needs to accurately sense changes in force or strain based on changes in electrical signals and have good detection sensitivity.

[0003] Polymer ion gel is a mixture of high molecular organic polymer and electrolyzable ionic liquid. In its structure, polymer molecular chains are cross-linked and entangled with each other to form a three-dimensional network structure. The ionic liquid is used as a dispersion medium and is confined in the gel skeleton composed of a solid matrix. The polymer gives the ion gel strength and resilience, and the ionic liquid gives the ion gel conductivity. The polymer ion gel film can be used for thin film capacitance sensors. However, the existing polymer ion gel film capacitance sensors rely on force or strain changes to cause film thickness changes, which cause capacitance changes and convert the capacitance changes into electrical signals to sense force or strain. The response amount of capacitance changes caused by unit force or strain changes is small, and the sensitivity is limited. At the same time, the thickness value of the film and the magnitude of the force or strain applied to the capacitance sensor do not correspond well, making it difficult to accurately sense force or strain.

[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 known technology. Summary of the invention

[0005] The purpose of the present invention is to overcome the defects of the existing polymer ion gel membrane, which has limited sensitivity and is difficult to accurately sense force or strain when used in a thin film capacitor sensor, and to provide a polymer ion gel membrane for a capacitor sensor, a preparation method and a capacitor sensor. The polymer ion gel membrane used in the capacitor sensor has high sensitivity and high accuracy in sensing force or strain.

[0006] In order to achieve the above-mentioned object, in a first aspect, the present invention provides a polymer ion gel membrane for a capacitive sensor, one side of which has a polymer ion gel particle layer formed by spontaneous crystallization, the polymer ion gel particles are spherical or quasi-spherical structures, and the polymer ion gel particle layer forms a concave-convex structure on the surface of one side of the gel membrane;

[0007] The polymer ion gel particles include a polymer skeleton with pores and an ionic liquid located in the pores, the polymer skeleton includes an enriched first PVDF-based polymer; adjacent polymer ion gel particles are mainly connected by a second PVDF-based polymer;

[0008] The polymer ion gel membrane comprises: a mass ratio of PVDF polymer to ionic liquid of 1:2-2:1, based on the mass of the PVDF polymer, a content of the first PVDF polymer of 80wt%-95wt%, and a content of the second PVDF polymer of 5wt%-20wt%.

[0009] In some preferred embodiments, a first PVDF-based polymer having a crystallinity of 40% to 60%, a second PVDF-based polymer having a crystallinity of 5% to 15%, an ionic liquid and a solvent are uniformly mixed to obtain a membrane liquid, and the membrane liquid is formed into a film to prepare the polymer ion gel membrane.

[0010] In some preferred embodiments, the diameter of the polymer ion gel particles is 0.2 μm to 10 μm.

[0011] In some preferred embodiments, the polymer ion gel membrane has a thickness of 5 μm to 100 μm.

[0012] In a second aspect, the present invention provides a polymer ion gel membrane for a capacitive sensor, one side of which has a polymer ion gel particle layer formed by spontaneous crystallization, the polymer ion gel particles are spherical or quasi-spherical structures, and the polymer ion gel particle layer forms a concave-convex structure on one side of the gel membrane surface;

[0013] The polymer ion gel particles include a polymer skeleton with pores and an ionic liquid located in the pores, the polymer skeleton includes an enriched first PVDF-based polymer; adjacent polymer ion gel particles are mainly connected by a second PVDF-based polymer;

[0014] The preparation of the polymer ion gel membrane comprises: uniformly mixing a PVDF polymer, an ionic liquid, a wetting agent, a solvent and a filler to obtain a membrane solution, and forming the membrane solution into a film to prepare the polymer ion gel membrane, wherein the PVDF polymer comprises a first PVDF polymer and a second PVDF polymer, the first PVDF polymer has a crystallinity of 40% to 60%, the second PVDF polymer has a crystallinity of 5% to 15%, based on the mass of the PVDF polymer, the content of the first PVDF polymer is 80wt% to 95wt%, the content of the second PVDF polymer is 5wt% to 20wt%, based on the mass of the membrane solution, the sum of the content of the PVDF polymer, the content of the ionic liquid and the content of the filler is 1wt% to 20wt%, and the ratio of the content of the PVDF polymer to the content of the ionic liquid is 1:2 to 2:1.

[0015] In a third aspect, the present invention provides a method for preparing the polymer ion gel membrane described in the first aspect or the polymer ion gel membrane described in the second aspect, comprising uniformly mixing a PVDF polymer, an ionic liquid, a wetting agent, a solvent and a filler to obtain a membrane liquid, forming the membrane liquid on a substrate to obtain a wet film, and post-treating the wet film to obtain a polymer ion gel membrane;

[0016] The PVDF-based polymer includes a first PVDF-based polymer and a second PVDF-based polymer, the first PVDF-based polymer has a crystallinity of 40% to 60%, the second PVDF-based polymer has a crystallinity of 5% to 15%, based on the mass of the PVDF-based polymer, the content of the first PVDF-based polymer is 80wt% to 95wt%, the content of the second PVDF-based polymer is 5wt% to 20wt%, based on the mass of the membrane liquid, the sum of the content of the PVDF-based polymer, the content of the ionic liquid, and the content of the filler is 1wt% to 20wt%, and the ratio of the content of the PVDF-based polymer to the content of the ionic liquid is 1:2 to 2:1.

[0017] In some preferred embodiments, based on the mass of the membrane solution, the content of the filler is 0.5% to 20% of the content of the PVDF-based polymer.

[0018] In some preferred embodiments, the thickness of the wet film is 50 μm to 2000 μm.

[0019] In some preferred embodiments, the anions of the ionic liquid include at least one of hexafluorophosphate anion, tetrafluoroborate anion, bistrifluoromethanesulfonyl imide anion, trifluoromethanesulfonate anion, acetate anion, dicyanamide anion, bromide anion, ethyl sulfate anion, and hydrogen sulfide anion, and the cations of the ionic liquid include at least one of 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-octyl-3-methylimidazolium cation;

[0020] The filler comprises at least one of nano iron oxide, nano ferroferric oxide, nano calcium oxide, nano zinc oxide, nano tin oxide, nano cerium oxide and fumed silicon dioxide.

[0021] Preferably, the ionic liquid includes 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, the filler includes nano-cerium oxide, the first PVDF-based polymer includes PVDF, and the second PVDF-based polymer includes PVDF-HFP.

[0022] In some preferred embodiments, the wetting agent includes dimethyl carbonate; the solvent includes at least one of acetone, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide.

[0023] In some preferred embodiments, after the PVDF-based polymer and the wetting agent are uniformly mixed, the solvent is added to dissolve the PVDF-based polymer, and then the ionic liquid and the filler are added and dispersed uniformly to obtain the membrane liquid.

[0024] In some preferred embodiments, the post-treatment includes flash drying and baking performed sequentially, and the post-treatment conditions include: flash drying time of 1 min to 1500 min, baking temperature of 10° C. to 300° C., and baking time of 10 h to 500 h.

[0025] Preferably, freezing is further included between the flash drying and the baking, so the freezing conditions include: the freezing temperature is below 4° C., and the freezing time is 0.5 h to 24 h.

[0026] In a fourth aspect, the present invention provides a capacitive sensor having electrodes and the polymer ion gel membrane described in the first aspect, the polymer ion gel membrane described in the second aspect, or the polymer ion gel membrane prepared by the preparation method described in the third aspect located between two electrodes.

[0027] The polymer ion gel membrane of the present invention has a polymer ion gel particle layer formed by spontaneous crystallization on one side, the polymer ion gel particles are spherical or quasi-spherical structures, the polymer ion gel particle layer forms a concave-convex structure on the surface of one side of the gel membrane, the polymer ion gel particles include a polymer skeleton with pores and an ionic liquid located in the pores, when the polymer ion gel membrane is used in a capacitive sensor, when the capacitive sensor is subjected to force or strain, the contact area between the gel membrane and the electrode is changed, and the capacitance is changed. In a first aspect, the size of the contact area between the gel membrane and the electrode is approximately proportional to the size of the force or strain, and the change of the force or strain can be more accurately sensed through the change of the capacitance. Secondly, when the capacitive sensor is not subjected to force or strain, the contact area between the gel film and the electrode is very small, and the initial capacitance is very small, which can amplify the relative capacitance change and improve the sensitivity of the capacitive sensor. Thirdly, the spherical or quasi-spherical gel particles have small surface tension, which can improve the resilience of the polymer ion gel film. When the capacitive sensor is subjected to force or strain, the gel film is deformed. When the force or strain disappears, the gel film will return to its original shape. The initial capacitance of the capacitive sensor (the capacitance when not subjected to force or strain) will not change due to force or strain, and can accurately sense force or strain, and there is no need to frequently calibrate the initial capacitance of the capacitive sensor. In the gel film provided by the present invention, the first PVDF spontaneously forms a spherical or quasi-spherical structure, and the second PVDF-based polymer is less involved in the process of forming a polymer skeleton of a spherical or quasi-spherical structure during the film-forming process, and plays the role of bonding the spherical or quasi-spherical structure formed by the first PVDF-based polymer together. The two together can form a stable polymer ion gel particle layer, so that the polymer ion gel particle layer structure is stable, can accurately sense the change of force or strain, improve the sensitivity of the capacitive sensor, reduce hysteresis, have good linearity, and spontaneously form to avoid the strength, resilience and sensitivity inconsistency of different points of the gel film. The polymer skeleton includes an enriched first PVDF-based polymer, which can effectively ensure the strength performance of the gel film, and the adjacent polymer ion gel particles are mainly connected by the second PVDF-based polymer to effectively ensure the toughness of the gel film. The combined effect of the two is more conducive to ensuring the strength and resilience of the ion gel film, reducing hysteresis, increasing the capacitance deformation per unit force or strain, and improving the sensing sensitivity. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0029] Figure 1This is a first schematic diagram of the working state of the capacitive sensor of the present invention.

[0030] Figure 2 This is a second schematic diagram of the working state of the capacitive sensor of the present invention.

[0031] Figure 3 This is a scanning electron microscope photograph of the surface morphology of the polymer ion gel membrane of Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The endpoints and any values ​​of the ranges disclosed in this article 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 endpoint values ​​of each range, the endpoint values ​​of each range and the 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 as specifically disclosed in this article.

[0033] The inventors of the present invention have found that the existing polymer ion gel membrane has limited sensitivity when used in a thin film capacitor sensor and is difficult to accurately sense force or strain.

[0034] In this regard, in a first aspect, the present invention provides a polymer ion gel membrane for a capacitive sensor, one side of which has a polymer ion gel particle layer formed by spontaneous crystallization, the polymer ion gel particles are spherical or quasi-spherical structures, and the polymer ion gel particle layer forms a concave-convex structure on one side of the gel membrane surface;

[0035] The polymer ion gel particles include a polymer skeleton with pores and an ionic liquid located in the pores, the polymer skeleton includes an enriched first PVDF-based polymer; adjacent polymer ion gel particles are mainly connected by a second PVDF-based polymer;

[0036] The polymer ion gel membrane comprises: a mass ratio of PVDF polymer to ionic liquid of 1:2-2:1, based on the mass of the PVDF polymer, a content of the first PVDF polymer of 80wt%-95wt%, and a content of the second PVDF polymer of 5wt%-20wt%.

[0037] The polymer ion gel membrane of the present invention has a polymer ion gel particle layer formed by spontaneous crystallization on one side, the polymer ion gel particles are spherical or quasi-spherical structures, the polymer ion gel particle layer forms a concave-convex structure on the surface of one side of the gel membrane, the polymer ion gel particles include a polymer skeleton with pores and ionic liquids located in the pores, when the polymer ion gel membrane is used in a capacitive sensor, when the capacitive sensor is subjected to force or strain, the contact area between the gel membrane and the electrode is changed, and the capacitance is changed. In the first aspect, the size of the contact area between the gel membrane and the electrode is approximately proportional to the size of the force or strain, and the change in force or strain can be more accurately sensed through the change in capacitance. In the second aspect, On the one hand, when the capacitive sensor is not subjected to force or strain, the contact area between the gel film and the electrode is very small, and the initial capacitance is very small, which can amplify the relative capacitance change and improve the sensitivity of the capacitive sensor. On the other hand, the polymer ion gel particles with spherical or quasi-spherical structures have low surface tension and can improve the resilience of the polymer ion gel film. When the capacitive sensor is subjected to force or strain, the gel film is deformed. When the force or strain disappears, the gel film will return to its original shape. The initial capacitance of the capacitive sensor (the capacitance when not subjected to force or strain) will not change due to force or strain, and can accurately sense force or strain, and there is no need to frequently calibrate the initial capacitance of the capacitive sensor. The polymer ion gel particle layer of the present invention is spontaneously formed by crystallization, which can improve the consistency of the concave-convex structure on one side of the gel film and avoid inconsistent strength, resilience and sensitivity at different points of the gel film. In the gel film provided by the present invention, the first PVDF spontaneously forms a spherical or quasi-spherical structure, and the second PVDF-based polymer is less involved in the process of forming a polymer skeleton of a spherical or quasi-spherical structure during the film-forming process, and plays a role in bonding the spherical or quasi-spherical structure formed by the first PVDF-based polymer together, and can form a stable polymer ion gel particle layer, so that the polymer ion gel particle layer structure is stable, can accurately sense the change of force or strain, improve the sensitivity of the capacitive sensor, reduce hysteresis, have good linearity, and spontaneously form to avoid the strength, resilience and sensitivity inconsistency of different points of the gel film. Wherein the polymer skeleton includes the enriched first PVDF-based polymer, which can effectively ensure the strength performance of the gel film, and the adjacent polymer ion gel particles are mainly connected by the second PVDF-based polymer to effectively ensure the toughness of the gel film, and the combined effect of the two is more conducive to ensuring the strength and resilience of the ion gel film, reducing hysteresis, and increasing the capacitance deformation per unit force or strain, thereby improving the sensing sensitivity.

[0038] The polymer ion gel membrane of the present invention, based on the mass of the PVDF-based polymer, has a first PVDF-based polymer content of 80wt% to 95wt% and a second PVDF-based polymer content of 5wt% to 20wt%, which can improve the strength, resilience and sensitivity of the capacitive sensor of the polymer ion gel membrane. If the content of the first PVDF-based polymer is less than 80wt% and the content of the second PVDF-based polymer is greater than 20wt%, the support degree of the protrusions of the concave-convex structure on one side of the gel membrane is insufficient, thereby causing the strength and resilience of the polymer ion gel membrane to deteriorate. If the content of the first PVDF-based polymer is greater than 95wt% and the content of the second PVDF-based polymer is less than 5wt%, the support degree of the protrusions is too strong, the microstructure is not easily deformed, micro-deformation is not easily caused, the sensitivity is not high, and the linearity of the sensing force or strain is reduced. The mass ratio of the PVDF polymer and the ionic liquid of the polymer ion gel membrane of the present invention is 1:2-2:1, which can improve the conductivity of the polymer ion gel membrane and thus improve the sensitivity of the capacitive sensor, and can improve the strength and resilience of the polymer ion gel membrane. If the mass ratio of the PVDF polymer and the ionic liquid is less than 0.5, the resilience performance is affected, which easily leads to the change of the initial capacitance of the capacitive sensor, thereby affecting the accurate sensing force or strain, or the initial capacitance of the capacitive sensor needs to be calibrated frequently. If the mass ratio of the PVDF polymer and the ionic liquid is greater than 2, the conductivity of the polymer ion gel membrane is easily reduced, thereby affecting the sensitivity of the capacitive sensor and the linearity of the sensing force or strain.

[0039] The polymer ion gel membrane of the present invention can be applied in different fields, such as lithium battery safety warning, and the health of the lithium battery can be evaluated by sensing the pressure caused by the expansion of the lithium battery.

[0040] In some preferred embodiments, a first PVDF polymer having a crystallinity of 40% to 60%, a second PVDF polymer having a crystallinity of 5% to 15%, an ionic liquid and a solvent are uniformly mixed to obtain a membrane liquid, and the membrane liquid is formed into a film to prepare the polymer ion gel membrane. Under this preferred embodiment, the polymer ion gel particle layer structure is more stable, which is more conducive to accurately sensing changes in force or strain, improving the sensitivity of the capacitive sensor, and avoiding inconsistent strength, resilience and sensitivity at different points of the gel membrane. The first PVDF polymer that meets the above crystallinity can more effectively guarantee the strength performance of the gel membrane, and the second PVDF polymer that meets the above crystallinity can more effectively guarantee the toughness of the gel membrane. The combined effect of the two is more conducive to improving the sensing sensitivity and other properties while ensuring the strength and resilience of the ion gel membrane.

[0041] In some preferred embodiments, the diameter of the polymer ion gel particles is 0.2 μm to 10 μm, which can simultaneously ensure the sensitivity of the capacitive sensor and the accurate sensing of force or strain. The diameter of the polymer ion gel particles of the present invention is preferably 0.5 μm to 8.5 μm, more preferably 1.5 μm to 7.6 μm, and even more preferably 2.5 μm to 6.8 μm.

[0042] In some preferred embodiments, the thickness of the polymer ion gel membrane is 5 μm to 100 μm. In this preferred embodiment, the thickness of the polymer ion gel membrane is 5 μm to 100 μm, which is more conducive to ensuring the linear relationship between the contact area between the gel membrane and the electrode and the force or strain, accurately sensing the force or strain, reducing the energy dissipation of the gel membrane after being subjected to the force or strain, thereby reducing the hysteresis of the detection and improving the sensitivity of the detection.

[0043] In some preferred embodiments, the anions of the ionic liquid include at least one of hexafluorophosphate anion, tetrafluoroborate anion, bistrifluoromethanesulfonyl imide anion, trifluoromethanesulfonate anion, acetate anion, dicyanamide anion, bromide anion, ethyl sulfate anion, and hydrogen sulfide anion, and the cations of the ionic liquid include at least one of 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-octyl-3-methylimidazolium cation.

[0044] Preferably, the ionic liquid includes 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt, the first PVDF-based polymer includes PVDF, and the second PVDF-based polymer includes PVDF-HFP. PVDF as the first PVDF-based polymer can more effectively ensure the strength performance of the gel membrane, and PVDF-HFP as the second PVDF-based polymer can more effectively ensure the toughness of the gel membrane. The combined effect of the two is more conducive to ensuring the strength and resilience of the ion gel membrane, reducing hysteresis, increasing the capacitance deformation per unit force or strain, and improving the sensing sensitivity.

[0045] In a second aspect, the present invention provides a polymer ion gel membrane for a capacitive sensor, one side of which has a polymer ion gel particle layer formed by spontaneous crystallization, the polymer ion gel particles are spherical or quasi-spherical structures, and the polymer ion gel particle layer forms a concave-convex structure on one side of the gel membrane surface;

[0046] The polymer ion gel particles include a polymer skeleton with pores and an ionic liquid located in the pores, the polymer skeleton includes an enriched first PVDF-based polymer; adjacent polymer ion gel particles are mainly connected by a second PVDF-based polymer;

[0047] The preparation of the polymer ion gel membrane comprises: uniformly mixing a PVDF polymer, an ionic liquid, a wetting agent, a solvent and a filler to obtain a membrane solution, and forming the membrane solution into a film to prepare the polymer ion gel membrane, wherein the PVDF polymer comprises a first PVDF polymer and a second PVDF polymer, the first PVDF polymer has a crystallinity of 40% to 60%, the second PVDF polymer has a crystallinity of 5% to 15%, based on the mass of the PVDF polymer, the content of the first PVDF polymer is 80wt% to 95wt%, the content of the second PVDF polymer is 5wt% to 20wt%, based on the mass of the membrane solution, the sum of the content of the PVDF polymer, the content of the ionic liquid and the content of the filler is 1wt% to 20wt%, and the ratio of the content of the PVDF polymer to the content of the ionic liquid is 1:2 to 2:1.

[0048] The preparation of the polymer ion gel membrane of the present invention comprises a first PVDF polymer and a second PVDF polymer, the first PVDF polymer has a crystallinity of 40% to 60%, the second PVDF polymer has a crystallinity of 5% to 15%, based on the mass of the PVDF polymer, the content of the first PVDF polymer is 80wt% to 95wt%, the content of the second PVDF polymer is 5wt% to 20wt%, the first PVDF polymer has a high crystallinity and a high content, and spontaneously forms a spherical or quasi-spherical structure, the second PVDF polymer has a low crystallinity and a low content, and in the process of film formation, is less involved in the process of forming a polymer skeleton of a spherical or quasi-spherical structure, plays a role in bonding the spherical or quasi-spherical structure formed by the first PVDF polymer, and can form a stable polymer ion gel particle layer. If the content of the first PVDF polymer is higher than 95wt%, and the content of the second PVDF polymer is less than 5wt%, the pulling force between the polymer ion gel particles is relatively large, and it is easy to pull out holes and destroy the polymer ion gel particle layer that has been formed. If the content of the first PVDF polymer is lower than 80wt%, and the content of the second PVDF polymer is higher than 20wt%, a uniform polymer ion gel particle layer cannot be formed during the film forming process. The ratio of the content of the PVDF polymer to the content of the ionic liquid is 1:2~2:1, which is more conducive to improving the conductivity of the polymer ion gel film, thereby improving the sensitivity of the capacitive sensor, and improving the strength and resilience of the polymer ion gel film. Adding fillers to the membrane liquid can promote the spontaneous formation of the polymer ion gel particle layer, can improve the consistency of the concave-convex structure of one side of the gel film, and avoid the inconsistency of the strength, resilience and sensitivity of different points of the gel film.

[0049] In a third aspect, the present invention provides a method for preparing the polymer ion gel membrane described in the first aspect or the polymer ion gel membrane described in the second aspect, comprising uniformly mixing a PVDF polymer, an ionic liquid, a wetting agent, a solvent and a filler to obtain a membrane liquid, forming the membrane liquid on a substrate to obtain a wet film, and post-treating the wet film to obtain a polymer ion gel membrane;

[0050] The PVDF-based polymer includes a first PVDF-based polymer and a second PVDF-based polymer, the first PVDF-based polymer has a crystallinity of 40% to 60%, the second PVDF-based polymer has a crystallinity of 5% to 15%, based on the mass of the PVDF-based polymer, the content of the first PVDF-based polymer is 80wt% to 95wt%, the content of the second PVDF-based polymer is 5wt% to 20wt%, based on the mass of the membrane liquid, the sum of the content of the PVDF-based polymer, the content of the ionic liquid, and the content of the filler is 1wt% to 20wt%, and the ratio of the content of the PVDF-based polymer to the content of the ionic liquid is 1:2 to 2:1.

[0051] The preparation of the polymer ion gel membrane of the present invention comprises a first PVDF polymer and a second PVDF polymer, the first PVDF polymer has a crystallinity of 40% to 60%, the second PVDF polymer has a crystallinity of 5% to 15%, based on the mass of the PVDF polymer, the content of the first PVDF polymer is 80wt% to 95wt%, the content of the second PVDF polymer is 5wt% to 20wt%, the first PVDF polymer has a high crystallinity and a high content, and spontaneously forms a spherical or quasi-spherical structure, the second PVDF polymer has a low crystallinity and a low content, and in the process of film formation, is less involved in the process of forming a polymer skeleton of a spherical or quasi-spherical structure, plays a role in bonding the spherical or quasi-spherical structure formed by the first PVDF polymer, and can form a stable polymer ion gel particle layer.

[0052] The present invention does not limit the film forming method, for example, it can be a self-leveling method, a spraying method, a spin coating method, a scraping method, etc. The type of substrate is also not limited, for example, it can be a glass plate, a stainless steel plate, an aluminum plate, a wood plate, a marble plate, a PET plate, a PC plate, etc. It can be understood that the present invention can separate the film and the substrate after post-processing.

[0053] In some preferred embodiments, based on the mass of the membrane solution, the content of the filler is 0.5% to 20% of the content of the PVDF polymer. Under this preferred solution, it is more conducive to controlling the diameter of the polymer ion gel particles to 0.2 μm to 10 μm.

[0054] In some preferred embodiments, the thickness of the wet film is 50 μm to 2000 μm. Based on the mass of the membrane liquid as the benchmark, the sum of the content of the PVDF polymer, the content of the ionic liquid, and the content of the filler is 1 wt% to 20 wt%. Under this preferred solution, when the thickness of the wet film is 50 μm to 2000 μm, it is more conducive to making the thickness of the polymer ion gel membrane after drying 5 μm to 100 μm.

[0055] In some preferred embodiments, the anions of the ionic liquid include at least one of hexafluorophosphate anion, tetrafluoroborate anion, bistrifluoromethanesulfonyl imide anion, trifluoromethanesulfonate anion, acetate anion, dicyanamide anion, bromide anion, ethyl sulfate anion, and hydrogen sulfide anion, and the cations of the ionic liquid include at least one of 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-octyl-3-methylimidazolium cation;

[0056] The filler comprises at least one of nano iron oxide, nano ferroferric oxide, nano calcium oxide, nano zinc oxide, nano tin oxide, nano cerium oxide and fumed silicon dioxide.

[0057] In this preferred embodiment, the filler includes at least one of nano iron oxide, nano ferroferric oxide, nano calcium oxide, nano zinc oxide, nano tin oxide, nano cerium oxide, and fumed silica, which is more conducive to the spontaneous formation of a polymer ion gel particle layer, improves the consistency of the concave-convex structure on one side of the gel film, avoids the inconsistency of the strength, resilience and sensitivity of different points of the gel film, and can also change the color of the gel film for subsequent quality inspection. In addition, the filler added in the present invention can also speed up the film forming speed, and the spontaneously formed surface concave-convex structure of the film is more uniform and controllable.

[0058] Preferably, the ionic liquid includes 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, the filler includes nano-cerium oxide, the first PVDF-based polymer includes PVDF, and the second PVDF-based polymer includes PVDF-HFP. Under this preferred embodiment, the filler includes nano-cerium oxide, which can promote the spontaneous formation of a polymer ion gel particle layer and improve the consistency of the concave-convex structure of one side of the gel film while reducing the amount of filler. The first PVDF-based polymer includes PVDF, and the second PVDF-based polymer includes PVDF-HFP, which is more conducive to ensuring the strength and resilience of the ion gel film and reducing hysteresis, while increasing the capacitance deformation per unit force or strain and improving the sensing sensitivity.

[0059] In some preferred embodiments, the wetting agent includes dimethyl carbonate; the solvent includes at least one of acetone, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide.

[0060] In some preferred embodiments, after the PVDF polymer and the wetting agent are uniformly mixed, the solvent is added to dissolve the PVDF polymer, and then the ionic liquid and the filler are added and dispersed uniformly to obtain the membrane solution. Under this preferred embodiment, before adding the solvent to dissolve the PVDF polymer, the PVDF polymer and the wetting agent are uniformly mixed, which is more conducive to shortening the time for dissolving the PVDF polymer, shortening the stirring time, improving production efficiency, preventing PVDF chain scission, and affecting the spontaneous crystallization process.

[0061] In some preferred embodiments, the post-treatment includes flash drying and baking in sequence, and the post-treatment conditions include: flash drying time of 1 min to 1500 min, baking temperature of 10°C to 300°C, and baking time of 10h to 500h. Under this preferred scheme, the solvent and wetting agent are quickly volatilized by flash drying, so that the gel film loses fluidity, and the microbubbles in the wet film are eliminated. The solvent is completely volatilized by baking, and the flash drying causes the film liquid to lose fluidity in a short time. In the production practice, the high flatness of a drying device is ensured, and the film liquid is quickly flash dried in this drying device to lose fluidity. After that, the film that loses fluidity is transferred to another drying device for further drying. The film has lost fluidity. Even if the other drying device is not flat enough, it will not affect the flatness of the gel film, which is more conducive to improving production efficiency and reducing equipment costs under the premise of ensuring the flatness of the gel film.

[0062] Preferably, freezing is also included between the flash drying and the baking, so the freezing conditions include: the freezing temperature is below 4°C and the freezing time is 0.5h~24h. Under this preferred embodiment, freezing below 4°C is performed between flash drying and baking. During the freezing process, the ionic liquid becomes solid or semi-solid, making the PVDF skeleton with pores more compact, which is more conducive to preventing the collapse and deformation of the pores during baking, and improving the resilience and strength of the polymer ion gel membrane. After the gel membrane is used in the capacitive sensor, the friction between molecules is reduced, and the energy dissipation of the gel membrane after being subjected to force or strain is reduced, thereby reducing the hysteresis of the detection, improving the accuracy of the sensing force or strain, and reducing the sensing error. In addition, after the gel membrane is used in the capacitive sensor, the sensing sensitivity is higher. The freezing time is 0.5h~24h, and the PVDF skeleton with pores is more compact, which is more conducive to improving the strength and resilience of the gel membrane. The freezing temperature is, for example, 4°C, 0°C, -5°C, -10°C, and the freezing time is, for example, 0.5h, 1h, 5h, 10h, 15h, 20h, 24h.

[0063] In a fourth aspect, the present invention provides a capacitive sensor having an electrode plate and the polymer ion gel membrane described in the first aspect, the polymer ion gel membrane described in the second aspect, or the polymer ion gel membrane prepared by the preparation method described in the third aspect, located between the two electrode plates. The capacitive sensor of the present invention has a high detection sensitivity.

[0064] The working principle of the capacitive sensor of the present invention is as follows Figure 1 and Figure 2 A double electric layer structure is formed between the electrode and the polymer ion gel membrane. When the capacitive sensor is subjected to force or strain, the contact area between the gel membrane and the electrode is changed, and the capacitance is changed. The force or strain is detected by detecting the change in capacitance. The anions and cations of the ionic liquid are not shown in the figure.

[0065] The present invention is further described in detail below with reference to specific embodiments.

[0066] Example 1

[0067] A method for preparing a polymer ion gel membrane comprises the following steps:

[0068] Step 1: Stir and mix the PVDF polymer and dimethyl carbonate (DMC) into a paste mixture, the PVDF polymer includes a first PVDF polymer and a second PVDF polymer, the first PVDF polymer is PVDF, the crystallinity of PVDF is 50%, the second PVDF polymer is PVDF-HFP, the crystallinity of PVDF-HFP is 10%, the first PVDF polymer accounts for 90wt% of the PVDF polymer, and the second PVDF polymer accounts for 10wt%, N,N-dimethylformamide (DMF) solvent is added to the paste mixture, and stirred to completely dissolve the PVDF polymer to obtain a PVDF polymer solution;

[0069] Step 2: Add 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt ionic liquid to the PVDF polymer solution of step 1, mix well to obtain an ionic solution, add nano-cerium oxide particles to the ionic solution, first use magnetic stirring to preliminarily disperse the nano-cerium oxide particles, and then use an ultrasonic disperser to further disperse the nano-cerium oxide particles until a translucent uniform liquid is obtained as a membrane liquid. Based on the mass of the membrane liquid, the sum of the content of the PVDF polymer, the content of the ionic liquid, and the content of the nano-cerium oxide filler is 15wt%, the ratio of the content of the PVDF polymer to the content of the ionic liquid is 1, and the content of the filler is 12% of the content of the PVDF polymer;

[0070] Step 3: Take a glass plate, wipe it with alcohol to remove moisture and oil on the surface of the glass plate, then wipe it with acetone solvent to remove the solvent residue, and use it as a substrate for standby use. Use the film liquid obtained in step 2 to form a wet film on the substrate by air spraying, and use a wet film thickness gauge to control the average thickness of the wet film to be 380μm. Before air spraying, clean the air spray gun with acetone solvent to remove impurities in the spray gun to ensure that the film liquid spray is well and evenly atomized. During the air spraying process, the air spray gun maintains uniform linear motion, and the spray fan is kept perpendicular to the substrate surface;

[0071] Step 4: The wet film obtained in step 3 is flash dried, frozen and baked in sequence to obtain a polymer ion gel membrane, with a flash drying time of 600 min, a freezing temperature of below 4°C, a freezing time of 12 h, a baking temperature of 70°C and a baking time of 50 h.

[0072] A polymer ion gel membrane is prepared by the above-mentioned method for preparing a polymer ion gel membrane, wherein the average thickness of the polymer ion gel membrane is 40 μm (measured by Elcometer The 456 coating film thickness gauge measures the thickness of the polymer ion gel film. During the measurement, a standard gasket with a thickness of 1-1000μm is added to prevent the polymer ion gel film from being deformed due to force. One side of the gel film has a polymer ion gel particle layer formed by spontaneous crystallization. The polymer ion gel particles are spherical or quasi-spherical. The polymer ion gel particle layer forms a concave-convex structure on the surface of one side of the gel film. The average diameter of the polymer ion gel particles is about 2.8μm. The polymer ion gel particles include a polymer skeleton with pores and 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt ionic liquid located in the pores. The polymer skeleton includes enriched PVDF. Adjacent polymer ion gel particles are mainly connected by PVDF-HFP. The composition of the polymer ion gel membrane is based on the mass of the PVDF-based polymer, the PVDF content is 90wt%, the PVDF-HFP content is 10wt%, and the mass ratio of the PVDF-based polymer to the 1-ethyl-3-methylimidazole bis(trifluoromethanesulfonyl)imide salt ionic liquid is 1. The morphology of the concave-convex structure surface of the polymer ion gel membrane can be found in Figure 3 .

[0073] A capacitive sensor comprises two parallel-arranged pole plates, between which is disposed the aforementioned polymer ion gel membrane which is arranged in parallel with the pole plates.

[0074] Example 2

[0075] The preparation method of the gel film is referred to in Example 1, except that in step 4, no freezing is performed.

[0076] Example 3

[0077] Referring to the preparation method of the gel film of Example 1, the difference is that in step three, the average thickness of the wet film is controlled to be 43 μm by a wet film thickness gauge, and referring to the polymer ion gel film of Example 1, the difference is that the average thickness of the polymer ion gel film is 4.8 μm.

[0078] Example 4

[0079] The preparation method of the gel membrane of Example 1 is different in that in step 2, based on the mass of the membrane liquid, the content of the filler is 0.3% of the content of the PVDF polymer. Referring to the polymer ion gel membrane of Example 1, the average diameter of the polymer ion gel particles is 11 μm.

[0080] Comparative Example 1

[0081] The preparation method of the gel membrane of Example 1 is different from that in step 1, in the PVDF polymer, the first PVDF polymer accounts for 98wt%, and the second PVDF polymer accounts for 2wt%. Referring to the polymer ion gel membrane of Example 1, the composition of the polymer ion gel membrane is based on the mass of the PVDF polymer, the content of PVDF is 98wt%, and the content of PVDF-HFP is 2wt%.

[0082] Comparative Example 2

[0083] The preparation method of the gel membrane of Example 1 is different from that in step 2, in the membrane solution, the ratio of the mass content of the PVDF polymer to the mass content of the ionic liquid is 2.3. The polymer ion gel membrane of Example 1 is different from that in step 2, in the membrane solution, the ratio of the mass content of the PVDF polymer to the mass content of the ionic liquid is 2.3.

[0084] Comparative Example 3

[0085] The preparation method of the gel membrane is referred to as Example 1, except that only PVDF-HFP is used to form the membrane. The average thickness of the polymer ion gel membrane is 45 μm, and one side of the gel membrane does not have an obvious concave-convex structure. The gel membrane includes a polymer skeleton with pores and an ionic liquid located in the pores.

[0086] The capacitive sensors obtained in the above embodiments and comparative examples were tested for hysteresis, linearity, sensitivity and sensing accuracy, and the results are shown in Table 1. The above performances were measured using the MARK-10 brand F105Easy electric measuring table combined with the FS05-20 tension and compression sensor, wherein the hysteresis, sensitivity and linearity data were measured with reference to the measurement method in the "Technical Specifications for Distributed Thin Film Pressure Sensors". Hysteresis indicates the ability of the gel film to recover deformation, sensitivity indicates the growth rate of the contact area between the gel film and the electrode as the pressure increases, and linearity indicates the linearity of the relationship between capacitance and pressure. The higher the linearity value in the table, the worse the linearity.

[0087] Table 1

[0088]

[0089] Comparative Example 1 and Comparative Example 1, based on the mass of the PVDF polymer, the content of the first PVDF polymer is 80wt%~95wt%, and the content of the second PVDF polymer is 5wt%~20wt%, which is more conducive to improving the sensing sensitivity and the linearity of the sensing force or strain. Comparative Example 2, the mass ratio of the PVDF polymer and the ionic liquid of the polymer ion gel membrane is 1:2~2:1, which is more conducive to improving the sensing sensitivity and the linearity of the sensing force or strain. Comparative Example 3, one side of the gel membrane has a polymer ion gel particle layer formed by spontaneous crystallization, the polymer ion gel particles are spherical or quasi-spherical structures, and the polymer ion gel particle layer forms a concave-convex structure on one side of the gel membrane, which can ensure the linear relationship between the contact area of ​​the gel membrane and the electrode and the force or strain, improve the linearity of the sensing force or strain, improve the accuracy of the sensing force or strain, reduce the hysteresis of the detection, and improve the sensitivity of the detection.

[0090] Comparing Example 1 and Example 2, freezing is also included between flash drying and baking. After the gel film is used in the capacitive sensor, it is more conducive to reducing the hysteresis of detection, improving the accuracy of sensing force or strain, and improving the sensing sensitivity. Comparing Example 1 and Example 3, the thickness of the polymer ion gel film is 5μm~100μm, which is more conducive to ensuring the linear relationship between capacitance and pressure, improving the linearity of sensing force or strain, improving the accuracy of sensing force or strain, reducing the hysteresis of detection, and improving the sensitivity of detection. Comparing Example 1 and Example 4, the diameter of the gel particles is not more than 10μm, which is more conducive to improving the sensing sensitivity.

[0091] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A polymer ion gel membrane for a capacitive sensor, characterized in that: One side of the gel film has a polymer ion gel particle layer formed by spontaneous crystallization, the polymer ion gel particles are spherical or quasi-spherical, and the polymer ion gel particle layer forms a concave-convex structure on the surface of one side of the gel film; The polymer ion gel particles include a polymer skeleton with pores and an ionic liquid located in the pores, wherein the polymer skeleton includes an enriched first PVDF-based polymer; Adjacent polymer ion gel particles are mainly connected by a second PVDF-based polymer; The polymer ion gel membrane comprises: a mass ratio of PVDF polymer to ionic liquid of 1:2 to 2:1, based on the mass of the PVDF polymer, a content of the first PVDF polymer of 80wt% to 95wt%, and a content of the second PVDF polymer of 5wt% to 20wt%; A mixture including a first PVDF polymer with a crystallinity of 40% to 60%, a second PVDF polymer with a crystallinity of 5% to 15%, an ionic liquid, a filler and a solvent is uniformly mixed to obtain a membrane liquid, and the membrane liquid is formed into a film to prepare the polymer ion gel membrane.

2. The polymer ion gel membrane according to claim 1, characterized in that The diameter of the polymer ion gel particles is 0.2 μm to 10 μm.

3. The polymer ion gel membrane according to claim 1, characterized in that The thickness of the polymer ion gel film is 5 μm-100 μm.

4. A polymer ion gel membrane for a capacitive sensor, characterized in that: One side of the gel film has a polymer ion gel particle layer formed by spontaneous crystallization, the polymer ion gel particles are spherical or quasi-spherical, and the polymer ion gel particle layer forms a concave-convex structure on the surface of one side of the gel film; The polymer ion gel particles include a polymer skeleton with pores and an ionic liquid located in the pores, wherein the polymer skeleton includes an enriched first PVDF-based polymer; Adjacent polymer ion gel particles are mainly connected by a second PVDF-based polymer; The preparation of the polymer ion gel membrane comprises: uniformly mixing a PVDF polymer, an ionic liquid, a wetting agent, a solvent and a filler to obtain a membrane solution, and forming the membrane solution into a film to prepare the polymer ion gel membrane, wherein the PVDF polymer comprises a first PVDF polymer and a second PVDF polymer, the first PVDF polymer has a crystallinity of 40% to 60%, the second PVDF polymer has a crystallinity of 5% to 15%, based on the mass of the PVDF polymer, the content of the first PVDF polymer is 80wt% to 95wt%, the content of the second PVDF polymer is 5wt% to 20wt%, based on the mass of the membrane solution, the sum of the content of the PVDF polymer, the content of the ionic liquid and the content of the filler is 1wt% to 20wt%, and the ratio of the content of the PVDF polymer to the content of the ionic liquid is 1:2 to 2:

1.

5. A method for preparing the polymer ion gel membrane according to any one of claims 1 to 3 or the polymer ion gel membrane according to claim 4, characterized in that: The PVDF polymer, ionic liquid, wetting agent, solvent and filler are uniformly mixed to obtain a membrane liquid, the membrane liquid is formed on a substrate to obtain a wet film, and the wet film is post-processed to obtain a polymer ion gel membrane; The PVDF-based polymer includes a first PVDF-based polymer and a second PVDF-based polymer, the first PVDF-based polymer has a crystallinity of 40% to 60%, the second PVDF-based polymer has a crystallinity of 5% to 15%, based on the mass of the PVDF-based polymer, the content of the first PVDF-based polymer is 80wt% to 95wt%, the content of the second PVDF-based polymer is 5wt% to 20wt%, based on the mass of the membrane liquid, the sum of the content of the PVDF-based polymer, the content of the ionic liquid, and the content of the filler is 1wt% to 20wt%, and the ratio of the content of the PVDF-based polymer to the content of the ionic liquid is 1:2 to 2:

1.

6. The preparation method according to claim 5, wherein the content of the filler is 0.5% to 20% of the content of the PVDF-based polymer, based on the mass of the membrane solution.

7. The preparation method according to claim 5, characterized in that: The thickness of the wet film is 50 μm to 2000 μm.

8. The preparation method according to claim 5, characterized in that: The anions of the ionic liquid include at least one of hexafluorophosphate anion, tetrafluoroborate anion, bistrifluoromethanesulfonyl imide anion, trifluoromethanesulfonate anion, acetate anion, dicyanamide anion, bromide anion, ethyl sulfate anion, and hydrogen sulfide anion, and the cations of the ionic liquid include at least one of 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-octyl-3-methylimidazolium cation; The filler comprises at least one of nano iron oxide, nano ferroferric oxide, nano calcium oxide, nano zinc oxide, nano tin oxide, nano cerium oxide and fumed silicon dioxide.

9. The preparation method according to claim 6, characterized in that: The ionic liquid includes 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, the filler includes nano-cerium oxide, the first PVDF-based polymer includes PVDF, and the second PVDF-based polymer includes PVDF-HFP.

10. The preparation method according to claim 5, characterized in that: The wetting agent includes dimethyl carbonate; the solvent includes at least one of acetone, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, and dimethyl sulfoxide.

11. The preparation method according to claim 5, characterized in that: After the PVDF-based polymer and the wetting agent are uniformly mixed, the solvent is added to dissolve the PVDF-based polymer, and then the ionic liquid and the filler are added and dispersed uniformly to obtain the membrane solution.

12. The preparation method according to claim 5, characterized in that: The post-treatment includes flash drying and baking in sequence, and the post-treatment conditions include: flash drying time is 1min~1500min, baking temperature is 10℃~300℃, and baking time is 10h~500h.

13. The preparation method according to claim 12, characterized in that: Freezing is also included between the flash drying and the baking, so the freezing conditions include: the freezing temperature is below 4° C., and the freezing time is 0.5 h to 24 h.

14. A capacitive sensor, characterized in that: The invention comprises an electrode plate and a polymer ion gel membrane according to any one of claims 1 to 3, a polymer ion gel membrane according to claim 4, or a polymer ion gel membrane prepared by the preparation method according to any one of claims 5 to 13, located between the two electrode plates.

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