Ionogel films, ionogel glues, and methods of making the same, capacitive sensors

Abstract

The application belongs to the technical field of pressure sensors, and particularly relates to an ionic gel film, ionic gel glue, a preparation method thereof, and a capacitive sensor. The second surface of the ionic gel film body is coated with an ionic gel glue film layer, the ionic gel glue film layer is used for tightly combining the electrode with the second surface, and the ratio of the ionic conductivity of the ionic gel glue film layer to the ionic conductivity of the ionic gel film body is 0.8-1.2. The application tightly combines the counter electrode with the second surface of the ionic gel film by using the ionic gel glue, effectively constructs a reference capacitance interface which is not disturbed by external pressure. The electrical properties of the glue and the film body are highly consistent, avoiding signal distortion or measurement error caused by interface impedance mismatch. Meanwhile, the firm bonding is realized by using a hot melt adhesive process, significantly improving the anti-creep, anti-thermal expansion and contraction, and anti-mechanical stress ability of the interface in long-term use, thereby effectively inhibiting interface peeling or baseline drift, and enhancing the long-term reliability and stability of the sensor.

Description

Technical Field

[0001] This invention belongs to the field of pressure sensor technology, specifically relating to an ion gel membrane, an ion gel adhesive and its preparation method, and a capacitive sensor. Background Technology

[0002] In recent years, capacitive sensors based on ion-conducting voltage-sensitive materials (such as ion gels and ion elastomers) have attracted widespread attention due to their excellent flexibility and high sensitivity. The core principle of these sensors relies on the double-layer capacitance formed at the interface between the electrode and the ion-conducting voltage-sensitive material. When pressure is applied to the sensor, the contact area between the ion-conducting voltage-sensitive material and the electrode changes, resulting in a change in the double-layer capacitance, thereby achieving pressure sensing.

[0003] Those skilled in the art have already conducted some research on the structure of ion-conducting voltage-sensitive materials. Some existing technologies (such as the Chinese patent with authorization announcement number CN119060476B) will form a double-layer structure that is affected by pressure on one side of the ion-conducting voltage-sensitive material, while forming a double-layer structure that is not affected by pressure on the other side, thereby avoiding the occurrence of additional capacitance effects, which would lead to signal distortion and reduce measurement accuracy.

[0004] However, the surfaces of the electrodes and ion-conducting voltage-sensitive materials in existing capacitive sensors are often not smooth enough, and the uneven electrodes and ion gel films cannot form a double-layer structure that is unaffected by pressure.

[0005] Chinese patent CN119564386B proposes a solution that involves casting a dielectric layer on the side of the second electrode layer facing the first electrode layer, so that the dielectric layer and the second electrode layer are completely bonded together, eliminating the gap between them. This ensures that even if the second electrode layer itself is not flat, it will not interfere with the capacitance measurement.

[0006] However, the aforementioned patents still have areas for improvement:

[0007] First, existing technologies employ the method of directly casting ionogel films onto electrodes to form a reference capacitance interface with a fixed contact area. However, this method has inherent drawbacks: the core function of ionogel films is ionic conductivity, thus requiring excellent ionic conductivity, mechanical strength, and creep resistance, while their first surface also needs to possess microstructure. To achieve these requirements, the polymers in the ionogel film components typically have high molecular weights (600,000 to 1.1 million), resulting in poor mechanical adhesion and deformation tracking. Under these conditions, the mechanical strength of the interface formed by directly casting the ionogel film onto the electrode is usually poor. During long-term use, due to the material's own creep, mismatch in thermal expansion coefficients with the electrode, or repeated external interfacial stress, adhesion failure or interfacial delamination gradually occurs, creating microscopic voids between the electrode and the ionogel film. These voids cause uncontrollable changes in the interfacial contact area, leading to a drift in the otherwise stable reference capacitance value, ultimately causing sensor baseline drift or response hysteresis, severely restricting the long-term reliability and stability of the sensor.

[0008] Secondly, the existing technology uses the method of casting ion gel films on electrodes, which is only suitable for casting on a single electrode and a flat electrode. This is because the casting technology must ensure that the casting surface, i.e. the electrode surface, is a complete plane. Otherwise, the ion gel will spread and cannot be uniformly formed. The inherent defects of the casting method determine that it cannot be adapted to multi-electrode or interdigitated electrode situations.

[0009] Therefore, there is an urgent need in the field for a capacitive sensor solution to overcome the aforementioned shortcomings of the prior art.

[0010] 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

[0011] This invention provides an ionogel membrane, an ionogel adhesive, a method for preparing the same, and a capacitive sensor, which at least solves the problems of insufficient process adaptability and interface stability of existing ionogel membranes.

[0012] To achieve the above objectives, in a first aspect, the present invention provides an ion gel membrane, comprising: an ion gel membrane body, a first surface of the ion gel membrane body having a microstructure, a second surface of the ion gel membrane body coated with an ion gel adhesive film layer, the ion gel adhesive film layer being used to tightly bond an electrode to the second surface, and the ratio of the ion conductivity of the ion gel adhesive film layer to that of the ion gel membrane body being 0.8 to 1.2.

[0013] Preferably, the thickness of the iontophoretic adhesive film is 1 μm to 50 μm.

[0014] Preferably, the peel strength between the ion gel adhesive film and the electrode is 0.8 N / cm to 2.0 N / cm.

[0015] Secondly, the present invention provides a method for preparing the above-mentioned ionogel membrane, comprising:

[0016] The ion gel adhesive is coated onto the second surface of the ion gel membrane body or onto the electrode.

[0017] Dry ionomer gel adhesive to form a solid hot melt adhesive;

[0018] Heat the solid hot melt adhesive at 65℃~80℃ until it softens.

[0019] The softened solid hot melt adhesive is bonded to the electrode or the second surface and cooled to form an ion gel adhesive film layer that tightly bonds the electrode to the second surface.

[0020] Thirdly, the present invention provides an ion gel adhesive for forming the above-mentioned ion gel membrane, comprising the following components by mass percentage: 15% to 17% polymer, 0.5% to 10% ionic liquid, and 75% to 83% solvent.

[0021] Preferably, the polymer is polycaprolactone with a weight-average molecular weight of 30,000 to 50,000.

[0022] Preferably, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

[0023] Preferably, the solvent is tetrahydrofuran.

[0024] Preferably, the mass ratio of ionic liquid to polymer is 1:(1.5~20).

[0025] Preferably, the solid content of the iontophoresis adhesive is 15%~25%, and the softening temperature is 55℃~65℃.

[0026] Fourthly, the present invention provides a method for preparing the above-mentioned ionic gel adhesive, comprising placing a polymer and an ionic liquid into a solvent, mixing and stirring until completely dissolved, to obtain the ionic gel adhesive.

[0027] Fifthly, the present invention provides a capacitive sensor, including the above-mentioned ion gel membrane, working electrode, counter electrode, and reference electrode; the working electrode abuts against a first surface of the ion gel membrane body to form a first capacitor; the counter electrode abuts against a second surface of the ion gel membrane body to form a second capacitor; and the reference electrode is disposed on the ion gel membrane.

[0028] The first surface has a microstructure, and the working electrode abuts against the microstructure surface so that the capacitance value of the first capacitor is configured to change with external pressure and noise signal; the counter electrode is tightly attached to the second surface through an ion gel adhesive film layer so that the capacitance value of the second capacitor is configured to change only with noise signal.

[0029] Preferably, the reference electrode is separately disposed on the counter electrode side, and the reference electrode is also tightly bonded to the second surface through an ion gel adhesive film layer.

[0030] The beneficial effects of this invention are as follows:

[0031] 1. This invention achieves a tight and stable bond between the counter electrode and the second surface of the ion gel membrane using ion gel adhesive, effectively constructing a reference capacitance interface unaffected by external pressure. The ratio of ionic conductivity between the ion gel adhesive layer and the ion gel membrane body is controlled within the range of 0.8 to 1.2, ensuring a high degree of consistency in their electrical properties and avoiding signal distortion or measurement errors caused by interface impedance mismatch. Simultaneously, the use of hot melt adhesive technology achieves a strong bond, significantly improving the interface's resistance to creep, thermal expansion and contraction, and mechanical stress during long-term use, thereby effectively suppressing interface peeling or baseline drift and enhancing the long-term reliability and stability of the sensor.

[0032] 2. This invention significantly improves the process adaptability and structural compatibility of capacitive sensors. The ionogel adhesive possesses excellent coating properties and is applicable to various electrode types (such as interdigitated electrodes, multi-electrode arrays, etc.), breaking through the limitation of traditional casting processes being only suitable for flat electrodes. This greatly expands the freedom of sensor design in complex structures. After curing, the adhesive can be bonded via hot-melt bonding, resulting in a simple process with highly controllable parameters. It is not only suitable for laboratory preparation but also easier to achieve mass production and application in complex integrated systems.

[0033] 3. This invention features significant innovations in material systems and preparation processes. The ionogel adhesive uses polycaprolactone (PCL) as the polymer matrix, combined with specific ionic liquids and solvents, to form a composite system with controllable conductivity, adhesion, and thermal fusion properties, exhibiting high compatibility with the ionogel membrane. Its preparation method is simple and reproducible, and performance can be optimized by adjusting the component ratios, demonstrating promising industrialization prospects and providing a foundation for the manufacture of high-performance capacitive sensors. Attached Figure Description

[0034] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0035] Figure 1 This is a schematic diagram of the structure of a capacitive sensor provided in an embodiment of the present invention.

[0036] Explanation of reference numerals in the attached figures:

[0037] 100. Capacitive sensor; 110. Ion gel membrane body; 120. Ion gel adhesive film layer; 130. Working electrode; 140. Counter electrode; 150. Reference electrode. Detailed Implementation

[0038] In this invention, unless otherwise stated, directional terms such as "up," "down," "left," and "right" are generally understood in conjunction with the accompanying drawings and the directions shown in actual applications.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0040] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0041] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. The terms "optional" and "discretionary" mean that they may or may not be included (or may or may not be present).

[0042] The present invention provides an ion gel membrane, comprising: an ion gel membrane body, a first surface of the ion gel membrane body having a microstructure, a second surface of the ion gel membrane body coated with an ion gel adhesive film layer, the ion gel adhesive film layer being used to tightly bond an electrode to the second surface, and the ratio of the ion conductivity of the ion gel adhesive film layer to that of the ion gel membrane body being 0.8 to 1.2.

[0043] Preferably, the ratio of the ionic conductivity of the ionogel adhesive film layer to that of the ionogel membrane body is 0.8 to 1.2, and can be 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, or any value between them. More preferably, the ratio of the ionic conductivity of the ionogel adhesive film layer to that of the ionogel membrane body is 0.9 to 1.1. Most preferably, the ratio of the ionic conductivity of the ionogel adhesive film layer to that of the ionogel membrane body is 1. This design ensures a high degree of electrical matching between the ionogel adhesive film layer and the ionogel membrane body, making the ion migration behavior at their interface continuous and stable, and minimizing the additional impedance and signal distortion caused by abrupt changes in interface conductivity. This significantly improves the purity and stability of the reference capacitance signal, enabling the reference capacitance composed of the electrode and the ionogel membrane to accurately and consistently reflect common-mode noise (such as temperature and humidity changes), ultimately enhancing the sensor's measurement accuracy, response consistency, and long-term reliability.

[0044] Preferably, the thickness of the ionogel adhesive film layer is 1μm to 50μm, and can be 1μm, 5μm, 10μm, 15μm, 20μm, 25μm, 30μm, 35μm, 40μm, 45μm, 50μm, or any value between them. The purpose of designing the thickness of the ionogel adhesive film layer in this way is to ensure that it can effectively fill the microscopic unevenness of the electrode and the film surface to achieve a firm bond, while controlling its bulk resistance and interfacial impedance as an ion-conducting channel. Within this thickness range, the adhesive layer can guarantee excellent mechanical adhesion and interfacial stability, avoiding signal attenuation or response lag caused by excessive thickness introducing significant additional resistance, while also preventing problems such as uneven coverage, weak adhesion, or easy local breakdown caused by excessive thinness. This achieves the best balance between electrical performance and mechanical reliability, ensuring the consistency and stability of the reference capacitance signal, and ultimately guaranteeing the overall measurement accuracy and long-term operational reliability of the sensor.

[0045] Preferably, the peel strength between the ionogel adhesive film and the electrode is 0.8 N / cm to 2.0 N / cm, and can be 0.8 N / cm, 0.9 N / cm, 1 N / cm, 1.1 N / cm, 1.2 N / cm, 1.3 N / cm, 1.4 N / cm, 1.5 N / cm, 1.6 N / cm, 1.7 N / cm, 1.8 N / cm, 1.9 N / cm, 2.0 N / cm, or any value between them. This invention, by controlling the peel strength, ensures a strong and stable interfacial bond between the ionogel adhesive film and the electrode, thereby overcoming the defects of existing casting processes that are prone to creep, peeling, or the formation of micro-voids due to insufficient interfacial bonding strength. This design not only significantly improves the interface's resistance to mechanical stress, thermal expansion and contraction, and fatigue damage during long-term use, but also effectively suppresses the drift of the reference capacitance value caused by changes in contact area, and provides a highly reliable noise signal reference for the sensor, ultimately ensuring the accuracy and stability of its long-term measurements.

[0046] Preferably, the ionogel membrane body is formed by crosslinking a uniformly dispersed ionic liquid in polyvinylidene fluoride. Specifically, in one embodiment, the ionogel membrane body can be formed by curing an ionogel solution. The ionogel solution can be obtained by uniformly mixing a PVDF-based polymer, an ionic liquid, a wetting agent, a solvent, and a filler. The PVDF-based polymer can include a first PVDF-based polymer and a second PVDF-based polymer; for example, the first PVDF-based polymer includes PVDF, and the second PVDF-based polymer includes PVDF-HFP. The anions of the ionic liquid include at least one selected from hexafluorophosphate anion, tetrafluoroborate anion, bis(trifluoromethanesulfonyl)imide anion, trifluoromethanesulfonate anion, acetate anion, dicyandiamide anion, bromide anion, ethyl sulfate anion, and hydrothioate anion. The cations of the ionic liquid include at least one selected from 1-ethyl-3-methylimidazolium cation, 1-butyl-3-methylimidazolium cation, 1-hexyl-3-methylimidazolium cation, and 1-octyl-3-methylimidazolium cation. The wetting agent includes dimethyl carbonate; the solvent includes at least one of acetone, N-methylpyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and tetrahydrofuran. The filler includes at least one of nano-iron oxide, nano-ferric oxide, nano-alumina, nano-calcium carbonate, nano-zinc oxide, nano-tin oxide, nano-cerium oxide, and fumed silica.

[0047] In this embodiment, the first PVDF-based polymer has high crystallinity and high content, enabling it to spontaneously form microstructures (spherical or near-spherical structures). The second PVDF-based polymer has low crystallinity and low content, and during film formation, it participates less in the formation of the polymer skeleton of spherical or near-spherical structures, acting as a bonder for the spherical or near-spherical structures formed by the first PVDF-based polymer, thus forming a stable polymer ionogel particle layer. Adding fillers to the ionogel solution promotes the spontaneous formation of the polymer ionogel particle layer, improves the consistency of the uneven structure on one side of the ionogel membrane, and avoids inconsistencies in strength, resilience, and sensitivity at different points on the gel membrane. As an example, the specific preparation method of the ionogel solution can be found in previous patents CN119060387A and CN119060476A. However, it should be noted that the ionogel solution in this application can also be prepared using other components, and this application does not impose any restrictions on this.

[0048] Furthermore, the first surface has microstructures, which can be in the form of nanopores, microchannels, microprotrusions, etc. These microstructures can increase the surface area of ​​the ion exchange membrane, improve ion conduction efficiency, and help improve the capacitance effect. The shape of the microstructure can be referred to in the descriptions in patents CN119060476B and CN119060387B, and will not be repeated here.

[0049] This invention provides a method for preparing the above-mentioned ionogel membrane, comprising:

[0050] The ion gel adhesive is coated onto the second surface of the ion gel membrane body or onto the electrode.

[0051] Dry ionomer gel adhesive to form a solid hot melt adhesive;

[0052] Heat the solid hot melt adhesive at 65℃~80℃ until it softens.

[0053] The softened solid hot melt adhesive is bonded to the electrode or the second surface and cooled to form an ion gel adhesive film layer that tightly bonds the electrode to the second surface.

[0054] The choice to coat the ionogel adhesive onto the second surface of the ionogel membrane or onto the electrodes is to adapt to different process scenarios and structural requirements: coating onto the electrodes (especially complex structures such as interdigitated electrodes) ensures that the adhesive more accurately fills the electrode's micro-contour, avoiding potential damage to the microstructure of the pre-formed membrane surface or solvent swelling; while coating onto the second surface of the membrane is more suitable for planar electrodes or applications requiring high bonding efficiency. The drying process needs to be carried out at a specific temperature (e.g., 40-60℃) for a sufficient time (e.g., 1-5 minutes) to ensure that the solvent (e.g., tetrahydrofuran) completely evaporates, forming a solid hot melt adhesive layer without residue, avoiding electrical property drift or interfacial bubbles caused by solvent residue. The subsequent hot pressing bonding temperature must be strictly controlled above the softening point of the ionogel hot melt adhesive (60-65℃) but below the heat distortion temperature of the ionogel membrane (usually >80℃), typically within the range of 65-80℃, to ensure that the adhesive layer softens and flows sufficiently to achieve a strong bond, while not damaging the membrane structure or microshape, and finally cooling to form a stable interfacial bonding layer with matching electrical properties.

[0055] The present invention provides an ion gel adhesive for forming the above-mentioned ion gel membrane, comprising the following components by mass percentage: 15% to 17% polymer, which can be 15%, 15.5%, 16%, 16.5%, 17% and any value between them;

[0056] The ionic liquid concentration is 0.5% to 10%, and can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between them;

[0057] The solvent is 75% to 83%, and can be 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, or any value between them.

[0058] Preferably, the polymer is polycaprolactone (PCL) with a weight-average molecular weight of 30,000 to 50,000, which can be 30,000, 33,000, 35,000, 38,000, 40,000, 43,000, 45,000, 48,000, 50,000, or any value between them. PCL is chosen as the polymer primarily because it possesses good biocompatibility, excellent flexibility, outstanding compatibility with ionic liquids, and controllable hot-melt properties (its melting point is approximately 60°C). This allows it to soften and flow at lower temperatures, achieving hot-melt bonding while avoiding high-temperature damage to the ionogel film or electrodes. Limiting the weight-average molecular weight to 30,000 to 50,000 ensures sufficient mechanical strength and adhesive durability after film formation, while maintaining a suitable solution viscosity to facilitate coating processing and ensuring good flowability and interfacial wettability in the hot-melt state.

[0059] Alternatively, other polymers that are soluble in polar solvents and compatible with ionic liquids (PVDF with a molecular weight of around 100,000, common hot melt adhesive stick materials, polyurethane) can theoretically also be considered as alternatives.

[0060] Preferably, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt. 1-Ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt ([EMIM][TFSI]) is chosen as the ionic liquid primarily because it possesses extremely high chemical stability, a wide electrochemical window, low viscosity, high ionic conductivity, and good compatibility with the selected polycaprolactone (PCL) polymer and solvents (such as tetrahydrofuran). These characteristics collectively ensure that the ionic gel adhesive formed from it can form a uniform and stable system, providing efficient and consistent ion migration channels at the interface after curing. Simultaneously, its excellent thermal stability (high decomposition temperature) ensures that its performance will not degrade during subsequent hot pressing processes (65~80℃).

[0061] Alternatively, other ionic liquids (such as those based on imidazole, pyrrolidone, or ammonium cations with [TFSI]) can be used. - [BF4] - Combinations of anions (such as isocyanates) can also be considered as alternatives in theory.

[0062] Preferably, the solvent is tetrahydrofuran. Tetrahydrofuran (THF) is chosen as the solvent mainly because it has excellent solubility for both the selected polymer polycaprolactone (PCL) and the ionic liquids [EMIM][TFSI], forming a homogeneous and stable solution system. At the same time, its high polarity ensures the full dissociation and uniform distribution of the ionic liquid in the system, providing consistent ionic conductivity after the adhesive has cured.

[0063] Alternatively, other polar aprotic solvents (such as N,N-dimethylformamide (DMF), N-methylpyrrolidone (NMP), and N,N-dimethylacetamide (DMAc)) may also be theoretically considered as alternatives.

[0064] Preferably, the mass ratio of ionic liquid to polymer is 1:(1.5~20), which can be (1:1.5), (1:2), (1:3), (1:4), (1:5), (1:6), (1:7), (1:8), (1:9), (1:10), (1:11), (1:12), (1:13), (1:14), (1:15), (1:16), (1:17), (1:18), (1:19), or (1:20). This design of the ionic liquid to polymer mass ratio aims to control the balance between the ionic conductivity and mechanical properties of the film layer after adhesive curing. Specifically, a higher ionic liquid ratio (e.g., 1:1.5) provides superior ionic conductivity, ensuring efficient interfacial charge migration, but may sacrifice some mechanical strength and adhesive durability; while a lower ionic liquid ratio (e.g., 1:20) enhances the mechanical strength and stability of the adhesive layer, but the conductivity is relatively lower. By limiting the ratio to the range of 1:(1.5~20), it can be ensured that the adhesive can form a sufficiently high ionic conductivity after curing (to match the film body and avoid interfacial impedance mismatch), while maintaining good film-forming properties, adhesive strength and creep resistance, thereby ensuring the electrical consistency and long-term mechanical reliability of the reference capacitor interface under complex working conditions.

[0065] Preferably, the solid content of the ionogel adhesive is 15%~25%, and the softening temperature is 55℃~65℃. A suitable solid content ensures that the adhesive has sufficient fluidity during coating to form a uniform, defect-free film, avoiding problems such as poor film formation and insufficient mechanical strength due to too low a solid content, or difficulties in coating and solvent residue due to too high a solid content. Controlling the softening temperature within the range of 55℃~65℃ allows the adhesive layer to soften and flow at a temperature far below the heat distortion temperature of the ionogel membrane itself. This ensures good interface wetting and strong adhesion in the subsequent hot-pressing bonding process, without damaging the inherent microstructure or electrochemical properties of the membrane due to high temperatures. Ultimately, this ensures that the prepared sensor interface has excellent electrical consistency, mechanical reliability, and long-term stability.

[0066] This invention provides a method for preparing the aforementioned ionic gel adhesive, comprising placing a polymer and an ionic liquid in a solvent, mixing and stirring until completely dissolved to obtain the ionic gel adhesive. This invention utilizes a solvent (such as THF) to simultaneously and fully dissolve both the polymer (such as PCL) and the ionic liquid (such as [EMIM] [TFSI]), achieving uniform dispersion and mixing of the components at the molecular level through physical stirring, thereby forming a homogeneous, stable colloidal solution with predetermined electrical and thermal properties. This method avoids complex chemical reactions, is simple in process, has good reproducibility, and is easy to scale up for production.

[0067] like Figure 1As shown, the present invention provides a capacitive sensor 100, including the above-mentioned ion gel membrane, a working electrode 130, a counter electrode 140, and a reference electrode 150; the working electrode 130 abuts against the first surface of the ion gel membrane body 110 and forms a first capacitor; the counter electrode 140 abuts against the second surface of the ion gel membrane body 110 and forms a second capacitor; the reference electrode 150 is disposed on the ion gel membrane.

[0068] The first surface has a microstructure, and the working electrode 130 abuts against the microstructure surface so that the capacitance of the first capacitor is configured to change with external pressure and noise signal; the counter electrode 140 is tightly attached to the second surface through an ion gel adhesive film layer 120 so that the capacitance of the second capacitor is configured to change only with noise signal.

[0069] It should be noted that the noise signals include: 1. Temperature fluctuation noise (caused by changes in ambient temperature leading to changes in the dielectric constant, viscosity, and ion mobility of the ionic liquid, resulting in capacitance drift); 2. Humidity change noise (caused by changes in ambient humidity leading to hygroscopic changes in capacitance due to hygroscopic impurities or hygroscopic absorption or loss of water by the ionic liquid); 3. Solvation effect noise (caused by residual high-boiling-point solvents, treatment agents, or moisture affecting the properties of the ionic liquid, resulting in nonlinear capacitance drift).

[0070] Preferably, the counter electrode is tightly bonded to the second surface via an ion gel adhesive film layer, so that the capacitance of the second capacitor is configured to vary only with the noise signal.

[0071] Specifically, the counter electrode is tightly and firmly bonded to the second surface via an ion-gel adhesive film layer, allowing for control of the interface state at both mechanical and electrical levels. Mechanically, the cured adhesive layer integrates the counter electrode and the membrane body into a single unit, completely fixing the contact area between them. External pressure cannot alter its geometry, thus isolating the capacitance value from pressure modulation. Electrically, the adhesive layer is designed as an ion conductor highly matched to the ion conductivity of the membrane body. It does not introduce significant interfacial impedance, ensuring the continuity of ion migration channels and enabling the double-layer capacitor to form normally and respond sensitively to noise signals (such as the drift in dielectric constant and conductivity of the ionic liquid caused by temperature and humidity changes). Therefore, the capacitance change of the second capacitor originates only from the common-mode influence of noise signals on the intrinsic electrochemical properties of the material, becoming a pure noise reference signal. This provides a crucial benchmark for efficiently canceling common-mode interference and accurately extracting pressure signals in subsequent differential processing.

[0072] Preferably, the reference electrode is separately disposed on the counter electrode side, and the reference electrode is also tightly bonded to the second surface through an ion gel adhesive film layer. The function of the reference electrode is to provide a stable potential reference point for the sensor system, used to measure the capacitive voltage difference between the working electrode and the counter electrode. Its working principle is that any electronically conductive electrode that can form a stable contact with the ion gel film can establish a stable electric double layer structure, thus serving as a reference electrode. From a circuit principle perspective, the reference electrode only needs to draw a point between the first capacitor and the second capacitor formed by the working electrode and the counter electrode to measure the voltage difference; its theoretical spatial arrangement is not particularly restricted.

[0073] Furthermore, in the actual design and manufacturing of this invention, it is preferable to separately arrange the reference electrode and the counter electrode on one side of the iontophoresis adhesive film layer (i.e., the second surface side). Both the reference electrode and the counter electrode need to establish stable and reliable electrical contact with the iontophoresis film. Arranging them together on the same surface of the sensor greatly facilitates the synchronous fixing and bonding of the two electrodes during manufacturing through a single synchronous process step (e.g., by coating or hot-pressing the same layer of iontophoresis adhesive). This layout simplifies the assembly process, improves production efficiency and consistency, and avoids the complex alignment and multiple bonding operations caused by dispersing the electrodes in different positions.

[0074] Furthermore, to achieve a tight, secure, and electrically stable bond between the reference electrode and the counter electrode—two independent electrodes—this invention employs a coatable and heat-fusible ionomer gel adhesive for bonding. This method enables precise and flexible integration and fixation of multiple separate electrodes simultaneously, ensuring low and consistent interfacial contact resistance between each electrode and the thin film. In contrast, common casting-type fixing methods in existing technologies are typically only suitable for simple planar electrode structures. They struggle to achieve synchronous and stable integration of multiple independent electrodes within complex and confined spaces, and are highly susceptible to contact failure due to uneven interfacial stress distribution or material creep. These methods fail to meet the requirements of this invention for interfacial consistency and long-term reliability in multi-electrode structures.

[0075] It should be noted that the surfaces of the second surface, the counter electrode, and the reference electrode can each be independently flat or uneven. However, if the ion gel membrane body or the electrodes adopt a flat structure, additional processing is required, resulting in higher costs. With the technical solution of this application, even if the second surface, the counter electrode, and the reference electrode are all uneven, close adhesion can be achieved, effectively reducing processing costs.

[0076] The embodiments of the present invention described below are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0077] Example 1

[0078] A method for preparing an ionic gel adhesive includes placing a polymer and an ionic liquid into a solvent, mixing and stirring until completely dissolved to obtain the ionic gel adhesive.

[0079] The polymer is PCL: 4.8g, with a weight-average molecular weight of 38,000;

[0080] The ionic liquid is [EMIM][TFSI]: 1.6g;

[0081] Solvent: THF: 24g;

[0082] The mass ratio of ionic liquid to polymer is 1:3.

[0083] A method for preparing an ionogel membrane, comprising:

[0084] Ion gel adhesive is applied to the counter electrode and the reference electrode; the ion gel adhesive is dried to allow the solvent to evaporate completely, forming a solid hot melt adhesive; the solid hot melt adhesive is heated at 70°C until it softens; the softened solid hot melt adhesive is bonded to the second surface and cooled to form an ion gel adhesive film layer that tightly bonds the counter electrode and the reference electrode to the second surface, with a thickness of 25 μm.

[0085] The ionogel membrane is formed by crosslinking a mixed solution of a polymer and an ionic liquid. The polymer is PVDF-HFP, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, and the solvent of the mixed solution is N,N-dimethylformamide. Based on the mass of the mixed solution, the polymer content is 6 wt%, the ionic liquid content is 4 wt%, and the solvent content is 90 wt%.

[0086] A capacitive sensor includes the aforementioned ion gel membrane, a working electrode, a counter electrode, and a reference electrode; the working electrode abuts against a first surface of the ion gel membrane body to form a first capacitor; the counter electrode abuts against a second surface of the ion gel membrane body to form a second capacitor; and the reference electrode is disposed on the ion gel membrane.

[0087] The first surface has a microstructure, and the working electrode abuts against the microstructure surface so that the capacitance value of the first capacitor is configured to change with external pressure and noise signal; the counter electrode is tightly attached to the second surface through an ion gel adhesive film layer so that the capacitance value of the second capacitor is configured to change only with noise signal.

[0088] Example 2

[0089] The preparation method is the same as in Example 1, except that...

[0090] The polymer is PCL: 4.8g, with a weight-average molecular weight of 38,000;

[0091] The ionic liquid is [EMIM][TFSI]: 3.2g;

[0092] Solvent: THF: 24g;

[0093] The mass ratio of ionic liquid to polymer is 1:1.5.

[0094] Example 3

[0095] The preparation method is the same as in Example 1, except that...

[0096] The polymer is PCL: 4.8g, with a weight-average molecular weight of 38,000;

[0097] The ionic liquid is [EMIM][TFSI]: 0.8g;

[0098] Solvent: THF: 24g;

[0099] The mass ratio of ionic liquid to polymer is 1:6.

[0100] Example 4

[0101] The preparation method is the same as in Example 1, except that...

[0102] The polymer is PCL: 4.8g, with a weight-average molecular weight of 38,000;

[0103] The ionic liquid is [EMIM][TFSI]: 0.4g;

[0104] Solvent: THF: 24g;

[0105] The mass ratio of ionic liquid to polymer is 1:12.

[0106] Example 5

[0107] The preparation method is the same as in Example 1, except that...

[0108] The polymer is PCL: 4.8g, with a weight-average molecular weight of 38,000;

[0109] The ionic liquid is [EMIM][TFSI]: 0.24 g;

[0110] Solvent: THF: 24g;

[0111] The mass ratio of ionic liquid to polymer is 1:20.

[0112] Comparative Example 1

[0113] Referring to CN119564386B, an ion gel solution, which is a mixture of PVDF polymer, ionic liquid, wetting agent, solvent and filler, is coated at the position corresponding to each sensing node on the side of the second electrode layer facing the first electrode layer. The ion gel solution forms a wet film on the second electrode layer, and the ion gel film obtained after curing is the dielectric layer.

[0114] Comparative Example 2

[0115] The preparation method is the same as in Example 1, except that...

[0116] The polymer is PCL: 4.8g, with a weight-average molecular weight of 38,000;

[0117] The ionic liquid is [EMIM][TFSI]: 4.8g;

[0118] Solvent: THF: 24g;

[0119] The mass ratio of ionic liquid to polymer is 1:1.

[0120] Comparative Example 3

[0121] The preparation method is the same as in Example 1, except that...

[0122] The polymer is PCL: 4.8g, with a weight-average molecular weight of 38,000;

[0123] The ionic liquid is [EMIM][TFSI]: 0.1g;

[0124] Solvent: THF: 24g;

[0125] The mass ratio of ionic liquid to polymer is 1:48.

[0126] Test case

[0127] The ion gel membranes and capacitive sensors obtained in the above embodiments and comparative examples were subjected to performance tests. The specific test results are shown in Table 1. The ionic conductivity of the ion gel adhesive film layer and the ion gel membrane body was determined by electrochemical impedance spectroscopy (EIS). The test method for the peel strength between the ion gel adhesive film layer and the electrode can refer to GB / T2792-2014. The test method for the sensor's service life is as follows: at 25℃ and 50% relative humidity, a continuous triangular wave pressure cycle (cycle 40s, pressure amplitude 1MPa, i.e., the full-scale pressure of the sensor) is applied to the sensor. When the baseline drift of the second capacitance value exceeds 10% of the initial value, the number of cycles is recorded and converted to hours (10,000 cycles ≈ 111.1 hours).

[0128] Table 1

[0129]

[0130] Based on the results of Examples 1 to 5, it can be seen that when the mass ratio of ionic liquid to polymer in the ionic gel adhesive is controlled within the range of 1:1.5 to 1:20, the prepared ionic gel adhesive film layer not only maintains a stable ionic conductivity ratio between itself and the ionic gel film body within the ideal range of 0.8 to 1.2, ensuring a high degree of matching of interfacial electrical properties, but also its peel strength increases with the increase of polymer content, achieving an excellent peel strength of 0.8 N / cm to 2.0 N / cm. This significantly improves the mechanical bonding reliability and long-term stability of the interface while maintaining high ion migration efficiency. In particular, Example 3 achieved the optimal balance between the ionic conductivity ratio and peel strength, thus obtaining the longest sensor lifespan. This fully demonstrates that the present invention, through component design, successfully achieves the synergistic optimization of interfacial electrical matching and mechanical bonding strength.

[0131] Based on the results of the embodiments and Comparative Example 1, it can be seen that the ion gel adhesive and its hot melt bonding process provided by the present invention solve the problems of baseline drift, response hysteresis and poor long-term reliability caused by insufficient interfacial bonding force in traditional casting processes, and significantly expand the process adaptability and stability of sensors in complex electrode structures.

[0132] Based on the results of Examples and Comparative Example 2, it can be seen that when the proportion of ionic liquid is too high, the prepared adhesive layer suffers from a relatively insufficient polymer backbone, resulting in a significant decrease in its mechanical strength and cohesive force, leading to extremely low peel strength and an inability to provide a strong interfacial bond. Simultaneously, the excessive ionic liquid causes its ionic conductivity to far exceed that of the membrane bulk. This electrical mismatch affects ion migration at the interface and also introduces unstable interfacial impedance.

[0133] Based on the results of the examples and Comparative Example 3, it can be seen that when the proportion of ionic liquid is too low, even with a higher polymer content, the peel strength decreases due to poor wettability of the adhesive layer. Simultaneously, the ionic conductivity ratio is severely low, indicating that the adhesive layer has almost lost its ionic conductivity function, introducing a large and unstable impedance at the interface. This directly leads to severe distortion and extreme instability of the reference capacitance signal, drastically shortening the sensor's lifespan.

[0134] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for preparing an ionogel membrane, characterized in that, The preparation method includes: The ion gel adhesive is coated onto the second surface of the ion gel membrane body or onto the electrode. Dry ionomer gel adhesive to form a solid hot melt adhesive; Heat the solid hot melt adhesive at 65℃~80℃ until it softens. The softened solid hot melt adhesive is bonded to the electrode or the second surface and cooled to form an ion gel adhesive film layer that tightly bonds the electrode to the second surface. The ratio of the ionic conductivity of the ion gel adhesive film layer to that of the ion gel film body is 0.8~1.2; The ionogel adhesive comprises the following components by mass percentage: 15%~17% polymer, 0.5%~10% ionic liquid, and 75%~83% solvent; The polymer is polycaprolactone, with a weight-average molecular weight of 30,000 to 50,000. And / or, the ionic liquid is 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt; And / or, the solvent is tetrahydrofuran; The mass ratio of the ionic liquid to the polymer is 1:(1.5~20).

2. The preparation method according to claim 1, characterized in that, The solid content of the iontophoresis adhesive is 15%~25%, and the softening temperature is 55℃~65℃.

3. The preparation method according to claim 1, characterized in that, The method for preparing the ionic gel adhesive includes placing the polymer and the ionic liquid into a solvent, mixing and stirring until completely dissolved to obtain the ionic gel adhesive.

4. An ionogel membrane prepared by the preparation method according to any one of claims 1 to 3, characterized in that, include: An ion gel membrane body has a first surface with a microstructure, and a second surface coated with an ion gel adhesive film layer. The ion gel adhesive film layer is used to tightly bond the electrode to the second surface, and the ratio of the ion conductivity of the ion gel adhesive film layer to that of the ion gel membrane body is 0.8 to 1.

2.

5. The ionogel membrane according to claim 4, characterized in that, The thickness of the ion gel adhesive film is 1μm~50μm.

6. The ionogel membrane according to claim 4, characterized in that, The peel strength between the ion gel adhesive film and the electrode is 0.8 N / cm to 2.0 N / cm.

7. A capacitive sensor, characterized in that, Includes an ion gel membrane as described in any one of claims 4 to 6, a working electrode, a counter electrode, and a reference electrode; the working electrode abuts against a first surface of the ion gel membrane body to form a first capacitor; the counter electrode abuts against a second surface of the ion gel membrane body to form a second capacitor; and the reference electrode is disposed on the ion gel membrane. The first surface has a microstructure, and the working electrode abuts against the microstructure surface so that the capacitance of the first capacitor is configured to change with external pressure and noise signals; the counter electrode is tightly attached to the second surface through an ion gel adhesive film layer so that the capacitance of the second capacitor is configured to change only with noise signals.

8. The capacitive sensor according to claim 7, characterized in that, The reference electrode is separately disposed on one side of the counter electrode, and the reference electrode is also tightly attached to the second surface through an ion gel adhesive film layer.

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