Gel capacitance sensor with gradient modulus structure and preparation method thereof

Abstract

The invention relates to a gel capacitance sensor with a gradient modulus structure and a preparation method of the gel capacitance sensor. The gel capacitance sensor with the gradient modulus structure structurally comprises an electrode layer, a low-modulus gel dielectric layer, an electrode layer, a medium-modulus gel dielectric layer, an electrode layer, a high-modulus gel dielectric layer and an electrode layer which are sequentially stacked, wherein the electrode layer comprises a conductive adhesive tape used for bonding the gel dielectric layer and a supporting substrate located in the middle of the conductive adhesive tape; each of the low-modulus gel dielectric layer, the medium-modulus gel dielectric layer and the high-modulus gel dielectric layer comprises low-modulus, medium-modulus and high-modulus force-electricity sensitive ion hydrogel with corresponding moduli and a gasket which is matched with the morphology structure of the gel dielectric layer with the corresponding modulus and supports the ion hydrogel; preferably, the surfaces of the low-modulus, medium-modulus and high-modulus force-electricity sensitive ion hydrogel are provided with convex micro-cone array microstructures.

Description

Technical Field

[0001] This invention belongs to the field of ion gel capacitive sensor technology, specifically relating to a gradient modulus structure gel capacitive sensor and its preparation method. Background Technology

[0002] Ion gel capacitors are widely used in wearable electronic devices, electronic skin, and soft robots due to their advantages such as high ionic conductivity, simple fabrication methods, and tunable structure and mechanical properties. However, the wide range of applications requires sensors to accurately sense and respond to a wide range of pressures, from minute to high levels. This necessitates that the sensors simultaneously possess high sensitivity, a wide detection range, and high linearity.

[0003] The elastic modulus E of ionogels plays a crucial role in regulating pressure sensing performance. Gel capacitors with a high E exhibit low sensitivity to slight pressure changes, while sensors with a low E modulus show little response to pressure changes under high pressure. Therefore, existing gel capacitors cannot simultaneously achieve both high sensitivity and a wide detection range. To achieve both high sensitivity and a wide detection range, gel capacitor devices should possess both high and low elastic moduli, and when organically combined into a capacitor device, they should exhibit high linearity in signal feedback. Summary of the Invention

[0004] To address the aforementioned technical problems, the present invention aims to provide a gradient modulus structure gel capacitive sensor and its fabrication method. The three gel capacitive layers with different moduli provided by the present invention, when connected in parallel, simultaneously possess the characteristics of low modulus, low voltage, and high sensitivity, as well as high modulus, high voltage, and wide detection range. Furthermore, high signal linearity is achieved by adjusting the modulus of the three gel layers.

[0005] In a first aspect, the present invention provides a gradient modulus gel capacitive sensor, the structure of which comprises: an electrode layer, a low-modulus gel dielectric layer, an electrode layer, a medium-modulus gel dielectric layer, an electrode layer, a high-modulus gel dielectric layer, and an electrode layer stacked sequentially; wherein: The electrode layer includes a conductive tape for bonding the gel medium layer and a supporting substrate located in the middle of the conductive tape; the low-modulus gel medium layer, the medium-modulus gel medium layer, and the high-modulus gel medium layer each include a low, medium, and high modulus force-electrosensitive ionic hydrogel and a gasket that matches the morphology and structure of the gel medium layer of the corresponding modulus and supports the ionic hydrogel; preferably, the surface of the low, medium, and high modulus force-electrosensitive ionic hydrogel has a raised microcone array microstructure.

[0006] Preferably, the conductive tape of the electrode layer is made of copper-nickel material, and the supporting substrate is polyethylene terephthalate (PET).

[0007] Preferably, the gasket is a high-modulus elastomer, preferably polydimethylsiloxane (PDMS) elastomer; wherein, the gasket can be formed by cutting PDMS into a cuboid with an upper and lower surface area of ​​1-4cm*1-4cm and an average thickness of 1.1mm, and removing a hollow area of ​​4-10mm*4-10mm*1.1mm from the center.

[0008] Preferably, the chemical composition of the low, medium, and high modulus force-electrosensitive ion hydrogels all includes: a basic solution, and network structure components, charge carrier components, crosslinking agent components, and photoinitiators dispersed in the basic solution.

[0009] Preferably, the basic solution comprises at least one of water, phytic acid (PA), and glycerol; The network structure component includes at least one of polyacrylamide (PAM), polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polyaniline (PANI), and the ratio of the network structure component to the basic solution is 0.1-0.5 g·ml. -1 ; The charge carrier component includes at least one selected from lithium bis(trifluorosulfonyl)imide (LiTFSI), lithium chloride (LiCl), and phosphoric acid (H3PO4). The ratio of the charge carrier component to the basic solution is 0-0.2 g·ml. -1 ; The crosslinking agent component includes N,N-methylenebis(acrylamide)MBA, and the mass ratio of the crosslinking agent component to the network structure component is 1:4-1000; in the low modulus gel medium layer, the mass ratio of the crosslinking agent component to the network structure component is 1g:10-20mg, in the medium modulus gel medium layer, the mass ratio of the crosslinking agent component to the network structure component is 3g:40-70mg, and in the high modulus gel medium layer, the mass ratio of the crosslinking agent component to the network structure component is 4g:250-500mg.

[0010] Preferably, the modulus of the low-modulus gel medium layer is 10-30 kPa, the modulus of the medium-modulus gel medium layer is 250-300 kPa, and the modulus of the high-modulus gel medium layer is 900-1200 kPa.

[0011] Preferably, the bottom diameter of the microcone array microstructures protruding on the surface of the low-modulus gel medium layer, the medium-modulus gel medium layer, and the high-modulus gel medium layer is 50-200 μm, the height is 50-200 μm, the spacing is 0-100 μm, and the number is 676-25600.

[0012] Secondly, the present invention provides a method for fabricating a gel capacitive sensor with the above-mentioned gradient modulus structure, the method comprising the following steps: (1) Prepare gel solutions of different moduli according to the chemical composition of the low, medium and high modulus force-electrosensitive ion hydrogels respectively, and then add the gel solutions of different moduli into the mold, and obtain the low, medium and high modulus force-electrosensitive ion hydrogels by photocuring and freeze curing. (2) Assemble the low, medium and high modulus force-electro-sensitive ion hydrogels with gaskets and electrode layers according to the structural composition of the gradient modulus structure gel capacitive sensor to obtain the gradient modulus structure gel capacitive sensor.

[0013] Preferably, in step (1), the photocuring is carried out 2 hours after the gel solutions of different moduli are added to the mold, the photocuring power is 90-100%, and the photocuring time is 1-2 min; the freeze curing temperature is -3 to -4℃, and the time is 23-24 h.

[0014] Beneficial effects Based on the capacitance-pressure response mechanism, this invention prepares a gel capacitive sensor with a gradient modulus structure, which has high sensitivity and wide detection range while also having high linearity. It can respond sensitively to both slight and high-level pressure and can be widely used in various human-computer interaction scenarios. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the side structure of a gradient modulus gel capacitive sensor as an example of the present invention; Figure 2 The stress-strain curves of the gels prepared in Examples 1-3 of this invention are shown. Figure 3 Impedance maps of the gels prepared in Examples 1-3 of this invention; Figure 4 The capacitance-pressure response diagrams of the sensors prepared in Examples 1-3 of this invention; Figure 5 This is the capacitance-pressure response diagram of the sensor prepared in Example 4 of the present invention. Detailed Implementation

[0016] The present invention will be further illustrated by the following embodiments. It should be understood that the following embodiments are for illustrative purposes only and are not intended to limit the present invention.

[0017] First, such as Figure 1 As shown, this invention provides a gel capacitive sensor with a gradient modulus structure. The structure of the gel capacitive sensor with the gradient modulus structure may include: an electrode layer, a low-modulus gel dielectric layer, an electrode layer, a medium-modulus gel dielectric layer, an electrode layer, a high-modulus gel dielectric layer, and an electrode layer stacked sequentially; wherein: The electrode layer may include a conductive tape for bonding the gel medium layer and a supporting substrate located in the middle of the conductive tape; the low-modulus gel medium layer, the medium-modulus gel medium layer, and the high-modulus gel medium layer may each include a low, medium, and high modulus force-electrosensitive ionic hydrogel of the corresponding modulus and a gasket that matches the morphology and structure of the corresponding modulus gel medium layer and supports the ionic hydrogel; preferably, the surface of the low, medium, and high modulus force-electrosensitive ionic hydrogel has a raised microcone array microstructure.

[0018] In some embodiments, the conductive tape of the electrode layer can be made of copper-nickel material, and the supporting substrate can be polyethylene terephthalate (PET). Preferably, the single-layer thickness of the conductive tape can be 0.1-0.11 mm, and the thickness of the supporting substrate can be 0.1-0.11 mm. The conductive tape mainly serves to conduct electricity.

[0019] In some embodiments, the gasket can be a high-modulus elastomer, preferably polydimethylsiloxane (PDMS) elastomer; wherein, the gasket can be formed by cutting PDMS into a cuboid with a top and bottom surface area of ​​1-4cm*1-4cm and a thickness of 1.1mm, and removing a hollow area of ​​4-10mm*4-10mm*1.1mm from the center, preferably by cutting it into a cuboid with a top and bottom surface area of ​​2cm*2cm and a thickness of 1.1mm, and removing a hollow area of ​​8mm*8mm*1.1mm from the center.

[0020] In this invention, the gel electrolyte is cut into 8mm*8mm*1.1mm cuboids and placed in the hollow area of ​​the gasket. This ensures that the microneedles on the surface of the gel electrolyte are not subjected to additional pressure during encapsulation, thus ensuring the accuracy of the initial capacitance of the capacitor. The gasket primarily serves as a supporting framework in this invention, while the force-electro-sensitive ionic hydrogel mainly functions as an electrical signal feedback mechanism.

[0021] In some embodiments, the chemical composition of the low, medium, and high modulus force-electrosensitive ion hydrogels may include: a base solution, and network structure components, charge carrier components, crosslinking agent components, and photoinitiators dispersed in the base solution.

[0022] The basic solution may include at least one of water, phytic acid (PA), and glycerol, preferably a mixed solution of water and phytic acid (PA); more preferably, the mass fraction of phytic acid (PA) in the mixed solution of water and phytic acid (PA) may be 50-70 wt%, preferably 70 wt%, or the volume ratio of water to phytic acid (PA) may be 9:1.

[0023] The network structure component may include at least one of polyacrylamide (PAM), polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polyaniline (PANI), and the ratio of the network structure component to the basic solution may be 0.1-0.5 g·ml. -1 The preferred network structure is a dual network structure formed by polyacrylamide (PAM) and polyvinyl alcohol (PVA), with PAM having a molecular weight of MW = 71.08 and PVA having a molecular weight of MW = 88000. More preferably, the ratio of PVA to the basic solution can be 0.1 g·ml. -1 .

[0024] A PAM / PVA interpenetrating network hydrogel with high organic strength was synthesized using a two-step aqueous solution polymerization method with polyacrylamide (PAM) as the matrix and polyvinyl alcohol (PVA) as the reinforcement. PAM plays a role in regulating the gel modulus; both excessively high and low PAM modulus affect the gel modulus and thus the device fabrication. PVA improves the mechanical strength of the gel, especially the mechanical strength of high-modulus gels, and enhances the compressive strength of the gel, ensuring the device's ability to operate under high pressure. Too low a modulus will result in insufficient device resilience and reduced device lifespan, while too high a modulus will make gel fabrication difficult.

[0025] The charge carrier component may include at least one of lithium bis(trifluorosulfonyl)imide (LiTFSI), lithium chloride (LiCl), and phosphoric acid (H3PO4), and the ratio of the charge carrier component to the basic solution may be 0-0.2 g·ml. -1 The preferred charge carrier component is lithium bis(trifluorosulfonyl)imide (LiTFSI), and more preferably, the ratio of LiTFSI to the basic solution is 0.2 g·ml. -1 The ion-carrying component mainly plays a role in signal stabilization. If it is too small, the device signal will be weak, the signal-to-noise ratio will be low, and it will be difficult to identify. If it is too large, it will destroy the network structure of the gel and reduce the device life.

[0026] The crosslinking agent component may include N,N-methylenebis(acrylamide)MBA, and the mass ratio of the crosslinking agent component to the network structure component can be 1:4-1000. The modulus of the gel can be controlled by changing this ratio. Preferably, in a low-modulus gel medium layer, the mass ratio of the crosslinking agent component to the network structure component can be 1g:10-20mg; in a medium-modulus gel medium layer, the mass ratio can be 3g:40-70mg; and in a high-modulus gel medium layer, the mass ratio can be 4g:250-500mg. If the mass of the network structure component monomer is too low, the gel modulus will be low and the gel will be brittle.

[0027] The photoinitiator may be 2-ketoglutaric acid, and the ratio of the photoinitiator to the basic solution may be 0.005-0.01 g·ml. -1 Preferably 0.01 g·ml -1 .

[0028] In some embodiments, the modulus of the low-modulus gel medium layer can be 10-30 kPa, the modulus of the medium-modulus gel medium layer can be 250-300 kPa, and the modulus of the high-modulus gel medium layer can be 900-1200 kPa.

[0029] In some embodiments, the low-modulus gel medium layer, the medium-modulus gel medium layer, and the high-modulus gel medium layer may all have a size of 1-10mm*1-10mm*1.1mm, preferably 8mm*8mm*1.1mm.

[0030] In some embodiments, the bottom diameter of the microcone array microstructures protruding on the surface of the low-modulus gel medium layer, the medium-modulus gel medium layer, and the high-modulus gel medium layer can be 50-200 μm, the height can be 50-200 μm, the spacing can be 0-100 μm, and the number can be 676-25600. Preferably, the bottom diameter is 100 μm, the height is 100 μm, the spacing is 50 μm, and the number is 2842.

[0031] This invention assembles three layers of gel with different moduli into a capacitor device, and then connects them in parallel. Gel capacitor devices with different moduli have different electrical properties; devices with lower moduli are more prone to electrical signal saturation. When the three layers are connected in parallel, the electrical signal can be organically fitted to achieve high linearity, high sensitivity, and a wide detection range. Lower moduli gel devices have higher sensitivity in low-pressure regions but a shorter detection range; while higher moduli gel devices have lower sensitivity in low-pressure regions but a wider detection range. By connecting them in parallel, the electrical signals over the entire pressure range are superimposed, thus fitting an electrical signal with high linearity, high sensitivity, and a wide detection range. The gradient modulus structure gel capacitive sensor provided by this invention can respond sensitively to both slight and high pressure levels, achieving high sensitivity, a wide detection range, and high linearity simultaneously.

[0032] Furthermore, the present invention provides a method for regulating gel properties, wherein the regulation of gel properties includes gel mechanical properties, electrical properties, and physical modification of the gel surface.

[0033] The regulation of the gel's mechanical properties includes adjusting the gel's elastic modulus, improving its toughness, and enhancing its water retention. The gel modulus is adjusted from 1 kPa to 1 MPa, preferably to 10 kPa, 150 kPa, or 1200 kPa. The improved gel toughness is achieved by introducing a polyvinyl alcohol (PVA) network after adding 1 g / mL of monomer to the PVA solution, which significantly enhances the gel's toughness. The enhanced water retention is achieved by introducing phytic acid (PA) into the gel and allowing it to stand at room temperature for three days, resulting in a gel weight retention rate of 75%.

[0034] The electrical properties of the gel are controlled by changing its mechanical properties while keeping its electrical properties essentially unchanged, so as to ensure that the device signal is only affected by the mechanical properties of the gel and to control the factors affecting the final performance of the device.

[0035] The surface physical modification of the gel is achieved by leaving a microneedle array on the gel surface through molding, thereby increasing the surface area of ​​the gel. The main factors affecting the capacitance-pressure signal feedback of the device are the dielectric constant of the dielectric layer and the changes in surface area and thickness during the pressure process. For the gel in this invention, the dielectric constant can be considered approximately the same. Therefore, it is necessary to increase the degree of change in the gel surface area to increase the signal feedback of the final device. Fabricating microstructures on the gel surface can effectively increase the change in the gel surface during the pressure process, thereby significantly increasing the sensitivity of the device.

[0036] The capacitance-pressure response mechanism involved in this invention includes: the electric double-layer capacitance (EDL) mechanism, the parallel-plate capacitor variation mechanism, and the parallel coupling of three-layer capacitors. The EDL mechanism involves the formation of an excess charge distribution with opposite signs on both sides of the electrode surface and the solution interface when a metal electrode is inserted into an electrolyte solution, resulting in an interphase potential difference. If a two-electrode system is inserted into the electrolyte and an external voltage lower than the solution decomposition voltage is applied, positive and negative ions in the electrolyte will migrate towards the electrodes under the drive of the electric field, ultimately forming a dense charge layer (i.e., an electric double layer) on the surfaces of the two electrodes. Because the charge spacing of the electric double layer is significantly smaller than the spacing between the plates of a traditional capacitor, it exhibits higher capacitance characteristics. For gel capacitors, an electric double layer capacitance is naturally formed, thus exhibiting higher capacitance. The parallel-plate capacitor variation mechanism refers to the influence of the capacitance change ΔC on the dielectric constant ε of the material itself, the change in the contact area ΔA between the parallel plates and the material, and the spacing d of the parallel plates. The specific relationships are as follows: By fabricating microneedle arrays on the surface of materials, the contact area between the material and the electrode can be increased. Meanwhile, the mechanical properties of the material affect the capacitance. Under the same pressure, the lower the modulus of the gel, the greater the change in contact area. Therefore, the capacitance changes more under low modulus and less under the same pressure under high modulus. However, pressure is more likely to saturate under low modulus, resulting in a narrow detection range, while pressure is less likely to saturate under high modulus, resulting in a wide detection range.

[0037] This invention organically combines the advantages of low and high modulus to design a three-layer gel capacitive sensor, which maintains a wide detection range of 0-2 MPa while retaining high sensitivity (i.e., capacitance change) of 1049.3 kPa. -1 It also has a linearity of 0.996.

[0038] The following is an exemplary description of a method for fabricating a gel capacitive sensor with a gradient modulus structure provided by the present invention. The fabrication method includes the following steps: (1) Prepare gel solutions of different moduli according to the chemical composition of the low, medium and high modulus force-electrosensitive ion hydrogels respectively, and then add the gel solutions of different moduli into the mold, and obtain the low, medium and high modulus force-electrosensitive ion hydrogels by photocuring and freeze curing. (2) Assemble the low, medium and high modulus force-electro-sensitive ion hydrogels with gaskets and electrode layers according to the structural composition of the gradient modulus structure gel capacitive sensor to obtain the gradient modulus structure gel capacitive sensor.

[0039] In some embodiments, the preparation process of the gel solutions with different moduli in step (1) may include: adding a portion of the network structure components to the basic solution and mixing them evenly to obtain a precursor solution, then adding the carrier components, the remaining network structure components and the crosslinking agent components to the precursor solution, mixing them evenly, and finally adding the photoinitiator and defoaming to obtain the gel solutions with different moduli.

[0040] The mixing method of the precursor liquid can be heating in an oil bath at 90-95℃ for 1-4 hours; the defoaming can be carried out in a refrigerated dryer at a pressure of 800-900 Pa for 30-40 minutes.

[0041] In some embodiments, the preparation process of the mold in step (1) may include: making a positive mold by uniformly distributing a microcone array microstructure with protrusions on the upper surface of the substrate, then pouring the polydimethylsiloxane PDMS precursor liquid into the customized positive mold and performing vacuum degassing treatment, with a degassing pressure of 900 Pa and a degassing time of 30 min, and then placing it in an oven at 80°C for curing for 3 h to obtain a PDMS negative mold.

[0042] In some embodiments, in step (1), the cover plate of the mold can be a 1cm*1cm square sheet cut from a polydimethylsiloxane (PDMS) cured elastomer sheet.

[0043] In some embodiments, in step (1), the mold and its cover plate are subjected to plasma treatment before use; preferably, the power of the plasma treatment is 100%, the plasma gas is oxygen, and the plasma treatment time is 2 minutes.

[0044] In some embodiments, in step (1), the photocuring is carried out 2 hours after the gel solution of different modulus is added to the mold, the photocuring power can be 90-100%, and the photocuring time can be 1-2 min; the freeze curing temperature can be -3 to -4℃, and the time can be 23-24 h.

[0045] In some embodiments, the preparation process of the gasket in step (2) may include the following steps: preparing a precursor solution of polydimethylsiloxane (PDMS) and curing agent, stirring it evenly, and then pouring it into a mold with a thickness of after defoaming treatment, and curing it to obtain a uniform elastomer sheet, which can be cut to obtain the desired product.

[0046] The mass ratio of polydimethylsiloxane (PDMS) to curing agent can be 1-20:1; the curing temperature is 70-80℃, and the curing time is 2-3 hours.

[0047] In some embodiments, step (2) may include the following process for preparing the electrode layer: attaching copper-nickel conductive tape to a square sheet of polyethylene terephthalate (PET); preferably, copper-nickel conductive tape is selected and cut into strips 1 cm wide and 2 cm long, and polyethylene terephthalate (PET) substrate with a thickness of 100 μm is cut into square sheets of 2 cm * 2 cm. Then, the cut conductive tape is attached to the center of one side of the sheet. This step is repeated to make two sheets. Then, two identical conductive tapes are cut and attached to the same positions on the upper and lower sides of the square sheet. This step is repeated to make two sheets.

[0048] In some implementations, in step (2), after assembly, medical tape is used for encapsulation, and after encapsulation, the conductive tape is connected in parallel to couple the signals.

[0049] Based on the capacitance-pressure response mechanism, this invention prepares a gel capacitive sensor with a gradient modulus structure, which has high sensitivity and wide detection range while also having high linearity. It can respond sensitively to both slight and high-level pressure and can be widely used in various human-computer interaction scenarios.

[0050] The following examples further illustrate the present invention in detail. It should also be understood that the following examples are only for further explanation of the present invention and should not be construed as limiting the scope of protection of the present invention. Any non-essential improvements and adjustments made by those skilled in the art based on the above description of the present invention are within the scope of protection of the present invention. The specific process parameters, etc., in the following examples are merely examples within a suitable range; that is, those skilled in the art can make appropriate selections within the range based on the description herein, and are not intended to be limited to the specific values ​​in the examples below. Unless otherwise specified, the technical means used in the examples are conventional means well known to those skilled in the art.

[0051] Example 1

[0052] The method for fabricating a low-modulus gel capacitive sensor provided in this embodiment includes the following steps: (1) Electrode layer preparation: Select copper-nickel conductive tape and cut it into strips 1cm wide and 2cm long. Select polyethylene terephthalate (PET) substrate with a thickness of 100μm and cut it into square sheets of 2cm*2cm. Then, paste the cut conductive tape to the center of one side of the sheet. Repeat this step to make two sheets. (2) Preparation of gasket: Prepare a precursor solution by mixing polydimethylsiloxane (PDMS) and curing agent at a mass ratio of 10:1, stir evenly, and after defoaming treatment, pour into a mold with a thickness of 1.1 mm, and cure in an oven at 80°C for 3 hours to obtain a uniform elastomer sheet; cut the sheet into a cuboid with a thickness of 1.1 mm and a top and bottom surface of 2 cm * 2 cm, and cut out an 8 mm * 8 mm rectangular area in the center; (3) Preparation of gel precursor solution: Deionized water and phytic acid PA were stirred in a volume ratio of 9 ml: 1 ml to form a basic solution, and then mixed in a ratio of polyvinyl alcohol: basic solution = 1 g: 10 ml. The mixed solution was placed in an oil bath at 90°C and stirred for 3 h until the solution became homogeneous, thus preparing the precursor solution. Preparation of low-modulus gel solution: After taking out the prepared precursor solution, cool it to room temperature. Add lithium bis(trifluorosulfonyl)imide and the base solution to the precursor solution at a ratio of 2g:10ml and mix and stir evenly to obtain mixed solution 1. Add polyacrylamide (PAM) and N,N-methylenebis(acrylamide)MBA at a ratio of 1g:20mg to obtain mixed solution 2. Stir for 1h to obtain mixed solution 2. Finally, add 100mg of photoinitiator 2-ketoglutarate to mixed solution 2 and stir for 30min to obtain mixed solution 3. Place the obtained mixed solution 3 in a refrigerated dryer and adjust the pressure to 900Pa to remove bubbles for 30min to obtain solution 4. Pretreatment of mold: The mold is subjected to plasma treatment. Oxygen is selected as the plasma gas, the power is 100%, and the treatment time is 2min before taking it out. Cover plate pretreatment: The prepared cover plate is subjected to plasma treatment. Oxygen is selected as the plasma gas, the power is 100%, and the treatment time is 2 minutes before it is taken out. Solution filling: uniformly drop solution 4 into the treated mold and let it stand at room temperature for 2 hours; Gel curing: Place the cover plate on the mold after the gel is filled to fix it, put it in a UV curing box, select 100% power to cure for 2 minutes, take it out and put it in a refrigerator at -4℃ for 24 hours to obtain the cured gel. Gel treatment: Remove the cured gel and cut it into 8mm*8mm rectangles; (4) Device assembly: The treated gel is placed in the hollow area of ​​the gasket, and the two electrode layers are placed on the top and bottom of the gasket respectively, with the conductive area facing the hollow area of ​​the gasket. After assembly, the device is finally obtained and encapsulated with medical tape.

[0053] Example 2

[0054] The method for fabricating a medium-modulus gel capacitive sensor provided in this embodiment includes the following steps: (1) Electrode layer preparation: Select copper-nickel conductive tape and cut it into strips 1cm wide and 2cm long. Select polyethylene terephthalate (PET) substrate with a thickness of 100μm and cut it into square sheets of 2cm*2cm. Then, paste the cut conductive tape to the center of one side of the sheet. Repeat this step to make two sheets. (2) Preparation of gasket: Prepare a precursor solution by mixing polydimethylsiloxane (PDMS) and curing agent at a mass ratio of 10:1. Stir the solution evenly and defoam it. Pour the solution into a mold with a thickness of 1.1 mm and cure it in an oven at 80°C for 3 hours to obtain a uniform elastomer sheet. Cut the sheet into a cuboid with a thickness of 1.1 mm and a top and bottom surface of 2 cm * 2 cm. Cut out an 8 mm * 8 mm rectangular area in the center. (3) Preparation of gel precursor solution: Deionized water and phytic acid PA were stirred into a basic solution at a volume ratio of 9 ml: 1 ml, and then mixed with polyvinyl alcohol at a ratio of 1 g: 10 ml. The mixed solution was placed in an oil bath at 90°C and stirred for 3 h until the solution became homogeneous, thus preparing the precursor solution. Preparation of medium modulus gel solution: After taking out the prepared precursor solution, cool it to room temperature at room temperature. Mix lithium bis(trifluorosulfonyl)imide with the precursor solution at a ratio of 2g:10ml and stir evenly to obtain mixed solution 1. Add polyacrylamide (PAM) and N,N-methylenebis(acrylamide)MBA at a ratio of 3g:50mg to obtain mixed solution 2. Stir for 1h to obtain mixed solution 2. Finally, add 100mg of photoinitiator 2-ketoglutarate to mixed solution 2 and stir for 30min to obtain mixed solution 3. Place the obtained mixed solution 3 in a refrigerated dryer and adjust the pressure to 900Pa to remove bubbles for 30min to obtain solution 4. Mold pretreatment: The mold is subjected to plasma treatment, with oxygen as the plasma gas, power at 100%, and treatment time of 2 minutes before removal; Cover plate pretreatment: The prepared cover plate is subjected to plasma treatment. Oxygen is selected as the plasma gas, the power is 100%, and the treatment time is 2 minutes before it is taken out. Solution filling: uniformly drop solution 4 into the treated mold and let it stand at room temperature for 2 hours; Gel curing: Place the cover plate on the mold after the gel is filled to fix it, put it in a UV curing box, select 100% power to cure for 2 minutes, take it out and put it in a refrigerator at -4℃ for 24 hours to obtain the cured gel. Gel treatment: Remove the cured gel and cut it into 8mm*8mm rectangles; (4) Device assembly: The treated gel is placed in the hollow area of ​​the gasket, and the two electrode layers are placed on the top and bottom of the gasket respectively, with the conductive area facing the hollow area of ​​the gasket. After assembly, the device is finally obtained and encapsulated with medical tape.

[0055] Example 3

[0056] The method for fabricating a high-modulus gel capacitive sensor provided in this embodiment includes the following steps: (1) Electrode layer preparation: Select copper-nickel conductive tape and cut it into strips 1cm wide and 2cm long. Select polyethylene terephthalate (PET) substrate with a thickness of 100μm and cut it into square sheets of 2cm*2cm. Then, paste the cut conductive tape to the center of one side of the sheet. Repeat this step to make two sheets. (2) Preparation of gasket: Prepare a precursor solution by mixing polydimethylsiloxane (PDMS) and curing agent at a mass ratio of 10:1, stir evenly, and after defoaming treatment, pour into a mold with a thickness of 1.1 mm, and cure in an oven at 80°C for 3 hours to obtain a uniform elastomer sheet; cut the sheet into a cuboid with a thickness of 1.1 mm and a top and bottom surface of 2 cm * 2 cm, and cut out an 8 mm * 8 mm rectangular area in the center; (3) Preparation of gel precursor solution: Deionized water and phytic acid PA were stirred into a basic solution at a volume ratio of 9 ml: 1 ml, and then mixed with polyvinyl alcohol at a ratio of 1 g: 10 ml. The mixed solution was placed in an oil bath at 90°C and stirred for 3 h until the solution became homogeneous, thus preparing the precursor solution. Preparation of high modulus gel solution: After removing the prepared precursor solution, cool it to room temperature. Mix lithium bis(trifluorosulfonyl)imide with the precursor solution at a ratio of 2g:10ml and stir until homogeneous to obtain mixed solution 1. Add polyacrylamide (PAM) and N,N-methylenebis(acrylamide)MBA at a ratio of 4g:300mg to obtain mixed solution 2. Stir for 1h to obtain mixed solution 2. Finally, add 100mg of photoinitiator 2-ketoglutaric acid to mixed solution 2 and stir for 30min to obtain mixed solution 3. Place the obtained mixed solution 3 in a refrigerated dryer and adjust the pressure to 900Pa to remove bubbles for 30min to obtain solution 4. Mold pretreatment: The mold is subjected to plasma treatment, with oxygen as the plasma gas, power at 100%, and the mold is removed after 1 minute of treatment. Cover plate pretreatment: The prepared cover plate is subjected to plasma treatment. Oxygen is selected as the plasma gas, the power is 100%, and the treatment time is 2 minutes before it is taken out. Solution filling: uniformly drop solution 4 into the treated mold and let it stand at room temperature for 2 hours; Gel curing: Place the cover plate on the mold after the gel is filled to fix it, put it in a UV curing box, select 100% power to cure for 1 minute, take it out and put it in a refrigerator at -4℃ for 24 hours to obtain the cured gel. Gel treatment: Remove the cured gel and cut it into 8mm*8mm rectangles; (4) Device assembly: The treated gel is placed in the hollow area of ​​the gasket, and the two electrode layers are placed on the top and bottom of the gasket respectively, with the conductive area facing the hollow area of ​​the gasket. After assembly, the device is finally obtained and encapsulated with medical tape.

[0057] Example 4

[0058] The method for fabricating low, medium, and high modulus gel capacitive sensors provided in this embodiment includes the following steps: (1) Electrode layer preparation: Select copper-nickel conductive tape and cut it into strips 1cm wide and 2cm long. Select polyethylene terephthalate (PET) substrate with a thickness of 100μm and cut it into square sheets of 2cm*2cm. Then, paste the cut conductive tape to the center of one side of the sheet. Repeat this step to make two sheets. Then cut two identical conductive tapes and paste them to the same positions on the top and bottom sides of the square sheet. Repeat this step to make two sheets. (2) Preparation of gaskets: A precursor solution was prepared by mixing polydimethylsiloxane (PDMS) and curing agent at a mass ratio of 10:1. After stirring evenly and defoaming, the solution was poured into a mold with a thickness of 1.1 mm and cured in an oven at 80°C for 3 hours to obtain a uniform elastomer sheet. The sheet was cut into cuboids with a top and bottom surface area of ​​2 cm * 2 cm and a thickness of 1.1 mm. An 8 mm * 8 mm rectangular area was removed from the center. This step was repeated to make three gaskets. (3) Preparation of gel precursor solution: Deionized water and phytic acid PA were stirred in a volume ratio of 36ml:4ml to form a basic solution, and then mixed in a ratio of polyvinyl alcohol: mixed solution = 4g:40ml. The mixed solution was placed in an oil bath at 90℃ and stirred for 3h until the solution became homogeneous, thus preparing the precursor solution. Preparation of low-modulus, medium-modulus, and high-modulus gel solutions: After removing the prepared precursor solution, cool it to room temperature. Divide 30 ml of the solution into three portions, labeled a, b, and c. Mix lithium bis(trifluorosulfonyl)imide with the precursor solution at a ratio of 2 g: 10 ml and stir until homogeneous to obtain mixed solutions a1, b1, and c1. Add polyacrylamide (PAM) and N,N-methylenebis(acrylamide)MBA at a ratio of 1 g: 20 mg to obtain mixed solution a1. Mixed solutions b1 were obtained by adding 3g:50mg of polyacrylamide (PAM) and N,N-methylenebis(acrylamide)MBA at a ratio of 4g:300mg. Mixed solutions c1 were obtained by stirring for 1 hour to obtain mixed solutions a2, b2, and c2. Finally, 100mg of photoinitiator 2-ketoglutaric acid was added to mixed solutions a2, b2, and c2 and stirred for 30 minutes to obtain mixed solutions a3, b3, and c3. Mixed solutions a3, b3, and c3 were placed in a refrigerated dryer and the pressure was adjusted to 900Pa to remove bubbles for 30 minutes to obtain solutions a4, b4, and c4. Mold pretreatment: The mold is subjected to plasma treatment, with oxygen as the plasma gas, power at 100%, and the mold is removed after 1 minute of treatment. Cover plate pretreatment: The prepared cover plate is subjected to plasma treatment. Oxygen is selected as the plasma gas, the power is 100%, and the treatment time is 2 minutes before it is taken out. Solution filling: uniformly drop solutions a4, b4, and c4 into the treated mold and let it stand at room temperature for 2 hours; Gel curing: Place the cover plate on the mold after gel filling to fix it, put it in a UV curing box, use 100% power for curing a4 and b4 for 2 minutes, use 100% power for curing c4 for 1 minute, take it out and put it in a refrigerator at -4℃ for 24 hours to obtain the cured gel. Gel treatment: Remove the cured gel and cut it into 8mm*8mm rectangles; (4) Device assembly: Place the treated gel in the hollow area of ​​the gasket, and finally assemble the four electrodes according to the reference. Figure 1 The conductive areas are aligned with the hollow areas of the gaskets. After assembly, the final device ABC is obtained and then sealed with medical tape.

[0059] Figure 2 The figures show the stress-strain curves of the gels prepared in Examples 1-3 of this invention. As can be seen from the figures, three different moduli of hydrogel media can be obtained by controlling the ratio of AM to its crosslinking agent.

[0060] Figure 3 Impedance maps of the gels prepared in Examples 1-3 of this invention. As can be seen from the figures, the addition of LiTFSI can make the ionic conductivity of the three gel electrolytes with different moduli similar.

[0061] Figure 4 The capacitance-pressure response diagrams of the sensors prepared in Examples 1-3 of this invention are shown. It can be seen from the diagrams that the devices composed of a single-layer gel electrolyte have limitations in both sensitivity and detection range.

[0062] Figure 5 This is the capacitance-pressure response diagram of the sensor prepared in Example 4 of this invention. As can be seen from the diagram, after the three-layer treatment, the sensitivity in the low-pressure region of the gel was improved, the overall detection range was expanded, and the linearity was enhanced.

[0063] Although the present invention has been described in detail through the preferred embodiments above, it should be understood that the above description should not be considered as a limitation of the present invention. Various modifications and substitutions to the present invention will be apparent to those skilled in the art after reading the above description. Therefore, the scope of protection of the present invention should be defined by the appended claims.

Claims

1. A gel capacitive sensor with a gradient modulus structure, characterized in that, The gradient modulus gel capacitive sensor comprises: an electrode layer, a low-modulus gel medium layer, an electrode layer, a medium-modulus gel medium layer, an electrode layer, a high-modulus gel medium layer, and an electrode layer stacked sequentially; wherein: The electrode layer includes a conductive tape for bonding the gel dielectric layer and a supporting substrate located in the middle of the conductive tape; The low-modulus gel medium layer, the medium-modulus gel medium layer, and the high-modulus gel medium layer each include low, medium, and high modulus force-electrosensitive ionic hydrogels of corresponding moduli and gaskets that match the morphology and structure of the gel medium layer of the corresponding modulus and support the ionic hydrogels; preferably, the surface of the low, medium, and high modulus force-electrosensitive ionic hydrogels has a raised microcone array microstructure.

2. The gradient modulus structure gel capacitive sensor according to claim 1, characterized in that, The conductive tape of the electrode layer is made of copper-nickel material, and the supporting substrate is polyethylene terephthalate (PET).

3. The gradient modulus structure gel capacitive sensor according to claim 1 or 2, characterized in that, The gasket is a high-modulus elastomer, preferably polydimethylsiloxane (PDMS) elastomer; wherein, the gasket can be formed by cutting PDMS into a cuboid with an upper and lower surface area of ​​1-4cm*1-4cm and an average thickness of 1.1mm, and removing a hollow area of ​​4-10mm*4-10mm*1.1mm from the center.

4. The gradient modulus structure gel capacitive sensor according to any one of claims 1-3, characterized in that, The chemical composition of the low, medium, and high modulus force-electrosensitive ion hydrogels all includes: a basic solution, and network structure components, charge carrier components, crosslinking agent components, and photoinitiators dispersed in the basic solution.

5. The gradient modulus structure gel capacitive sensor according to any one of claims 1-4, characterized in that, The basic solution includes at least one of water, phytic acid (PA), and glycerol. The network structure component includes at least one of polyacrylamide (PAM), polyacrylic acid (PAA), polyvinyl alcohol (PVA), and polyaniline (PANI), and the ratio of the network structure component to the basic solution is 0.1-0.5 g·ml. -1 ; The charge carrier component includes at least one selected from lithium bis(trifluorosulfonyl)imide (LiTFSI), lithium chloride (LiCl), and phosphoric acid (H3PO4). The ratio of the charge carrier component to the basic solution is 0-0.2 g·ml. -1 ; The crosslinking agent component includes N,N-methylenebis(acrylamide)MBA, and the mass ratio of the crosslinking agent component to the network structure component is 1:4-1000; in the low modulus gel medium layer, the mass ratio of the crosslinking agent component to the network structure component is 1g:10-20mg, in the medium modulus gel medium layer, the mass ratio of the crosslinking agent component to the network structure component is 3g:40-70mg, and in the high modulus gel medium layer, the mass ratio of the crosslinking agent component to the network structure component is 4g:250-500mg.

6. The gradient modulus structure gel capacitive sensor according to any one of claims 1-5, characterized in that, The modulus of the low-modulus gel medium layer is 10-30 kPa, the modulus of the medium-modulus gel medium layer is 250-300 kPa, and the modulus of the high-modulus gel medium layer is 900-1200 kPa.

7. The gradient modulus structure gel capacitive sensor according to any one of claims 1-6, characterized in that, The microcone array microstructures protruding on the surface of the low-modulus gel medium layer, medium-modulus gel medium layer, and high-modulus gel medium layer have a bottom diameter of 50-200 μm, a height of 50-200 μm, a spacing of 0-100 μm, and a number of 676-25600.

8. A method for preparing a gel capacitive sensor with a gradient modulus structure according to any one of claims 1-7, characterized in that, The preparation method includes the following steps: (1) Prepare gel solutions of different moduli according to the chemical composition of the low, medium and high modulus force-electrosensitive ion hydrogels respectively, and then add the gel solutions of different moduli into the mold, and obtain the low, medium and high modulus force-electrosensitive ion hydrogels by photocuring and freeze curing. (2) Assemble the low, medium and high modulus force-electro-sensitive ion hydrogels with gaskets and electrode layers according to the structural composition of the gradient modulus structure gel capacitive sensor to obtain the gradient modulus structure gel capacitive sensor.

9. The preparation method according to claim 8, characterized in that, In step (1), the photocuring is carried out 2 hours after the gel solutions of different moduli are added to the mold, the photocuring power is 90-100%, and the photocuring time is 1-2 min; the freeze curing temperature is -3 to -4℃ and the time is 23-24 h.

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