Composite gel, preparation method thereof, strain sensor and application thereof

Abstract

The application discloses a composite gel and a preparation method thereof, a strain sensor and application of the strain sensor. The preparation method of the composite gel comprises the following steps: mixing and matching raw materials including a hydrophilic polymerizable monomer, an initiator, a crosslinking agent, water, a hydrophobic ionic liquid and an amphiphilic metal salt into a precursor solution, and preparing the composite gel through a polymerization reaction. By introducing the amphiphilic metal salt as a molecular bridge, the compatible connection of the hydrophilic network and the hydrophobic ionic liquid can be realized. By introducing the relatively inexpensive water phase, the use amount of the hydrophobic ionic liquid can be reduced, and the cost can be effectively controlled. By adjusting the ratio of the hydrophobic ionic liquid and the water, the Young's modulus can be accurately controlled in a wide range to match different human tissues. The obtained composite gel has excellent anti-drying, anti-freezing and environmental stability, and simultaneously has low hysteresis and self-adhesion characteristics. The composite gel is suitable for the strain sensor, and stable and reliable dynamic monitoring can be realized. Moreover, the process is simple, the conditions are mild, and the composite gel is easy to produce on a large scale.

Description

Technical Field

[0001] This invention relates to the field of flexible sensing materials technology, and in particular to a composite gel and its preparation method, a strain sensor and its application. Background Technology

[0002] With the rapid development of flexible wearable electronic devices, sensors that match the modulus of human skin and organs and can be comfortably worn have attracted widespread attention. Among many flexible sensing materials, hydrogels have garnered significant interest due to their excellent flexibility, adhesion, ionic conductivity, and biocompatibility. Similarly, ionogels, which use ionic liquids as dispersion media, are considered promising new materials that could potentially replace hydrogels due to their outstanding ionic conductivity, thermal stability, and superior environmental stability (such as antifreeze and anti-drying properties).

[0003] However, both types of materials have their limitations in practical applications. Hydrogels use water as a solvent and are prone to dehydration and failure when exposed to air for extended periods. Furthermore, they are susceptible to freezing at low temperatures, leading to significant degradation or even failure of their mechanical and electrical properties. While ionic gels can overcome the environmental stability issues of hydrogels, their commonly used hydrophobic ionic liquids (such as 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt, [EMIM][TFSI]) have poor compatibility with most hydrophilic hydrogel network monomers, making it difficult to directly polymerize them using existing hydrogel preparation processes and formulations. In addition, ionic liquids are expensive, resulting in high costs for preparing pure ionic gels, and the range of available polymer monomers is limited, restricting their widespread application.

[0004] On the other hand, as wearable strain sensors, in addition to good conductivity and environmental stability, the mechanical properties of the materials are crucial. Ideal sensor materials should typically possess characteristics such as relatively low modulus, high tensile strength, and low energy dissipation (low hysteresis) during cyclic deformation, matching those of human tissue, to ensure the accuracy and repeatability of signal acquisition. Simultaneously, if the material has a certain degree of adhesion to the skin, it can reduce signal noise caused by interface slippage during use. However, existing gel materials struggle to simultaneously address issues such as low hysteresis and adhesion.

[0005] Therefore, there is an urgent need to develop a novel gel material that can take into account simple preparation process, environmental stability, and solve the compatibility problem of hydrophilic / hydrophobic phases, so as to achieve flexible modulus control, low hysteresis and good adhesion, thereby meeting the application requirements of next-generation high-performance flexible wearable strain sensors. Summary of the Invention

[0006] The present invention aims to at least solve one of the technical problems existing in the prior art. Therefore, one objective of the present invention is to provide a method for preparing a composite gel.

[0007] A second objective of this invention is to provide a composite gel.

[0008] A third objective of this invention is to provide a strain sensor.

[0009] The fourth objective of this invention is to provide an application of the aforementioned strain sensor in wearable devices.

[0010] In a first aspect, the present invention provides a method for preparing a composite gel, comprising the following steps: A precursor solution is prepared by mixing raw materials including hydrophilic polymerizable monomers, initiators, crosslinking agents, water, hydrophobic ionic liquids and amphiphilic metal salts, and then a composite gel is obtained by polymerization reaction.

[0011] The method for preparing the composite gel according to embodiments of the present invention has at least the following beneficial effects: The preparation method of this composite gel uses hydrophilic polymerizable monomers, crosslinking agents, and initiators as basic raw materials, while simultaneously employing water and hydrophobic ionic liquids, and adding amphiphilic metal salts, to prepare it through one-step polymerization. By introducing amphiphilic metal salts, the incompatibility problem between the hydrophilic network and the hydrophobic ionic liquid in traditional hydrogels is successfully solved. Therefore, traditional hydrogel preparation processes and formulations can be directly used, and the one-step polymerization preparation is simple, mild, and easy to scale up.

[0012] Amphiphilic metal salts can act as "molecular bridges," effectively connecting water molecules and hydrophobic ionic liquids. This integrates the originally incompatible hydrophilic and hydrophobic phases into a unified composite system that is macroscopically homogeneous and may exhibit controllable phase separation at the microscopic level. This lays the foundation for the environmental stability of ionic gels. Specifically, amphiphilic metal salts can connect with hydrophobic ionic liquids and hydrophilic phases (including water molecules and hydrophilic polymer networks) to form a hydrophobic ionic liquid-amphiphilic metal salt-hydrophilic phase structure. This significantly improves the anti-drying and anti-freezing properties of the composite gel, enabling it to maintain material quality and flexibility for a long time in low-humidity environments and retain flexibility and ionic conductivity in low-temperature environments (such as sub-zero temperatures). This greatly expands its application scenarios, making it suitable for harsh environments such as cold regions, outdoor activities, and cold chain transportation.

[0013] Using the above preparation method, the degree of internal microphase separation can be effectively controlled by adjusting the ratio of hydrophobic ionic liquid to water in the composite gel, and correspondingly adjusting the ratio of amphiphilic metal salt to water. This allows for precise adjustment of the Young's modulus of the composite gel over a wide range (from kPa to MPa), enabling flexible modulus control and better matching of the composite gel to different human tissues. Furthermore, the resulting composite gel exhibits self-adhesion properties on various substrates (including skin, glass, metal, and fabric), achieving stable adhesion without additional adhesives, which is beneficial for constructing stable and interference-resistant sensing interfaces. Simultaneously, the composite gel exhibits extremely low hysteresis in cyclic tensile testing, with hysteresis below 10% at 200% strain, even below 5%. The material experiences minimal energy loss during repeated deformation and can quickly and accurately recover its original state. This composite gel is suitable for strain sensors and other sensor devices, and its low hysteresis ensures signal stability and reliability in dynamic monitoring (such as joint movement, pulse, and respiration).

[0014] In addition, the above preparation method introduces a relatively inexpensive aqueous phase, which can reduce the amount of high-cost hydrophobic ionic liquid used. It can effectively control material costs while ensuring the performance of the composite gel, and has significant economic benefits and industrialization prospects.

[0015] According to some embodiments of the present invention, the preparation of the precursor solution specifically includes: first mixing a hydrophobic ionic liquid, an amphiphilic metal salt and water to form a mixed solution; and then adding a hydrophilic polymerizable monomer, an initiator and a crosslinking agent to the mixed solution to form the precursor solution.

[0016] According to some embodiments of the present invention, the mass ratio of the hydrophobic ionic liquid to water is 99:1 to 1:99, the mass ratio of the amphiphilic metal salt to water is (0.6 to 2.5):1, and the mass ratio of the hydrophilic polymerizable monomer to the mixture is (0.08 to 0.6):1. In some embodiments, the mass ratio of the hydrophobic ionic liquid to water is 9:1 to 1:9, and the mass ratio of the amphiphilic metal salt to water is (0.7 to 1.28):1.

[0017] For example, the mass ratio of hydrophobic ionic liquid to water can be 90:1, 85:1, 82:1, 80:1, 70:1, 65:1, 60:1, 50:1, 40:1, 35:1, 30:1, 20:1, 15:1, 12:1, 10:1, 9:1, 8:1, 5:1, 4:1, 3.5:1, 3:1, 2.5:1, 7:3, 2.3:1, 2:1, 1.5:1, 1.2: 1. Any value or a range of any two of the following: 1:1, 1:2, 1:1.5, 1:2, 1:2.3, 3:7, 1:2.5, 1:3, 1:3.5, 1:4, 1:5, 1:8, 1:9, 1:10, 1:12, 1:15, 1:20, 1:30, 1:35, 1:40, 1:50, 1:60, 1:65, 1:70, 1:80, 1:82, 1:85, 1:90.

[0018] The mass ratio of the amphiphilic metal salt to water can be any value or a range of any two of the following: 0.6:1, 0.7:1, 0.71:1, 0.8:1, 0.9:1, 1:1, 1.14:1, 1.2:1, 1.28:1, 1.3:1, 1.4:1, 1.5:1, 1.6:1, 1.65:1, 1.7:1, 1.8:1, 1.85:1, 1.9:1, 2:1, 2.1:1, 2.15:1, 2.2:1, 2.3:1, 2.4:1, 2.5:1.

[0019] The mass ratio of the hydrophilic polymerizable monomer to the mixture can be 0.08:1, 0.09:1, 0.1:1, 0.12:1, 0.13:1, 0.15:1, 0.16:1, 0.18:1, 0.2:1, 0.22:1, 0.24:1, 0.25:1, 0.26:1, 0.27:1, 0.28:1, 0.3:1, 0.31:1, 0.33... The range of any one of the following values, or any two of them: 0.35:1, 0.37:1, 0.39:1, 0.4:1, 0.41:1, 0.42:1, 0.44:1, 0.45:1, 0.46:1, 0.47:1, 0.49:1, 0.5:1, 0.52:1, 0.53:1, 0.55:1, 0.57:1, 0.58:1, 0.6:1.

[0020] Specifically, amphiphilic metal salts are salt compounds composed of metal cations and organic anions. These amphiphilic metal salts contain both lipophilic (hydrophobic) and hydrophilic (polar) groups in their molecular structure. Furthermore, the organic anions in amphiphilic metal salts generally contain both hydrophobic and hydrophilic groups; that is, the amphiphilicity of the amphiphilic metal salt originates from the anionic ligand.

[0021] In some embodiments, the organic anion is a fluorinated organic anion. Fluorinated organic anions may include, but are not limited to, trifluoromethanesulfonate.

[0022] In some embodiments, the metal cation may include, but is not limited to, zinc ions and iron ions.

[0023] According to some embodiments of the present invention, the amphiphilic metal salt includes at least one of zinc trifluoromethanesulfonate and iron trifluoromethanesulfonate.

[0024] According to some embodiments of the present invention, the hydrophobic ionic liquid includes at least one of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide ([EMIM][TFSI]) and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide.

[0025] According to some embodiments of the present invention, the hydrophilic polymerizable monomer includes at least one of acrylamide monomer and acrylic acid.

[0026] According to some embodiments of the present invention, the water is specifically deionized water.

[0027] According to some embodiments of the present invention, the crosslinking agent includes at least one of N,N'-methylenebisacrylamide and N,N'-methylenebismethylacrylamide.

[0028] According to some embodiments of the present invention, the mass ratio of the crosslinking agent to the hydrophilic polymerizable monomer is (0.0001~0.005):1. For example, the mass ratio of the crosslinking agent to the hydrophilic polymerizable monomer can be 0.0001:1, 0.0002:1, 0.0004:1, 0.0005:1, 0.0006:1, 0.0008:1, 0.001:1, 0.0012:1, 0.0014:1, 0.0015:1, 0.0017:1, 0.0019:1, 0.002:1, etc. The range of any one of the following values, or any two of them: 0.0023:1, 0.0025:1, 0.0028:1, 0.003:1, 0.0033:1, 0.0035:1, 0.0037:1, 0.004:1, 0.0042:1, 0.0044:1, 0.0045:1, 0.0046:1, 0.0048:1, 0.005:1.

[0029] According to some embodiments of the present invention, the initiator is a photoinitiator, and the polymerization reaction is a photopolymerization reaction, specifically initiated by light irradiation.

[0030] In some embodiments, the photoinitiator may include at least one of 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone and 1-hydroxycyclohexylphenyl ketone.

[0031] In some embodiments, the mass ratio of the photoinitiator to the hydrophilic polymerizable monomer is (0.002~0.05):1. For example, the mass ratio of the photoinitiator to the hydrophilic polymerizable monomer can be 0.002:1, 0.003:1, 0.0045:1, 0.005:1, 0.006:1, 0.0065:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, 0.012:1, 0.015:1, 0.018:1, 0.02:1, etc. 1. Any value or a range of any two of the following: 0.023:1, 0.025:1, 0.027:1, 0.03:1, 0.032:1, 0.034:1, 0.035:1, 0.038:1, 0.04:1, 0.042:1, 0.044:1, 0.045:1, 0.047:1, 0.049:1, 0.05:1.

[0032] In some embodiments, the photopolymerization reaction is an ultraviolet photopolymerization reaction, that is, the polymerization reaction is initiated by ultraviolet light irradiation; further, ultraviolet light with a wavelength of 365nm can be used for irradiation; the irradiation time can be controlled within 5min~360min, such as any value or a range of any two of the following: 5min, 10min, 15min, 20min, 30min, 45min, 60min, 75min, 90min, 120min, 135min, 150min, 165min, 180min, 200min, 240min, 265min, 275min, 300min, 320min, 360min.

[0033] According to some embodiments of the present invention, after preparing the precursor solution, a degassing treatment is performed to remove air bubbles, followed by a polymerization reaction to obtain the composite gel. The degassing treatment helps eliminate defects, avoids oxygen-induced polymerization inhibition, and ensures structural uniformity and mechanical properties. In some embodiments, the degassing treatment may include at least one of ultrasonic degassing, vacuum degassing, and refrigerated settling.

[0034] In a second aspect, the present invention provides a composite gel prepared by any of the aforementioned methods for preparing composite gels.

[0035] The technical solution of the present invention regarding composite gel has at least the following beneficial effects: the composite gel of the present invention is prepared by the aforementioned preparation method of composite gel of the present invention, and thus has all the beneficial effects of the above preparation method of composite gel, which will not be repeated here.

[0036] According to some embodiments of the present invention, the composite gel comprises a hydrophilic polymer network, an amphiphilic metal salt, a hydrophobic ionic liquid, and water. The hydrophilic polymer network is formed by polymerization of raw materials including a hydrophilic polymerizable monomer, an initiator, and a crosslinking agent. The hydrophobic ionic liquid is dispersed and connected in the hydrophilic polymer network through the amphiphilic metal salt, and both the hydrophobic ionic liquid and the water are connected to the amphiphilic metal salt.

[0037] According to some embodiments of the present invention, the hysteresis of the composite gel is less than 10%, specifically, the cyclic tensile hysteresis of the composite gel at 200% strain is less than 10%; further, in some embodiments, the hysteresis of the composite gel is less than 5%, specifically, the cyclic tensile hysteresis of the composite gel at 200% strain is less than 5%.

[0038] A third aspect of the present invention provides a strain sensor comprising an electrode and any of the aforementioned composite gels of the present invention, wherein the electrode comprises a first electrode and a second electrode, the first electrode and the second electrode being disposed at an interval and both being connected to the composite gel.

[0039] The technical solution of the present invention regarding the strain sensor has at least the following beneficial effects: The strain sensor of the embodiment of the present invention includes a composite gel prepared by any of the aforementioned composite gels or composite gel preparation methods of the present invention, thereby having all the beneficial effects of the aforementioned composite gels or composite gel preparation methods, which will not be repeated here.

[0040] According to some embodiments of the present invention, the first electrode and the second electrode are connected to both ends of the composite adhesive.

[0041] According to some embodiments of the present invention, the electrode is a metal electrode; that is, the first electrode and the second electrode are each independently metal electrodes.

[0042] According to some embodiments of the present invention, the electrode is a platinum-plated metal foil or a silver electrode. The platinum-plated metal foil may be a platinum-plated copper foil; the silver electrode may be made of conductive silver paste.

[0043] According to some embodiments of the present invention, the strain sensor can be manufactured by cutting a composite gel into a specific shape, assembling it with an electrode, and then encapsulating it.

[0044] In a fourth aspect, the present invention proposes an application of the aforementioned strain sensor in a wearable device.

[0045] In some embodiments, the strain sensor is used in wearable devices, specifically for monitoring motion deformation of the human body or animal, such as joint bending, muscle stretching, or minute vibrations.

[0046] According to some embodiments of the present invention, the wearable device is a flexible wearable device. Attached Figure Description

[0047] The present invention will be further described below with reference to the accompanying drawings and embodiments, wherein: Figure 1 Photographs of the mixtures prepared during the preparation of the composite gels of Comparative Example 1 (without zinc trifluoromethanesulfonate) and Example 1 (with zinc trifluoromethanesulfonate); Figure 2 This is a photograph of the composite gel from Example 1. Figure 3 The stress-strain curves of the composite gels in Examples 1-2 and Comparative Example 2 are shown. Figure 4 The loading and unloading curves of the composite gel in Example 1 during cyclic tensile testing are shown. Figure 5 The differential scanning calorimetry curve of the composite gel in Example 1 at low temperature; Figure 6 The curve showing the weight change of the composite gel in air over time in Example 1 is shown. Figure 7 This is a diagram demonstrating the adhesion performance of the composite gel to different substrate materials in Example 1; Figure 8 The resistance change curve of the strain sensor assembled based on the composite gel of Example 1 during joint bending-straightening is shown. Detailed Implementation

[0048] The following will describe the concept and technical effects of the present invention clearly and completely with reference to embodiments, so as to fully understand the purpose, features and effects of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are all within the scope of protection of the present invention.

[0049] Example 1 This embodiment proposes a composite gel, which is prepared by a method including the following steps: S1. Weigh 0.9 g of hydrophobic ionic liquid [EMIM][TFSI] and 2.1 g of deionized water (mass ratio 3:7) into a sample bottle, mix with magnetic stirring, and allow to stand until stratification occurs; then add 2.4 g of zinc trifluoromethanesulfonate (mass ratio of zinc trifluoromethanesulfonate to deionized water 1.14:1), and continue stirring for about 10 minutes until the solution becomes homogeneous and clear, obtaining the mixture, as shown below. Figure 1 As shown (specifically) Figure 1 (Right image in the middle)

[0050] S2. Add 0.75g of acrylamide monomer (mass ratio of 0.25:1 to the mixture), 0.0015g of crosslinking agent N,N'-methylenebisacrylamide (mass ratio of 0.002:1 to the acrylamide monomer), and 0.0035g of photoinitiator 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylphenylacetone (mass ratio of 0.0047:1 to the acrylamide monomer) to the mixture obtained in step S1. Stir and sonicate the mixture until all solids are completely dissolved to obtain a homogeneous precursor solution.

[0051] S3. Inject the precursor solution into the mold, remove air bubbles, and irradiate under 365nm ultraviolet light for 120 minutes to carry out the polymerization reaction; after the reaction is complete, demold to obtain a transparent and flexible composite gel, namely an ionogel-hydrogel composite, whose macroscopic morphology is as follows. Figure 2 As shown.

[0052] Example 2 This embodiment proposes a composite gel, specifically an ionic gel-hydrogel composite, which differs from Example 1 in that: in the preparation process of the composite gel in this embodiment, in step S2, the mass ratio of hydrophobic ionic liquid [EMIM][TFSI] to deionized water is 7:3 (i.e., 2.1g of hydrophobic ionic liquid to 0.9g of deionized water), and the amount of zinc trifluoromethanesulfonate added is 1.08g (its mass ratio to deionized water is 1.2:1). Other operations are the same as the preparation operation of the composite gel in Example 1.

[0053] Example 3 This embodiment proposes a composite gel, specifically an ionic gel-hydrogel composite, which differs from Example 1 in that: in the preparation process of the composite gel in this embodiment, in step S2, the mass ratio of hydrophobic ionic liquid [EMIM][TFSI] to deionized water is 1:9 (i.e., 0.3 g of ionic liquid to 2.7 g of deionized water), and the amount of zinc trifluoromethanesulfonate added is 1.92 g (its mass ratio to deionized water is 0.71:1). Other operations are the same as the preparation operation of the composite gel in Example 1.

[0054] Example 4 This embodiment proposes a composite gel, specifically an ionic gel-hydrogel composite, which differs from Example 1 in that: in the preparation process of the composite gel in this embodiment, in step S2, the mass ratio of hydrophobic ionic liquid [EMIM][TFSI] to deionized water is 1:1 (i.e., 1.5 g of ionic liquid to 1.5 g of deionized water), and the amount of zinc trifluoromethanesulfonate added is 1.92 g (its mass ratio to deionized water is 1.28:1). Other operations are the same as the preparation operation of the composite gel in Example 1.

[0055] Comparative Example 1 This comparative example presents a composite gel, which differs from Example 1 in that: in the preparation process of this comparative example composite gel, the addition of zinc trifluoromethanesulfonate is omitted in step S1. Instead, 0.9 g of hydrophobic ionic liquid [EMIM][TFSI] and 2.1 g of deionized water (mass ratio 3:7) are mixed to prepare a mixture. Furthermore, even after prolonged stirring, the mixture cannot form a homogeneous solution and always exhibits a macroscopic phase separation state. Figure 1 As shown (specifically) Figure 1 (Middle left figure); other operations are the same as those for the preparation of the composite gel in Example 1.

[0056] Comparative Example 2 This comparative example presents a hydrogel, specifically a polyacrylamide hydrogel, which differs from Example 1 in that: in the preparation process of the hydrogel in this comparative example, the addition of hydrophobic ionic liquids [EMIM][TFSI] and zinc trifluoromethanesulfonate is omitted in step S1, and the solution is only water. Other operations are the same as the preparation operations of the composite gel in Example 1.

[0057] Performance testing (1) Mechanical property testing The composite gels of Examples 1 and 2 and the hydrogel of Comparative Example 2 were cut into standard dumbbell-shaped strips and subjected to uniaxial tensile tests using a universal tensile testing machine. The composite gel of Example 1 was also subjected to a load-unload cyclic tensile test. The results are as follows: Figure 3 and Figure 4 As shown.

[0058] Test results show that the modulus and elongation at break of the composite gels in Examples 1 and 2 were effectively controlled by changing the mass ratio of the hydrophobic ionic liquid to water. The composite gel in Example 1 exhibited the largest fracture strain, while the maximum fracture strain of the composite gel in Example 2 was also increased compared to that of the hydrogel in Comparative Example 2, and the Young's modulus was also improved. The results of 5 load-unload cyclic tensile tests (strain up to 200%) show that the composite gel in Example 1 exhibits excellent resilience, with a hysteresis of less than 4%.

[0059] (2) Environmental stability test The composite gel of Example 1 and the hydrogel of Comparative Example 2 were prepared into bulk samples, such as... Figure 5 As shown, the differential scanning calorimetry (DSC) test results indicate that the composite gel of Example 1 did not freeze in the range of room temperature to -80°C, indicating that it can maintain flexibility at low temperatures and has antifreeze ability.

[0060] The sample was placed in a constant temperature and humidity chamber at 25℃ and 30%RH, and the relative mass change of the sample was recorded over 180 hours. The results are as follows: Figure 6As shown in the figure. The results show that the composite gel of Example 1 has a mass retention rate of over 82%, which is far superior to the polyacrylamide hydrogel of Comparative Example 2 (<50%).

[0061] (3) Self-adhesion demonstration The composite gel of Example 1 was directly applied to human arm skin, a glass slide, and plastic, respectively, as shown in the diagram. Figure 7 As shown in (a), (b), and (c), it can be seen that it can adhere stably.

[0062] (4) Strain sensing applications The composite gel from Example 1 was cut into strips, and platinum-plated copper foil electrodes were attached to both ends to create strain sensors. These sensors were fixed to the finger joints of volunteers to monitor the resistance changes during repeated flexion and extension of the joints. The results are as follows: Figure 8 As shown in the figure. The results show that the sensor output signal is stable and has good repeatability, and can clearly identify different degrees of bending.

[0063] Following a similar method, the mechanical properties, environmental stability, and self-adhesion of the composite gels of Examples 2-4 were tested. The tests showed that the composite gels of Examples 2-4 also have excellent resilience, self-adhesion, and anti-drying and anti-freezing properties.

[0064] In addition, the composite gels of Examples 2 to 4 were applied to construct strain sensors according to the above method and fixed to the finger joints of volunteers to monitor the resistance changes during repeated bending and straightening of the joints. The results showed that the output signals of each sensor were stable and had good repeatability, and could also clearly identify different degrees of bending.

[0065] The embodiments described above are merely examples of several implementations of the present invention, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing a composite gel, characterized in that, Includes the following steps: A precursor solution is prepared by mixing raw materials including hydrophilic polymerizable monomers, initiators, crosslinking agents, water, hydrophobic ionic liquids and amphiphilic metal salts, and then a composite gel is obtained by polymerization reaction.

2. The method for preparing the composite gel according to claim 1, characterized in that, The preparation of the precursor solution specifically includes: first, mixing the hydrophobic ionic liquid, amphiphilic metal salt, and water to form a mixed solution; then, adding the hydrophilic polymerizable monomer, initiator, and crosslinking agent to the mixed solution to form the precursor solution.

3. The method for preparing the composite gel according to claim 2, characterized in that, The mass ratio of the hydrophobic ionic liquid to water is 99:1 to 1:99, the mass ratio of the amphiphilic metal salt to water is (0.6 to 2.5):1, and the mass ratio of the hydrophilic polymerizable monomer to the mixture is (0.08 to 0.6):

1.

4. The method for preparing the composite gel according to claim 1, characterized in that, The amphiphilic metal salt includes at least one of zinc trifluoromethanesulfonate and iron trifluoromethanesulfonate.

5. The method for preparing the composite gel according to claim 1, characterized in that, The hydrophobic ionic liquid includes at least one of 1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt and 1-butyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide salt.

6. The method for preparing the composite gel according to claim 1, characterized in that, The hydrophilic polymerizable monomer includes at least one of acrylamide monomer and acrylic acid.

7. The method for preparing the composite gel according to any one of claims 1 to 6, characterized in that, The initiator is a photoinitiator; and the polymerization reaction is a photopolymerization reaction.

8. A composite gel, characterized in that, It is prepared by the method of any one of claims 1 to 7.

9. A strain sensor, characterized in that, The device includes electrodes and the composite gel of claim 8, wherein the electrodes include a first electrode and a second electrode, the first electrode and the second electrode being spaced apart and both connected to the composite gel.

10. The application of the strain sensor of claim 9 in a wearable device.

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