High-performance ionic gel, preparation method therefor, and use thereof

Abstract

Disclosed in the present application are a high-performance ionic gel, a preparation method therefor, and a use thereof. The high-performance ionic gel comprises an ionic gel substrate and a thermally conductive filler; the thermally conductive filler is filled within the ionic gel substrate; tannic acid is adsorbed on a surface of the thermally conductive filler; the ionic gel substrate comprises a polymer framework and an ionic liquid; the ionic liquid, the thermally conductive filler, and the polymer framework are interconnected through hydrogen bonds and ionic bonds to form a composite polymer network. The high-performance ionic gel is characterized by high sensitivity, fast response speed, and strong self-healing ability. Said gel effectively overcomes the limitations of traditional flexible thermal sensors, such as poor environmental stability, slow response speed, and low thermal sensitivity. The present application proposes a novel method for manufacturing flexible sensors, broadening the potential application fields of flexible thermal sensors.

Description

A high-performance ion gel and its preparation method and application Technical Field

[0001] The present application relates to a high-performance ion gel and a preparation method and application thereof, belonging to the technical field of sensor materials. Background Art

[0002] Continuous monitoring of biological temperature is crucial for conveying important health information. Thermal sensors such as thermocouples are widely used in monitoring biological temperature. However, due to the delicate skin of organisms, using these thermal sensors for long-term temperature monitoring may cause harm to the body. The current development of flexible thermal sensors is expected to solve this problem.

[0003] Flexible thermal sensors are widely used in aerospace, industry, and various other fields, but issues such as environmental stability, response time, and thermal sensitivity have hindered their continued development. In recent years, flexible thermal sensors using materials such as hydrogels and ion gels have been developed. However, hydrogel-based thermal sensors face challenges in environmental stability. The main reason is that hydrogels have a high water content, which leads to inevitable water evaporation. This solvent loss changes the ionic conductivity and reduces the practicality of the device under dry conditions. Ion gels using ionic liquids as solvents can solve the water evaporation problem, and the sensors produced have stronger environmental stability. However, the heat transfer pathways of pure ion gels are limited and can only rely on vibrations within the polymer chain, resulting in a prolonged thermal response time. Therefore, there is still a need to develop a flexible sensor with both excellent environmental stability and fast response capabilities.

[0004] Introducing thermally conductive fillers into flexible substrates is a practical solution. Adding thermally conductive fillers to flexible polymer substrates can enhance the heat transfer mechanism within the flexible material. This shift goes beyond simple vibrational heat transfer between polymer chains to encompass a variety of heat transfer mechanisms, including interactions between fillers, between fillers and the substrate, and between different substrate components, significantly shortening heat transfer time. In recent years, the integration of thermally conductive fillers into flexible substrates has become increasingly evident. However, these flexible substrates are primarily made of materials such as PDMS and PVDF, which have poor electrical conductivity and minimal resistance change. While the addition of conductive fillers shortens response time, sensitivity remains low, typically hovering around 0.1°C per percentage change. Therefore, there is a need to develop highly sensitive, fast-responding flexible temperature sensors.

[0005] Summary of the Invention

[0006] In order to solve the above problems, the present application designs a flexible thermal sensor with ionic liquid as solvent and CNTs as thermal conductive filler. The presence of ionic liquid in the polymer network enhances thermal stability, while CNTs establish a dual heat conduction pathway (CNTs-CNTs and CNTs-polymer chain segments), thereby achieving a fast thermal response time. The ionic liquid begins to dissociate at high temperatures, increasing the carrier density, thereby greatly improving the thermal sensitivity. In addition, this material also has significant self-healing properties, which extends the service life of the flexible sensor. A flexible thermometer for measuring biological temperature has been developed using this material, which can reduce the risk of injury caused by sharp surfaces. This material can also be used to manufacture heat-driven robots, providing an attractive solution for human operations in extreme environments.

[0007] This application adopts the following technical solutions:

[0008] According to one aspect of the present application, there is provided a

[0009] A high-performance ion gel, comprising an ion gel substrate and a thermally conductive filler;

[0010] The thermally conductive filler is filled in the ion gel matrix;

[0011] Tannic acid is adsorbed on the surface of the thermally conductive filler;

[0012] The ion gel substrate comprises a polymer skeleton and an ionic liquid;

[0013] The ionic liquid, the thermal conductive filler and the polymer skeleton are connected through hydrogen bonds and ionic bonds to form a composite polymer network.

[0014] Optionally, the thermally conductive filler is selected from at least one of CNTs and graphene.

[0015] Optionally, the ionic liquid is selected from at least one of 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium methanesulfonate.

[0016] Optionally, the material of the polymer skeleton is selected from at least one of acrylic polymers and acrylate polymers.

[0017] Optionally, the acrylic polymer is selected from acrylic acid polymers.

[0018] Optionally, the acrylate polymer is selected from butyl acrylate polymer.

[0019] Optionally, the content of the polymer in the high-performance ion gel is 20-40 wt%.

[0020] Optionally, the content of the polymer in the high-performance ion gel is selected from any value among 20 wt%, 25 wt%, 30 wt%, 35 wt%, 40 wt%, or any range therebetween.

[0021] Optionally, the content of polymer in the high-performance ion gel is preferably 30%.

[0022] Optionally, the content of the thermal conductive filler in the high-performance ion gel is 0.1-0.5 wt%.

[0023] Optionally, the content of the thermally conductive filler in the high-performance ion gel is selected from any value of 0.1 wt%, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, or any range therebetween.

[0024] Optionally, the content of the thermally conductive filler in the high-performance ion gel is preferably 0.5 wt %.

[0025] Optionally, the thermal resistance coefficient of the high-performance ion gel is 0.24-12.04% / °C.

[0026] Optionally, after the high-performance ion gel is cut and self-healed, the recovery rate of conductivity, tensile strength and stress is independently greater than 90%.

[0027] According to another aspect of the present application, a method for preparing the high-performance ion gel is provided, characterized in that it comprises the following steps:

[0028] A conductive filler is added to a mixed solution containing tannic acid and an ionic liquid, and ultrasonic treatment is performed to obtain a dispersion containing the conductive filler. Then, a crosslinking agent and an initiator are added to the dispersion containing the conductive filler, and after ultrasonic treatment, a monomer is added and solidified to obtain the high-performance ion gel.

[0029] Optionally, the weight ratio of the ionic liquid, tannic acid and conductive filler is 1:(0.0001-0.0008):(0.001-0.008).

[0030] Optionally, the cross-linking agent is selected from at least one of N,N'-methylenebisacrylamide and PEGDA.

[0031] Optionally, the initiator is selected from at least one of ammonium persulfate and azobisisobutyronitrile.

[0032] Optionally, the monomer is selected from at least one of acrylic monomers and acrylate monomers.

[0033] Optionally, the curing conditions include: curing at 75-95° C. for 0.5-2 h.

[0034] Optionally, the weight ratio of the ionic liquid, the monomer, the crosslinking agent, and the initiator is 1:(0.2-0.4):(0.0005-0.0035):(0.0001-0.0011).

[0035] According to another aspect of the present application, there is provided an application of the above-mentioned high-performance ion gel as a thermoelectric material in a flexible temperature sensor, a flexible wearable thermal sensor, and a thermally driven robot.

[0036] In this application, the ion gel was fabricated using a highly thermally stable ionic liquid (1-ethyl-3-methylimidazolium tetrafluoroborate) (>350°C) as a solvent and a highly thermally stable polyacrylic acid (PAA) as a polymer backbone, ensuring the material's exceptional thermal stability. The ionic liquid's viscosity decreases with increasing temperature, triggering ion dissociation at high temperatures, significantly improving ionic conductivity and achieving a high thermal sensitivity of 5.059°C / %. The high aspect ratio of CNTs promotes interconnection, establishing two distinct thermal conduction modes: CNTs-CNTs and CNTs-polymer chains, leading to a rapid thermal response (16 seconds). Specifically, when CNTs are dispersed in a tannic acid ionic liquid solution, they interact with the PAA through hydrogen and ionic bonds, forming a robust gel network. Furthermore, driven by extensive hydrogen bonding and strong electrostatic interactions, the T-CNTs synthesized in this manner exhibit remarkable self-healing abilities. This CNT-doped ion gel is an ideal candidate for flexible thermal sensors and holds great potential.

[0037] The beneficial effects of this application include:

[0038] The flexible T-CNT thermal sensor provided by this application has the characteristics of high sensitivity, fast response speed and strong self-healing ability, which effectively overcomes the limitations of traditional flexible thermal sensors such as poor environmental stability, slow response speed and low thermal sensitivity. In addition, this application also designs it as a wearable thermometer for monitoring biological body temperature, thereby reducing the risks associated with rigid thermometers. And through innovative structural design, this application also discloses a heat-driven soft robot that can utilize thermal energy in the environment, thereby reducing energy consumption and opening up potential application areas for exploration and detection of hazardous environments. In short, this application proposes an innovative method for manufacturing flexible sensors, which broadens the potential application areas of flexible thermal sensors. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 (a) is a schematic diagram of the T-CNT structure of the present application; (b) is the interaction between the components in the T-CNT structure; and (c) is a schematic diagram of the self-healing mechanism of the ion gel.

[0040] Figure 2 compares the performance of the three flexible materials used in this application. (a) Photographs and infrared images of the three materials' morphological changes during oven heating. (b) Resistance changes of the three materials after they were transferred from room temperature to an 85°C heating station and held there for a period of time. (c) Comparison of the response times of the three gel materials when heated to the same temperature.

[0041] Figure 3 shows (a) the electrical properties of T-CNTs with different CNT contents. (b) the tensile properties of T-CNTs with different CNT contents. (c) the response time of T-CNTs with different CNT contents. (d) the thermal sensitivity between 25°C and 37°C. (e) a comparison of the thermal sensitivity of flexible thermal sensors in recent years. (f) the resistance change remains stable after 10 thermal cycles.

[0042] Figure 4 shows a comparison between conventional thermal sensors and gels (a, b) of this application. (c) A physical image of T-CNT stretching at different self-healing times. (d) The stretching characteristics of T-CNT at different self-healing times. (e) Brightness change of a small bulb before and after gel self-healing. (f) Self-healing efficiency. (g) Comparison of thermal resistance before and after self-healing.

[0043] Figure 5 illustrates the fabrication of the flexible thermal sensor and soft robot used in this application. (a) Photo of a T-CNT sensor monitoring forehead temperature. (b) A T-CNT sensor monitoring forehead temperature. (c) An infrared image of the T-CNT after a stable change in resistance. (d) Photo of a T-CNT sensor monitoring the oral temperature of a giant salamander. (e) A T-CNT sensor monitoring the oral temperature of a giant salamander. (f) An infrared image of the T-CNT after a stable change in resistance. (g) A long robot bending at high temperatures. (h) A petal-shaped robot bending at high temperatures.

[0044] FIG6 is a schematic diagram of the heat conduction mechanism of CNTs of the present application.

[0045] FIG7 is a TEM image of the present application: (a) CNTs (the scale line is 100 nm), (b) TA-CNTs (the scale line is 100 nm).

[0046] FIG8 shows (a) electrical properties of ion gels with different polymer contents; (b) mechanical properties of ion gels with different polymer contents in this application.

[0047] FIG9 shows the Fourier transform infrared (FTIR) spectra of AA, ILs, TA, blank gel and T-CNT of the present application.

[0048] FIG10 is a comparison of the quality of the three materials of the present application before and after heating.

[0049] FIG11 is a comparison of the tensile properties of the three materials of the present application before and after heating.

[0050] FIG12 is a comparison of the electrical properties of the three materials of this application before and after heating.

[0051] FIG13 shows the Young's modulus of T-CNTs with different CNTs contents in this application.

[0052] FIG14 shows the maximum strain of T-CNT at different CNT contents in this application.

[0053] FIG15 is a scanning electron microscope image of the T-CNT of the present application (the scale bar is 200 nm).

[0054] FIG16 is a thermal resistance relationship test platform of this application.

[0055] FIG17 shows that under high heat conditions, the conductive particles in the T-CNT accelerate thermal motion in this application.

[0056] FIG18 shows that the electrical conductivity of the T-CNT of the present application increases with increasing heat.

[0057] FIG19 is a thermal resistance relationship curve (TCR) of T-CNT in different temperature ranges of the present application.

[0058] Figure 20 shows (a) 400 cycles of stretching at 50% strain and (b) comparison of gel thermal conductivity before and after cyclic stretching.

[0059] FIG21 shows the strain self-healing efficiency of T-CNT at different times in this application.

[0060] FIG22 shows the electrical performance healing process of T-CNT in this application.

[0061] Figure 23 shows the application for measuring the body temperature of sturgeons.

[0062] Figure 24 shows (a) the thermal sensitivity of T-GO at 25-100°C in this application. (b) Comparison of the response time of two gel materials during heating. DETAILED DESCRIPTION

[0063] The present application is described in detail below with reference to embodiments, but the present application is not limited to these embodiments.

[0064] Unless otherwise specified, the raw materials in the examples of this application were purchased through commercial channels.

[0065] Unless otherwise specified, conventional methods were used for testing, and instrument settings were those recommended by the manufacturer.

[0066] Materials used in this application: 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIm][BF4], 98%) ionic liquid (abbreviated as Ils), tannic acid (TA), and acrylic acid (AA) were purchased from Macklin. Acrylamide (AAm, ≥99%), N,N'-methylenebis(acrylamide) (Abbreviated as Bis, MBAA, 99%), ammonium persulfate (APS, ≥98%), N,N,N',N'-tetramethylethylenediamine (TEMED, 99%), and methylene blue were purchased from Sigma Co Ltd (USA). CNTs (CNTs) were purchased from Jiangsu Pioneer nm Materials Technology Co., Ltd. (Nanjing, China). All chemical reagents were not further purified. Deionized water (18 MΩ·cm) was used in the experiments.

[0067] In this application, the test method:

[0068] Mechanical properties test: The mechanical properties of the ion gel were evaluated by a common mechanical testing machine (ZQ-990LB, Qianzhu Company, China). Unless otherwise stated, tensile tests were carried out under ambient conditions (25°C, relative humidity 40%) at a constant strain rate of 100 mm / min, and the load sensor was 100 N. The tensile release test was carried out under the same conditions, and the specimens were cut into dumbbell shapes (36 mm long, 18 mm wide, and 2.5 mm thick). The cyclic tensile test was carried out using a uniaxial tensile machine at a constant compression rate. The cylindrical specimens were 20 mm long, 10 mm wide, and 2 mm thick. Each mechanical test was repeated for at least three independent specimens. Finally, the Young's modulus was further calculated based on the average slope of the strain-stress curve (within the range of 10-30% of the strain value).

[0069] Conductivity test: The resistance (R) of the material was measured using an LCR digital bridge meter (EA4980AL, Keysight), and the conductivity (σ) was obtained from the following formula:

[0070] Where (L) and (S) represent the gauge length and cross-sectional area of ​​the ion conductor, respectively. The prepared sample was 20 mm long, 10 mm wide, and 2 mm thick. The relative resistance was also measured using LCR. The relative resistance change (ΔR / R0) of the stretched sample was calculated as follows:

[0071] Where (R_t) and (R_0) represent the relative resistance and initial resistance of the ionic conductor, respectively. The gauge factor (GF) is defined as

[0072] where (ε) is the applied strain.

[0073] Thermal conductivity test: The material is 20*20mm in length and width, and the thickness is greater than 4mm. Based on the transient plane heat source method, Hotdisk can directly measure the thermal conductivity of the sample.

[0074] Biological Cryogenic Scanning Electron Microscopy (Cryo-SEM): The sample preparation process involves applying a conductive carbon adhesive to the sample stage, gently picking up the sample with tweezers, and attaching it to the conductive carbon adhesive. Subsequently, the sample stage is immersed in a liquid nitrogen slurry for 30 seconds. Afterwards, the sample is transferred to the sample preparation chamber using a cryogenic cryo-preparation transfer system in a vacuum environment. In the sample preparation chamber, the sample is sublimated at -90°C for 10 minutes. The sample is then transferred to the SEM sample chamber. In the sample chamber, the cold stage temperature is maintained at 140°C, and the accelerating voltage is set to 5 kV.

[0075] Preparation Example 1 Preparation of T-CNT

[0076] Tannic acid TA (1.852 mg) was mixed with [EMIm][BF4] ionic liquid Ils (2.588 g) and then ultrasonically dissolved to obtain a good solution. CNTsCNTs (18.52 mg) was added and ultrasonicated for 40 minutes to obtain a uniform dispersion of TA-CNTs. N,N'-methylenebis(acrylamide) BIS (5.55 mg) and ammonium persulfate APS (1.11 mg) were added to the above solution and ultrasonically dissolved before adding acrylic acid AA (1.109 g). After thorough shaking, the mixture was evacuated with a diaphragm pump for 15 minutes, poured into a polytetrafluoroethylene mold, and baked in an 85°C oven for 1 hour to obtain an ion gel containing CNTs, which was recorded as T-CNTs.

[0077] The schematic diagram of the structure of T-CNTs is shown in Figure 1a. When CNTs are dispersed in a tannic acid ionic liquid solution, they interact with acrylic acid through hydrogen bonds and ionic bonds to form a strong composite polymer network (the component connections are shown in Figure 1b).

[0078] Preparation Example 2 Preparation of blank ion gel

[0079] N,N'-methylenebis(acrylamide) BIS (5.55 mg) and ammonium persulfate APS (1.11 mg) were added to [EMIm][BF4] ionic liquid Ils (2.588 g), sonicated, and then acrylic acid AA (1.109 g) was added. The mixture was thoroughly shaken, evacuated with a diaphragm pump for 15 minutes, poured into a polytetrafluoroethylene mold, and baked in an 85°C oven for 1 hour to obtain a blank ion gel (control group).

[0080] Preparation Example 3 Hydrogel Preparation

[0081] A hydrogel was prepared by mixing AAm (2.75 ml, 19%), APS (70 μL, 1.0 mol L⁻¹), and MBAA (600 μL, 2 wt⁻¹) solutions, degassing in a vacuum oven for 50 minutes, and then curing in an ultraviolet (UV) oven (365 nm, 1 hour). MBAA and APS served as crosslinkers and photoinitiators, respectively. A blue hydrogel was prepared by adding 0.1% methylene blue to the AAM solution and following the above process, and is denoted as "hydrogel."

[0082] Due to their high content of fluorine atoms and C-F bonds, ionic liquids possess properties such as high stability and inertness. For this preparation, 1-ethyl-3-methylimidazolium tetrafluoroborate, which also contains a large number of fluorine atoms, was selected. It exhibits high conductivity (14 mS / cm at 25°C) and excellent thermal stability (thermal decomposition temperature of 412°C). Furthermore, considering the poor solubility of high-molecular-weight monomers in ionic liquids, we polymerized traditional liquid monomers acrylic acid (AA) and N,N-methylenebisacrylamide (BIS) into the polymer matrix. By adjusting the amount of AA added, the mechanical properties of the ion gel can be effectively tuned.

[0083] Carbon nanotubes (CNTs) are one-dimensional nanomaterials with diameters ranging from a few nm to tens of nm and lengths ranging from tens of μm to several mm. This one-dimensional structure facilitates the unrestricted transmission of electrons and phonons within the tube, resulting in excellent thermal conductivity (~10 3 W / (mK), with the thermal conductivity mechanism shown in Figure 6. The addition of CNTs reduces the polymer's porosity, increases the heat transfer area, and shortens the response time. The unique structure of imidazolyl ionic liquids ensures that CNTs are not deformed by electrostatic interactions between the IL ring and the aromatic rings of the CNTs, thereby maintaining the CNT's electrical properties. Therefore, CNTs were used as fillers in this preparation example.

[0084] This preparation example utilizes a simple one-pot method. After forming a homogeneous solution of tannic acid and ionic liquid, CNTs are added and ultrasonically dispersed. Subsequently, an initiator and crosslinker are dissolved in the mixture and shaken with AA. After thorough degassing, the resulting T-CNTs are successfully infused into polytetrafluoroethylene. The underlying network of T-CNTs is constructed by covalently crosslinking acrylic acid (AA) with N,N'-methylenebis(acrylamide) (BIS). This entraps ILs within the network through electrostatic crosslinking and hydrogen bonding between PAA carboxyl groups and EMIm. TA molecules interact with CNTs through hydrogen bonding, resulting in adsorption on the CNT surface. This adsorbed TA increases inter-tube repulsion, stabilizing the CNTs in the ionic liquid. Transmission electron microscopy reveals that untreated CNTs tend to intertwine due to their high aspect ratio and poor dispersibility. In contrast, TA-modified CNTs exhibit improved dispersibility. (As shown in Figure 7), the surface of TA-CNT contains a large number of hydroxyl groups, which interact with PAA and free-state ionic liquids, further improving the stability of CNTs in the ion gel network.

[0085] To tailor the properties of the gel matrix, the mass fractions of AA and ionic liquid were systematically varied using the same method as in Preparation Example 2 (as shown in Figure 8 and Table 1). The mass fraction of AA represents the polymer content. When the polymer content was below 20%, the gel did not gel; when the polymer content reached 30%, the gel gelled. The decrease in conductivity may be due to the increased electrostatic interactions between the -COOH groups of the PAA network and the ionic liquid ions, which restricts ion mobility under the electric field. Furthermore, higher polymer content reduces the tensile properties of the ion gel. This is because a denser polymer network and more network nodes result in greater stress and less strain. Such a gel may not be able to withstand the stress concentrations encountered during application. Therefore, in this preparation example, an ion gel with a polymer content of 30% was selected and CNTs were added. Ultimately, the T-CNTs were stabilized by covalent crosslinks between the AA chains, electrostatic interactions between the PAA chains and the ionic liquid, and multiple hydrogen bonding interactions. These changes were characterized by Fourier transform infrared spectroscopy (Figure 9).

[0086] Table 1. Composition of CNTs ion gels with different polymer contents

[0087] Test Example 1 Thermoelectric Calculation and Thermoelectric Properties of T-CNT

[0088] During the heating phase, the hydrogel, ion gel, and T-CNT were simultaneously heated at 85°C. Their properties before and after heating were compared, and infrared imaging equipment was used to capture the states of the three materials. The results showed that after heating at 85°C for 30 minutes, the hydrogel's volume decreased significantly, forming a dry, sheet-like structure, while the blank ion gel and T-CNT showed no significant shape changes, indicating that the hydrogel is thermally unstable under high heat (as shown in Figures 2a and 2b). Further measurements of the changes in the three materials before and after heating showed that the mass of the hydrogel decreased by nearly 90%, while the mass of the blank ion gel and T-CNT remained almost unchanged. This difference can be attributed to the strong interaction between the ionic liquids (as shown in Figure 10). The loss of a large amount of water from the hydrogel led to a decrease in conductivity and a loss of tensile properties (as shown in Figure 11). The ion gel and T-CNT retained their ionic liquid, electrical conductivity, and tensile properties after heating (as shown in Figure 12).

[0089] All three materials can calculate the response time based on the resistance-heat relationship. These three materials were placed on an 85°C heating platform and their resistance changes were monitored when heated from 25°C to 85°C. During the heating process, the resistance of the hydrogel first decreased and then increased. The initial resistance drop was attributed to the acceleration of molecular thermal motion. The subsequent resistance increase (close to that of an insulator) was due to the rapid evaporation of water due to the higher heat, resulting in water loss inside the hydrogel. The subsequent movement of the particles under the action of the electric field slowed down. This behavior highlights the thermal instability of the hydrogel as a thermosensitive material. In contrast, the ion gel and T-CNT have high thermal stability. Even if exposed to the 85°C heating platform for a long time, the resistance will not increase significantly.

[0090] The time it takes for the resistance change to stabilize when the material is heated from 25°C to 85°C is called the response time. T-CNTs have a shorter response time because the CNTs are evenly distributed within the gel network structure and have good thermal conductivity. Therefore, the CNTs are initially subjected to the increased heat, which is then efficiently transferred to the adjacent PAA network structure and the interconnected CNTs, forming two distinct heat transfer pathways. Consequently, heat conduction is faster than with a pure PAA network (as shown in Figure 2c).

[0091] Adding CNTs can effectively improve the electrical, mechanical and thermal properties of the gel matrix. This application synthesized ion gels with different CNTs contents, prepared ion gels with different nm tube contents based on the method of Preparation Example 1, and studied the effect of CNTs content on the conductivity of ion gels using LCR testing (as shown in Figure 3a and Table 2). Due to the high aspect ratio of CNTs, they connect to each other and form a bridging structure, forming a partial conductive path, thereby reducing the resistance of the gel. When the CNTs content reaches 0.5% by weight, the conductivity can reach 1.1mS / cm. Normally, adding rigid CNTs increases the Young's modulus and reduces the strain of the polymer network. However, in this system, tannic acid, as a polyphenol compound, has multiple electrophilic hydroxyl functional groups. When tannic acid reacts with free radical polymerized acrylic acid in the ion gel, the electrophilic groups of the polyphenols may compete with the free radicals, resulting in a reduction in the number of crosslinking points in the gel. This reduction weakens the hardness of the gel network and reduces the Young's modulus (as shown in Figure 13). Furthermore, some polyphenol functional groups in TA physically interact with the acrylic chains in the ion gel, extending the average length of the gel segments. This chain extension makes the gel more susceptible to stretching, leading to increased strain. When the CNT content is 0.5% wt, the strain can reach 1100% (as shown in Figures 3b and 14). This reduction in modulus and increase in strain help extend the sensor's lifespan.

[0092] Table 2. Composition of T-CNTs with different CNT contents

[0093] Because the CNTs are uniformly distributed on the surface and within the gel, when the gel absorbs heat, the CNTs rapidly transfer the heat to the gel matrix or to the interconnected CNTs, resulting in a rapid response of the T-CNTs. With increasing CNT loading, the T-CNT response time to the same temperature decreases (as shown in Figures 3c and 15). The electrical and thermal relationships of the T-CNTs were investigated using an LCR meter and a heating stage (as shown in Figure 16). The relationship between ionic conductivity and temperature follows the VTF equation. For a given ionic conductor, ionic conductivity has a corresponding relationship with heat. Ionic dissociation at higher temperatures leads to an increase in charge carrier concentration, resulting in a decrease in the resistance of the ionic conductor with increasing temperature (as shown in Figures 17 and 18). Ionic liquids exhibit enhanced mobility at higher temperatures, resulting in an increase in conductivity from room temperature to 100°C. When the T-CNTs were connected in series with a small light bulb, the bulb gradually brightened as the temperature increased from room temperature to 100°C, indicating a decrease in the T-CNT's resistance.

[0094] To demonstrate the capability of T-CNTs as thermal sensors, we tested their resistance changes over a temperature range of 5–100°C. Data fitting revealed that the thermal resistivity of T-CNTs ranged from 0.24% to 12.04% / °C (Figure 19). Considering the sensor's characteristics, we compared its thermal resistivity, slightly above room temperature, with that of various flexible thermal sensors reported in recent years and found that its sensitivity exceeded that of most resistive thermal sensors (Figures 3d and 3e). To evaluate the thermal stability of T-CNTs, we subjected them to 10 thermal cycles between room temperature and 60°C, observing virtually no change in resistance, demonstrating their thermal stability (Figure 3f). During the application of flexible thermal sensors, they may deform and bend. Using a sliding platform, we subjected T-CNTs to 400 cycles of stretching and recovery, and characterized their thermal conductivity before and after stretching. No significant difference was observed, confirming that T-CNTs maintain good thermal conductivity even after stretching and deformation (Figure 20).

[0095] Test Example 2 Self-healing properties of T-CNT

[0096] Self-healing is a highly desirable property of thermosensitive sensors, prioritizing their extended service life. Existing rigid thermometers often become damaged or lose their original properties when subjected to external forces or dropped, and this damage is irreversible (as shown in Figures 4a and 4d). T-CNTs address this issue, so we systematically investigated the self-healing properties of T-CNTs. Due to multiple hydrogen bonding interactions between carboxyl groups in the T-CNT polymer chain, between carboxyl groups and ionic liquid anions, and between carboxyl groups and tannic acid, T-CNTs exhibit remarkable self-healing properties at room temperature (as shown in Figure 1c).

[0097] To further demonstrate the self-healing ability of T-CNTs, their mechanical, electrical, and thermal properties were tested. When the sample was cut into two pieces and reconnected for a period of time, it showed self-healing and could withstand a certain degree of stretching. To quantify the tensile properties of T-CNTs at different healing times, tensile tests were conducted. As the healing time increased, the tensile strength and strain of the healed T-CNTs gradually increased, indicating that their tensile resistance was improved (as shown in Figures 4c, 4d, and 21). When the T-CNTs were connected in series with a small light bulb, it was found that there was almost no difference in brightness before and after self-healing, indicating that when the two T-CNTs were reconnected, the electrical properties of the T-CNTs were almost completely restored, and the resistance quickly returned to its original value (as shown in Figures 4e and 22).

[0098] After calculating the recovery rate of the conductivity, tensile strength, and stress of the T-CNT after self-healing, the results showed that the recovery rate of T-CNT in all three aspects exceeded 90%, demonstrating its excellent self-healing ability. This means that T-CNT can continue to work normally even after suffering external damage (as shown in Figure 4f). In addition, the thermal sensitivity of T-CNT before and after self-healing was also measured (as shown in Figure 4g). Compared with other thermistors, there is no significant difference in the thermal sensitivity of T-CNT, which shows its superiority.

[0099] Application Example 1: Fabrication of Flexible Thermal Sensors and Soft Robots

[0100] This application uses T-CNT to develop a flexible wearable thermal sensor. Traditional sensors for continuous biological thermal monitoring are rigid and require tape to be firmly fixed. In contrast, this sensor is soft and self-adhesive, which can effectively prevent potential damage to the organism during the test. In addition, the self-adhesiveness of T-CNT allows the sensor to be directly adhered to human skin without the need for additional adhesives and without worrying about falling off. As shown in Figure 5a, a strip thermal sensor is installed on the forehead. Before use, the sensor is stored at room temperature (25°C). After it is installed on the forehead, the heat of the sensor will gradually increase, resulting in a decrease in resistance. When the heat of the sensor matches the heat of the forehead, the resistance will stabilize. According to Figure 2d, the forehead temperature is 36°C (as shown in Figure 5b).

[0101] To verify the accuracy of the thermal sensor, an infrared imaging device was used after the resistance stabilized, confirming a thermal reading of 35.1°C (Figure 5c). To further demonstrate the advantages of the flexible sensor, it was used to monitor the body temperature of giant salamanders as an indicator of their health (Figure 5d). Similar to human thermal monitoring, the flexible sensor was placed in a room temperature environment and then attached to the giant salamander's mouth. The sensor's resistance increased, indicating that the temperature was below room temperature. When the resistance change stabilized, the temperature of the giant salamander's mouth was determined to be 12.4°C (Figure 5e), compared to Figure 18a. Infrared imaging further verified this thermal value as 12.2°C (Figure 5f). We also applied it to temperature monitoring of other fish, such as grass carp. The temperature measured by the T-CNT differed only 0.4°C from that displayed by the infrared imager, further demonstrating the accuracy of the T-CNT (Figure 23).

[0102] T-CNT is combined with hydrogel to make a thermally driven robot. The construction of the robot utilizes the driving force generated by the transfer of water within the hydrogel, thereby achieving control over the curling direction of the T-CNT. Thermal regulation determines the speed of water transfer, thereby controlling the curling speed of the robot. As shown in Figure 5g, the robot initially takes on a long strip shape. After heating, the water begins to transfer, causing the robot to gradually transition to a curved shape. Further, more complex petal shapes are made. The robot is in an expanded state before heating, and after heating, the petals gradually curl up, just like a flower. This controllable soft robot is a new type of material that can be used in a variety of applications, including grasping, material transportation, and operations in extreme environments (as shown in Figure 5h).

[0103] Application Example 2: Flexible Temperature Sensor

[0104] This application develops a flexible temperature sensor with high environmental stability and rapid thermal response capabilities by incorporating a highly thermally stable solvent and a large amount of thermally conductive filler. To explore the applicability and versatility of this approach, 1-ethyl-3-methylimidazolium tetrafluoroborate was replaced with 1-butyl-3-methylimidazolium methanesulfonate, and carbon nanotubes (CNTs) were replaced with graphene (GO). As shown in Figure 24, in this system, the gel continues to exhibit remarkable environmental stability and rapid thermal response, demonstrating that this approach can be extended to a wider range of ionic liquids and thermally conductive materials.

[0105] The above descriptions are merely a few embodiments of the present application and do not constitute any form of limitation to the present application. Although the present application discloses the preferred embodiments as above, they are not intended to limit the present application. Any technical personnel familiar with the present profession, without departing from the scope of the technical solution of the present application, using the technical content disclosed above to make slight changes or modifications are equivalent to equivalent implementation cases and fall within the scope of the technical solution.

Claims

1. A high-performance ion gel, characterized in that: The high-performance ion gel comprises an ion gel substrate and a thermally conductive filler; The thermally conductive filler is filled in the ion gel matrix; Tannic acid is adsorbed on the surface of the thermally conductive filler; The ion gel substrate comprises a polymer skeleton and an ionic liquid; The ionic liquid, the thermal conductive filler and the polymer skeleton are connected through hydrogen bonds and ionic bonds to form a composite polymer network.

2. The high-performance ion gel according to claim 1, characterized in that The thermally conductive filler is selected from at least one of CNTs and graphene.

3. The high-performance ion gel according to any one of claims 1 to 2, characterized in that The ionic liquid is selected from at least one of 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium methanesulfonate.

4. The high-performance ion gel according to any one of claims 1 to 3, characterized in that The material of the polymer skeleton is selected from at least one of acrylic polymers and acrylate polymers.

5. The high-performance ion gel according to any one of claims 1 to 4, characterized in that The content of the polymer in the high-performance ion gel is 20-40 wt%.

6. The high-performance ion gel according to any one of claims 1 to 5, characterized in that The content of the thermal conductive filler in the high-performance ion gel is 0.1-0.5 wt%.

7. The high-performance ion gel according to any one of claims 1 to 6, characterized in that The thermal resistance coefficient of the high-performance ion gel is 0.24-12.04% / °C.

8. The high-performance ion gel according to any one of claims 1 to 7, characterized in that After being cut and self-healed, the recovery rates of conductivity, tensile strength and stress of the high-performance ion gel are independently greater than 90%.

9. The method for preparing the high-performance ion gel according to any one of claims 1 to 8, characterized in that: The steps include: A conductive filler is added to a mixed solution containing tannic acid and an ionic liquid, and ultrasonic treatment is performed to obtain a dispersion containing the conductive filler. Then, a crosslinking agent and an initiator are added to the dispersion containing the conductive filler, and after ultrasonic treatment, a monomer is added and solidified to obtain the high-performance ion gel.

10. The preparation method according to claim 9, characterized in that The weight ratio of the ionic liquid, tannic acid and conductive filler is 1:(0.0001-0.0008):(0.001-0.008).

11. The preparation method according to any one of claims 9 to 10, characterized in that: The cross-linking agent is selected from at least one of N,N'-methylenebisacrylamide and PEGDA.

12. The preparation method according to any one of claims 9 to 11, characterized in that: The initiator is selected from at least one of ammonium persulfate and azobisisobutyronitrile.

13. The preparation method according to any one of claims 9 to 12, characterized in that: The monomer is selected from at least one of acrylic monomers and acrylate monomers.

14. The preparation method according to any one of claims 9 to 13, characterized in that: The curing conditions include: curing at 75-95° C. for 0.5-2 hours.

15. The preparation method according to any one of claims 9 to 14, characterized in that: The weight ratio of the ionic liquid, the monomer, the crosslinking agent and the initiator is 1: (0.2-0.4): (0.0005-0.0035): (0.0001-0.0011).

16. Use of the high-performance ion gel according to any one of claims 1 to 8 as a thermoelectric material in a flexible temperature sensor, a flexible wearable thermal sensor, and a thermally driven robot.

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