Ionic liquid gel with temperature response as well as preparation method and application of ionic liquid gel

Abstract

The invention relates to the technical field of ionic gels, in particular to an ionic liquid gel with temperature response and a preparation method and application thereof.The ionic liquid gel comprises an ionic liquid and a polymer with a macromolecular network structure, the polymer is prepared through a cross-linking reaction with an acrylate monomer as a main raw material, the ionic liquid is dispersed in the macromolecular network structure of the polymer in the form of a dispersion medium; compared with the prior art that polyacrylic acid hydrogel, polyvinyl alcohol hydrogel or commercial electroencephalogram conductive paste cannot have light transmittance change when the temperature rises, that is, the technical problem of no corresponding temperature is solved, the light transmittance of the ionic liquid gel prepared by the method is reduced to be less than or equal to 80% when the temperature rises from room temperature to phase separation temperature, and the light transmittance of the ionic liquid gel is reduced to be less than or equal to 80% when the temperature rises from room temperature to phase separation temperature. Particularly, the ionic liquid gel with the phase separation temperature of about 37 DEG C can be prepared, and hydrogel and conductive paste in the prior art can be completely replaced to be used in electroencephalogram signal collection.

Description

Technical Field

[0001] The present invention relates to the technical field of ionic gels, and in particular to a temperature-responsive ionic liquid gel, a preparation method thereof, and an application thereof. Background Art

[0002] Long-term, stable, and high-fidelity electroencephalogram (EEG) signal acquisition is crucial for the applications of brain-computer interfaces, such as neuroscience, neuroprosthetics, bioelectronic medicine, virtual and augmented reality, etc. As the first interface for the brain to interact with external devices, electrodes not only have to undertake the tasks of sensing, converting, and transmitting signals, but also have to exhibit good biocompatibility and comfort during long-term wearing. Usually, their contact with the scalp is often hindered by hair, and the weak amplitude (3 - 300 μV) of EEG signals further exacerbates the challenge of establishing a reliable electrode-skin interface. Currently, Ag / AgCl electrodes and commercial conductive pastes (referred to as wet electrodes) are widely regarded as the gold standard for non-invasive brain-computer interfaces. Commercial conductive pastes can penetrate hair, ensuring seamless contact with the scalp, with an impedance less than 5 kΩ, enabling high-quality signal recording. However, using commercial conductive pastes requires the assistance of others before use and needs to be cleaned after use, making the process both cumbersome and time-consuming. During use, the fluidity of commercial conductive pastes may cause leakage between adjacent electrodes, posing a potential short-circuit risk. In addition, concerns about the drying sensitivity of commercial conductive pastes lead to a gradual decline in signal quality over time. Although CN119279595A discloses an EEG sensing electrode and a using method thereof, by injecting a conductive liquid to make a semi-dry electrode or by injecting a conductive paste to make a wet electrode, through a fluid valve, a slow-release material, a capillary plug, a fast-flow hole, and a slow-flow hole, the electrode can quickly supply liquid to reduce the resistance between the electrode and the scalp and slowly supply liquid to reduce the resistance, and the impedance of the electrode-scalp interface can be quickly reduced and balanced and stabilized for a long time. However, it still cannot avoid the above-mentioned objective technical problems existing when using conductive pastes.

[0003] In recent years, with the rapid development of brain-computer interface technology, various materials suitable for EEG signal acquisition have received increasing attention, and a large number of materials used for EEG signal acquisition have been reported. For example, contact dry electrodes with special shapes such as claw-shaped or comb-shaped designs, reservoir-type semi-dry electrodes that slowly release electrolytes by applying pressure or capillary action, and pre-gel EEG electrodes made of hydrogel materials. However, generally speaking, the key to truly achieving long-term and reliable EEG recording lies in constructing a stable and efficient signal transmission channel between the scalp and the electrode interface. And this depends on the conformal contact between the electrode and the hairy scalp and avoiding the adverse effects of dehydration.

[0004] Ionic liquids are substances composed of ions that are liquid at room temperature or near room temperature, and are also known as room temperature molten salts. They have many excellent properties that cannot be compared with conventional solvents. For example, they have high thermal stability and chemical stability; low vapor pressure and hardly any volatility; high ionic conductivity; non-flammability and adjustable cation and anion properties. Therefore, ionic liquid gels prepared using ionic liquids as solvents can not only overcome the problems caused by the volatilization or crystallization of traditional solvents, but their good thermal stability and high ionic conductivity also enable the prepared quasi-solid gel electrolytes to play an important role in electronic components such as supercapacitors, lithium batteries, fuel cells, diodes, and transistors. Therefore, introducing ionic liquids into the gel system for electroencephalogram signal acquisition is a promising solution to the problem of water loss and failure of gel electrode materials. However, in the prior art, when some ionic liquids are applied to prepare corresponding gel materials, they cannot reach the ideal state of heat response, which will result in the performance of the prepared gel being the same as that of the hydrogel in the prior art, and only increasing the cost. This means that there is an urgent need for a conductive material for electrodes that can simultaneously provide high-fidelity signals for wet electrodes, the stability of semi-dry electrodes, and the maintenance-free and long-term capabilities of dry electrodes.

[0005] Based on the above situation of the prior art, in the prior art, when collecting electroencephalogram signals, there are technical problems that need to be solved urgently, such as hydrogels being prone to water loss, or conductive pastes being cumbersome to use and not reusable. Summary of the Invention

[0006] To solve the above technical problems, the present invention provides an ionic liquid gel with temperature response. The ionic liquid gel includes an ionic liquid and a polymer with a polymer network structure. The polymer is prepared by a cross-linking reaction using acrylate monomers as the main raw materials. The ionic liquid is dispersed in the polymer network structure of the polymer in the form of a dispersion medium. When the temperature of the ionic liquid gel rises from room temperature to the phase separation temperature, the light transmittance drops to ≤80%.

[0007] Further, the phase separation temperature is 0 - 85 °C.

[0008] Further, the mass ratio of the acrylate monomer to the ionic liquid is (2 - 9) : (1 - 8).

[0009] Further, the structural formula of the acrylate monomer is: , where 1 ≤ m ≤ 8 and m is an integer.

[0010] Further, the ionic liquid is composed of an organic cation and an organic anion.

[0011] Further, the structural formula of the organic cation is: , , one or more of them; wherein, 1 ≤ a ≤ 10, 1 ≤ b ≤ 10, a is an integer, and b is an integer.

[0012] Furthermore, the structural formula of the organic anion is: , one or more of them.

[0013] The present invention also provides a preparation method of the above temperature-responsive ionic liquid gel. A cross-linking agent and an initiator are added to a mixed solution of an acrylate monomer and an ionic liquid. After mixing, ultraviolet light irradiation is used for radical polymerization reaction to obtain the ionic liquid gel; The relationship between the mass percentage of the acrylate monomer in the mixed solution and the phase separation temperature satisfies the following formula: y = (2.99635 ± 0.03821)x - (83.93166 ± 1.75208); wherein, x is the mass percentage of butyl acrylate and methyl acrylate in the mixed solution A, in wt%; y is the phase separation temperature, in °C; The initiator generates free radicals under the action of ultraviolet light. The free radicals undergo an addition reaction with the carbon-carbon double bond of the acrylate monomer to form monomer free radicals. At the same time, the free radicals also undergo an addition reaction with the carbon-carbon double bond of the cross-linking agent to form cross-linking agent free radicals. The monomer free radicals and / or the cross-linking agent free radicals continue to undergo an addition reaction with the remaining acrylate monomers and / or cross-linking agents to form polymer chain free radicals; When two polymer chain free radicals meet, a coupling termination or disproportionation termination reaction occurs to form a polymer with a high molecular network structure; In the mixing stage, the organic cations and organic anions contained in the ionic liquid form hydrogen bonds and / or electrostatic interactions with the acrylate monomer, cross-linking agent, and initiator to maintain the molecular dispersion state and form a homogeneous mixed system; in the stage of generating the polymer, they form hydrogen bonds and / or electrostatic interactions with the polymer, and finally exist in the form of a dispersion medium in the polymer with a high molecular network structure.

[0014] Furthermore, when the acrylate monomer includes butyl acrylate and methyl acrylate, the mass percentage of methyl acrylate in the mixed solution satisfies the following formula: y = (13.49485 ± 0.48072)x - (58.91753 ± 3.50569), Among them, x is the mass percentage of methyl acrylate in the mixed solution A, with the unit of wt%; y is the phase separation temperature, with the unit of °C.

[0015] Furthermore, the crosslinking agent contains carbon-carbon double bonds.

[0016] Furthermore, the molecular structure of the crosslinking agent contains at least two carbon-carbon double bonds.

[0017] Furthermore, the crosslinking agent is an acrylate crosslinking agent or an acrylamide crosslinking agent.

[0018] Furthermore, the structural formula of the acrylate crosslinking agent is: Where p≥1, p is an integer, R 11 , R 12 are independent hydrogen or alkyl groups with 1-5 carbon atoms.

[0019] Furthermore, the structural formula of the acrylamide crosslinking agent is: Where 1≤q≤5, q is an integer, R 21 , R 22 are independent hydrogen or alkyl groups with 1-5 carbon atoms.

[0020] Furthermore, the initiator is a photoinitiator.

[0021] Furthermore, the initiator is a 2,2-dialkoxyacetophenone photoinitiator.

[0022] Furthermore, the structural formula of the initiator is: , where, R 31 , R 32 are alkyl groups with 1-8 carbon atoms.

[0023] Furthermore, when the photoinitiator is 2,2-dialkoxyacetophenone, under the irradiation of ultraviolet light, the generated free radicals are ethoxy radicals and acetophenone radicals.

[0024] Furthermore, the wavelength of the ultraviolet light is 350-390 nm.

[0025] Furthermore, the wavelength of the ultraviolet light is preferably 365 nm.

[0026] Furthermore, the power range of the ultraviolet light is 0.8-10 W / cm 2 .

[0027] Furthermore, the irradiation time of the ultraviolet light is based on completing the free radical polymerization reaction.

[0028] Furthermore, the light irradiation time is preferably 0.1 - 0.5 h.

[0029] Furthermore, the preparation method of the ionic liquid gel specifically includes the following steps: Step 1: Mix acrylate monomers and an ionic liquid evenly to obtain a mixed solution A; Step 2: Add a crosslinking agent and an initiator to the mixed solution A, and mix evenly to obtain a mixed solution B; at the same time, when the monomer concentration is high, polymerization may occur directly, and polymerization may also occur under natural light Step 3: Irradiate the mixed solution B with ultraviolet light to initiate a free radical polymerization reaction to obtain the crude ionic liquid gel; Step 4: Soak the crude ionic liquid gel with the same ionic liquid as that in Step 1 to obtain the ionic liquid gel.

[0030] Furthermore, the mass ratio of the acrylate monomers to the ionic liquid is (2 - 9):(1 - 8).

[0031] Furthermore, the mass ratio of the acrylate monomers to the ionic liquid is preferably 2:3.

[0032] Furthermore, when both butyl acrylate and methyl acrylate are selected as the acrylate monomers, the mass ratio of butyl acrylate to methyl acrylate is 33:7.

[0033] Furthermore, the molar ratio of the crosslinking agent to the acrylate monomers is (0.3 - 5.0):100.

[0034] Furthermore, the molar ratio of the crosslinking agent to the acrylate monomers is preferably 0.5:100.

[0035] Furthermore, when the molar ratio of the crosslinking agent to the acrylate monomers increases from 0.3:100 to 5.0:100, the tensile modulus of the ionic liquid gel increases from 32 KPa to 392 KPa, and the compressive modulus increases from 50 KPa to 312 KPa.

[0036] Furthermore, the mass ratio of the initiator to the mixed solution A is 1:1000.

[0037] Furthermore, the temperature of the soaking is 0 - 80 °C, the soaking time is at least 12 h, and a new batch of the same ionic liquid as that in Step 1 needs to be replaced every 6 h; The soaking is to soak and wash out small molecules that have not fully reacted, including but not limited to acrylate monomers, crosslinking agents, and initiators, from the ionic liquid gel through solvent replacement.

[0038] The present invention also provides a layered structure, and the raw materials for preparing the layered structure include the above-mentioned temperature-responsive ionic liquid gel.

[0039] Further, the layered structure is fixedly or detachably connected to the electrode.

[0040] Further, the electrode is an electrode used for electroencephalogram signal acquisition.

[0041] Further, the device for electroencephalogram signal acquisition is a wearable device. The wearable device includes an electrode, and the layered structure is used at one end of the electrode close to the scalp of the subject; When the subject wears the device for electroencephalogram signal acquisition, the layered structure can undergo phase separation according to the body temperature of the subject, and the ionic liquid oozes out of the surface of the layered structure to construct a signal transmission channel between the scalp of the subject and the electrode.

[0042] The beneficial effects of the present invention are as follows: 1. The present invention provides a temperature-responsive ionic liquid gel, which includes an ionic liquid and a polymer with a polymer network structure. The polymer is prepared by a cross-linking reaction using acrylate monomers as the main raw materials, and the ionic liquid is dispersed in the polymer network structure of the polymer in the form of a dispersion medium; compared with the prior art, polyacrylic acid hydrogel, polyvinyl alcohol hydrogel, or commercial electroencephalogram conductive paste cannot have a change in light transmittance when the temperature rises, that is, there is no corresponding technology for temperature. For the problem, the ionic liquid gel prepared by the present invention has a light transmittance drop to ≤80% when the temperature rises from room temperature to the phase separation temperature. That is, the ionic liquid gel prepared by the present invention has a significant change in light transmittance at the phase separation temperature, indicating that the ionic liquid gel undergoes phase separation near this temperature and changes from a transparent homogeneous gel without phase separation to a white phase-separated gel state. In particular, an ionic liquid gel with a phase separation temperature of about 37 °C can be prepared, which can completely replace the hydrogel and conductive paste in the prior art and be used in electroencephalogram signal acquisition. The ionic liquid gel electrode can not only record electroencephalogram signals with high fidelity, but also has excellent characteristics of maintenance-free, reusable, and ready-to-wear; essentially solves the problems such as the limited actual use of traditional hydrogel materials as brain-computer interface electrodes, and can also provide a material basis for the research and development of current rapidly developing flexible wearable devices; 2. The present invention also provides a preparation method for a temperature-responsive ionic liquid gel. A cross-linking agent and an initiator are added to a mixed solution of acrylate monomers and an ionic liquid, and after mixing, ultraviolet light irradiation is used for free radical polymerization reaction to obtain the ionic liquid gel; In order to ensure that the free radical polymerization is carried out under ultraviolet light irradiation, the present invention specifically selects to add a crosslinking agent and an initiator to the already mixed acrylic ester monomer and ionic liquid at the same time and then directly irradiate with ultraviolet light, rather than selecting a method of blending the above raw materials together or blending them one by one, so as to avoid as much as possible the uneven mixing caused by blending together, or the polymerization caused by sunlight irradiation when blending one by one, that is, to avoid the problems of the polymerization reaction generated during sunlight polymerization being difficult to control, low initiation efficiency, difficulty in achieving precise polymerization, or the generation of side reactions; The initiator generates free radicals under the action of ultraviolet light, and the free radicals react with the carbon-carbon double bonds of the acrylate monomers to generate monomer free radicals. At the same time, the free radicals also react with the carbon-carbon double bonds of the cross-linking agent to generate cross-linking agent free radicals. The monomer free radicals and / or the cross-linking agent free radicals continue to react with the remaining acrylate monomers and / or the cross-linking agent to generate polymer chain free radicals. When two polymer chain free radicals meet, coupling termination or disproportionation termination reaction occurs to form a polymer with a high molecular network structure; The organic cations and anions contained in the ionic liquid form hydrogen bonds and / or electrostatic interactions with the acrylic monomers, crosslinking agents, and initiators during the mixing stage to maintain the dispersion of the molecules and form a uniform mixed system. In the polymer generation stage, the ionic liquid forms hydrogen bonds and / or electrostatic interactions with the polymers and finally exists as a dispersion medium in the polymer having a high molecular network structure. At the same time, in terms of the selection of raw materials, the present invention specifically selects acrylic ester monomers. As the polymer chains grow and crosslink, the phase state of the system may change, and a phase separation trend may occur. However, under the action of ionic liquids having specific organic cations and organic anions, this phase separation process is inhibited, so that the polymer chains can grow and crosslink uniformly in the ionic liquid to form a uniform polymer network structure; and as the temperature rises, the hydrogen bonds and electrostatic interactions between the ionic liquid and the polymer weaken. When the electrostatic interaction between the ionic liquids is stronger than the affinity between the ionic liquid and the polymer, the ionic liquid seeps out of the ionic liquid gel to produce a phase separation state. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 This is a comparison diagram of the ionic liquid gel prepared in Example 1 of the present invention before and after phase separation; Figure 2 This is a curve diagram showing the change in light transmittance of the ionic liquid gel prepared in Example 1 of the present invention as a function of temperature; Figure 3 This is a curve diagram showing the change in mass percentage of the acrylic acid ester monomer in the mixed solution A and the phase separation temperature in Example 4 of the present invention; Figure 4Graph of the change in the mass percentage of methyl acrylate in mixed solution A and the phase separation temperature in Example 5 of the present invention; Figure 5 Bar graph of the change in the molar percentage of the crosslinking agent in the total amount of acrylate monomers and the tensile and compressive Young's moduli in Example 6 of the present invention; Figure 6 Stress-strain curve graphs of the ionic liquid gel in Example 6 of the present invention compressed cyclically 1 time, 10 times, 50 times, and 100 times; Figure 7 Optical photos of the gel compression comparison between the ionic liquid gel compressed cyclically 1 time and 100 times in Example 6 of the present invention; Figure 8 Micrograph of the ionic liquid gel with a microarray structure prepared in Example 7 of the present invention; Figure 9 Graph of the interface change between the ionic liquid gel and the rough scalp during the wearing of the EEG cap in Example 8 of the present invention; Figure 10 Graph of the change in the optical microscopic recording of the phase separation process of the ionic liquid gel with a smooth surface prepared in Example 1 in Example 8 of the present invention; Figure 11 Graph of the change in the interface impedance between two ionic gel metal electrodes with a microarray structure with temperature in Example 8 of the present invention; Figure 12 Graph of the change in the light transmittance of the commercially available polyacrylic acid hydrogel in Comparative Example 1 of the present invention with temperature; Figure 13 Graph of the change in the light transmittance of the commercially available polyvinyl alcohol hydrogel in Comparative Example 2 of the present invention with temperature; Figure 14 Graph of the change in the light transmittance of the gel prepared in Comparative Example 4 of the present invention with temperature; Figure 15 Comparison graph of the water loss of each gel or conductive paste within 9 hours in Comparative Example 1 of the present invention; Figure 16 Comparison graph of the change rule of the accuracy rate in the 40-target paradigm test between the ionic liquid gel in Example 1 and the commercial EEG conductive paste in Comparative Example 3 in Comparative Example 2 of the present invention; Figure 17 Comparison graph of the change rules of the ionic liquid gel and the commercial EEG conductive paste in terms of accuracy rate and signal transmission rate in Comparative Example 3 of the present invention; Figure 18 Comparison graph of the change rules of the ionic liquid gel and the commercial EEG conductive paste in terms of the average signal-to-noise ratio in Comparative Example 3 of the present invention; Figure 19This is a comparison chart of the average impedance change law at the scalp between the ionic liquid gel and the commercial electroencephalogram conductive paste in Comparative Example 4 of the present invention within 5 hours; Figure 20 This is a comparison chart of the change law of the area under the receiver operating characteristic curve between the ionic liquid gel and the commercial electroencephalogram conductive paste in Comparative Example 5 of the present invention within 50 days. Detailed implementation mode

[0044] Example 1 This example provides an ionic liquid gel with temperature response. The ionic liquid gel includes an ionic liquid and a polymer with a polymer network structure. The polymer is prepared by a cross-linking reaction using acrylate monomers as the main raw materials. The ionic liquid is dispersed in the polymer network structure of the polymer in the form of a dispersion medium; In this example, the acrylate monomers are butyl acrylate and methyl acrylate; The ionic liquid is choline bis(trifluoromethanesulfonyl)imide salt, and the structural formula of the organic cation is: , and the structural formula of the organic anion is .

[0045] The preparation method of the ionic liquid gel in this example specifically includes the following steps: Step 1: Mix 0.66 g of butyl acrylate, 0.14 g of methyl acrylate and 1.2 g of choline bis(trifluoromethanesulfonyl)imide salt evenly to obtain a mixed solution A; Step 2: Add 6.6 mg of cross-linking agent ethylene glycol dimethacrylate and 2 mg of photoinitiator 2,2 - diethoxyacetophenone to the mixed solution A, and mix evenly to obtain a mixed solution B; Step 3: Irradiate the mixed solution B with ultraviolet light. The wavelength of the ultraviolet light is 365 nm, and the power is 0.8 W / cm 2 , initiate a free radical polymerization reaction, and the irradiation time is 10 min to obtain the crude ionic liquid gel; Step 4: Soak the crude ionic liquid gel with the ionic liquid choline bis(trifluoromethanesulfonyl)imide salt having the same components as in Step 1. The soaking temperature is controlled between 35 - 40 °C, and the soaking time is 12 h. And replace the fresh ionic liquid every 6 h to obtain the ionic liquid gel; Among them, the amount of the ionic liquid used for each soaking is based on completely soaking the crude ionic liquid gel. And during the above mixing process, ultrasonic treatment can also be used to make the liquid mixture more fully and evenly mixed.

[0046] As Figure 1 shown, this is a comparison chart before and after phase separation of the ionic liquid gel prepared in this example. As Figure 2As shown in the figure, it is a graph of the transmittance of the ionic liquid gel prepared in this embodiment varying with temperature. It can be seen that the ionic liquid gel prepared in this embodiment has a significant change in transmittance at around 37°C. The transmittance of the ionic liquid gel drops by less than 80%, indicating that phase separation occurs in the ionic liquid gel near this temperature, and it changes from a transparent homogeneous gel without phase separation to a white phase-separated gel state; Among them, the transmittance is measured using a particle size analyzer.

[0047] Example 2 In this embodiment, ionic liquid gels with different phase separation temperatures are obtained by replacing different acrylate monomers and types of ionic liquids compared with Example 1.

[0048] That is, this embodiment provides an ionic liquid gel with temperature responsiveness. The ionic liquid gel includes an ionic liquid and a polymer with a polymer network structure. The polymer is prepared by a cross-linking reaction using acrylate monomers as the main raw materials, and the ionic liquid is dispersed in the polymer network structure of the polymer in the form of a dispersion medium; In this embodiment, the acrylate monomer is selected as butyl acrylate.

[0049] The ionic liquid is 1-propyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide, and the structural formula of the organic cation is: , and the structural formula of the organic anion is .

[0050] The preparation method of the ionic liquid gel in this embodiment specifically includes the following steps: Step 1: Mix 1.2 g of butyl acrylate and 0.8 g of 1-propyl-3-methylimidazolium bis(fluoromethylsulfonyl)imide evenly to obtain a mixed solution A; Step 2: Add 9.3 mg of cross-linking agent ethylene glycol dimethacrylate and 2 mg of photoinitiator 2,2-diethoxyacetophenone to the mixed solution A and mix evenly to obtain a mixed solution B; Step 3: Irradiate the mixed solution B with ultraviolet light. The wavelength of the ultraviolet light is 365 nm, and the power is 0.8 W / cm 2 , initiate a free radical polymerization reaction, and the irradiation time is 10 min to obtain the crude ionic liquid gel; Step 4: Soak the crude ionic liquid gel with the ionic liquid 1-propyl-3-methylbis(fluoromethylsulfonyl)imide having the same components as in Step 1. The soaking temperature is controlled between 50-55°C, and the soaking time is 12 h, and the fresh ionic liquid is replaced every 6 h to obtain the ionic liquid gel; The ion liquid gel prepared in this example was detected by a particle size analyzer for the change in light transmittance with temperature, which proved that the prepared ion liquid gel had a phase separation temperature of 52 °C.

[0051] Example 3 In this example, the type of butyl acrylate monomer was kept unchanged compared with Example 2, and the type of ion liquid was changed.

[0052] That is, this example provides an ion liquid gel with temperature response. The ion liquid gel includes an ion liquid and a polymer with a polymer network structure. The polymer is prepared by a cross-linking reaction using acrylate monomers as the main raw materials. The ion liquid is dispersed in the polymer network structure of the polymer in the form of a dispersion medium. In this example, the acrylate monomer was selected as butyl acrylate.

[0053] The ion liquid is 1-propyl-2,3-methylimidazolium bis(trifluoromethylsulfonyl)imide, and the structural formula of the organic cation is , and the structural formula of the organic anion is .

[0054] The preparation method of the ion liquid gel in this example specifically includes the following steps: Step 1: Mix 1.2 g of butyl acrylate and 0.8 g of 1-propyl-2,3-methylimidazolium bis(trifluoromethylsulfonyl)imide evenly to obtain a mixed solution A; Step 2: Add 9.3 mg of cross-linking agent ethylene glycol dimethacrylate and 2 mg of photoinitiator 2,2-diethoxyacetophenone to the mixed solution A and mix evenly to obtain a mixed solution B; Step 3: Irradiate the mixed solution B with ultraviolet light, where the wavelength of the ultraviolet light is 365 nm and the power is 0.8 W / cm 2 , initiate a free radical polymerization reaction, and the irradiation time is 10 min to obtain the crude ion liquid gel; Step 4: Soak the crude ion liquid gel with the ion liquid 1-propyl-2,3-methylimidazolium bis(trifluoromethylsulfonyl)imide having the same components as in Step 1. The soaking temperature is controlled between 20 - 30 °C, the soaking time is 12 h, and the fresh ion liquid is replaced every 6 h to obtain the ion liquid gel; The ion liquid gel prepared in this example was detected by a particle size analyzer for the change in light transmittance with temperature, which proved that the prepared ion liquid gel had a phase separation temperature of 0 °C.

[0055] Example 4 In this example, the amounts of butyl acrylate and methyl acrylate in Example 1 were changed so that the total mass percentage of the acrylate monomers in the mixed solution A was 35 wt%, 45 wt%, 50 wt%, 55 wt%. In Example 1, the total mass percentage of the acrylate monomers in the mixed solution A was 40 wt%, and the mass ratio of butyl acrylate to methyl acrylate in this example was ensured to be 33:7. The specific amounts and mass percentages of butyl acrylate and methyl acrylate are shown in Table 1, and the variation of the mass percentage of the acrylate monomers in the mixed solution A with the phase separation temperature is as Figure 3 shown: Table 1 Amounts and mass percentages of butyl acrylate and methyl acrylate

[0056] From Figure 3 it can be seen that the mass percentage of butyl acrylate and methyl acrylate in the mixed solution A and the phase separation temperature satisfy a linear function relationship, specifically: y = (2.99635 ± 0.03821)x - (83.93166 ± 1.75208); where x is the mass percentage (wt%) of butyl acrylate and methyl acrylate in the mixed solution A, and y is the phase separation temperature (°C).

[0057] From the above experimental results, it can be seen that by regulating the total mass percentage of the acrylate monomers in the mixed solution A, that is, from 35 - 55 wt%, continuous and precise regulation of the thermal response temperature of the ionic liquid gel in the range of 20 - 80 °C can be achieved.

[0058] Example 5 In this example, the amounts of butyl acrylate and methyl acrylate in Example 1 were changed so that the mass percentage of methyl acrylate in the mixed solution A was 6 wt%, 8 wt%, 9 wt%, 10 wt%. In Example 1, the mass percentage of methyl acrylate in the mixed solution A was 7 wt%, and the total amount of butyl acrylate and methyl acrylate in this example was ensured to be unchanged, which was consistent with the total amount of 0.8 g of the acrylate monomers in Example 1. The specific amounts and mass percentages of methyl acrylate are shown in Table 2, and the variation of the mass percentage of methyl acrylate in the mixed solution A with the phase separation temperature is as Figure 4 shown: Table 2 Amounts and mass percentages of methyl acrylate

[0059] From Figure 4 it can be seen that the mass percentage of methyl acrylate in the mixed solution A and the phase separation temperature satisfy a linear function relationship, specifically: y = (13.49485 ± 0.48072)x - (58.91753 ± 3.50569), where x is the mass percentage (wt%) of methyl acrylate in the mixed solution A, and y is the phase separation temperature (°C).

[0060] It can be seen from the above experimental results that by regulating the mass percentage of methyl acrylate in the mixed solution A, i.e., from 6 - 10 wt%, the thermal response temperature of the gel can be continuously and precisely regulated within the range of 20 - 80 °C.

[0061] From the overall regulation of Example 4 and Example 5, it can be seen that for the ionic liquid gel prepared with a specific content of acrylate monomers (total content of 40 wt%, where butyl acrylate:methyl acrylate = 33:7), an ionic gel electrode with a thermal response temperature of about 37 °C (body temperature) can be regulated for electroencephalogram signal acquisition at the scalp. Therefore, the ionic liquid gel prepared by the present invention can be applied to electroencephalogram signal acquisition to replace the conductive paste or hydrogel in the prior art.

[0062] Example 6 In this example, the molar ratio of the crosslinking agent to the total amount of acrylate monomers in Example 1 is such that the molar percentage of the crosslinking agent in the acrylate monomers is 0.3 mol%, 1.0 mol%, 2.0 mol%, 5.0 mol%. The molar percentage of the crosslinking agent in the acrylate monomers in Example 1 is 0.5 mol%, and the usage amounts of the remaining substances in this example are ensured to be unchanged. The specific changes in the molar percentage of the crosslinking agent in the total amount of acrylate monomers and the tensile and compressive Young's moduli are as Figure 5 shown:[[]] It can be seen from the figure that by changing the content of the added crosslinking agent, the mechanical properties of the prepared ionic liquid gel can be regulated. Increasing the content of the crosslinking agent, the tensile and compressive moduli of the ionic gel become larger. Through analysis, it can be obtained that as the molar percentage of the crosslinking agent increases from 0.3 mol% to 5.0 mol%, its tensile modulus increases from 32 KPa to 392 KPa, and the compressive modulus increases from 50 KPa to 312 KPa.

[0063] In this example, the fatigue resistance of the gel material of the ionic liquid gel with a molar percentage of the crosslinking agent of 0.5 mol% is characterized. The ionic liquid gel is gradually compressed from a 0% strain state to a 50% strain state, and the stress-strain curves for cyclic compression 1 time, 10 times, 50 times, and 100 times are obtained respectively as Figure 6 shown.[[]]

[0064] It can be seen from the curves in the figure that multiple stress-strain curves coincide with each other, indicating that the ionic liquid gel has excellent mechanical property stability. By comparing the areas of multiple cyclic curves, it can be known that the integral area of the curve of the ionic liquid gel during cycling is less than 10%, which represents that the ionic liquid gel has low energy dissipation. Figure 6 The gel compression optical photograph in the illustration (the enlarged view is as Figure 7 shown) shows that the morphology of the ionic liquid gel does not change after 100 cycles of compression, indicating that the ionic liquid gel prepared in the present invention has a fast deformation recovery rate during repeated compression, and the polymer network of the ionic liquid gel does not suffer irreversible damage, demonstrating the excellent anti-fatigue property of the ionic liquid gel.

[0065] Example 7 In this example, based on Example 1, a microarray structure about 50 μm wide and 30 μm deep was scribed on a silicon wafer using a dicing machine, and then polydimethylsiloxane (PDMS) was used to replicate the structure on the silicon wafer to obtain an anti-mold with the corresponding structure for the target mold for subsequent polymerization to form a gel; the mixed solution B obtained in step 2 of Example 1 was transferred to the target mold and irradiated with ultraviolet light. The conditions of ultraviolet light irradiation and the post-treatment conditions were the same as those in step 3 and step 4 of Example 1. In this example, as Figure 8 shown (scale: 50 μm), the prepared ionic liquid gel surface has a microarray structure about 50 μm wide and 30 μm deep.

[0066] Example 8 In this example, based on the raw materials, ratios and preparation methods of the ionic liquid gel numbered as Example 5-4 in Table 2 of Example 5, a microarray structure about 50 μm wide and 30 μm deep was scribed on a silicon wafer using a dicing machine, and then polydimethylsiloxane (PDMS) was used to replicate the structure on the silicon wafer to obtain an anti-mold with the corresponding structure for the target mold for subsequent polymerization to form a gel; the mixed solution B obtained in step 2 of Example 5.4 was transferred to the target mold and irradiated with ultraviolet light. The conditions of ultraviolet light irradiation and the post-treatment conditions were the same as those in step 3 and step 4 of Example 5.4. The prepared ionic liquid gel surface has a microarray structure about 50 μm wide and 30 μm deep, that is, the microarray structure is the same as that in Example 7.

[0067] Explore the variation law of the interfacial impedance of the above two ionic gels with microarray structures during the heating process. As Figure 9 shown, the ionic liquid gel was brought into contact with the smooth electrode surface to simulate the interface between the ionic liquid gel and the rough scalp during the wearing of the EEG cap. The ionic liquid exuded from the ionic liquid gel with a microarray structure in Example 7 filled the interfacial voids.

[0068] Meanwhile, the above tests were also carried out on the ionic liquid gel with a smooth surface prepared in Example 1. Through Figure 10 the optical microscope images, it can be seen that the ionic liquid gel prepared by the present invention has a body temperature-responsive phase separation behavior. The surface overflow during the phase separation process can play a role in wetting the interface, thereby reducing the interface impedance. By repeatedly heating and cooling the ionic liquid gel under optical microscope observation, it is proved that the body temperature-responsive phase separation behavior of the prepared ionic liquid gel induces a reversible process of ionic liquid release and reabsorption, which also shows that the ionic liquid gel of the present invention has reusability in practical applications. The above experimental results can indirectly verify that the prepared ionic liquid gel can ensure high-quality EEG signals during signal transmission and enable the electrodes to be reused by reducing the interface impedance between the electrode and the scalp.

[0069] After that, two ionic gels with microarray structures (i.e., T 分相 = 37 °C and T 分相 = 80 °C) obtained according to the raw materials, ratios, and preparation methods of Example 5.4 in Example 7 and this example were compared, and the change of the interface impedance between them and the metal electrode with temperature (25 °C - 37 °C) was characterized. From Figure 11 the curve in it, it can be found that the interface impedance of both shows a downward trend at each heating gradient. However, compared with each other, the impedance of the phase-separated ionic liquid gel (T 分相 = 37 °C) drops more.

[0070] Comparative Example 1 Commercially available polyacrylic acid hydrogel. As Figure 12 shown, this polyacrylic acid hydrogel does not have a phase separation phenomenon, that is, when the temperature rises, there is no change in the light transmittance, that is, it has no response to temperature.

[0071] Comparative Example 2 Commercially available polyvinyl alcohol hydrogel. As Figure 13 shown, this polyvinyl alcohol hydrogel does not have a phase separation phenomenon, that is, when the temperature rises, there is no change in the light transmittance, that is, it has no response to temperature.

[0072] Moreover, the commercially available hydrogels all have the technical problem of poor moisture retention, which is not conducive to long-term use.

[0073] Comparative Example 3 Commercially available EEG conductive paste.

[0074] Comparative Example 4 In this comparative example, compared with Example 1, the ionic liquid was replaced with 1-butyl-3-methylimidazolium trifluoromethanesulfonate, and the structural formula is: , The remaining raw materials, ratios, and preparation methods are the same as those in Example 1. The gel in this comparative example was prepared, and its light transmittance was also tested. The test results are as Figure 14 shown. There is no decrease in light transmittance in the range of 20 - 80 °C, that is, there is no corresponding response to temperature.

[0075] The product performances of the examples and comparative examples were compared one by one. The comparison process and results are as follows: Comparative Example 1 This comparative example was to compare the volatilization characteristics of Example 1, Comparative Example 1, and Comparative Example 3. Specifically, it was the water loss situation of each gel or conductive paste within 9 h. The comparison results are as Figure 15 shown: By comparing the volatilization degree of the solvent of the ordinary hydrogel and commercial conductive paste with the ionic liquid gel prepared by the present invention during long-term use, it was found that the hydrogel in Comparative Example 1 and the electroencephalogram conductive paste in Comparative Example 3 would lose water at a relatively fast rate and lose water to less than 40% of the original after 5 h, which would greatly affect their application as electrodes in electroencephalogram signal acquisition. For the ionic liquid gel prepared by the present invention, due to the non-volatile property of the ionic liquid itself at room temperature and its dispersion in the polymer with a polymer network structure as a dispersion medium, and the mutual microscopic interaction between the two, the weight of the ionic liquid gel prepared by the present invention hardly changes within 9 h. This also enables the ionic liquid gel to form a reliable interface for long-term, stable, and effective contact with the scalp. Therefore, the ionic liquid gel prepared by the present invention has great advantages as an electrode in long-term electroencephalogram signal acquisition.

[0076] Comparative Example 2 This comparative example shows the variation law of accuracy in the 40-target paradigm test (the 40-target paradigm test specifically characterizes the long-term, stable, and high-quality electroencephalogram performance of SWIGE through an experiment of a 40-target brain-computer interface system based on SSVEP) of the ionic liquid gel in Example 1 and the commercial electroencephalogram conductive paste in Comparative Example 3 under different stimulation times. The comparison results are as Figure 16 shown.

[0077] The ionic liquid gel of the present invention was installed as an electrode in an electroencephalogram cap to collect electroencephalogram signals and compared with the signals collected using a commercial conductive paste. At different stimulation times, the ionic liquid gel showed comparable recognition accuracy to the commercial conductive paste. At shorter stimulation times, due to the shorter reaction time of the subjects, both electrodes showed low accuracy. However, compared with each other, the ionic liquid gel as an electrode performed slightly better. As the stimulation time gradually increased to 2.0 s, the accuracy of both could quickly increase to over 90%. This result indicates that the ionic liquid gel prepared by the present invention has great potential to replace the conductive paste, which is the gold standard, for use as an electrode.

[0078] Comparative Example 3 This comparative example shows the variation laws of accuracy and signal transmission rate in the 40-target paradigm test of the ionic liquid gel in Example 1 for 48 h and the commercial electroencephalogram conductive paste in Comparative Example 3, and the variation law of the average signal-to-noise ratio in the 40-target paradigm test of the ionic liquid gel in Example 1 for 5 h and the commercial electroencephalogram conductive paste in Comparative Example 3. The comparison result figures are shown in Figures 17 - 18.

[0079] As Figure 17-18 shown, in the long-term 40-target paradigm test, the ionic liquid gel has more excellent performance than the commercial electroencephalogram conductive paste in terms of accuracy, signal transmission rate, and average signal-to-noise ratio. Among them,Figure 17 It shows the variation rules of the accuracy rate and signal transmission rate of the ionic liquid gel and commercial electroencephalogram conductive paste in the 40-target paradigm test within 48 hours. In the initial 2 hours, both showed high accuracy rates and signal transmission rates. As the usage time extended, due to the gradual volatilization of moisture, the accuracy rate and signal transmission rate of the electroencephalogram conductive paste decreased to nearly 0 after 5 hours and could no longer be used. In contrast, the ionic liquid gel prepared by the present invention can be stably used for 48 hours without performance degradation, which also benefits from the non-volatile property of the ionic liquid itself at room temperature and its dispersion in the polymer with a polymer network structure as a dispersion medium, as well as the mutual microscopic interaction between the two. In addition, 48 hours is only the test time, and theoretically, this ionic liquid gel can be used without time limit. Figure 18 It shows the variation rule of the average signal-to-noise ratio of the ionic liquid gel and commercial electroencephalogram conductive paste in the 40-target paradigm test within 5 hours. The electroencephalogram signals recorded by the electroencephalogram conductive paste decayed after 2 hours and lost the ability to record signals with high fidelity after 4 hours. The ionic liquid gel prepared by the present invention can maintain a high average signal-to-noise ratio within 5 hours. The above results indicate that compared with using commercial electroencephalogram conductive paste to collect electroencephalogram signals, the ionic liquid gel of the present invention has more advantages in stably collecting electroencephalogram signals for a long time.

[0080] Comparative Example 4 This comparative example shows the variation rule of the average impedance at the scalp of the ionic liquid gel in Example 1 and the commercial electroencephalogram conductive paste in Comparative Example 3 within 5 hours. The comparison results are as Figure 19 shown. To verify that the difference in recording electroencephalogram signals between the ionic liquid gel and commercial conductive paste is due to the change in interfacial impedance, the variation rule of the interfacial impedance at the scalp of both with time was tested, and the results are as Figure 18 shown. The initial interfacial impedance of the ionic liquid gel was relatively high and dropped significantly to a lower level after 1 hour. This is because the phase separation of the ionic gel generates ionic liquid that slowly wets the scalp interface, thereby effectively reducing the interfacial impedance. The interfacial impedance of the electroencephalogram conductive paste began to rise after 2 hours, which is due to the gradual volatilization of moisture in the conductive paste. This change trend can be mutually confirmed with the change in the quality of the above electroencephalogram signals. These results indicate that due to the non-volatile property of the ionic liquid in the ionic liquid gel as an electrode and the interfacial self-wetting induced by phase separation, the interfacial impedance in contact with the scalp can be stably maintained at a low level for a long time, thus ensuring the recording of electroencephalogram signals with high fidelity.

[0081] Comparative Example 5 This comparative example is a test for brain pattern recognition application, specifically showing the variation rule of the area under the receiver operating characteristic curve of the ionic liquid gel in Example 1 and the commercial electroencephalogram conductive paste in Comparative Example 3 within 50 days. The comparison results are Figure 20 shown.

[0082] In the electroencephalogram (EEG)-based brainprint recognition test, the EEG signal characteristics of the subject are recorded, and the brainprint verification template is obtained through analysis and processing. Then, the recorded template is repeatedly verified for multiple days to detect the conformity with the subject's brainprint characteristics. The 15-day continuous brainprint recognition verification results using ionic liquid gel and commercial EEG conductive paste are shown as Figure 19 follows. The area under the receiver operating characteristic (ROC) curve of the subjects tested with the same set of gel electrodes for 50 consecutive days is approximately around 0.8 (the closer the area under the ROC curve is to 1, the better the performance), which is comparable to the performance of the commercial EEG conductive paste that needs to be replaced daily. This result shows that the ionic liquid gel prepared by the present invention can not only record EEG signals with high fidelity, but also has excellent characteristics of maintenance-free, reusable, and ready-to-wear

[0083] It should be understood that the present invention is not limited to what has been described above and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present invention is only limited by the appended claims

Claims

1. A temperature-responsive ionic liquid gel, characterized in that, The ionic liquid gel includes an ionic liquid and a polymer having a polymer network structure. The polymer is prepared by a crosslinking reaction using acrylate monomers as the main raw materials. The ionic liquid is dispersed in the polymer network structure in the form of a dispersion medium; When the temperature of the ionic liquid gel rises from room temperature to the phase separation temperature, the light transmittance drops to ≤80%.

2. The temperature-responsive ionic liquid gel according to claim 1, wherein The phase separation temperature is 0 - 85 °C.

3. The temperature-responsive ionic liquid gel according to claim 1, wherein The mass ratio of the acrylate monomer to the ionic liquid is (2 - 9):(1 - 8).

4. The temperature-responsive ionic liquid gel according to claim 3, characterized in that, The structural formula of the acrylate monomer is: , where 1 ≤ m ≤ 8 and m is an integer.

5. The temperature-responsive ionic liquid gel according to claim 3, characterized in that The ionic liquid is composed of an organic cation and an organic anion; The structural formula of the organic cation is: , , one or more of; wherein, 1 ≤ a ≤ 10, 1 ≤ b ≤ 10, a is an integer, b is an integer; The structural formula of the organic anion is: , one or more of the following.

6. A method for preparing the temperature-responsive ionic liquid gel according to any one of claims 1-5, characterized in that, A crosslinking agent and an initiator are added to the mixed solution of the acrylate monomer and the ionic liquid. After mixing, ultraviolet light irradiation is used to carry out a free radical polymerization reaction to obtain the ionic liquid gel; The relationship between the mass percentage of the acrylate monomer in the mixed solution and the phase separation temperature satisfies the following formula: y = (2.99635 ± 0.03821)x - (83.93166 ± 1.75208); Wherein, x is the mass percentage of butyl acrylate and methyl acrylate in the mixed solution A, with the unit of wt%; y is the phase separation temperature, with the unit of °C.

7. The preparation method of the temperature-responsive ionic liquid gel according to claim 6, characterized in that, The crosslinking agent is an acrylate crosslinking agent or an acrylamide crosslinking agent; The structural formula of the acrylate crosslinking agent is: where p≥1, p is an integer, R 11 , R 12 is independently hydrogen or an alkyl group having 1 to 5 carbon atoms; The structural formula of the acrylamide crosslinking agent is: where 1 ≤ q ≤ 5, q is an integer, and R 21 , and R 22 is independently hydrogen or an alkyl group having 1 to 5 carbon atoms.

8. The preparation method of the temperature-responsive ionic liquid gel according to claim 6, characterized in that, The structural formula of the initiator is: , wherein R 31 , R 32 is an alkyl group having 1 to 8 carbon atoms.

9. The preparation method of the temperature-responsive ionic liquid gel according to claim 6, wherein, Specifically, it includes the following steps: Step 1: Mix the acrylate monomer and the ionic liquid evenly to obtain a mixed solution A; Step 2: Add a crosslinking agent and an initiator to the mixed solution A and mix evenly to obtain a mixed solution B; At the same time, when adding, the monomer concentration is high, and polymerization may occur directly, and polymerization may also occur under natural light Step 3: Carry out ultraviolet light irradiation on the mixed solution B to initiate a free radical polymerization reaction to obtain the crude ionic liquid gel; Step 4: Soak the crude ionic liquid gel with the ionic liquid having the same components as in Step 1 to obtain the ionic liquid gel.

10. A layered structure, characterized in that, The raw materials for preparing the layered structure include the temperature-responsive ionic liquid gel according to any one of Claims 1 - 5.

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