A dual-network ionic gel, a preparation method thereof and a flexible sensor

Abstract

The application belongs to the field of polymer materials and flexible electronic technology, and particularly relates to a double-network ionic gel, a preparation method thereof and a flexible sensor. The ionic gel takes an ionic liquid as a medium, forms a first chemical network through acrylamide polymerization, introduces cellulose to construct a second physical network, and adds carbon nanotubes as a conductive reinforcing phase, and is cured and formed in one step by adopting a blue light initiation polymerization technology. Through the joint action of the components, the obtained ionic gel has high toughness, high conductivity, excellent anti-freezing and temperature resistance and high strain sensitivity. The flexible sensor taking the ionic gel as a sensitive element has rapid response and wide detection range, and can accurately monitor human motion in real time. The application has simple process, mild conditions and is suitable for large-scale production, and has wide application prospect in the field of wearable electronics and intelligent sensing.

Description

Technical Field

[0001] This invention specifically relates to a dual-network ion gel, its preparation method, and a flexible sensor, belonging to the fields of polymer materials and flexible electronic materials technology. Background Technology

[0002] With the rapid development of wearable health monitoring and human-computer interaction technologies, the market demand for flexible electronic devices that can withstand repeated mechanical deformation and maintain stable performance in complex environments is increasing. Hydrogel-based flexible sensors have been extensively studied due to their good biocompatibility and stretchability; however, their inherent defects—such as easy freezing at low temperatures and easy water loss at high temperatures—severely limit their application in real-world environments.

[0003] Ionic gels, using ionic liquids as the dispersion medium, fundamentally solve the problems of volatilization and freezing, and possess inherent ionic conductivity, making them an ideal alternative to hydrogels. However, existing ionic gels generally suffer from limited mechanical properties, insufficient toughness, limited sensing sensitivity, complex preparation processes, and high costs. Furthermore, traditional preparation processes often rely on thermal initiation or ultraviolet (UV) curing. The former is time-consuming and energy-intensive, while the latter has limitations such as limited UV penetration depth, potential for material aging, or adverse effects on human tissues.

[0004] In recent years, researchers have attempted to improve the performance of ionogels by constructing dual-network structures and introducing nano-reinforcing phases. Cellulose, as a renewable and biocompatible natural polymer, can serve as a physical cross-linking point to effectively reinforce and toughen the gel network. Carbon nanotubes (CNTs), due to their excellent conductivity, mechanical strength, and large specific surface area, are considered ideal nanofillers for constructing high-performance conductive polymer composites. Introducing them into gel systems is expected to create efficient conductive pathways at the nanoscale, significantly improving the electrical and sensing properties of the materials. Furthermore, blue light curing technology, with its higher penetration depth, better biosafety, and milder curing conditions, shows great potential in biomedical materials and flexible electronics manufacturing. However, preparing ionogels with good uniformity and excellent interfacial bonding without compromising the superior properties of each component remains a significant challenge.

[0005] In summary, existing technologies have obvious shortcomings. It is of great significance to prepare an ionogel with high toughness, excellent freeze-thaw resistance, high ionic conductivity, and high strain sensitivity through mild methods and simple processes. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by providing a dual-network ionogel, its preparation method, and a flexible sensor. The ionogel uses an imidazole-based ion liquid as a medium, forming a first chemical network through acrylamide polymerization, introducing cellulose to construct a second physical network, and incorporating carbon nanotubes as a conductive reinforcement phase. It is then cured in one step using blue light-initiated polymerization. Through the combined effect of these components, the resulting ionogel possesses high toughness, high conductivity, excellent freeze-thaw resistance, and high strain sensitivity. The flexible sensor using this ionogel as a sensing element exhibits rapid response, a wide detection range, and can accurately monitor human movement in real time. This invention features a simple process, mild conditions, and suitability for mass production, showing broad application prospects in wearable electronics and intelligent sensing.

[0007] The technical solution of the present invention to solve the above-mentioned technical problems is as follows: a dual-network ionic gel, the dual-network ionic gel comprising acrylamide monomer, crosslinking agent, cellulose powder, carbon nanotubes, ionic liquid and blue light initiator.

[0008] Furthermore, the mass ratio between acrylamide and crosslinking agent is (10~100):1; preferably 50:1.

[0009] Furthermore, the mass ratio between acrylamide and cellulose powder is (10~100):1; preferably 50:1.

[0010] Furthermore, the mass ratio of acrylamide, carbon nanotubes and ionic liquid is 1:(0.001~0.05):(2~5), preferably 1:(0.005~0.02):2.5.

[0011] Furthermore, the mass ratio between acrylamide and blue light initiator is (50~200):1, preferably 100:1.

[0012] Furthermore, the crosslinking agent is at least one selected from polyethylene glycol diacrylate, N,N'-methylenebisacrylamide, divinylbenzene, glyoxal, dicumyl peroxide, benzoyl peroxide, ethylenediamine, diethylenetriamine, trimethylolpropane-tris(3-aziridinyl)propionate, borax, aluminum chloride, and aluminum sulfate; preferably polyethylene glycol diacrylate.

[0013] Furthermore, the ionic liquid is at least one of imidazolium salts, pyridinium salts, quaternary ammonium salts, and quaternary phosphonium salts.

[0014] Furthermore, the imidazolium salt is at least one selected from 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium nitrate, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium hexafluorophosphate, 1,1'-ethylene-bis(3-methylimidazolium)dibromide, and 1-(2-hydroxyethyl)-3-methylimidazolium chloride; preferably 1-ethyl-3-methylimidazolium acetate.

[0015] Furthermore, the carbon nanotube is at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, hydroxylated carbon nanotubes, aminated carbon nanotubes, polymer-grafted carbon nanotubes, non-covalent functionalized carbon nanotubes, and carboxylated carbon nanotubes; preferably, it is a carboxylated multi-walled carbon nanotube.

[0016] Furthermore, the blue light initiator is at least one of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl(2,4,6-trimethylbenzoyl)phenylphosphine ester, camphorquinone, and bis(4-tert-butylphenyl)iodomonium hexafluorophosphate; preferably phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0017] This invention also discloses a method for preparing a dual-network ionic gel, the method comprising the following steps: S1. Add acrylamide monomer, crosslinking agent, cellulose powder, and carbon nanotubes to the ionic liquid, heat and stir to fully disperse the components and obtain a uniform and stable precursor dispersion. S2. Add the blue light initiator to the uniform and stable precursor dispersion obtained in S1, heat and stir under light-protected conditions to completely dissolve and mix it evenly to form a polymerizable precursor solution. S3. Inject the polymerizable precursor solution obtained in step S2 into the mold and irradiate it under a blue light source to complete the polymerization of monomers and the solidification of the gel network. After demolding, a double-network ionic gel is obtained.

[0018] Furthermore, in step S1, the reaction temperature is 30~70℃ and the reaction time is 1~2 hours; in step S2, the reaction temperature is 30~70℃ and the reaction time is 30~60 minutes.

[0019] Furthermore, in step S3, the blue light source is 405~460 nanometers, and the irradiation time is 20~60 minutes.

[0020] The present invention also discloses a flexible sensor comprising a dual-network ion gel.

[0021] Furthermore, by connecting two separate copper electrodes to both ends of a dual-network ionic liquid gel strip, a flexible strain sensor based on ionic liquid gel can be obtained. The changes in electrical signals after deformation of the ionic liquid gel can be detected and recorded by a digital bridge system.

[0022] The beneficial effects of this invention are: (1) The dual-network ion gel provided by the present invention has excellent mechanical and electrical properties. By constructing a ternary synergistic system of "polyacrylamide chemical network - cellulose physical network - carbon nanotube conductive network", cellulose provides strong toughness and energy dissipation ability, and carbon nanotubes construct an efficient three-dimensional conductive pathway, so that the ion gel has high toughness, high tensile strength and high ionic conductivity at the same time.

[0023] (2) The dual-network ionic gel provided by the present invention has excellent environmental stability: with ionic liquid as the continuous phase, the freezing and evaporation of water are completely avoided, so that the gel maintains flexibility and performance stability in a wide temperature range and is suitable for extreme environments.

[0024] (3) The flexible sensor prepared by the present invention through dual-network ion gel has high sensitivity: the introduction of carbon nanotubes greatly enhances the piezoresistive effect of the gel, and the prepared flexible sensor has high sensitivity, wide detection range, fast response time and excellent cycle stability.

[0025] (4) The preparation process of the dual-network ionogel provided by this invention is simple, safe, efficient, and easy to promote. Blue light-initiated polymerization is used instead of traditional ultraviolet light curing, which makes the light source safer and more penetrating, enabling uniform curing of thicker samples. The conditions are also milder, making it more suitable for integration with biological tissues or electronic components. The "one-pot" mixing and one-step blue light curing method uses readily available raw materials, is easy to operate, requires no complex equipment, has a short production cycle, and has the potential for large-scale industrial production. Attached Figure Description

[0026] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings: Figure 1 The image shows the microstructure of the dual-network ionogel obtained in Example 1 of this invention under a scanning electron microscope (SEM). Figure 2 This is a stretching diagram of the dual-network ionogel obtained in Example 1 of the present invention; Figure 3 This is a schematic diagram of the stretching cycle of the dual-network ionogel obtained in Example 1 of the present invention; Figure 4This is a schematic diagram of the thermal stability and antifreeze properties of the dual-network ionogel obtained in Example 1 of the present invention; Figure 5 This is a schematic diagram of the aluminum alloy plate overlap shear adhesion test of the dual-network ionogel obtained in Example 1 of the present invention; Figure 6 This is a schematic diagram illustrating the application of the dual-network ionogel obtained in Example 1 of the present invention in elbow motion detection. Detailed Implementation

[0027] The specific embodiments of the present invention will be described in detail below. The present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed.

[0028] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used is for describing particular embodiments only and is not intended to limit the invention.

[0029] The present invention provides a dual-network ionic gel, which comprises acrylamide monomer, crosslinking agent, cellulose powder (purchased from Shanghai Aladdin Biochemical Technology Co., Ltd., CAS No.: 9004-34-6), carbon nanotubes, ionic liquid and blue light initiator.

[0030] Specifically, the mass ratio between acrylamide and crosslinking agent is (10~100):1; preferably 50:1.

[0031] Specifically, the mass ratio between acrylamide and cellulose powder is (10~100):1; preferably 50:1.

[0032] Specifically, the mass ratio of acrylamide, carbon nanotubes and ionic liquid is 1:(0.001~0.05):(2~5), preferably 1:(0.005~0.02):2.5.

[0033] Specifically, the mass ratio between acrylamide and blue light initiator is (50~200):1, preferably 100:1.

[0034] Specifically, the crosslinking agent is at least one of polyethylene glycol diacrylate, N,N'-methylenebisacrylamide, divinylbenzene, glyoxal, dicumyl peroxide, benzoyl peroxide, ethylenediamine, diethylenetriamine, trimethylolpropane-tris(3-aziridinyl)propionate, borax, aluminum chloride, and aluminum sulfate; preferably polyethylene glycol diacrylate.

[0035] Specifically, the ionic liquid is at least one of imidazolium salts, pyridinium salts, quaternary ammonium salts, and quaternary phosphonium salts.

[0036] More specifically, the imidazolium salts are at least one of 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium nitrate, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium hexafluorophosphate, 1,1'-ethylene-bis(3-methylimidazolium)dibromide, and 1-(2-hydroxyethyl)-3-methylimidazolium chloride; preferably 1-ethyl-3-methylimidazolium acetate.

[0037] Specifically, the carbon nanotubes are at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, hydroxylated carbon nanotubes, aminated carbon nanotubes, polymer-grafted carbon nanotubes, non-covalent functionalized carbon nanotubes, and carboxylated carbon nanotubes; preferably, carboxylated multi-walled carbon nanotubes.

[0038] Specifically, the blue light initiator is at least one of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl(2,4,6-trimethylbenzoyl)phenylphosphine ester, camphorquinone, and bis(4-tert-butylphenyl)iodomonium hexafluorophosphate; preferably phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0039] The dual-network ionogel provided by this invention has excellent mechanical properties, environmental stability, high conductivity, and high sensitivity sensing performance.

[0040] This invention constructs a multi-level energy dissipation network. The first level of dissipation involves acrylamide forming a covalently cross-linked polyacrylamide (PAM) network under the action of a cross-linking agent, providing basic elastic recovery force as the main framework. The second level of dissipation involves a cellulose network, where the abundant hydroxyl groups on the cellulose surface form numerous reversible hydrogen bonds with the amide groups on the PAM chains. Under external force, these hydrogen bonds preferentially break, absorbing a large amount of energy; after the force is removed, the hydrogen bonds can be rebuilt. Ion-dipole interactions occur, where cations in imidazole ionic liquids interact strongly with the polar groups (-OH, -C=O, -NH2) on the cellulose and PAM chains, forming dynamic physical cross-linking points. The third level of dissipation involves the bridging and pull-out effect of carbon nanotubes. Well-dispersed carboxylated carbon nanotubes (CNTs) form hydrogen or ionic bonds with the PAM / cellulose network through their surface carboxyl groups. When cracks propagate, CNTs act like "nanorhines," bridging the crack sides; their high strength and interfacial slippage (pull-out process) with the matrix require enormous energy. When the crack deflects, CNTs and cellulose act as nanoscale barriers, forcing the crack propagation path to bend and branch, thus lengthening the crack path and improving fracture toughness. In summary, the chemical network provides "rigidity," the dynamic physical bonds act as "sacrificial units" to dissipate energy, and the nanofillers prevent crack propagation; the three work together to achieve exceptionally high toughness.

[0041] This invention completely replaces water with an ionic liquid, which possesses an extremely low freezing point and extremely high thermal stability. As a continuous phase, it completely replaces water in traditional hydrogels, thus fundamentally eliminating the fatal weakness of hydrogels: "ice crystal formation-network destruction." The complex ion-pair and hydrogen bond network in the ionic liquid allows it to maintain an amorphous state at low temperatures, rather than crystallizing. Simultaneously, the strong ion-dipole interactions between the cations and anions in the ionic liquid and the polar groups on the polymer network "lock" the ionic liquid molecules within the gel network. The dense PAM / cellulose / CNTs composite network significantly restricts the free volume and mobility of the ionic liquid molecules, effectively suppressing their volatilization or seepage at high temperatures. Therefore, the environmental stability of this material is jointly ensured by the intrinsic properties of the ionic liquid and the strong binding effect of the network.

[0042] Ionic liquids are excellent ionic conductors. In gels, they form a continuous ionic conductive phase. Although PAM and cellulose networks are not conductive, their high hydrophilicity stabilizes and fixes ion channels, ensuring that ion migration paths remain connected even under deformation. Introduced carbon nanotubes (CNTs) contact and overlap within the insulating polymer matrix, forming a three-dimensional permeable network through which electrons can tunnel or conduct directly. In some cases, a hybrid ion-electron conductive interface may form within the gel, creating an electrical double layer on the CNT surface, further enhancing charge transport capabilities. Therefore, ionic liquids provide ionic conductivity, while the CNT network provides electronic conductivity, enabling the gel to simultaneously possess the ionic conductivity of liquid electrolytes and the electronic conductivity of solids.

[0043] For the ionicly conductive portion, stretching lengthens and tortuouss the ion migration path, decreasing ionic conductivity (increasing ΔR). However, this effect typically contributes only a small amount. For the electronically conductive portion, stretching causes slippage and separation between contacting CNTs, drastically reducing contact points and significantly increasing contact resistance. When the CNT spacing is increased, the electron tunneling probability decreases exponentially, leading to a dramatic increase in resistance. Under large strain, some CNT connections completely break, the conductive pathway is reconstructed, and the resistance experiences a nonlinear jump. The cellulose and PAM networks ensure uniform deformation of the gel under strain, rather than localized tearing. This makes the destruction of the CNT network gradual and predictable, resulting in a stable, high signal-to-noise ratio resistance change signal. In short, the high sensitivity stems from the extremely sensitive "disconnect-connect" behavior of the CNT permeation network under strain, where minute deformations are amplified into huge resistance signal changes.

[0044] This invention provides a method for preparing a dual-network ionic gel, the method comprising the following steps: S1. Add acrylamide monomer, crosslinking agent, cellulose powder, and carbon nanotubes to the ionic liquid, heat and stir to fully disperse the components and obtain a uniform and stable precursor dispersion. S2. Add the blue light initiator to the uniform and stable precursor dispersion obtained in S1, heat and stir under light-protected conditions to completely dissolve and mix it evenly to form a polymerizable precursor solution. S3. Inject the polymerizable precursor solution obtained in step S2 into the mold and irradiate it under a blue light source to complete the polymerization of monomers and the solidification of the gel network. After demolding, a double-network ionic gel is obtained.

[0045] Specifically, in step S1, the reaction temperature is 30~70℃ and the reaction time is 1~2 hours; in step S2, the reaction temperature is 30~70℃ and the reaction time is 30~60 minutes.

[0046] Specifically, in step S3, the blue light source is 405~460 nanometers, and the irradiation time is 20~60 minutes.

[0047] The stirring speed in this embodiment of the invention is 500 rpm, but this does not limit the technology of the invention. It can be adjusted according to actual needs, as long as the material is evenly dispersed.

[0048] This invention provides a method for preparing a dual-network ionic gel that is low in cost and simple in process. All raw materials (monomers, crosslinking agents, cellulose, CNTs, and initiators) exhibit good solubility or dispersibility in the ionic liquid. The ionic liquid, as a solvent, has a moderate viscosity and can achieve uniform molecular and nanoscale precursor dispersion through stirring and sonication, which is a prerequisite for the subsequent formation of a homogeneous network. The selected blue light initiator (such as BAPO) generates free radicals efficiently under 405nm light excitation, and its photon energy is lower than that of ultraviolet light, making it less likely to trigger unnecessary side reactions and ensuring network integrity. Blue light scatters weakly than ultraviolet light and has stronger penetrating power in dark systems containing CNTs, enabling uniform bulk polymerization and avoiding surface solidification and internal stickiness. Blue light is not harmful to human cells and tissues like ultraviolet light, making it more suitable for future fabrication of devices directly integrated with biological tissues.

[0049] The present invention also provides a flexible sensor comprising a dual-network ion gel.

[0050] Specifically, by connecting two separate copper electrodes to both ends of a dual-network ionic liquid gel strip, a flexible strain sensor based on ionic liquid gel can be obtained. The changes in electrical signals after deformation of the ionic liquid gel can be detected and recorded by a digital bridge system.

[0051] The flexible sensor provided by this invention is low in cost and simple to manufacture. It has high tensile strength, high toughness, excellent adhesion, high sensitivity, rapid response, good stability, and low response time. It can accurately and repeatedly detect the activities of fingers, elbows, and knees in real time and has the ability to monitor various human movements. It can be widely used in fields such as electronic skin, intelligent robots, and artificial muscles.

[0052] Example 1 The preparation of a dual-network ionic gel includes the following steps: S1. 2.7g acrylamide monomer, 0.054g polyethylene glycol diacrylate, 0.054g cellulose powder, and 0.027g carboxylated multi-walled carbon nanotubes (purchased from Shanghai Maclean Biochemical Technology Co., Ltd., CAS No.: 308068-56-6, item number: C828604) were added to 6.3g 1-ethyl-3-methylimidazolium acetate ionic liquid. The mixture was heated to 50℃ and stirred for 1.5h to fully disperse the components and obtain a uniform and stable precursor dispersion. S2. Add 0.027g of blue photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide to the uniform and stable precursor dispersion obtained in S1, heat to 50℃ and stir for 30min under light-protected conditions to completely dissolve and mix evenly to form a polymerizable precursor solution. S3. Inject the polymerizable precursor solution obtained in step S2 into the mold and irradiate it under a blue light source with a wavelength of 405nm for 30 minutes to complete the polymerization of monomers and the solidification of the gel network. After demolding, a double-network ionic gel is obtained.

[0053] The microstructure of the dual-network ionogel obtained in this embodiment is shown in the scanning electron microscope (SEM) image below. Figure 1 As shown in the figure, its internal porous interconnected network structure can be seen; the stretched schematic diagram is shown below. Figure 2 As shown in the figure, its tensile strain reaches 3109% and its tensile strength reaches 246 kPa, reflecting its high tensile properties; the tensile cycle diagram is shown below. Figure 3 As shown, the figure reflects the mechanical response of the material during multiple cyclic loading-unloading processes. It can be seen from the figure that it exhibits low hysteresis and good repeated tensile stability; the schematic diagrams of thermal stability and freeze-thaw resistance are shown below. Figure 4 As shown in the figure, the mass change rate of the material under both low temperature (e.g., -20℃) and high temperature (e.g., 45℃) conditions is less than 8%, indicating that the gel maintains a stable morphology over a wide temperature range; a schematic diagram of the aluminum alloy plate overlap shear adhesion test is shown below. Figure 5 As shown in the figure, the good interfacial adhesion between the gel and the metal substrate can be seen; a schematic diagram of its application in elbow motion detection is shown below. Figure 6 As shown in the figure, it can be seen that it has the characteristics of fast response and high sensitivity in wearable motion sensing.

[0054] A flexible strain sensor based on ionic liquid gel can be obtained by connecting two separate copper electrodes to both ends of a dual-network ionogel strip prepared in this embodiment.

[0055] Example 2 The preparation of a dual-network ionogel is carried out using the same method as in Example 1, except that the amount of cellulose powder used in step S1 is 0.027g.

[0056] Example 3 The preparation of a dual-network ionogel is carried out in this embodiment using the same method as in Example 1, except that in step S1, the amount of carboxylated multi-walled carbon nanotubes used is 0.054 g.

[0057] Example 4 The preparation of a dual-network ionic gel is carried out using the same method as in Example 1, except that in step S1, the amount of ionic liquid 1-ethyl-3-methylimidazolium acetate is 13.5g.

[0058] Example 5 The preparation of a dual-network ionic gel is carried out using the same method as in Example 1, except that in step S1, N,N'-methylenebisacrylamide is used instead of polyethylene glycol diacrylate.

[0059] Example 6 The preparation of a dual-network ionic gel is carried out using the same method as in Example 1, except that in step S1, 1-butyl-3-methylimidazolium bromide is used instead of 1-ethyl-3-methylimidazolium acetate.

[0060] Example 7 The preparation of a dual-network ionic gel is carried out in this embodiment using the same method as in Example 1, except that in step S1, multi-walled carbon nanotubes (purchased from Shanghai Maclean Biochemical Technology Co., Ltd., CAS No.: 308068-56-6, item number: C805983) are used instead of carboxylated multi-walled carbon nanotubes.

[0061] Example 8 The preparation of a dual-network ionic gel is carried out using the same method as in Example 1, except that in step S2, bis(4-tert-butylphenyl)iodonium hexafluorophosphate is used instead of phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide.

[0062] Example 9 The preparation of a dual-network ionic gel is carried out using the same method as in Example 1, except that in step S3, the gel is irradiated under a 405nm blue light source for 60 minutes.

[0063] Example 10 The preparation of a dual-network ionic gel is carried out using the same method as in Example 1, except that in step S2, the amount of blue photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide is 0.054 g.

[0064] Example 11 The preparation of a dual-network ionic gel includes the following steps: S1. Add 2.7g acrylamide monomer, 0.027g polyethylene glycol diacrylate, 0.27g cellulose powder, and 0.0027g carboxylated multi-walled carbon nanotubes to 6.3g 1-ethyl-3-methylimidazolium acetate ionic liquid, heat to 30℃ and stir for 2h to fully disperse the components and obtain a uniform and stable precursor dispersion. S2. Add 0.054g of blue photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide to the uniform and stable precursor dispersion obtained in S1, heat to 30℃ under light-protected conditions and stir for 60min to completely dissolve and mix evenly to form a polymerizable precursor solution. S3. Inject the polymerizable precursor solution obtained in step S2 into the mold and irradiate it under a blue light source with a wavelength of 405nm for 20 minutes to complete the polymerization of monomers and the solidification of the gel network. After demolding, a double-network ionic gel is obtained.

[0065] Example 12 The preparation of a dual-network ionic gel includes the following steps: S1. Add 2.7g acrylamide monomer, 0.27g polyethylene glycol diacrylate, 0.09g cellulose powder, and 0.135g carboxylated multi-walled carbon nanotubes to 6.75g 1-ethyl-3-methylimidazolium acetate ionic liquid, heat to 70℃ and stir for 2h to fully disperse the components and obtain a uniform and stable precursor dispersion. S2. Add 0.018g of blue photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide to the uniform and stable precursor dispersion obtained in S1, heat to 50℃ and stir for 50min under light-protected conditions to completely dissolve and mix evenly to form a polymerizable precursor solution. S3. Inject the polymerizable precursor solution obtained in step S2 into the mold and irradiate it under a blue light source with a wavelength of 405nm for 40 minutes to complete the polymerization of monomers and the solidification of the gel network. After demolding, a double-network ionic gel is obtained.

[0066] Comparative Example 1 The preparation of a dual-network ionic gel is carried out using the same method as in Example 5, except that cellulose powder is not added in step S1.

[0067] Comparative Example 2 The preparation of a dual-network ionic gel is carried out using the same method as in Example 5, except that in step S1, deionized water is used instead of ionic liquid.

[0068] Comparative Example 3 The preparation of a dual-network ionic gel is carried out using the same method as in Example 1, except that no cross-linking agent is added in step S1.

[0069] Comparative Example 4 The preparation of a dual-network ionic gel follows the same method as in Example 5, except that an ultraviolet photoinitiator and an ultraviolet curing process are used. Specifically, in step S2, ultraviolet photoinitiator 2959 is used instead of blue photoinitiator phenylbis(2,4,6-trimethylbenzoyl)phosphine oxide; in step S3, the gel is irradiated under an ultraviolet lamp with a wavelength of 365 nm for 1 hour.

[0070] The phenomenon observed during the preparation process of this comparative example: the sample could not be cured.

[0071] Comparative Example 5 The preparation of a dual-network ionic gel is carried out in this embodiment using the same method as in Example 1, except that carbon nanotubes are not added in step S1.

[0072] Comparative Example 6 The preparation of a dual-network ionogel is carried out using the same method as in Example 1, except that in step S1, the amount of cellulose powder used is 0.3g, and the mass ratio between acrylamide and cellulose powder is 9:1.

[0073] Comparative Example 7 The preparation of a dual-network ionic gel is carried out using the same method as in Example 1, except that in step S1, the amount of carboxylated multi-walled carbon nanotubes used is 0.216 g, and the mass ratio of acrylamide to carboxylated multi-walled carbon nanotubes is 1:0.08.

[0074] The performance test data of the dual-network ionic gels obtained in the embodiments and comparative examples of this invention are shown in Table 1. The specific performance test methods involved are as follows: (1) Tensile strength: In the tensile test, all samples were prepared in a polytetrafluoroethylene mold, maintaining a dumbbell shape. Uniaxial tensile tests were performed on the ionogels using an electronic universal testing machine. Refer to GB / T 10654-2001 standard.

[0075] (2) Tensile toughness: The integral area under the stress-strain curve, i.e., the energy consumed per unit volume of gel to fracture. Refer to GB / T 10654-2001 standard.

[0076] (3) Freeze-thaw resistance: The mass change of the gel sample was measured by placing it in environments of -20℃ and 45℃. Refer to DIN ISO 1625-2001 standard.

[0077] (4) Adhesion performance: A 1×1cm piece 2 The ionogel sample is flatly adhered to one end of two aluminum alloy plates. The prepared lapped sample is then vertically mounted in the upper and lower clamps of the universal testing machine for tensile testing. Refer to NF G37-107-1983 standard.

[0078] (5) Conductivity: Cover the upper and lower surfaces of the sample with copper foil, lead out the copper foil and connect it to the electrode of the electrochemical workstation, test the resistance of the ion gel, and calculate the conductivity of the ion gel. Refer to NF T51-080-1999 standard.

[0079] (6) Sensing performance: The ion gel flexible strain sensor is prepared by attaching copper foil to both ends of a hydrogel and connecting the copper foil to conductive wires. The hydrogel bioelectrode is attached to the skin, a constant voltage is applied to both ends, and a force is applied to cause strain in the sensor. The strain value at a certain moment, the resistance value under that strain, and the initial resistance value are recorded to calculate the sensitivity of the gel. Refer to NF T51-080-1999 standard.

[0080] Table 1 Performance test data of the dual-network ionogels obtained in the examples and comparative examples The dual-network ionogel provided in this application is formed by acrylamide polymerization to create a first chemical network, the introduction of cellulose to construct a second physical network, and the addition of carbon nanotubes as a conductive reinforcing phase. An ionic liquid is used as the mixing and dispersion medium, and the gel is cured in one step using blue light-initiated polymerization technology. The interaction of these components synergistically achieves the excellent mechanical properties, conductivity, and wide-temperature stability of the dual-network ionogel. In Example 1, the ionogel exhibits a toughness as high as 4861 kJ·m⁻³, an electrical conductivity of 1.76 mS·cm⁻¹, and a strain sensitivity of 1.08, demonstrating excellent performance in the field of flexible sensing.

[0081] Based on the data in Table 1, a comparison between Comparative Example 1 and Example 5 shows that the absence of cellulose in Comparative Example 1 resulted in a significant decrease in the toughness of the ionogel to 2100 kJ·m⁻³, with a sensitivity of only 0.60. This is because cellulose, acting as a second physical network, forms numerous reversible hydrogen bonds with PAM chains through its abundant surface hydroxyl groups, and acts as a nanoscale barrier to promote crack deflection, significantly enhancing energy dissipation and fracture toughness. The lack of a cellulose network leads to a lack of effective physical cross-linking and energy dissipation mechanisms during the stretching process, resulting in a substantial reduction in toughness and sensing sensitivity.

[0082] Based on the data in Table 1, a comparison between Comparative Example 2 and Example 5 shows that in Comparative Example 2, where water was used instead of ionic liquid, the resulting hydrogel was prone to freezing at low temperatures and exhibited extremely low conductivity (0.05 mS·cm⁻¹). This is because the hydrogel system easily forms ice crystals at low temperatures, disrupting the network structure, and easily loses water at high temperatures, resulting in poor environmental stability. Simultaneously, water's ionic conductivity is far lower than that of ionic liquids, and the lack of strong ionic dipole interactions between the ionic liquid and the polymer network leads to a significant decrease in conductivity and sensing performance.

[0083] Based on the data in Table 1, a comparison between Comparative Example 3 and Example 1 shows that the mechanical properties of the material in Comparative Example 3, without the addition of a chemical crosslinking agent, are severely reduced (toughness 1200 kJ·m⁻³). This is because the chemical crosslinking network provides the basic structural integrity and elastic recovery force for the gel. Without it, relying solely on physical entanglement cannot form a stable three-dimensional network, resulting in low gel strength, easy plastic deformation, and significantly reduced toughness and sensing stability.

[0084] Based on the data in Table 1, a comparison between Comparative Example 4 and Example 5 shows that the material in Comparative Example 4, which uses a UV photoinitiator and UV curing process, cannot be uniformly cured. This is because UV light has poor penetration in systems containing dark carbon nanotubes, easily leading to surface over-curing while the interior remains unpolymerized, failing to form a complete gel structure, and thus failing to obtain effective performance data.

[0085] Based on the data in Table 1, a comparison between Comparative Example 5 and Example 1 shows that Comparative Example 5, without the addition of carbon nanotubes, has a conductivity of only 0.12 mS·cm⁻¹ and a sensitivity reduced to 0.40. This indicates that carbon nanotubes, as a conductive reinforcing phase, play a decisive role in constructing a three-dimensional permeable network, realizing electron tunneling conduction, and sensing changes in strain-sensitive resistance. The carboxyl groups on their surface form hydrogen / ionic bonds with the polymer network, not only enhancing mechanical properties but also amplifying minute deformations into significant resistance signals under strain through a "disconnect-connect" behavior, which is crucial for achieving high-sensitivity sensing.

[0086] Based on the data in Table 1, a comparison between Comparative Example 6 and Example 1 shows that in Comparative Example 6, when the amount of cellulose powder was excessive, the mechanical properties and sensing sensitivity decreased significantly. This is because excessive cellulose may lead to an overly dense physical network, restricting the mobility of polymer chains and potentially affecting the dispersion of carbon nanotubes and the construction of the conductive network.

[0087] Based on the data in Table 1, a comparison between Comparative Example 7 and Example 1 shows that in Comparative Example 7, when the amount of carboxylated multi-walled carbon nanotubes was excessive, the performance did not continue to improve and even decreased. This is because excessive carbon nanotubes are prone to aggregation, forming local conductive aggregates but disrupting the overall network uniformity. Simultaneously, it may hinder the interaction between polymer chains, leading to a decrease in mechanical properties and interfacial bonding strength.

[0088] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are exhaustively listed. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0089] For those skilled in the art, various modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements are all within the scope of protection of the present invention. The scope of protection of the present invention is defined by the appended claims.

Claims

1. A dual-network ionic gel, characterized in that, The dual-network ionogel comprises acrylamide monomer, crosslinking agent, cellulose powder, carbon nanotubes, ionic liquid, and blue light initiator.

2. The dual-network ionogel according to claim 1, characterized in that, The mass ratio of the acrylamide to the crosslinking agent is (10~100):1; The mass ratio of the acrylamide to the cellulose powder is (10~100):1; The mass ratio of the acrylamide, the carbon nanotubes, and the ionic liquid is 1:(0.001~0.05):(2~5). The mass ratio of the acrylamide to the blue light initiator is (50~200):

1.

3. The dual-network ionogel according to claim 1, characterized in that, The crosslinking agent is at least one of polyethylene glycol diacrylate, N,N'-methylenebisacrylamide, divinylbenzene, glyoxal, dicumyl peroxide, benzoyl peroxide, ethylenediamine, diethylenetriamine, trimethylolpropane-tris(3-aziridinyl)propionate, borax, aluminum chloride, and aluminum sulfate. The ionic liquid is at least one of imidazolium salts, pyridinium salts, quaternary ammonium salts, and quaternary phosphonium salts.

4. The dual-network ionogel according to claim 3, characterized in that, The imidazolium salts are at least one of the following: 1-ethyl-3-methylimidazolium acetate, 1-ethyl-3-methylimidazolium bromide, 1-propyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium bromide, 1-butyl-3-methylimidazolium chloride, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium nitrate, 1-hexyl-3-methylimidazolium hexafluorophosphate, 1-octyl-3-methylimidazolium hexafluorophosphate, 1,1'-ethylene-bis(3-methylimidazolium)dibromophosphate, and 1-(2-hydroxyethyl)-3-methylimidazolium chloride.

5. The dual-network ionogel according to claim 1, characterized in that, The carbon nanotubes are at least one of single-walled carbon nanotubes, multi-walled carbon nanotubes, hydroxylated carbon nanotubes, aminated carbon nanotubes, polymer-grafted carbon nanotubes, non-covalent functionalized carbon nanotubes, or carboxylated carbon nanotubes.

6. The dual-network ionogel according to claim 1, characterized in that, The blue light initiator is at least one of phenyl bis(2,4,6-trimethylbenzoyl)phosphine oxide, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, ethyl(2,4,6-trimethylbenzoyl)phenylphosphinate, camphorquinone, and bis(4-tert-butylphenyl)iodonium hexafluorophosphate.

7. A method for preparing a dual-network ionic gel according to any one of claims 1-6, characterized in that, The preparation method includes the following steps: S1. Add acrylamide monomer, crosslinking agent, cellulose powder, and carbon nanotubes to the ionic liquid, heat and stir to fully disperse the components and obtain a uniform and stable precursor dispersion. S2. Add the blue light initiator to the uniform and stable precursor dispersion obtained in S1, heat and stir under light-protected conditions to completely dissolve and mix it evenly to form a polymerizable precursor solution. S3. Inject the polymerizable precursor solution obtained in step S2 into the mold and irradiate it under a blue light source to complete the polymerization of monomers and the solidification of the gel network. After demolding, a double-network ionic gel is obtained.

8. The method for preparing a dual-network ionic gel according to claim 7, characterized in that, In step S1, the reaction temperature is 30~70℃; In step S2, the reaction temperature is 30~70℃.

9. The method for preparing a dual-network ionic gel according to claim 7, characterized in that, In step S3, the blue light source is 405~460 nanometers, and the irradiation time is 20~60 minutes.

10. A flexible sensor, characterized in that, Includes the dual-network ionogel as described in any one of claims 1-6.

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