Anti-swelling cellulose-based supramolecular ion hydrogel sensing material as well as preparation method and application thereof

Abstract

The invention discloses an anti-swelling cellulose-based supramolecular ion hydrogel sensing material as well as a preparation method and application thereof. The method comprises the following steps: esterifying hydroxypropyl methyl cellulose in ethyl acetate by using acryloyl chloride to obtain hydroxypropyl methyl cellulose acrylate; the preparation method comprises the following steps: dissolving 1-vinyl imidazole and 3-bromopropionic acid in N, N-dimethylformamide to prepare an imidazole ionic liquid; the preparation method comprises the following steps: dissolving hydroxypropyl methyl cellulose acrylate in deionized water, adding imidazole ionic liquid, acrylic acid, N, N-methylene bisacrylamide and ammonium persulfate, and reacting to obtain the anti-swelling cellulose-based supramolecular ionized water gel sensing material. The anti-swelling cellulose-based supramolecular ion hydrogel sensing material prepared by a free radical copolymerization strategy has the characteristics of good strength, flexibility, swelling resistance, freezing resistance, antibacterial property, biocompatibility, high conductivity, high sensitivity and strong environmental adaptability.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of cellulose ion hydrogel composite materials, and particularly relates to an anti-swelling cellulose-based supramolecular ion hydrogel sensing material, a preparation method and application thereof. BACKGROUND

[0002] With the advent of the artificial intelligence era, intelligent wearable devices show broad development prospects in the fields of human-computer interaction, humanoid robots, electronic skin, human motion and health monitoring. At present, traditional materials (such as silicone and synthetic polymers) still have obvious limitations in biodegradability, skin adaptability and other aspects, and it is difficult to meet the dual needs of long-term wear and green environmental protection. In contrast, hydrogel materials based on natural macromolecules, such as cellulose, starch, protein, chitosan and sodium alginate, have gradually become a research hotspot because of their wide sources, environmental friendliness, easy modification and good biocompatibility. However, the existing hydrogel materials still face many challenges in terms of tear resistance, long-term stability and sensing reliability, and breakthroughs in material design and structure control are urgently needed.

[0003] Hydrogel materials based on natural macromolecules (such as cellulose, chitosan, gelatin, and sodium alginate) have attracted extensive attention due to their renewable sources, good biocompatibility, and strong designability. Among them, cellulose and its derivatives, especially hydroxypropyl methyl cellulose (HPMC), are considered as important candidate materials for constructing ideal hydrogel matrices due to their excellent water solubility, renewability, and flexible chemical modifiability. Existing research mainly uses physical blending, nanocomposites (such as adding nanocellulose and clay), or chemical copolymerization / interpenetrating network with synthetic polymers (such as polyacrylamide and polyacrylic acid) to improve the mechanical strength and toughness of pure cellulose hydrogel. At the same time, in order to endow the hydrogel with stable conductive properties, researchers often introduce conductive media such as salt solution, conductive polymer or conductive nanomaterials. In recent years, ionic liquids, as a kind of intrinsically ion-conducting, thermally stable, and low-volatility green solvent and functional additive, have been introduced into the hydrogel system, not only providing efficient ion transport paths, but also improving the mechanical properties and environmental stability of the material through interaction with the polymer network, forming an important research direction of composite conductive hydrogel of ionic liquid and high polymer.

[0004] However, the current cellulose-based ion-conductive hydrogel also faces a series of key problems that have not been solved: the balance between mechanical properties and durability: many strategies to enhance mechanical properties (such as high-density chemical crosslinking) often come at the expense of material flexibility, self-healing ability or biocompatibility; at the same time, the hydrogel network is prone to mechanical property degradation, structure damage or size instability due to water evaporation or excessive water absorption (swelling) in long-term use or humid environment. Lack of environmental adaptability and sensing reliability: ordinary hydrogels are prone to freeze and inactivate at low temperatures, limiting their application in a wide temperature range; in addition, the conductivity and sensing sensitivity of the hydrogel are easily affected by environmental humidity, temperature and its own swelling state, leading to signal drift or instability. Limitation of functional integration: existing material design often focuses on the improvement of one or two properties, lacks systematic consideration and collaborative design of antibacterial, anti-swelling, anti-freezing, high-sensitivity sensing and self-repairing, and is difficult to meet the stringent requirements of intelligent wearable devices for comprehensive performance of materials. SUMMARY

[0005] In order to overcome the above-mentioned shortcomings of the prior art, the purpose of the present application is to provide an anti-swelling cellulose-based supramolecular ion hydrogel sensing material, a preparation method and an application, so as to solve the technical problem of how to construct a wearable sensing material based on cellulose, which can cooperatively realize high strength, high flexibility, anti-swelling, anti-freezing, self-repairing, antibacterial, high conductivity and high sensitivity, so as to meet the comprehensive requirements of long-term stability and reliable monitoring in complex environment.

[0006] In order to achieve the above-mentioned purpose, the present application adopts the following technical solutions: The application discloses a preparation method of an anti-swelling cellulose-based supramolecular ion hydrogel sensing material, comprising the following steps: Step 1, hydroxypropyl methyl cellulose is added into ethyl acetate, stirred and dissolved, then pyridine is added, and acryloyl chloride ethyl acetate solution is slowly added dropwise under stirring, and the reaction is stirred in a dark environment, then ice ethanol is added to terminate the reaction and precipitate the product, and the product is filtered, washed and dried in vacuum to obtain hydroxypropyl methyl cellulose acrylate; Step 2, 1-vinylimidazole and 3-bromopropionic acid are added into N, N-dimethylformamide and stirred and dissolved, then the reaction is heated under a nitrogen atmosphere, and then ethyl acetate is added to precipitate a solid, and the solid is washed and dried to obtain an imidazole ionic liquid; Step 3, the hydroxypropyl methyl cellulose acrylate prepared in step 1 is dissolved in deionized water, then acrylic acid, N, N-methylenebisacrylamide, ammonium persulfate and the imidazole ionic liquid prepared in step 2 are added and stirred and dissolved to obtain a hydrogel precursor, and then the hydrogel precursor is irradiated under ultraviolet light to obtain the anti-swelling cellulose-based supramolecular ion hydrogel sensing material.

[0007] Preferably, in step 1, the mass ratio of the ethyl acetate solution of hydroxypropyl methylcellulose, ethyl acetate, pyridine, acryloyl chloride and icy ethanol is (5~10):(100~200):(0.15~0.3):(0.5~1.2):(50~100).

[0008] Preferably, in step 1, the stirring reaction conditions include: stirring at 45~55 °C for 3~5 h; washing the product with ice-cold ethanol; and drying conditions include: drying at 40~50 °C for 12~24 h.

[0009] Preferably, in step 1, the viscosity of the hydroxypropyl methylcellulose is in the range of 1.8 × 10⁻⁶. 5 ~2.2×10 5 mPa·s, average molecular weight 3.0×10 5 Da, with a methoxy degree of substitution of 1.8 to 2.0 and a hydroxypropoxy molar degree of substitution of 0.2 to 0.3; the degree of esterification of hydroxypropyl methylcellulose acrylate is 1.0% to 3.0%; hydroxypropyl methylcellulose acrylate should be stored away from air.

[0010] Preferably, in step 2, the mass ratio of 1-vinylimidazole, 3-bromopropionic acid, N,N-dimethylformamide and ethyl acetate is (0.5~2.5):(0.65~3.8):(10~60):(20~60).

[0011] Preferably, in step 2, the heating reaction conditions include: heating at 55~70℃ for 24~30 h; washing the product with ethyl acetate; and drying conditions include: vacuum drying at 40~50℃ for 12~24 h; and storing the product in an air-isolated environment with imidazole ionic liquid.

[0012] Preferably, in step 3, the mass ratio of hydroxypropyl methylcellulose acrylate, deionized water, acrylic acid, N,N-methylenebisacrylamide, ammonium persulfate and imidazole ionic liquid is (0.5~2.5):(150~160):(40~50):(0.2~0.3):(0.1~0.2):(0.5~2.5).

[0013] Preferably, in step 3, the irradiation time under ultraviolet light is 1~2 hours.

[0014] This invention discloses a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material, which is prepared by the above-mentioned method for preparing the swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material.

[0015] This invention discloses the application of the above-mentioned method for preparing anti-swelling cellulose-based supramolecular ionic hydrogel sensing materials in the preparation of wearable human devices or underwater stress-strain sensing materials.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This invention discloses a method for preparing an anti-swelling cellulose-based supramolecular ionic hydrogel sensing material. First, hydroxypropyl methylcellulose (HMC) is esterified and modified using acryloyl chloride as a modifier to selectively replace the hydroxyl groups in the hydroxymethyl group on the glucose ring, introducing polymerizable acrylate groups to synthesize HMC methylcellulose acrylate. Subsequently, the prepared HMC methylcellulose acrylate is composited with an imidazole ionic liquid and acrylic monomers, and a one-step free radical copolymerization reaction is performed to construct a structurally stable ternary copolymer ionic conductive hydrogel. The unique feature of this hydrogel lies in the stable cross-linked network structure formed by multiple interactions between functional groups such as hydroxyl and carboxyl groups through intermolecular forces, hydrogen bonds, ionic bonds, and covalent bonds. This cross-linked network not only enhances the mechanical strength and flexibility of the hydrogel but also provides reliable performance in complex application environments, ensuring its effectiveness and stability as an ionic hydrogel sensing material. By using chemical modification and supramolecular strategies, a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material with good mechanical strength, flexibility, swelling resistance, freeze resistance, antibacterial properties, biocompatibility, high conductivity, high sensitivity, and strong environmental adaptability can be prepared. This material can be used as a wearable and underwater stress-strain sensing material.

[0017] Furthermore, the mass ratio of ethyl acetate solution of hydroxypropyl methylcellulose, ethyl acetate, pyridine, acryloyl chloride, and glacial ethanol is (5~10):(100~200):(0.15~0.3):(0.5~1.2):(50~100). This ensures sufficient contact and reaction between acryloyl chloride and cellulose hydroxyl groups, while avoiding side reactions caused by excessively high local concentrations. This is a prerequisite for obtaining high-quality hydroxypropyl methylcellulose acrylate with controllable esterification degree and preserved double bond activity, ensuring the uniformity and mechanical properties of the final hydrogel network structure.

[0018] Furthermore, the moderate temperature and sufficient time ensured that the substitution reaction proceeded fully and uniformly, avoiding the degradation of cellulose or deactivation of double bonds that could occur due to high temperatures. Washing with ice-cold ethanol effectively removed unreacted acryloyl chloride, pyridine catalyst, and its salts, while the low temperature helped prevent the product from sticking or polymerizing during the washing process. Mild vacuum drying conditions thoroughly removed the solvent, yielding a dry, loose solid product, and avoiding the damage that high temperatures might cause to ester and double bonds, thus ensuring the stability and reactivity of the intermediate.

[0019] Furthermore, the specific specifications of cellulose raw materials possess suitable solubility, which is beneficial for subsequent homogeneous modification and for effectively reinforcing and toughening the network. Controlling the degree of esterification between 1.0% and 3.0% balances the introduction of sufficient polymerizable sites to strengthen the network with maintaining the good hydrophilicity and biocompatibility of cellulose itself. The requirement for air-isolated storage effectively prevents the prepolymerization or decomposition of acrylate double bonds in the product during storage due to light or oxygen, ensuring the consistency and reliability of its activity when used for subsequent copolymerization.

[0020] Furthermore, the mass ratio of 1-vinylimidazole, 3-bromopropionic acid, N,N-dimethylformamide, and ethyl acetate is (0.5~2.5):(0.65~3.8):(10~60):(20~60); this ensures the complete quaternization reaction and the acquisition of high-purity target ionic liquid monomers, thereby ensuring the continuity of ionic conductive pathways and the density of the dynamic cross-linking network in the final hydrogel.

[0021] Furthermore, the combination of a reaction time of 24–30 h and a temperature of 55–70 °C ensures the complete completion of the nucleophilic substitution reaction of quaternization, resulting in a product with high conversion. Washing with ethyl acetate effectively removes unreacted starting materials and low-polarity byproducts. Vacuum drying thoroughly removes residual volatile solvents and moisture at a relatively low temperature, yielding a pure, dry ionic liquid. Storage in the absence of air prevents the ionic liquid from absorbing moisture or undergoing other changes, maintaining its chemical stability and reactivity.

[0022] Furthermore, the mass ratio of hydroxypropyl methylcellulose acrylate, deionized water, acrylic acid, N,N-methylenebisacrylamide, ammonium persulfate, and imidazole ionic liquid is (0.5~2.5):(150~160):(40~50):(0.2~0.3):(0.1~0.2):(0.5~2.5). The proportion of each monomer determines the crosslinking density and segment length of the covalent crosslinking network, directly affecting the strength, toughness, and elasticity of the material. The ratio of cellulose derivative, ionic liquid, and acrylic acid jointly affects the hydrophilic and hydrophobic properties of the network. A dense network containing hydrophobic association can effectively limit water intrusion, which is key to achieving a low swelling rate (11.5%~13.5%). The amount of ionic liquid directly affects the concentration of mobile ions in the material (affecting conductivity), the dynamic ionic bond density (affecting self-healing and freeze resistance), and the number of antibacterial groups. This optimized ratio enables the synergistic achievement of multiple excellent properties such as high mechanical properties, low swelling, high conductivity, self-healing, and freeze resistance.

[0023] Furthermore, the irradiation time under ultraviolet light is 1-2 hours to ensure complete polymerization of the hydrogel precursor, forming a uniform and stable three-dimensional network structure. Too short a time may lead to incomplete polymerization, resulting in unreacted monomers or structurally defective networks, thus weakening the material's mechanical strength and stability; too long a time may cause excessive cross-linking or partial chain segment degradation, impairing the material's flexibility and elasticity. This time range ensures that all polymerizable double bonds (from cellulose acrylate, ionic liquids, and acrylic acid) fully react under the action of the initiator, constructing a complete and uniform covalent network framework, ensuring the long-term stability and reproducible performance of the hydrogel.

[0024] The swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material disclosed in this invention possesses excellent mechanical properties and flexibility. These enhanced properties are attributed to multiple interactions within the hydrogel, including the synergistic effects of intermolecular forces, hydrogen bonds, ionic bonds, and covalent bonds. This not only strengthens the overall strength of the material but also significantly improves its flexibility. Specifically, the tensile strength is 0.44–0.52 MPa, and the elongation at break is 753%–855%, exhibiting excellent ductility and good pressure-bearing capacity. These properties allow the hydrogel to effectively adapt to various complex movements of the human body, possessing good flexibility and deformation resistance, thus preventing cracking and deformation. The interwoven cross-linked network structure improves the hydrogel's resistance to puncture, tearing, and shearing, ensuring stability and durability during long-term wear. Furthermore, the supramolecular network structure of the hydrogel endows it with strong resistance to puncture, tearing, and shearing. This unique network structure acts like a tightly woven protective net, effectively resisting various external damages. During long-term wear, it ensures the integrity and stability of the material. The material is not easily damaged by daily friction and collisions, thus effectively extending its service life. The prepared anti-swelling cellulose-based supramolecular ionic hydrogel sensing material exhibits excellent anti-swelling properties. Physical cross-linking and hydrophobic association occur between esterified cellulose, imidazole ionic liquid, and acrylic acid segments, forming a dense three-dimensional network structure. This restricts the penetration of water molecules and excessive extension of chain segments, effectively reducing the volume expansion of the hydrogel after water absorption. The swelling rate of the hydrogel in water is 11.5%~13.5%. The prepared anti-swelling cellulose-based supramolecular ionic hydrogel sensing material also exhibits excellent self-healing properties. The three-dimensional network structure in these hydrogels mainly achieves its self-healing mechanism through reversible ionic pairing between imidazole cations in the imidazole ionic liquid and carboxyl groups in acrylic acid, as well as the formation of numerous reversible hydrogen bonds between esterified cellulose segments. Simultaneously, water molecules mediate and promote the synergistic reconstruction of short-range segment interpenetration and physical entanglement, effectively repairing cracks and defects. After 200 minutes of healing, the stress self-healing efficiency of the hydrogel reached 90%–94%. The prepared anti-swelling cellulose-based supramolecular ionic hydrogel sensing material exhibited good antifreeze and antibacterial properties. In the imidazole ionic liquid, the imidazole onium cation, bromide anion, and carboxylic acid anion formed a strong coordination-hydration layer with water molecules through ion-dipole / electrostatic interactions and numerous hydrogen bonds. These bound water / strongly coordinated water molecules reduced the proportion of "crystallizable free water," disrupting ice nucleus formation and lattice growth, thereby significantly lowering the freezing point of the system. The freezing and freezing temperature range was -28.5°C to -32.4°C, with a minimum of -32.4°C.Meanwhile, the positively charged imidazolium groups in the hydrogel sensing material exhibit significant inhibitory effects on various pathogenic bacteria, with an inhibition rate of 83%–92% against Staphylococcus aureus and 85%–89% against Escherichia coli, increasing the safety and durability of the hydrogel sensing material. This synergistic effect of antifreeze and antibacterial properties enhances the material's application potential in wearable devices, providing strong support for long-term stable monitoring and health protection under extreme temperature environments. The prepared anti-swelling cellulose-based supramolecular ionic hydrogel sensing material exhibits excellent high conductivity and high sensitivity. The efficient dispersion and synergistic effect of imidazolium cation / bromine anion pairs and carboxylic acid anions in the polymer network significantly increases the density of ion transport channels within the hydrogel and optimizes the continuous path of charge migration, improving the high conductivity and high sensitivity of the wearable hydrogel sensing material. The conductivity is 5.32–5.62 S / m, and the sensing sensitivity at 400%–500% strain is 6.89–7.47.

[0025] This invention discloses the application of a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material in the preparation of wearable devices or underwater stress-strain sensing materials. The swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material is environmentally friendly, low-cost, and highly practical. Using water-soluble cellulose as the base raw material not only ensures its abundance and easy degradation, reducing environmental pollution, but also offers advantages such as convenient processing and simple preparation techniques. The swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material has a wide range of applications, strong practicality, and promising prospects. Due to its mechanical strength, flexibility, swelling resistance, freeze resistance, antibacterial properties, and biocompatibility, along with high conductivity, high sensitivity, and broad environmental adaptability, it is suitable as a sensing material for various intelligent wearable devices, such as biosensors, flexible electrodes, and smart medical patches, and can respond to mechanical stimuli in real time. Attached Figure Description

[0026] Figure 1 A schematic diagram of the interwoven cross-linked network structure in an anti-swelling cellulose-based supramolecular ionic hydrogel sensing material; Figure 2 A schematic diagram of the preparation process of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material; wherein, (1) is a schematic diagram of the preparation process of imidazole ionic liquid; (2) is a schematic diagram of the preparation process of hydroxypropyl methylcellulose acrylate; and (3) is a schematic diagram of the preparation process of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material. Figure 3 Scanning electron microscope (SEM) image (a) of the hydrogel prepared in Comparative Example 1 and SEM image (b) of the swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3. Figure 4Photographs of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3, in its original state (left) and under tension (right); Figure 5 Photographs of the hydrogel prepared in the original state (a1) and the expanded state (a2) of Example 1; and photographs of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3 in the original state (b1) and the expanded state (b2). Figure 6 These are photographs of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3 before (left) and after (right) self-healing. Figure 7 The images show the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3, with LED lights lit at room temperature (left) and -20°C (right). Figure 8 The image shows the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3, with an LED lit underwater in its original (left) and stretched (right) states. Detailed Implementation

[0027] The technical solution of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise specified, all embodiments and preferred embodiments mentioned herein can be combined to form new technical solutions.

[0029] Unless otherwise specified, all the technical features and preferred features mentioned herein can be combined to form new technical solutions.

[0030] In this invention, unless otherwise specified, percentage (%) or parts refer to weight percentage or parts relative to the composition.

[0031] Unless otherwise specified, the components or preferred components involved in this invention can be combined with each other to form new technical solutions.

[0032] In this invention, unless otherwise specified, the numerical range "a~b" represents an abbreviation of any combination of real numbers between a and b, where a and b are both real numbers. For example, the numerical range "6~22" means that all real numbers between "6~22" have been listed in this document, and "6~22" is just an abbreviation of these numerical combinations.

[0033] The "scope" disclosed in this invention can be in the form of a lower limit and an upper limit, and can be one or more lower limits and one or more upper limits, respectively.

[0034] In this invention, the term "and / or" as used herein refers to any combination of one or more of the associated listed items, as well as all possible combinations, and includes such combinations.

[0035] In this invention, unless otherwise stated, the various reaction or operation steps may be performed sequentially or in a particular order. Preferably, the reaction methods described herein are performed sequentially.

[0036] Unless otherwise stated, the technical and scientific terms used herein have the same meanings as those familiar to those skilled in the art. Furthermore, any methods or materials similar to or equivalent to those described herein may also be used in this invention.

[0037] This invention provides a method for preparing and applying an anti-swelling cellulose-based supramolecular ionic hydrogel sensing material, comprising the following steps: Step 1: By weight, add 5-10 parts of hydroxypropyl methylcellulose to 100-200 parts of ethyl acetate, stir to dissolve, then add 0.15-0.3 parts of pyridine, and continue stirring for 15 min to precatalyze the hydroxypropyl methylcellulose. Stir and slowly add 0.5-1.2 parts of a 5%-7% (w / w) ethyl acetate solution of acryloyl chloride, and stir at 45-55 °C for 3-5 h in a light-protected environment. Add 50-100 parts of ice-cold ethanol to terminate the reaction and precipitate the product. Vacuum filter to obtain a white solid, wash the product three times with 100-200 parts of ice-cold ethanol, and then dry in a forced-air condition at 40-50 °C for 12-24 h to obtain hydroxypropyl methylcellulose acrylate. Step 2: Dissolve 0.5-2.5 parts by mass of 1-vinylimidazole and 0.65-3.8 parts by mass of 3-bromopropionic acid in 10-60 parts by mass of N,N-dimethylformamide and stir until dissolved. Heat the mixture to 55-70 °C under a nitrogen atmosphere and react for 24-30 h. Add 20-60 parts by mass of ethyl acetate to precipitate a solid. Wash the solid three times with 60-100 parts by mass of ethyl acetate. Dry the solid under vacuum at 40-50 °C for 12-24 h to obtain imidazole and an ionic liquid. Step 3: Dissolve 0.5-2.5 parts by weight of hydroxypropyl methylcellulose acrylate in 150-160 parts of deionized water, then add 0.5-2.5 parts of imidazole ionic liquid, 40-50 parts of acrylic acid, 0.2-0.3 parts of N,N-methylenebisacrylamide and 0.1-0.2 parts of ammonium persulfate, and continue stirring to dissolve to obtain a hydrogel precursor. Irradiate under ultraviolet light for 1-2 hours to obtain a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material.

[0038] The viscosity range of the hydroxypropyl methylcellulose in Examples 1-6 is 1.8~2.2×10⁻⁶. 5 mPa·s, average molecular weight 3.0×10 5 Da has a methoxy degree of substitution of 1.8 to 2.0 and a hydroxypropoxy molar degree of substitution of 0.2 to 0.3.

[0039] The degree of esterification of hydroxypropyl methylcellulose acrylate in Examples 1-6 is 1.0% to 3.0%.

[0040] The hydroxypropyl methylcellulose acrylate and imidazole ionic liquid in Examples 1-6 should be stored in an air-free environment.

[0041] All chemical reagents in Examples 1-6 were analytical grade with a purity of 99%.

[0042] The present invention discloses a cellulose-based supramolecular ionic hydrogel. The prepared hydrogel has good mechanical strength, flexibility, anti-swelling, antifreeze, antibacterial, biocompatibility, high conductivity, high sensitivity and strong environmental adaptability, and can be used as a wearable and underwater stress-strain sensing material.

[0043] Ionic liquids, as a novel functional medium, possess intrinsic ionic conductivity, excellent thermal stability, and highly tunable physicochemical properties, demonstrating unique advantages in constructing high-performance flexible conductors. In recent years, researchers have introduced them as multifunctional additives into cellulose-based hydrogel systems, providing stable and efficient ion transport channels while maintaining good electrical performance over a wide temperature range. This synergistic combination of natural polymers and functional ionic liquids not only aligns with the principles of green and intensive material development but also opens up promising research avenues for developing next-generation wearable sensing materials with high environmental adaptability and multifunctional integration.

[0044] Therefore, this invention uses hydroxypropyl methylcellulose as a matrix and first modifies it by esterification with acryloyl chloride to obtain polymerizable hydroxypropyl methylcellulose acrylate. Then, it is successfully constructed into a ternary copolymer ionic conductive hydrogel by one-step free radical polymerization with imidazole ionic liquid and acrylic acid. This hydrogel exhibits excellent mechanical strength, flexibility, anti-swelling properties, antifreeze properties, antibacterial properties, and biocompatibility, while also possessing high conductivity, high sensitivity, and broad environmental adaptability, aiming to meet the urgent need for high-performance flexible sensing materials in complex application environments. Further modification of cellulose through physical or chemical crosslinking to enhance its structure and integrate its functions is expected to significantly improve its overall performance and expand its application potential in the field of flexible sensing.

[0045] This invention introduces polymerizable carbon-carbon double bonds through selective acrylylation of hydroxypropyl methylcellulose. This allows the originally non-polymerizable natural polymer to participate as a macromonomer in subsequent free radical copolymerization reactions, forming the basis for a stable and uniform three-dimensional cross-linked network structure. Instead of directly using commercial products, a specific structure of imidazole ionic liquid (1-vinyl-3-carboxypropylimidazolium bromide) was synthesized in-house. This ensures that both ends of the ionic liquid monomer contain polymerizable vinyl groups and carboxyl groups capable of forming ionic interactions, enabling it to chemically bond to the polymer network as a multifunctional cross-linking agent and conductive medium. This is the core of achieving the material's antifreeze, antibacterial, high conductivity, and self-healing properties. Modified cellulose, functional ionic liquid, and acrylic monomers are copolymerized in one step via UV initiation. This method is simple and efficient, directly forming a ternary interpenetrating network in the aqueous phase with a covalent backbone and various supramolecular interactions such as hydrogen bonds and ionic bonds. This unique synergistic network of covalent bonds and supramolecular interactions is the fundamental reason for the excellent mechanical properties, environmental stability, and intelligent responsiveness of the hydrogel.

[0046] This invention ensures the full and controllable execution of the cellulose esterification reaction in step 1 and the ionic liquid synthesis reaction in step 2 by specifying the reactant ratio (such as the ratio of hydroxypropyl methylcellulose to acryloyl chloride), reaction temperature, time, and washing and drying conditions. This results in obtaining a key intermediate with moderate esterification degree and high purity, laying the foundation for the uniformity and reproducibility of the final hydrogel properties.

[0047] By limiting the viscosity, molecular weight, and degree of substitution of hydroxypropyl methylcellulose, its good solubility and modifiability were ensured, thereby obtaining cellulose acrylates with ideal grafting density and network structure. Specifying the esterification range of the intermediates and storing them in an air-isolated environment prevented premature decomposition or polymerization of double bonds, ensuring subsequent copolymerization activity.

[0048] Optimizing the mass ratio of each component in the hydrogel precursor directly determines key factors such as the covalent crosslinking density, ionic interaction strength, and hydrophilicity-hydrophobicity balance of the final polymer network. This is crucial for achieving the optimal balance between seemingly contradictory properties such as high strength, high elongation, low swelling, and high conductivity in the material.

[0049] A UV irradiation time of 1-2 hours ensures that the monomers are fully polymerized to form a complete and uniform network structure, avoiding weak mechanical properties or uneven performance due to incomplete polymerization.

[0050] The anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared by this invention has excellent mechanical properties (high strength, high toughness, tear resistance), significantly low swelling (swelling rate in water is only 11.5%~13.5%), high self-healing ability (stress self-healing efficiency >90%), excellent environmental adaptability (freezing temperature -28.5℃~-32.4℃, broad-spectrum antibacterial properties), and high ionic conductivity (5.32~5.62 S / m) and strain sensitivity (GF: 6.89~7.47).

[0051] The swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material prepared by this invention possesses excellent flexibility, biocompatibility, swelling resistance, freeze resistance, and antibacterial properties, enabling its reliable application in wearable devices (such as flexible sensors and electronic skin) and underwater sensing fields with extremely demanding material requirements. This demonstrates the practical value and broad prospects of the material from an application perspective, solving the technical challenges of traditional hydrogels such as easy swelling, freezing, mechanical failure, and bacterial growth in complex, humid, or low-temperature environments.

[0052] This invention designs and prepares two key intermediates, hydroxypropyl methylcellulose acrylate and a bifunctional imidazole ionic liquid, and successfully constructs a swelling-resistant cellulose-based ionic hydrogel with both covalent network and multiple supramolecular interactions using a one-step UV copolymerization method. This method utilizes environmentally friendly raw materials and is simple to implement. The resulting hydrogel material achieves an excellent balance and synergy of multiple properties; it possesses high strength, high elongation, and puncture resistance; extremely low water swelling rate; high self-healing ability; excellent antifreeze and antibacterial properties; and high ionic conductivity and strain sensitivity. This comprehensive combination of properties enables its stable and reliable application in wearable devices and underwater environments, demonstrating great application potential as a high-performance stress-strain sensing material in flexible electronics, health monitoring, and human-computer interaction.

[0053] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. The components of the embodiments of the present invention described and shown in the accompanying drawings can generally be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the claimed invention, but merely to illustrate selected embodiments of the invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort are within the scope of protection of the present invention.

[0054] Example 1 Step 1: By weight, 5 parts of hydroxypropyl methylcellulose were added to 100 parts of ethyl acetate. After stirring and dissolving, 0.15 parts of pyridine were added, and stirring was continued for 15 min to precatalyze the hydroxypropyl methylcellulose. Then, 0.5 parts of a 5% (w / w) ethyl acetate solution of acryloyl chloride were slowly added dropwise. The mixture was stirred at 45 °C for 3 h in the dark. The reaction was terminated by adding 50 parts of ice-cold ethanol, and the product precipitated. The product was obtained by vacuum filtration and washed three times with 100 parts of ice-cold ethanol. Finally, the product was dried at 40 °C for 12 h to obtain hydroxypropyl methylcellulose acrylate. Step 2: Dissolve 0.5 parts of 1-vinylimidazole and 0.65 parts of 3-bromopropionic acid in 10 parts of N,N-dimethylformamide by mass and stir until dissolved. Heat to 55 °C for 24 h under nitrogen atmosphere. Add 20 parts of ethyl acetate to precipitate solid. Wash the solid three times with 60 parts of ethyl acetate. Dry under vacuum at 40 °C for 12 h to obtain imidazole ionic liquid. Step 3: Dissolve 0.5 parts by weight of hydroxypropyl methylcellulose acrylate in 150 parts of deionized water, then add 0.5 parts of imidazole ionic liquid, 40 parts of acrylic acid, 0.2 parts of N,N-methylenebisacrylamide and 0.1 parts of ammonium persulfate, and continue stirring to dissolve to obtain a hydrogel precursor. Irradiate under ultraviolet light for 1.0 h to obtain a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material.

[0055] Example 2 Step 1: By mass, 6 parts of hydroxypropyl methylcellulose were added to 120 parts of ethyl acetate. After stirring and dissolving, 0.18 parts of pyridine were added, and stirring was continued for 15 min to precatalyze the hydroxypropyl methylcellulose. Then, 0.6 parts of a 6% (w / w) ethyl acetate solution of acryloyl chloride were slowly added dropwise. The mixture was stirred at 50 °C for 4 h in the dark. The reaction was terminated by adding 60 parts of ice-cold ethanol, and the product precipitated. The product was obtained by vacuum filtration and washed three times with 120 parts of ice-cold ethanol. Finally, the product was dried at 45 °C for 16 h to obtain hydroxypropyl methylcellulose acrylate. Step 2: Dissolve 1.0 part of 1-vinylimidazolium and 1.3 parts of 3-bromopropionic acid in 20 parts of N,N-dimethylformamide by mass and stir until dissolved. Heat to 60 °C for 28 h under nitrogen atmosphere. Add 30 parts of ethyl acetate to precipitate solid. Wash the solid three times with 70 parts of ethyl acetate. Dry under vacuum at 45 °C for 16 h to obtain imidazolium ionic liquid. Step 3: Dissolve 1.0 part by weight of hydroxypropyl methylcellulose acrylate in 160 parts of deionized water, then add 0.8 parts of imidazole ionic liquid, 45 parts of acrylic acid, 0.25 parts of N,N-methylenebisacrylamide and 0.15 parts of ammonium persulfate, and continue stirring to dissolve to obtain a hydrogel precursor. Irradiate under ultraviolet light for 1.5 h to obtain a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material.

[0056] Example 3 Step 1: By mass, 7 parts of hydroxypropyl methylcellulose were added to 140 parts of ethyl acetate, stirred and dissolved, and then 0.22 parts of pyridine were added. The mixture was stirred for 15 min to precatalyze the hydroxypropyl methylcellulose. 0.75 parts of a 5% acryloyl chloride / ethyl acetate solution were added dropwise while stirring. The mixture was stirred at 55 °C for 4.5 h in the dark. 70 parts of ice-cold ethanol were added to terminate the reaction and precipitate the product. The product was obtained by vacuum filtration and washed three times with 160 parts of ice-cold ethanol. The product was then dried at 45 °C for 18 h to obtain hydroxypropyl methylcellulose acrylate. Step 2: Dissolve 1.5 parts of 1-vinylimidazolium and 2.0 parts of 3-bromopropionic acid in 30 parts of N,N-dimethylformamide by mass and stir until dissolved. Heat to 60 °C for 26 h under nitrogen atmosphere, add 40 parts of ethyl acetate to precipitate solid, wash the solid three times with 80 parts of ethyl acetate, and dry under vacuum at 45 °C for 20 h to obtain imidazolium ionic liquid; Step 3: Dissolve 1.5 parts by weight of hydroxypropyl methylcellulose acrylate in 150 parts of deionized water, then add 1.5 parts of imidazole ionic liquid, 45 parts of acrylic acid, 0.3 parts of N,N-methylenebisacrylamide and 0.15 parts of ammonium persulfate, stir to dissolve and obtain hydrogel precursor, and irradiate under ultraviolet light for 2 h to obtain swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material.

[0057] Example 4 Step 1: By mass, 8 parts of hydroxypropyl methylcellulose were added to 160 parts of ethyl acetate, stirred and dissolved, and then 0.26 parts of pyridine were added. The mixture was stirred for 15 min to precatalyze the hydroxypropyl methylcellulose. 0.9 parts of 7% acryloyl chloride / ethyl acetate solution were added dropwise while stirring. The mixture was stirred at 50 °C for 5 h in the dark. 80 parts of ice-cold ethanol were added to terminate the reaction and precipitate the product. The product was obtained by vacuum filtration and washed three times with 180 parts of ice-cold ethanol. The product was then dried at 45 °C for 20 h to obtain hydroxypropyl methylcellulose acrylate. Step 2: Dissolve 2.0 parts of 1-vinylimidazolium and 2.6 parts of 3-bromopropionic acid in 50 parts of N,N-dimethylformamide by mass and stir until dissolved. Heat to 60 °C for 24 h under nitrogen atmosphere, add 55 parts of ethyl acetate to precipitate solid, wash the solid three times with 90 parts of ethyl acetate, and dry under vacuum at 45 °C for 19 h to obtain imidazolium ionic liquid; Step 3: Dissolve 2.0 parts by weight of hydroxypropyl methylcellulose acrylate in 150 parts of deionized water, add 2.0 parts of imidazole ionic liquid, add 40 parts of acrylic acid and stir to dissolve, then add 0.2 parts of N,N-methylenebisacrylamide and 0.15 parts of ammonium persulfate, and continue stirring to dissolve to obtain a hydrogel precursor. Irradiate under ultraviolet light for 2.0 h to obtain a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material.

[0058] Example 5 Step 1: By mass, 9 parts of hydroxypropyl methylcellulose were added to 180 parts of ethyl acetate, stirred and dissolved, and then 0.28 parts of pyridine were added. The mixture was stirred for 15 min to precatalyze the hydroxypropyl methylcellulose. 1.0 part of a 7% acryloyl chloride / ethyl acetate solution was added dropwise while stirring. The mixture was stirred at 55 °C for 5 h in the dark. 90 parts of ice-cold ethanol were added to terminate the reaction and precipitate the product. The product was obtained by vacuum filtration and washed three times with 190 parts of ice-cold ethanol. Then, the product was dried at 50 °C for 24 h to obtain hydroxypropyl methylcellulose acrylate. Step 2: Dissolve 2.3 parts by mass of 1-vinylimidazolium and 3.3 parts by mass of 3-bromopropionic acid in 55 parts by mass of N,N-dimethylformamide and stir until dissolved. Heat to 65 °C for 28 h under nitrogen atmosphere, add 55 parts by mass of ethyl acetate to precipitate solid, wash the solid three times with 90 parts by mass of ethyl acetate, and dry under vacuum at 45 °C for 22 h to obtain imidazolium ionic liquid; Step 3: Dissolve 2.3 parts by weight of hydroxypropyl methylcellulose acrylate in 150 parts of deionized water, then add 2.2 parts of imidazole ionic liquid, 40 parts of acrylic acid, 0.25 parts of N,N-methylenebisacrylamide and 0.20 parts of ammonium persulfate, stir to dissolve and obtain hydrogel precursor, and irradiate under ultraviolet light for 2.0 h to obtain swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material.

[0059] Example 6 Step 1: By mass, add 10 parts of hydroxypropyl methylcellulose to 200 parts of ethyl acetate, stir to dissolve, then add 0.3 parts of pyridine, and continue stirring for 15 min to precatalyze the hydroxypropyl methylcellulose. Stir and slowly add 1.2 parts of 7% acryloyl chloride / ethyl acetate solution, stir at 55 °C for 5 h in the dark, add 100 parts of ice-cold ethanol to terminate the reaction and precipitate the product, filter under vacuum to obtain a white solid, wash the product three times with 200 parts of ice-cold ethanol, and then dry at 50 °C for 24 h to obtain hydroxypropyl methylcellulose acrylate; Step 2: Dissolve 2.5 parts by mass of 1-vinylimidazolium and 3.8 parts by mass of 3-bromopropionic acid in 60 parts by mass of N,N-dimethylformamide and stir until dissolved. Heat to 70 °C under nitrogen atmosphere and react for 30 h. Add 60 parts by mass of ethyl acetate to precipitate solid. Wash the solid three times with 100 parts by mass of ethyl acetate. Dry under vacuum at 50 °C for 24 h to obtain imidazolium ionic liquid. Step 3: Dissolve 2.5 parts by weight of hydroxypropyl methylcellulose acrylate in 160 parts of deionized water, then add 2.5 parts of imidazole ionic liquid, 50 parts of acrylic acid, 0.3 parts of N,N-methylenebisacrylamide and 0.2 parts of ammonium persulfate, and continue stirring to dissolve to obtain a hydrogel precursor. Irradiate under ultraviolet light for 2.0 h to obtain a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material.

[0060] Comparison Example Comparative Example 1 and Comparative Example 2 are hydrogels without hydroxypropyl methylcellulose acrylate and hydrogels without imidazole ionic liquid, respectively, prepared according to step (3) of the methods in Example 3 and Example 5.

[0061] The performance of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing materials prepared in Examples 1 to 6 was tested. At the same time, the performance parameters of Control Example 1 and Control Example 2 were also tested. The results are shown in Table 1.

[0062] Table 1. Comparison of performance parameters of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing materials prepared in Examples 1-6 and the hydrogels prepared in Comparative Examples 1 and 2.

[0063] Table 1 compares the performance parameters of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing materials prepared in Examples 1-6 with those of the hydrogels prepared in Control Examples 1 and 2. As can be seen from Table 1, the anti-swelling cellulose-based supramolecular ionic hydrogels prepared in Examples 1-6 have a tensile strength of 0.44-0.52 MPa, a fracture strain of 753%-855%, an electrical conductivity of 5.32-5.62 S / m, a sensing sensitivity of 6.89-7.47, a freeze-thaw temperature range of -28.5°C to -32.4°C, an inhibition rate of 83%-92% against Staphylococcus aureus, an inhibition rate of 85%-89% against Escherichia coli, and a swelling rate of 11.5-13.5%. In contrast, the tensile strengths of Control Examples 1 and 2, which do not contain hydroxypropyl methylcellulose acrylate hydrogel and imidazole ionic liquid, were 0.12 MPa and 0.07 MPa, respectively; the fracture strains were 363% and 49%, respectively; the electrical conductivity was 3.21 S / m and 0.34 S / m, respectively; the sensitivities were 3.24 and 1.2, respectively; the inhibition rates against Staphylococcus aureus were 13% and 0.6%, respectively; the inhibition rates against Escherichia coli were 14% and 0.44%, respectively; and the swelling ratios were 1573%–845%. The performance parameters in the examples are significantly better than those in the control group. This is because the hydrogels prepared in Examples 1-6 are composed of hydroxypropyl methylcellulose acrylate hydrogel, imidazole ionic liquid, and acrylic acid and N,N-methylenebisacrylamide crosslinked polymer, which have an interwoven crosslinked structure. The molecular chains contain imidazole cations, hydroxyl groups, ester groups, etc., which can form intermolecular forces, hydrogen bonds, ionic bonds, etc., leading to the formation of a supramolecular network structure between the hydroxypropyl methylcellulose acrylate hydrogel, imidazole ionic liquid and acrylic acid molecular chains. This synergistically improves the mechanical properties, conductivity, high sensitivity, biocompatibility and antibacterial properties of the hydrogel.

[0064] Figure 1 This diagram illustrates the interwoven cross-linked network structure in an anti-swelling cellulose-based supramolecular ionic hydrogel sensing material. As shown, the prepared hydrogel is composed of hydroxypropyl methylcellulose acrylate, imidazole ionic liquid, and a cross-linked polymer formed by acrylic acid and N,N-methylenebisacrylamide. Its structure is a supramolecular network structure, with molecular chains containing imidazole cations, hydroxyl groups, carboxyl groups, and oxygen ether bonds. These bonds interact through intermolecular forces, hydrogen bonds, and ionic bonds to form an interwoven cross-linked network structure, thus laying the foundation for the prepared hydrogel with excellent mechanical strength, flexibility, anti-swelling properties, antifreeze properties, antibacterial properties, high conductivity, and high sensitivity.

[0065] Figure 2This is a schematic diagram of the preparation process of an anti-swelling cellulose-based supramolecular ionic hydrogel sensing material. (1) is a schematic diagram of the preparation process of an imidazole ionic liquid; (2) is a schematic diagram of the preparation process of hydroxypropyl methylcellulose acrylate; (3) is a schematic diagram of the preparation process of an anti-swelling cellulose-based supramolecular ionic hydrogel sensing material. From (1), it can be seen that the quaternization reaction of 1-vinylimidazolium and 3-bromopropionic acid to prepare an imidazole ionic liquid results in an imidazole cation in its structure, which can impart antibacterial properties, conductivity, and enhance intermolecular interactions to the hydrogel. From (2), it can be seen that hydroxypropyl methylcellulose is esterified with acryloyl chloride to form polymerizable hydroxypropyl methylcellulose acrylate. As can be seen from (3), the hydrogel is composed of hydroxypropyl methylcellulose acrylate, imidazole ionic liquid and acrylic acid and N,N-methylenebisacrylamide crosslinked polymer. The hydrogel molecule contains carboxyl groups, hydroxyl groups, ester groups, imidazole cations, bromide anions, oxygen ether bonds, etc. They can form a supramolecular network structure through intermolecular forces, hydrogen bonds, ionic bonds, etc., providing a reliable ionic hydrogel sensing material for wearable sensing in multiple scenarios.

[0066] Figure 3 Scanning electron microscope (SEM) images (a) of the hydrogel prepared in Comparative Example 1 and (b) of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3 are shown. (a) shows the hydrogel prepared in Comparative Example 1, exhibiting a relatively dense microstructure without pores. (b) shows the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3, revealing a porous microstructure. These pores serve as ion transport channels within the hydrogel, contributing to its superior sensing performance. The hydrogel in Comparative Example 1 exhibits a rough and irregularly curled polymer stacked surface. This morphological change indicates that hydroxypropyl methylcellulose participated in the copolymerization reaction via acryloyl chloride esterification, enhancing wall thickness and creating more wrinkles and roughness. After introducing the imidazole ionic liquid, the hydrogels of the examples exhibit a highly uniform and regular multi-scale porous layered structure. This structure features smooth pore walls and tightly connected channels, forming a composite morphology—a mixture of macroscopic cavities and microscale membrane-like septa.

[0067] Figure 4 The images show the original (left) and stretched (right) states of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3. It can be seen that the hydrogel of Example 3 exhibits excellent tensile toughness, indicating its suitability for wearable hydrogel sensing materials.

[0068] Figure 5The figures show photographs of the hydrogel prepared in the original state (a1) and the expanded state (a2) of the control example 1; and photographs of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3 in the original state (b1) and the expanded state (b2). As can be seen from the figures, (a2) shows that after the hydrogel prepared in control example 1 was soaked in water for 6 days, the diameter of the sample increased from 17.0 mm in the original state to 39.1 mm. The significant expansion indicates that the cross-linking strength between its structures is weak and cannot resist swelling in water. Figure (b2) shows that after the hydrogel prepared in example 3 was soaked in water for 6 days, the diameter of the sample increased from 17.0 mm in the original state to 19.3 mm. The small swelling degree indicates that the cross-linking strength between its structures is strong and can resist swelling in water. The hydrogel has a stable volume, which can ensure its stable sensing effect and sensitivity. The hydrogel of Example 3 showed no significant change in diameter after immersion in water for 0 and 6 days, and no cracking occurred. In contrast, the hydrogel of Control Example 1 expanded to 39.1 mm after immersion for 6 days, and surface cracking occurred, showing obvious dimensional changes and structural damage. This indicates that the hydrogel of Example 3 has better water stability and structural integrity.

[0069] Figure 6 These are photographs of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3, showing its condition before (left) and after (right) self-healing. The hydrogel in Example 3, after being cut along its midline, healed well after 6 hours and was able to withstand external forces effectively. Before healing, the hydrogel had a diameter of 1.5 cm, and it maintained the same diameter after healing, demonstrating its excellent self-healing ability and structural stability.

[0070] Figure 7 The images show the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3, demonstrating its ability to light an LED at 25°C (left) and -20°C (right). As can be seen from the images, the hydrogel successfully lights the LED at 25°C; and it remains effective at -20°C, proving its excellent sensing performance and stability under extreme temperature conditions.

[0071] Figure 8 The images show the swollen cellulose-based supramolecular ionic hydrogel sensing material prepared in Example 3, used to illuminate an LED in both underwater (left) and stretched (right) states. The figures demonstrate that the hydrogel exhibits excellent electrical conductivity in the stretched state, and the LEDs using the hydrogel as a conductive path in both the unstretched (left) and stretched (right) states have the same brightness.

[0072] In summary, the present invention discloses an anti-swelling cellulose-based supramolecular ionic hydrogel sensing material, its preparation method, and its application. The method includes: esterifying hydroxypropyl methylcellulose in ethyl acetate with acryloyl chloride to obtain hydroxypropyl methylcellulose acrylate; dissolving 1-vinylimidazolium and 3-bromopropionic acid in N,N-dimethylformamide to prepare an imidazole ionic liquid; dissolving the hydroxypropyl methylcellulose acrylate in deionized water, adding the imidazole ionic liquid, acrylic acid, N,N-methylenebisacrylamide, and ammonium persulfate to react and obtain the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material. The anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared by the free radical copolymerization strategy of the present invention has good strength, flexibility, anti-swelling properties, antifreeze properties, antibacterial properties, biocompatibility, high conductivity, high sensitivity, and strong environmental adaptability.

[0073] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material, characterized in that, Includes the following steps: Step 1: Add hydroxypropyl methylcellulose to ethyl acetate, stir to dissolve, add pyridine, slowly add ethyl acetate solution of acryloyl chloride dropwise while stirring, stir the reaction under light-protected conditions, add ice-cold ethanol to terminate the reaction and precipitate the product, filter under vacuum, wash and dry to obtain hydroxypropyl methylcellulose acrylate. Step 2: Add 1-vinylimidazolium and 3-bromopropionic acid to N,N-dimethylformamide and stir to dissolve. After heating and reacting under nitrogen atmosphere, add ethyl acetate to precipitate the solid. After washing and drying, obtain imidazolium ionic liquid. Step 3: Dissolve the hydroxypropyl methylcellulose acrylate obtained in Step 1 in deionized water, then add acrylic acid, N,N-methylenebisacrylamide, ammonium persulfate and the imidazole ionic liquid obtained in Step 2, stir and dissolve to obtain a hydrogel precursor, and then irradiate it under ultraviolet light to obtain a swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material.

2. The method for preparing the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material according to claim 1, characterized in that, In step 1, the mass ratio of the ethyl acetate solution of hydroxypropyl methylcellulose, ethyl acetate, pyridine, acryloyl chloride and icy ethanol is (5~10):(100~200):(0.15~0.3):(0.5~1.2):(50~100).

3. The method for preparing the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material according to claim 1, characterized in that, In step 1, the stirring reaction conditions include: stirring at 45~55 °C for 3~5 h; washing the product with ice-cold ethanol; and drying the product at 40~50 °C for 12~24 h.

4. The method for preparing the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material according to claim 1, characterized in that, In step 1, the viscosity range of hydroxypropyl methylcellulose is 1.8 × 10⁻⁶. 5 ~2.2×10 5 mPa·s, with an average molecular weight of 3.0 × 10⁻⁶ mPa·s. 5 Da, with a methoxy degree of substitution of 1.8 to 2.0 and a hydroxypropoxy molar degree of substitution of 0.2 to 0.3; the degree of esterification of the hydroxypropyl methylcellulose acrylate is 1.0% to 3.0%; the hydroxypropyl methylcellulose acrylate is stored in an air-free environment.

5. The method for preparing the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material according to claim 1, characterized in that, In step 2, the mass ratio of 1-vinylimidazole, 3-bromopropionic acid, N,N-dimethylformamide and ethyl acetate is (0.5~2.5):(0.65~3.8):(10~60):(20~60).

6. The method for preparing the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material according to claim 1, characterized in that, In step 2, the heating reaction conditions include: heating at 55~70℃ for 24~30 h; washing the product with ethyl acetate; the drying conditions include: vacuum drying at 40~50℃ for 12~24 h; and storing the imidazole ionic liquid in the absence of air.

7. The method for preparing the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material according to claim 1, characterized in that, In step 3, the mass ratio of the hydroxypropyl methylcellulose acrylate, deionized water, acrylic acid, N,N-methylenebisacrylamide, ammonium persulfate and imidazole ionic liquid is (0.5~2.5):(150~160):(40~50):(0.2~0.3):(0.1~0.2):(0.5~2.5) by mass parts.

8. The method for preparing the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material according to claim 1, characterized in that, In step 3, the irradiation time under ultraviolet light is 1~2 hours.

9. A swelling-resistant cellulose-based supramolecular ionic hydrogel sensing material, characterized in that, The material was prepared using the method described in any one of claims 1 to 8 for the preparation of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material.

10. The application of the anti-swelling cellulose-based supramolecular ionic hydrogel sensing material prepared by the preparation method of any one of claims 1 to 8 in the preparation of wearable human devices or underwater stress-strain sensing materials.

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