Ionized water gel as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of polymer gel materials, and discloses ionized water gel as well as a preparation method and application thereof. Raw materials of the ionized water gel comprise a precursor solution and water, the precursor solution is an acidic hydrophilic ionic liquid and a vinyl monomer containing a hydrophilic group, and the water is used for adjusting the interaction between the acidic hydrophilic ionic liquid and the vinyl monomer. The ionized hydrogel is prepared through a water-mediated polymer network recombination strategy, the technical problems that the toughness and hysteresis of a traditional gel material are difficult to balance and the comprehensive performance is insufficient are effectively solved, the problem that the toughness and hysteresis of the traditional gel material are mutually restricted is broken through, and the prepared ionized hydrogel has good mechanical deformation resistance when bearing mechanical deformation. According to the material, energy can be effectively dissipated to prevent breakage, energy loss and signal distortion caused by lagging can be reduced, the reliability of the material in dynamic mechanics application is greatly improved, and for example, the material can still work stably when a wearable device deforms frequently.

Description

Technical Field

[0001] The present invention relates to the technical field of polymer gel materials, and particularly to ionic hydrogels and their preparation methods and applications. Background Art

[0002] The application scenarios and service life of polymer gel materials in emerging fields (such as intelligent sensors and bioactuators) largely depend on their toughness and low hysteresis. However, traditional gel materials often exhibit poor mechanical properties due to the lack of an effective energy dissipation mechanism. Although dissociable dynamic interactions can achieve effective energy dissipation through network reorganization, under large deformation, a large amount of energy dissipation will cause significant hysteresis. Under repeated loading, traditional gel materials usually show poor sensitivity due to the resistance drift caused by high hysteresis, which affects the signal fidelity in real-time strain sensing applications. Therefore, it is necessary to endow gel materials with both high toughness and low hysteresis characteristics to extend the service life of gel-based devices and expand their applicability in emerging applications.

[0003] High toughness and low hysteresis are inherently contradictory properties of traditional gel materials, and this contradiction stems from the internal conflict between the energy storage and dissipation mechanisms of the materials. Specifically, energy-dissipating units (such as sacrificial bonds or dynamic crosslinks) can effectively increase the fracture energy through reversible fracture, but at the same time, they will increase the frictional resistance between molecular chains, resulting in significant stress relaxation and mechanical hysteresis. In addition, polymer materials will also undergo multiple energy dissipation pathways such as chemical bond fracture and pendant chain segment relaxation during large deformation, further reducing the elastic energy storage efficiency. Therefore, achieving high-performance gels requires a delicate balance strategy that can not only improve the elastic energy storage efficiency by optimizing the network structure but also suppress non-elastic energy dissipation through molecular design.

[0004] Previous studies have explored various strategies to alleviate this contradiction. For example, sliding crosslinkers (such as polyrotaxanes) can reduce the chain segment friction while maintaining the crosslink density through the sliding ring structure of topological entanglement. The nanostructure reinforcement strategy (such as silica nanoparticles) can disperse stress through rigid fillers, which can reduce the hysteresis rate while improving toughness. In addition, solvent swelling regulation or increasing the physical entanglement density can also effectively improve the comprehensive performance of gels by effectively regulating the molecular chain relaxation. However, the applicability of these strategies in ionic liquid (ILs) systems is limited. Because the high viscosity of ILs as a solvent increases the friction between molecular chains, and during the gel deformation process, strong intermolecular interactions drive a large amount of energy dissipation, and it is necessary to extend the time for dynamic network reconstruction. Therefore, designing polymer gel materials with both high toughness and low hysteresis in ILs-containing systems remains an ongoing challenge. Summary of the Invention

[0005] To solve the above problems, the present invention provides an ionic hydrogel and its preparation method and application. The ionic hydrogel of the present invention has both high toughness and low hysteresis and can be applied to health monitoring devices.

[0006] To achieve the above object, the first technical solution adopted by the present invention is: An ionic hydrogel, the raw materials comprising a precursor solution and water; the precursor solution is an acidic hydrophilic ionic liquid and a vinyl monomer containing a hydrophilic group, and the water is used to adjust the interaction between the acidic hydrophilic ionic liquid and the vinyl monomer.

[0007] Preferably, the acidic hydrophilic ionic liquid includes at least one of 1-ethyl-3-methylimidazolium dihydrogen phosphate, 1-butyl-3-methylimidazolium dihydrogen phosphate, 1-ethyl-3-methylimidazolium hydrogen sulfate, and 1-butyl-3-methylimidazolium hydrogen sulfate.

[0008] Preferably, the vinyl monomer containing a hydrophilic group includes at least one of acrylic acid, acrylamide, and methacrylic acid.

[0009] Preferably, the mass ratio of the vinyl monomer to the acidic hydrophilic ionic liquid is 1:(1-5).

[0010] Preferably, the mass of water is 10% - 50% of the total mass of the precursor solution and water.

[0011] Preferably, the water includes deionized water or distilled water.

[0012] The second technical solution adopted by the present invention is: A preparation method of the ionic hydrogel in the first technical solution, after uniformly mixing the acidic hydrophilic ionic liquid, the vinyl monomer, and water, adding a crosslinking agent and a photoinitiator and mixing them uniformly, and performing photo-polymerization under ultraviolet light.

[0013] Preferably, the mass of the photoinitiator is 0.5% - 2% of the mass of the vinyl monomer, and the mass of the crosslinking agent is 0.1% - 0.5% of the mass of the vinyl monomer.

[0014] Preferably, the crosslinking agent includes any one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, and divinylbenzene.

[0015] Preferably, the photoinitiator includes any one of photoinitiator 2959, photoinitiator 1373, and photoinitiator 184.

[0016] The third technical solution adopted by the present invention is: The application of the ionic hydrogel in the first technical solution in a health monitoring device.

[0017] Preferably, the health monitoring device comprises a wearable sensor and an epidermal electrode.

[0018] Compared with the prior art, the present invention has the following beneficial effects: 1. The present invention prepares ionic hydrogels (IHGs) through a water-mediated polymer network reorganization strategy, which effectively solves the technical problems of the difficulty in balancing the toughness and hysteresis of traditional gel materials and the insufficient comprehensive performance, and breaks through the problem of the mutual restriction of toughness and hysteresis in traditional gel materials. The water-mediated strategy enables IHGs to have high toughness (2.2MJ m -3 ) while achieving low hysteresis (8.1% at 400% strain). This balance allows the gel to effectively dissipate energy and prevent breakage when subjected to mechanical deformation, while also reducing energy loss and signal distortion caused by hysteresis, greatly improving the reliability of the material in dynamic mechanical applications, such as wearable devices that can still work stably when they are frequently deformed.

[0019] 2. The mechanical properties of the ionic hydrogel provided by the present invention are improved: it has high tensile properties (1100% strain) and good tensile strength (0.4 MPa), and the Young's modulus (10-50 kPa) is lower than that of human skin. It has excellent flexibility and can withstand complex deformations such as knotting and bending. This allows it to better fit the human body in wearable device applications, reduce restrictions on human activities, and improve wearing comfort.

[0020] 3. The electrical properties of the ionic hydrogel provided by the present invention are enhanced: the electrical conductivity reaches 2.4 mS cm -1 , and the resistance changes are stable and the response is fast under different strains (response time is about 274 ms, recovery time is about 292 ms), and the signal drift is very small during 500 consecutive loading-unloading cycles. In the field of wearable sensors, it can accurately and quickly sense changes in human body movement and convert them into stable electrical signal output, ensuring high-fidelity signal transmission.

[0021] 4. The ionic hydrogel provided by the present invention has good biocompatibility: according to CCK-8 test, L929 fibroblasts still maintain high activity after contacting with IHGs for 48 hours, and they adhere well to the human epidermis, leaving no residue and no irritation to the skin when removed. This feature makes IHGs widely used in the biomedical field, such as when used as epidermal electrodes to collect electromyographic signals, it can ensure the safety and comfort of long-term use.

[0022] 5. The ionic hydrogel provided by the present invention has the advantage of high transparency: the transmittance is greater than 90%. When used in wearable devices, it is convenient to observe the condition of the epidermis in real time, such as monitoring whether there are abnormal changes in the skin, which provides intuitive convenience for health monitoring.

[0023] 6. The ionic hydrogel provided by the present invention can be applied to health monitoring devices, including products such as wearable sensors and epidermal electrodes prepared based on the ionic hydrogel, and the structure is relatively simple. Due to the excellent properties of the ionic hydrogel itself, the use of additional functional layers or components is reduced. As a wearable sensor, a single ionic hydrogel material can simultaneously achieve multiple functions such as high-sensitivity sensing, good mechanical adaptability, and biocompatibility, avoiding the complex multi-layer structure design in traditional sensors, reducing the weight and volume of the product, and improving the integration and portability of the product. Description of the Drawings

[0024] Figure 1 In which, a and b are respectively the toughness and hysteresis result diagrams of the ionic hydrogel prepared in Example 1; Figure 2 In which, a and b are respectively the toughness and hysteresis result diagrams of the ionic hydrogel prepared in Example 2; Figure 3 In which, a and b are respectively the toughness and hysteresis result diagrams of the ionic hydrogel prepared in Example 3; Figure 4 In which, a and b are respectively the toughness and hysteresis result diagrams of the ionic hydrogel prepared in Example 4; Figure 5 In which, a and b are respectively the toughness and hysteresis result diagrams of the ionic hydrogel prepared in Example 5; Figure 6 In which, a and b are respectively the toughness and hysteresis result diagrams of the ionic hydrogel prepared in Comparative Example 1; Figure 7 For the health monitoring results in Application Example 1; Figure 8 For the health monitoring results in Application Example 2; Figure 9 For the water content detection results of the ionic hydrogels in Example 1 and Example 4 in the experimental example. Detailed Description of the Embodiments

[0025] It should be understood that the following detailed description is illustrative and is intended to provide further description of the present application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present application belongs. In order to enable those skilled in the art to more clearly understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with specific embodiments. The experimental materials used in the embodiments and comparative examples of the present invention are all conventional experimental materials in the art and can be obtained through commercial channels.

[0026] The first embodiment of the present invention provides an ionic hydrogel, the raw materials of which include a precursor solution and water; the precursor solution is an acidic hydrophilic ionic liquid and a vinyl monomer containing a hydrophilic group, and the water is used to adjust the interaction between the acidic hydrophilic ionic liquid and the vinyl monomer.

[0027] In this embodiment, water is added to the acrylic acid-ionic liquid system. As a functional agent, water moderately weakens the interaction between the acidic hydrophilic ionic liquid and the polymer chain, promoting the formation of a dynamic adaptive network. Water preferentially binds to the acidic hydrophilic ionic liquid, reducing the strong interaction between the acidic hydrophilic ionic liquid and the polymer chain. When the water concentration is relatively high (such as 40% or more by mass), dynamic lubrication can also be achieved through free water, changing the energy dissipation pathway. This strategy enables the prepared ionic hydrogel to have both high toughness (2.2 MJ m -3 ) and low hysteresis (8.1% at 400% strain), breaking the inherent contradiction between these two properties of traditional gel materials.

[0028] It should be noted that the water that can be used in the embodiments of the present invention includes deionized water, distilled water, etc.

[0029] It should also be noted that all acidic hydrophilic ionic liquids are applicable to the present invention. As a solvent, the acidic hydrophilic ionic liquid can not only ensure its strong interaction with the vinyl monomer but also ensure its miscibility with water. This solubility is to ensure the homogeneity of the reaction system. The main role of water is to adjust the interaction between the acidic hydrophilic ionic liquid and the vinyl monomer. For example, the acidic hydrophilic ionic liquid can include at least one of 1-ethyl-3-methylimidazolium dihydrogen phosphate, 1-butyl-3-methylimidazolium dihydrogen phosphate, 1-ethyl-3-methylimidazolium hydrogen sulfate, and 1-butyl-3-methylimidazolium hydrogen sulfate. It can be understood that only the ionic liquid that can form a strong interaction with the vinyl monomer of the present application is applicable to the present invention. At this time, water can act as a lubricating medium to adjust the interaction between the ionic liquid and the polymer chain. Otherwise, water can only act as a solvent and does not play a regulatory role.

[0030] Common vinyl monomers containing hydrophilic groups in the embodiments of the present invention are applicable to the present invention, such as acrylic acid, acrylamide, and methacrylic acid, because their hydrophilic groups can have a strong interaction with the acidic hydrophilic ionic liquid and are miscible with water.

[0031] There is no special limitation on the amounts of the acidic hydrophilic ionic liquid and the vinyl monomer, and it is advisable to form a homogeneous solution system. Those skilled in the art can adjust the amounts according to the actual situation. For example, the mass ratio of the vinyl monomer to the acidic hydrophilic ionic liquid can be 1:(1 - 5).

[0032] In some preferred embodiments, the mass of water is 10% - 50% of the total mass of the precursor solution and water. Insufficient water usage (such as less than 10%) will result in an ion hydrogel with high toughness but also high hysteresis; excessive water (such as more than 50%) will lead to an ion hydrogel with low toughness but the hysteresis remains basically unchanged.

[0033] The second embodiment of the present invention provides a method for preparing the ion hydrogel of the first embodiment. After uniformly mixing an acidic hydrophilic ionic liquid, a vinyl monomer, and water, a crosslinking agent and a photoinitiator are added and mixed evenly, and then photopolymerization is carried out under ultraviolet light.

[0034] It should be noted that since the purpose of water is to regulate the interaction between the acidic hydrophilic ionic liquid and the vinyl monomer, water should be mixed with the acidic hydrophilic ionic liquid and the vinyl monomer simultaneously, rather than adding water for adjustment after the acidic hydrophilic ionic liquid and the vinyl monomer polymerize to form a bulk gel or a solution-bulk gel biphasic system. The crosslinking agent used in this preparation method is a commonly used crosslinking agent in gel preparation, and it can achieve molecular chain crosslinking, such as N, N'-methylenebisacrylamide, polyethylene glycol diacrylate, divinylbenzene, etc. The photoinitiator is a commonly used photoinitiator in the art, such as photoinitiator 2959 (2-hydroxy-2-methyl-1-[4-(2-hydroxyethoxy)phenyl]-1-propanone), photoinitiator 1373 (2-hydroxy-2-methyl-1-phenyl-1-propanone), photoinitiator 184 (fluoro boron acrylate), etc.

[0035] There is no special limitation on the dosage of the crosslinking agent and the photoinitiator, and it is appropriate to achieve crosslinking between the raw materials. Those skilled in the art can adjust according to the adaptability of the reaction raw materials. In some preferred embodiments, the mass of the photoinitiator is 0.5% - 2% of the mass of the vinyl monomer, and the mass of the crosslinking agent is 0.1% - 0.5% of the mass of the vinyl monomer.

[0036] The third embodiment of the present invention provides the application of the ion hydrogel of the first embodiment in a health monitoring device.

[0037] Health monitoring scenarios include monitoring human movements (such as finger movements, swallowing, coughing, breathing, etc.) and physiological signals (such as electromyogram signals, etc.), and can obtain human health information in real time.

[0038] The health monitoring devices applicable to the present invention include wearable sensors and epidermal electrodes. When these health monitoring devices monitor human body movements, the specific monitoring principles are as follows: 1) When the fingers are bent, the health monitoring device bends for a short time to generate an electrical signal corresponding to the "point", and the long-term bending represents the "stroke", thereby efficiently transmitting complex information such as "SOS", "HELP", "CALL", etc.; 2) The health monitoring device is attached to the throat, and can distinguish monosyllabic and polysyllabic words, even phrases, by analyzing the waveform, and can also monitor swallowing and coughing movements; 3) The health monitoring device is attached to the chest, and can monitor the respiratory rate based on the periodic resistance fluctuations, and issue a breathing abnormality alarm in time.

[0039] The working principle of health monitoring equipment when monitoring physiological signals is as follows: when monitoring electromyographic signals, the grasping action test can be used to sensitively distinguish different grip strength levels; when used to analyze muscle fatigue, sEMG signals are collected through repeated muscle movements, and after processing, it is found that the mean frequency (MNF) value continues to decrease, thereby judging the degree of muscle fatigue.

[0040] The IHGs provided by the present invention have good biocompatibility, and L929 fibroblasts still maintain high activity after contacting with the IHGs for 48 hours. At the same time, the interface impedance between the IHGs and the human forearm skin is significantly lower than that of commercial Ag / AgCl electrodes, and the signal-to-noise ratio (SNR) is higher.

[0041] The ionic hydrogel and its properties are described in detail below through a number of specific examples.

[0042] Example 1 Preparation of ionic hydrogel Weigh 0.5 g of acrylic acid (AAc), 0.5 g of 1-ethyl-3-methylimidazole dihydrogen phosphate ([Emim][H2PO4]) and 0.11 g of water, mix them evenly, stir for 1 h and ultrasonicate for 1 h, then add 1 mg of N,N'-methylenebisacrylamide (MBAA) and 7 mg of photoinitiator 2959, continue stirring for 1 h and ultrasonicate for 1 h, and irradiate under 365 nm ultraviolet light for 1 h to obtain ionic hydrogel.

[0043] The prepared ionic hydrogel is placed in a tensile machine and stretched until it breaks, and a stress-strain graph is obtained. Its toughness is the area enclosed by the stress-strain curve. After it is stretched to 4 times its own length and then recovered, its stress-strain curve is recorded as a hysteresis graph, and its hysteresis rate is the ratio of the enclosed area to the enclosed area when it is 4 times the normal length. Its toughness and hysteresis are shown in Figure 1 As shown (the same below).

[0044] Example 2 Preparation of ionic hydrogel Same as Example 1, except that 0.25 g of water was added. Figure 2 shown.

[0045] Example 3 Preparation of Ionic Hydrogel Same as Example 1, except that 0.43 g of water was added. Its toughness and hysteresis are as Figure 3 shown.

[0046] Example 4 Preparation of Ionic Hydrogel Same as Example 1, except that 0.67 g of water was added. Its toughness and hysteresis are as Figure 4 shown.

[0047] Example 5 Preparation of Ionic Hydrogel Same as Example 1, except that 1 g of water was added. Its toughness and hysteresis are as Figure 5 shown.

[0048] Example 6 Preparation of Ionic Hydrogel Same as Example 5, except that 2 mg of MBAA was added.

[0049] Example 7 Preparation of Ionic Hydrogel Same as Example 5, except that 4.5 mg of photoinitiator 2959 was added.

[0050] Comparative Example 1 Compared with Example 1, the difference is only that no water was added.

[0051] The prepared ionic hydrogel was placed in a tensile machine for stretching until it broke, and a stress-strain diagram could be obtained. Its toughness is the area enclosed by the stress-strain curve; after it was stretched to twice its original length and then recovered, the stress-strain curve was recorded as the hysteresis diagram, and its hysteresis rate is the ratio of the enclosed area to the enclosed area at twice the normal length. The results are as Figure 6 shown.

[0052] Comparative Example 2 Compared with Example 4, the difference is only that MBAA was not added.

[0053] Comparative Example 3 Compared with Example 4, the difference is only that 14 mg of photoinitiator 2959 was added.

[0054] It can be seen from Figures 1 - 6 that the more water is added, the lower the toughness of the obtained ionic hydrogel, which indicates that the addition of water gradually weakens the interaction between the acidic hydrophilic ionic liquid and acrylic acid, the molecular chains can move freely, and then a dynamic adaptive network is formed, reducing the hysteresis of the ionic hydrogel.

[0055] Application Example 1 Ionic Hydrogel for Health Monitoring Place the ionic hydrogel of Example 4 on the chest, connect both ends to an LCR bridge, and perform breathing (slow and fast). The corresponding resistance change rate can be obtained, and the response data can be obtained by recording the resistance and time, as Figure 7 shown.

[0056] Application Example 2: Ionic Hydrogel for Health Monitoring Place the material of Example 4 on the flexor muscle of the left arm of the human body at intervals of 2 cm, place the reference electrode at the elbow, and perform long-term fist clenching to record the electromyogram signal. As Figure 8 shown.

[0057] Experimental Example Perform low-field nuclear magnetic characterization on the materials of Example 1 and Example 4 to detect the water content of their bound water and free water, as shown in Figure 9 a and b respectively.

[0058] It can be seen from Figure 9 that the water content added in Example 1 is 10%, and only bound water exists in the obtained ionic hydrogel, which proves that the added water combines with the acidic hydrophilic ionic liquid, thereby weakening the interaction between the acidic hydrophilic ionic liquid and acrylic acid. The water content added in Example 4 is 50%, and the water concentration is relatively high. Both bound water and free water exist in the obtained ionic hydrogel, which proves that in addition to weakening the interaction, a large amount of free water acts as a lubricant, and this effect can further reduce the gel hysteresis.

[0059] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. An ion hydrogel, characterized in that, The raw materials include a precursor liquid solution and water; the precursor solution is an acidic hydrophilic ionic liquid and a vinyl monomer containing a hydrophilic group, and the water is used to adjust the interaction between the acidic hydrophilic ionic liquid and the vinyl monomer.

2. The ionic hydrogel according to claim 1, characterized in that, The acidic hydrophilic ionic liquid includes at least one of 1-ethyl-3-methylimidazolium dihydrogen phosphate, 1-butyl-3-methylimidazolium dihydrogen phosphate, 1-ethyl-3-methylimidazolium hydrogen sulfate, and 1-butyl-3-methylimidazolium hydrogen sulfate.

3. The ionic hydrogel according to claim 1, wherein The vinyl monomer containing a hydrophilic group includes at least one of acrylic acid, acrylamide, and methacrylic acid.

4. The ionic hydrogel according to any one of claims 1-3, characterized in that, The mass ratio of the vinyl monomer to the acidic hydrophilic ionic liquid is 1:(1-5).

5. The ionic hydrogel according to claim 1, characterized in that, The mass of water is 10%-50% of the total mass of the precursor liquid solution and water.

6. The preparation method of the ionic hydrogel according to any one of claims 1-5, characterized in that, After uniformly mixing the acidic hydrophilic ionic liquid, the vinyl monomer, and water, a crosslinking agent and a photoinitiator are added and mixed evenly, and then photopolymerization is carried out under ultraviolet light.

7. The preparation method according to claim 6, characterized in that, The mass of the photoinitiator is 0.5%-2% of the mass of the vinyl monomer, and the mass of the crosslinking agent is 0.1%-0.5% of the mass of the vinyl monomer.

8. The preparation method according to claim 6, characterized in that, The crosslinking agent includes any one of N,N'-methylenebisacrylamide, polyethylene glycol diacrylate, and divinylbenzene.

9. The application of the ionic hydrogel according to any one of claims 1-5 in a health monitoring device.

10. The application according to claim 9, wherein The health monitoring device includes a wearable sensor and an epidermal electrode.

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