Tough anti-freezing conductive hydrogel as well as preparation method and application thereof in friction nano-generator

Abstract

The invention belongs to the technical field of polymer hydrogel, and particularly relates to tough anti-freezing conductive hydrogel, a preparation method of the tough anti-freezing conductive hydrogel and application of the tough anti-freezing conductive hydrogel in a friction nano-generator. The preparation method comprises the following steps: mixing polysaccharide, polyvinyl alcohol and a solvent, and freezing an obtained polymer solution to obtain pre-organic gel; performing first solvent replacement on the pre-organic gel to obtain initial hydrogel; drying the initial hydrogel to obtain dry gel; drying is carried out under a prestretching strain condition; treating the xerogel with an inorganic metal salt aqueous solution to obtain hydrogel containing metal ions; and carrying out second solvent replacement on the hydrogel containing the metal ions by adopting a deep-eutectic solvent to obtain the tough anti-freezing conductive hydrogel. The strength and toughness of a polymer network are improved, and the obtained tough anti-freezing conductive hydrogel is stable in mechanical property and long in service life; meanwhile, the tough anti-freezing conductive hydrogel provided by the invention still has good conductivity under a low-temperature condition.

Description

Technical Field

[0001] The present invention belongs to the technical field of polymer hydrogels, and particularly relates to a tough and antifreeze conductive hydrogel, a preparation method thereof, and an application thereof in a triboelectric nanogenerator. Background Art

[0002] With the diversification and complexity of the application scenarios of intelligent electronic devices, designing electronic devices that can meet the requirements of multiple scenarios and are portable and flexible has been a research hotspot in recent years. Among them, wearable electronic devices such as flexible batteries and supercapacitors have received extensive attention and made significant progress in replacing traditional electrochemical batteries. However, these materials still have problems such as limited lifespan and lack of self-charging ability. In view of this, flexible triboelectric nanogenerators have become a new type of sustainable energy harvesting device in the field of flexible wearable electronic devices due to their low cost, high output, lightweight, and inherent self-powered performance.

[0003] Among many flexible triboelectric nanogenerators, hydrogel nanogenerators have the advantages of high flexibility, stable signal output, and simple device assembly, and are widely used in the fields of energy harvesting and motion sensing. In order to ensure that the generator has a good service life and stable signal output, the hydrogel substrate should have high toughness to maintain integrity under large stresses, and still maintain good conductivity in extreme environments, such as low temperatures.

[0004] One of the effective methods for toughening hydrogels is to add rigid materials as mechanical property enhancers to the hydrogels. For example, in related technologies, polybutyl acrylate macromolecular microspheres are added to gel materials, so that the fracture strength of the hydrogel reaches 1.8 MPa; inorganic particles such as iron oxide particles are added, so that the fracture stress of polyacrylamide / chitosan hydrogels is increased from 1.5 MPa to 6.0 MPa. Although the strategy of introducing rigid materials can improve the toughness of the hydrogel substrate, the obtained tough hydrogels benefit from the rigid materials rather than the polymer network itself. When subjected to large stresses or after long-term use, the rigid materials detach from the polymer network, seriously affecting the mechanical performance and service life of the hydrogel. In addition, the main principle of power generation of hydrogel triboelectric nanogenerators is contact electrification and electrostatic induction of the friction layer. Ions that can move freely inside the hydrogel move, and electrons flow out along the wire to generate current. Most of these generators use ion-conductive hydrogels as electrodes. Although the freezing point of hydrogels containing salt ions is reduced to some extent, the outdoor temperature in extremely cold regions such as Northeast China can reach as low as -30°C to -40°C, and such hydrogels still cannot meet the actual use requirements. Summary of the Invention

[0005] The object of the present invention is to provide a tough anti-freezing conductive hydrogel, a preparation method thereof, and an application thereof in a triboelectric nanogenerator. The tough anti-freezing conductive hydrogel provided by the present invention has stable mechanical properties and a long service life. At the same time, the tough anti-freezing conductive hydrogel provided by the present invention still has good electrical conductivity under low-temperature conditions.

[0006] In order to achieve the above object, the present invention provides the following technical solutions:

[0007] The present invention provides a preparation method of a tough anti-freezing conductive hydrogel, comprising the following steps:

[0008] Mix a polysaccharide, polyvinyl alcohol, and a solvent to obtain a polymer solution, wherein the polysaccharide contains carboxyl groups, and the solvent includes water and an organic solvent;

[0009] Freeze the polymer solution to obtain a pre-organic gel;

[0010] Perform a first solvent replacement on the pre-organic gel to obtain an initial hydrogel;

[0011] Dry the initial hydrogel to obtain a dry gel; the drying is performed under a pre-stretching strain condition;

[0012] Treat the dry gel with an inorganic metal salt aqueous solution to obtain a hydrogel containing metal ions;

[0013] Perform a second solvent replacement on the hydrogel containing metal ions with a deep eutectic solvent to obtain the tough anti-freezing conductive hydrogel.

[0014] Preferably, the polysaccharide includes one or more of carboxymethyl cellulose, carboxylated nanocellulose, carboxymethyl chitosan, sodium alginate, and hyaluronic acid.

[0015] Preferably, the weight-average molecular weight of the polyvinyl alcohol is 9,000 to 205,000;

[0016] The mass ratio of the polysaccharide to the polyvinyl alcohol is 0.5:100 to 20:100.

[0017] Preferably, the pre-stretching strain is 20 to 200%;

[0018] Preferably, the inorganic metal salt in the inorganic metal salt aqueous solution includes one or more of ferric chloride, calcium chloride, and copper chloride;

[0019] The content of the inorganic metal salt in the inorganic metal salt aqueous solution is 0.5 to 10 wt%.

[0020] Preferably, the deep eutectic solvent includes one or more of choline chloride-urea deep eutectic solvent, choline chloride-acrylic acid deep eutectic solvent, and choline chloride-malonic acid deep eutectic solvent;

[0021] The time for the second solvent replacement is 1 to 30 minutes.

[0022] The present invention provides a tough, anti-freezing and conductive hydrogel prepared by the preparation method described in the above technical solution, which includes a polymer network formed by polysaccharide, polyvinyl alcohol and metal ions, and a solvent, and the solvent includes water and a deep eutectic solvent.

[0023] Preferably, in the tough, anti-freezing and conductive hydrogel: the content of polyvinyl alcohol is 5 to 15 wt%, the content of polysaccharide is 0.025 to 3 wt%, and the content of metal ions is 10 to 20 mg / g.

[0024] The present invention provides an application of the tough, anti-freezing and conductive hydrogel described in the above technical solution in a hydrogel nanogenerator.

[0025] The present invention provides a hydrogel triboelectric nanogenerator, which includes a positive friction layer, an electrode and a negative friction layer, and the electrode is wrapped inside the negative friction layer; the electrode is the tough, anti-freezing and conductive hydrogel described in the above technical solution.

[0026] The present invention provides a method for preparing a tough and antifreeze conductive hydrogel, comprising the following steps: mixing a polysaccharide, polyvinyl alcohol and a solvent to obtain a polymer solution, wherein the polysaccharide contains carboxyl groups, and the solvent comprises water and an organic solvent; freezing the polymer solution to obtain a pre-organogel; performing a first solvent replacement on the pre-organogel to obtain an initial hydrogel; drying the initial hydrogel to obtain a dry gel, wherein the drying is performed under a pre-stretching strain condition; treating the dry gel with an inorganic metal salt aqueous solution to obtain a hydrogel containing metal ions; and performing a second solvent replacement on the hydrogel containing metal ions with a deep eutectic solvent to obtain the tough and antifreeze conductive hydrogel. By drying the initial hydrogel under a pre-stretching strain condition, fiber orientation rearrangement is achieved during the drying process by inducing the fibers to align along the direction of the directional pulling force. Subsequently, the present invention treats the dry gel with an inorganic metal salt aqueous solution to introduce two types of bonding interactions, namely metal ion bonds and coordination bonds (the coordination bonds are formed between the metal ions and the hydroxyl groups on the polysaccharide and the hydroxyl groups of polyvinyl alcohol), into the hydrogel. Finally, the present invention performs a second solvent replacement on the hydrogel containing metal ions with a deep eutectic solvent. Since the deep eutectic solvent is a "non-solvent" for polyvinyl alcohol and the polysaccharide, more hydrogen bonds will be induced to form due to hydrophobic interactions after the second solvent exchange, improving the strength of the hydrogel. Thus, the preparation method provided by the present invention improves the orientation of the fibers and induces the formation of hydrogen bonds through a structural design strategy of "fiber rearrangement - introduction of bonding - network reconstruction", thereby enhancing the strength and toughness of the polymer network itself, and obtaining a tough and antifreeze conductive hydrogel with stable mechanical properties and a long service life.

[0027] Meanwhile, the present invention performs a second solvent replacement on the hydrogel containing metal ions with a deep eutectic solvent. The deep eutectic solvent in the obtained hydrogel can significantly reduce its freezing point, effectively improving the stability of the hydrogel under low-temperature conditions and ensuring good ionic conductivity under low-temperature conditions. Thus, the tough and antifreeze conductive hydrogel prepared by the present invention still has good conductive performance under low-temperature conditions.

[0028] The present invention provides a tough and antifreeze conductive hydrogel prepared by the preparation method described in the above technical solution, comprising a polymer network formed by a polysaccharide, polyvinyl alcohol and metal ions and a solvent, wherein the solvent comprises water and a deep eutectic solvent. The tough and antifreeze conductive hydrogel provided by the present invention has both a tough network structure and low-temperature antifreeze characteristics, and has a wider application in hydrogel triboelectric nanogenerators. Description of the Drawings

[0029] Figure 1 SEM comparison diagrams of the products prepared in Example 1 and Comparative Example 2;

[0030] Figure 2 XRD comparison diagrams of the products prepared in Example 1 and Comparative Example 5;

[0031] Figure 3 Mechanical property test results of the products prepared in Examples 1-3 and Comparative Examples 1-4;

[0032] Figure 4 Characterization results of the total tensile energy, dissipated energy, and energy dissipation rate of the product prepared in Example 1 under cyclic tensile loading with a gradient strain;

[0033] Figure 5 Performance test results of the product prepared in Example 1 after being immersed in a deep eutectic solvent;

[0034] Figure 6 Performance test results of the product prepared in Example 1 after being assembled into a triboelectric nanogenerator;

[0035] Figure 7 Sensor signal images for monitoring the flexion and extension of the human wrist and elbow using the hydrogel-based flexible triboelectric nanogenerator assembled from the product prepared in Example 1;

[0036] Figure 8 Sensor signal images for monitoring slow walking and fast walking of the human body using the triboelectric nanogenerator assembled from Example 1;

[0037] Figure 9 Sensor signal images for monitoring jogging, fast running, and jumping of the human body using the triboelectric nanogenerator assembled from Example 1;

[0038] Figure 10 Morphological comparison diagrams of the product prepared in Example 1 before and after stretching, bending, twisting, and curling. Detailed implementation manners

[0039] The present invention provides a method for preparing a tough, antifreeze, and conductive hydrogel, comprising the following steps:

[0040] Mix a polysaccharide, polyvinyl alcohol, and a solvent to obtain a polymer solution, wherein the polysaccharide contains carboxyl groups, and the solvent includes water and an organic solvent;

[0041] Freeze the polymer solution to obtain a pre-organic gel;

[0042] Perform a first solvent replacement on the pre-organic gel to obtain an initial hydrogel;

[0043] Dry the initial hydrogel to obtain a dry gel; the drying is carried out under a pre-stretching strain condition;

[0044] Treat the dry gel with an inorganic metal salt aqueous solution to obtain a hydrogel containing metal ions;

[0045] The hydrogel containing metal ions is subjected to a second solvent replacement using a deep eutectic solvent to obtain the tough antifreeze conductive hydrogel.

[0046] In the present invention, unless otherwise specified, all preparation raw materials / components are commercially available products well-known to those skilled in the art.

[0047] In the present invention, a polysaccharide, polyvinyl alcohol, and a solvent are mixed to obtain a polymer solution. The polysaccharide contains carboxyl groups, and the solvent includes water and an organic solvent. In the present invention, the polysaccharide preferably includes one or more of carboxymethyl cellulose, carboxylated nanocellulose, carboxymethyl chitosan, sodium alginate, and hyaluronic acid, and may be carboxymethyl cellulose, carboxylated nanocellulose, carboxymethyl chitosan, or sodium alginate in the examples. The viscosity of the carboxymethyl cellulose in the examples of the present invention may be 1000 - 1400 mPa·s. The degree of substitution of the carboxymethyl chitosan in the examples of the present invention is preferably ≥80%. The weight-average molecular weight of the polyvinyl alcohol is preferably 9000 - 205000, more preferably 89000 - 98000, and may be 89000 - 98000, 31000 - 50000, or 47000 in the examples. The degree of hydrolysis of the polyvinyl alcohol in the examples of the present invention may be 80 - 99%. The mass ratio of the polysaccharide to the polyvinyl alcohol is preferably 0.5:100 - 20:100, more preferably 1:100 - 15:100, further preferably 2:100 - 10:100, and most preferably 5:100, and may be 1:20, 1:37.5, 1:50, or 1:18.75 in the examples. In the present invention, the solvent includes water and an organic solvent, and the water is preferably deionized water. The organic solvent is an organic solvent capable of dissolving the polyvinyl alcohol, and the organic solvent may be dimethyl sulfoxide in the examples. The present invention has no special requirements for the amounts of the water and the organic solvent, as long as the polysaccharide and the polyvinyl alcohol are completely dissolved. In the present invention, the mixing preferably includes the following steps: dissolving the polysaccharide in a part of the solvent to obtain a polysaccharide solution, and the part of the solvent is preferably water; mixing the polysaccharide solution and the remaining solvent, and finally stirring and mixing with the polyvinyl alcohol; the remaining solvent is preferably an organic solvent. The content of the polysaccharide in the polymer solution is preferably 0.5 - 3 wt%, more preferably 1 - 2.5 wt%, and most preferably 2 wt%, and may be 0.5%, 0.4%, 0.3%, or 0.8% in the examples. The temperature of the stirring and mixing is preferably 90 - 95 °C, and the time is preferably 4 - 5 h. The content of the polyvinyl alcohol in the polymer solution is preferably 5 - 20 wt%, more preferably 8 - 15 wt%, and most preferably 10 wt%, and may be 10% or 15% in the examples.

[0048] After obtaining the polymer solution, the present invention freezes the polymer solution to obtain a pre-organogel. In the present invention, the freezing is preferably carried out in a mold. Before the freezing, the present invention preferably degasses the polymer solution, and the degassing treatment is preferably centrifugal degassing. In the present invention, the temperature of the freezing is preferably -20°C to -10°C, and the time is preferably 12 to 24 h.

[0049] After obtaining the pre-organogel, the present invention performs a first solvent replacement on the pre-organogel to obtain an initial hydrogel. In the present invention, the replacement solvent used for the first solvent replacement is preferably hydrochloric acid. The molar concentration of the hydrochloric acid is preferably 0.05 to 0.1 mol / L. The temperature of the first solvent replacement is preferably room temperature, and the present invention does not limit the time of the first solvent replacement, and it is only necessary to completely replace the organic solvent in the organic gel.

[0050] After obtaining the initial hydrogel, the present invention dries the initial hydrogel to obtain a dry gel; the drying is carried out under a pre-stretching strain condition. In the present invention, the pre-stretching strain is preferably 20 to 200%, more preferably 50 to 150%, further preferably 60 to 100%, and most preferably 80%. In the examples, it can be 80%, 100%, 160%, 60% or 120%. The pre-stretching strain of 20 to 200% is 20 to 200% of the initial hydrogel stretched to its original length.

[0051] In the present invention, the specific implementation manner of the drying preferably includes: stretching the initial hydrogel to 20 to 200% of its original length, and then fixing it in place for drying.

[0052] In the present invention, the temperature of drying under the pre-stretching strain condition is preferably normal temperature. By controlling the pre-stretching strain to be most preferably 80%, the present invention can achieve a better technical effect that the hydrogel material has both strength and toughness and certain stretchability at the same time.

[0053] In the present invention, if the pre-stretching strain is less than 20%, the formation of oriented fibers may not be fully induced, and if it is higher than 200%, there is a risk of sample fracture.

[0054] The present invention has no special requirements for the drying time, and the initial hydrogel can be dried to absolute dryness to obtain a dry gel.

[0055] After obtaining the dry gel, the present invention uses an inorganic metal salt aqueous solution to treat the dry gel to obtain a hydrogel containing metal ions. In the present invention, the inorganic metal salt in the inorganic metal salt aqueous solution preferably includes one or more of ferric chloride, calcium chloride, and copper chloride, and may be ferric chloride in this embodiment. The content of the inorganic metal salt in the inorganic metal salt aqueous solution is preferably 0.5-10 wt%, more preferably 1-10 wt%, and further preferably 5-8 wt%, and may be 5 wt%, 10 wt%, or 8 wt% in the embodiment. The method of treating the dry gel with the inorganic metal salt aqueous solution is preferably: immersing the dry gel in the inorganic metal salt aqueous solution, and the temperature of the immersion is preferably room temperature. The present invention has no special requirements for the immersion time, and it can be immersed until the mass of the hydrogel does not change.

[0056] After obtaining the hydrogel containing metal ions, the present invention uses a deep eutectic solvent to perform a second solvent replacement on the hydrogel containing metal ions to obtain the tough anti-freezing conductive hydrogel. In the present invention, the deep eutectic solvent preferably includes one or more of choline chloride-urea deep eutectic solvent, choline chloride-acrylic acid deep eutectic solvent, and choline chloride-malonic acid deep eutectic solvent, and may be choline chloride-urea deep eutectic solvent in the embodiment. In the present invention, the molar ratio of choline chloride to urea in the choline chloride-urea deep eutectic solvent is preferably 1:2. The implementation method of the second solvent replacement is preferably: immersing the hydrogel containing metal ions in the deep eutectic solvent. The temperature of the second solvent replacement is preferably room temperature, and the time of the second solvent replacement is preferably 1-30 min, more preferably 1-20 min, more preferably 1-10 min, and most preferably 5 min.

[0057] In the present invention, during the process of the second solvent replacement with the deep eutectic solvent, crystallization can be induced. Since the deep eutectic solvent is a "non-solvent" for the polysaccharide and the polyvinyl alcohol, it can induce the two to further form a crystalline region through hydrophobic interactions. Therefore, in the present invention, the role of the deep eutectic solvent can not only provide the ability of low-temperature stability, but also toughen the hydrogel.

[0058] The present invention provides a tough anti-freezing conductive hydrogel prepared by the preparation method described in the above technical solution, including a polymer network formed by a polysaccharide, polyvinyl alcohol, and metal ions and a solvent, and the solvent includes water and a deep eutectic solvent.

[0059] In the present invention, in the tough anti-freezing conductive hydrogel: the content of polyvinyl alcohol is preferably 5-15 wt%, and may be 10 wt% in the embodiment; the content of the polysaccharide is preferably 0.025-3 wt%, and may be 2 wt% in the embodiment; the content of the metal ions is 10-20 mg / g, and may be 18.66 mg / g in the embodiment.

[0060] The present invention provides an application of the tough anti-freezing conductive hydrogel described in the above technical solution in a hydrogel nanogenerator.

[0061] The present invention provides a hydrogel triboelectric nanogenerator, which includes a positive friction layer, an electrode, and a negative friction layer. The electrode is wrapped inside the negative friction layer; the electrode is the tough anti-freezing conductive hydrogel described in the above technical solution.

[0062] In the present invention, the positive friction layer can be nitrile rubber. The negative friction layer can be VHB TM 4905 elastomer.

[0063] The hydrogel triboelectric nanogenerator provided by the present invention further includes a wire. One end of the wire is connected to the tough anti-freezing conductive hydrogel, and the other end of the wire passes through the negative friction layer and is connected to an external circuit to conduct current.

[0064] To further illustrate the present invention, the technical solutions provided by the present invention will be described in detail below in conjunction with embodiments, but they should not be construed as limiting the protection scope of the present invention.

[0065] The types and sources of raw materials in the following embodiments:

[0066] All raw materials used in the following embodiments are of commercial origin. Among them, polyvinyl alcohol (M w 89000 - 98000, 99% hydrolysis, CAS: 9002 - 89 - 5; Mw 9000 - 10000, 80% hydrolysis; Mw 13000 - 23000, 98% hydrolysis; Mw 31000 - 50000, 87 - 89% hydrolysis; Mw 31000 - 50000, 98 - 99% hydrolysis; Mw89000 - 98000, 99% hydrolysis; Mw~205000; Mw~195000; Mw~47000; Mw~67000), ferric chloride (AR, CAS: 7705 - 08 - 0), carboxymethyl cellulose (1000 - 1400 mpa·s, USP grade, CAS: 9004 - 32 - 4) are all purchased from Shanghai Aladdin Biochemical Technology Co., Ltd. Choline chloride (98%, CAS: 67 - 48 - 1), carboxymethyl chitosan (degree of substitution ≥80%, CAS: 83512 - 85 - 0), sodium alginate (90%, CAS: 9005 - 38 - 3), hyaluronic acid (97%, CAS: 9004 - 61 - 9) are purchased from Shanghai Macklin Biochemical Co., Ltd. Urea (AR, CAS: 57 - 13 - 6) is purchased from Shanghai Sinopharm Chemical Reagent Co., Ltd. Carboxylated nanocellulose (1 wt% solid content) is purchased from Guilin Qihong Technology Co., Ltd.

[0067] Example 1

[0068] Dissolve 0.5 g of carboxymethyl cellulose in 24.5 g of deionized water, then add 65 g of dimethyl sulfoxide and 10 g of polyvinyl alcohol with a weight-average molecular weight of 89,000 - 98,000. Stir the mixed system at 95 °C for 5 h to obtain a clear and homogeneous solution. After centrifugal degassing, pour the viscous liquid into a mold, store it at -20 °C for 12 h, and then take it out to obtain a pre-organogel. Immerse the pre-organogel in 0.1 mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organogel is replaced, obtaining an initial hydrogel. Stretch the initial hydrogel to 80% of its original length and fix it in place, and dry it at room temperature until it is completely dry to obtain a dry gel. Immerse the dry gel in an 8 wt% iron chloride solution and swell it fully until the mass of the hydrogel remains unchanged, obtaining a hydrogel containing iron ions. Subsequently, immerse the hydrogel containing iron ions in a deep eutectic solvent composed of choline chloride and urea (the molar ratio of choline chloride to urea is preferably 1:2) for 5 min to obtain a tough, antifreeze, and conductive hydrogel.

[0069] Further assemble the tough, antifreeze, and conductive hydrogel into a triboelectric nanogenerator, where nitrile rubber is the positive friction layer, and VHB TM 4905 elastomer is the negative friction layer, and the tough, antifreeze, and conductive hydrogel is used as the electrode to construct a hydrogel triboelectric nanogenerator; VHB TM 4905 elastomer wraps the hydrogel electrode to form a sandwich structure. One end of the wire is connected to the tough, antifreeze, and conductive hydrogel, and the other end passes through VHB TM 4905 elastomer and is connected to an external circuit to conduct the current out.

[0070] Example 2

[0071] Dissolve a mixture of 0.4 g of carboxymethyl chitosan and carboxylated nanocellulose in 24.6 g of deionized water, then add 60 g of dimethyl sulfoxide and 15 g of polyvinyl alcohol with a weight-average molecular weight of 31,000 - 50,000. Stir the mixed system at 95 °C for 5 h to obtain a clear and homogeneous solution. After centrifugal degassing, pour the viscous liquid into a mold, store it at -20 °C for 12 h, and then take it out to obtain a pre-organogel. Immerse the pre-organogel in 0.1 mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organogel is replaced, obtaining an initial hydrogel. Stretch the initial hydrogel to 80% of its original length and fix it in place, and dry it at room temperature until it is completely dry to obtain a dry gel. Immerse the dry gel in an 8 wt% iron chloride solution and swell it fully until the mass of the hydrogel remains unchanged, obtaining a hydrogel containing iron ions. Subsequently, immerse the hydrogel containing iron ions in a deep eutectic solvent composed of choline chloride and urea (the molar ratio of choline chloride to urea is preferably 1:2) for 5 min to obtain a tough, antifreeze, and conductive hydrogel.

[0072] Furthermore, the tough anti-freezing conductive hydrogel was assembled into a triboelectric nanogenerator, where nitrile rubber served as the positive friction layer, and VHB TM 4905 elastomer served as the negative friction layer, and the tough anti-freezing conductive hydrogel served as the electrode to construct a hydrogel triboelectric nanogenerator; VHB TM 4905 elastomer wrapped the hydrogel electrode to form a sandwich structure. One end of the wire was connected to the tough anti-freezing conductive hydrogel, and the other end passed through VHB TM 4905 elastomer to connect to an external circuit to conduct the current out.

[0073] Example 3

[0074] 0.3 g of the mixture of sodium alginate and hyaluronic acid was dissolved in 24.7 g of deionized water, then 60 g of dimethyl sulfoxide and 15 g of polyvinyl alcohol with a weight average molecular weight of 13,000 - 23,000 were added. The mixed system was stirred at 95 °C for 5 h to obtain a clear and homogeneous solution. After centrifugation and degassing, the viscous liquid was poured into a mold and stored at -20 °C for 12 h and then taken out to obtain a pre-organic gel. The pre-organic gel was soaked in 0.1 mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organic gel was replaced, obtaining an initial hydrogel. The initial hydrogel was stretched to 100% of its original length and fixed, and dried at room temperature until completely dry to obtain a dry gel. The dry gel was soaked in 8 wt% ferric chloride solution and swollen sufficiently until the mass of the hydrogel remained unchanged to obtain a hydrogel containing iron ions. Subsequently, the hydrogel containing iron ions was soaked in a deep eutectic solvent composed of choline chloride and urea (the molar ratio of choline chloride to urea was preferably 1:2) for 5 min to obtain a tough anti-freezing conductive hydrogel.

[0075] Furthermore, the tough anti-freezing conductive hydrogel was assembled into a triboelectric nanogenerator, where nitrile rubber served as the positive friction layer, and VHB TM 4905 elastomer served as the negative friction layer, and the tough anti-freezing conductive hydrogel served as the electrode to construct a hydrogel triboelectric nanogenerator; VHB TM 4905 elastomer wrapped the hydrogel electrode to form a sandwich structure. One end of the wire was connected to the tough anti-freezing conductive hydrogel, and the other end passed through VHB TM 4905 elastomer to connect to an external circuit to conduct the current out.

[0076] Example 4

[0077] Dissolve 0.5 g of carboxymethyl cellulose in 24.5 g of deionized water, then add 65 g of dimethyl sulfoxide and 10 g of polyvinyl alcohol with a weight-average molecular weight of 89,000 - 98,000. Stir the mixed system at 95 °C for 5 h to obtain a clear and homogeneous solution. After centrifugal degassing, pour the viscous liquid into a mold, and take it out after storing at -20 °C for 12 h to obtain a pre-organic gel. Immerse the pre-organic gel in 0.1 mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organic gel is replaced, obtaining an initial hydrogel. Stretch the initial hydrogel to 160% of its original length and fix it in place, and dry it to absolute dryness at room temperature to obtain a dry gel. Immerse the dry gel in 10 wt% ferric chloride solution and swell it fully until the mass of the hydrogel remains unchanged, obtaining a hydrogel containing iron ions. Subsequently, immerse the hydrogel containing iron ions in a eutectic solvent composed of choline chloride and urea (the molar ratio of choline chloride to urea is preferably 1:2) for 8 min to obtain a tough, anti-freezing and conductive hydrogel. Further assemble the tough, anti-freezing and conductive hydrogel into a triboelectric nanogenerator, where nitrile rubber is the positive friction layer, VHB TM 4905 elastomer is the negative friction layer, and the tough, anti-freezing and conductive hydrogel is used as the electrode to construct a hydrogel triboelectric nanogenerator; VHB TM 4905 elastomer wraps the hydrogel electrode to form a sandwich structure. One end of the wire is connected to the tough, anti-freezing and conductive hydrogel, and the other end passes through VHB TM 4905 elastomer to connect to an external circuit to conduct out the current.

[0078] Example 5

[0079] Dissolve a mixture of 0.5 g of carboxylated nanocellulose and hyaluronic acid in 24.5 g of deionized water, then add 65 g of dimethyl sulfoxide and 10 g of polyvinyl alcohol with a weight-average molecular weight of ~47,000. Stir the mixed system at 95 °C for 5 h to obtain a clear and homogeneous solution. After centrifugal degassing, pour the viscous liquid into a mold, and take it out after storing at -20 °C for 12 h to obtain a pre-organic gel. Immerse the pre-organic gel in 0.1 mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organic gel is replaced, obtaining an initial hydrogel. Stretch the initial hydrogel to 60% of its original length and fix it in place, and dry it to absolute dryness at room temperature to obtain a dry gel. Immerse the dry gel in 5 wt% ferric chloride solution and swell it fully until the mass of the hydrogel remains unchanged, obtaining a hydrogel containing iron ions. Subsequently, immerse the hydrogel containing iron ions in a eutectic solvent composed of choline chloride and urea (the molar ratio of choline chloride to urea is preferably 1:2) for 3 min to obtain a tough, anti-freezing and conductive hydrogel. Further assemble the tough, anti-freezing and conductive hydrogel into a triboelectric nanogenerator, where nitrile rubber is the positive friction layer, VHB TMThe 4905 elastomer serves as the negative friction layer, and the tough anti-freezing conductive hydrogel serves as the electrode to construct a hydrogel triboelectric nanogenerator; VHB TM The 4905 elastomer wraps the hydrogel electrode to form a sandwich structure. One end of the wire is connected to the tough anti-freezing conductive hydrogel, and the other end passes through VHB TM The 4905 elastomer is connected to an external circuit to conduct the current out.

[0080] Example 6

[0081] Dissolve 0.8 g of sodium alginate in 24.2 g of deionized water, then add 60 g of dimethyl sulfoxide and 15 g of polyvinyl alcohol with a weight average molecular weight of ~47000. The mixed system is stirred at 95 °C for 5 h to obtain a clear and homogeneous solution. After centrifugation and degassing, the viscous liquid is poured into a mold and stored at -20 °C for 12 h and then taken out to obtain a pre-organic gel. The pre-organic gel is soaked in 0.1 mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organic gel is replaced, obtaining an initial hydrogel. The initial hydrogel is stretched to 120% of its original length and fixed, and dried at room temperature until completely dry to obtain a dry gel. The dry gel is soaked in 5 wt% ferric chloride solution and swollen sufficiently until the mass of the hydrogel remains unchanged, obtaining a hydrogel containing iron ions. Subsequently, the hydrogel containing iron ions is soaked in a deep eutectic solvent composed of choline chloride and urea (the molar ratio of choline chloride to urea is preferably 1:2) for 3 min to obtain a tough anti-freezing conductive hydrogel. Further, the tough anti-freezing conductive hydrogel is assembled into a triboelectric nanogenerator, where nitrile rubber serves as the positive friction layer, VHB TM The 4905 elastomer serves as the negative friction layer, and the tough anti-freezing conductive hydrogel serves as the electrode to construct a hydrogel triboelectric nanogenerator; VHB TM The 4905 elastomer wraps the hydrogel electrode to form a sandwich structure. One end of the wire is connected to the tough anti-freezing conductive hydrogel, and the other end passes through VHB TM The 4905 elastomer is connected to an external circuit to conduct the current out.

[0082] Comparative Example 1

[0083] Add 65 g of dimethyl sulfoxide and 10 g of polyvinyl alcohol with a weight average molecular weight of 89000 - 98000 to 24.5 g of deionized water. The mixed system is stirred at 95 °C for 5 h to obtain a clear and homogeneous solution. After centrifugation and degassing, the viscous liquid is poured into a mold and stored at -20 °C for 12 h and then taken out to obtain a pre-organic gel. The pre-organic gel is soaked in 0.1 mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organic gel is replaced, obtaining an initial hydrogel. The initial hydrogel is stretched to 80% of its original length and fixed, and dried at room temperature until completely dry to obtain a dry gel. The dry gel is soaked in water and swollen sufficiently to obtain a hydrogel.

[0084] Comparative Example 2

[0085] Dissolve 0.5g of carboxymethyl cellulose in 24.5g of deionized water, add 65g of dimethyl sulfoxide and 10g of polyvinyl alcohol with a weight average molecular weight of 89,000 to 98,000, stir the mixed system at 95°C for 5h to obtain a clear and uniform solution, centrifuge and degas, pour the viscous liquid into a mold, store it at -20°C for 12h, and then take it out to obtain a pre-organogel. Soak the pre-organogel in 0.1mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organogel is replaced to obtain an initial hydrogel. Fix the initial hydrogel at its original length and dry it at room temperature until it is absolutely dry to obtain a dry gel. Soak the dry gel in an 8wt% ferric chloride solution to fully swell until the mass of the hydrogel remains unchanged to obtain a hydrogel containing iron ions.

[0086] Comparative Example 3

[0087] 10 g of polyvinyl alcohol with a weight average molecular weight of 89,000 to 98,000 was added to 100 g of deionized water and heated and stirred at 95°C for 5 h to obtain a viscous, clear, uniform solution. After centrifugal degassing, the viscous liquid was poured into a mold, stored at -20°C for 12 h, and then taken out and allowed to stand at room temperature for 2 h. The above "freezing-room temperature standing" was set as a freeze-thaw cycle, and polyvinyl alcohol hydrogel was obtained after three consecutive freeze-thaw cycles.

[0088] Comparative Example 4

[0089] Dissolve 0.5g of carboxymethyl cellulose in 24.5g of deionized water, add 65g of dimethyl sulfoxide and 10g of polyvinyl alcohol with a weight average molecular weight of 89000-98000, stir the mixed system at 95°C for 5h to obtain a clear and uniform solution, centrifuge and degas, pour the viscous liquid into a mold, store it at -20°C for 12h and then take it out to obtain a pre-organogel. Soak the pre-organogel in 0.1mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organogel is replaced to obtain an initial hydrogel. Soak the initial hydrogel in a low eutectic solvent composed of choline chloride and urea (the molar ratio of choline chloride to urea is preferably 1:2) for 5min to obtain a gel.

[0090] Comparative Example 5

[0091] Dissolve 0.5 g of carboxymethyl cellulose in 24.5 g of deionized water, then add 65 g of dimethyl sulfoxide and 10 g of polyvinyl alcohol with a weight-average molecular weight of 89,000 - 98,000. Stir the mixed system at 95 °C for 5 h to obtain a clear and homogeneous solution. After centrifugal degassing, pour the viscous liquid into a mold, and take it out after storing at -20 °C for 12 h to obtain a pre-organic gel. Immerse the pre-organic gel in 0.1 mol / L dilute hydrochloric acid for sufficient solvent exchange until all the dimethyl sulfoxide in the pre-organic gel is replaced to obtain an initial hydrogel. Stretch the initial hydrogel to 80% of its original length and fix it, and dry it at room temperature until it is completely dry to obtain a dry gel. Immerse the dry gel in 8 wt% ferric chloride solution and swell it sufficiently until the mass of the hydrogel remains unchanged to obtain a hydrogel containing iron ions.

[0092] Analysis of test results:

[0093] Figure 1 In (a) is the SEM image of the gel product prepared in Comparative Example 2. Figure 1 In (b) is the SEM image of the gel product prepared in Example 1.

[0094] From Figure 1 it can be seen that compared with the gel product prepared in Comparative Example 2, the gel product prepared in Example 1 has an obvious anisotropic structure with fibers arranged along the pre-stretching direction, indicating that pre-stretching drying can induce fiber orientation.

[0095] Figure 2 are the XRD images of the gel products prepared in Comparative Example 5 and Example 1.

[0096] From Figure 2 it can be seen that the gel product prepared in Example 1 shows characteristic peaks at 19.80° and 40.58°, which represent the (101) characteristic reflection plane and (102) reflection plane in semi-crystalline polyvinyl alcohol, respectively. Comparative Example 5 also observes characteristic peaks at similar positions, but their intensities are weaker than those of Example 1, indicating that soaking in the deep eutectic solvent can significantly promote the formation of the crystalline region of polyvinyl alcohol.

[0097] Figure 3 In (a) are the tensile curves of the hydrogel products prepared in Examples 1 - 3 and Comparative Examples 1 - 4, Figure 3 In (b) are the Young's moduli and fracture stresses of the hydrogel products prepared in Examples 1 - 3 and Comparative Examples 1 - 4.

[0098] From Figure 3It can be seen that the Young's modulus and fracture stress of the hydrogel products prepared in Examples 1 to 3 are significantly higher than those of the gel products prepared in Comparative Examples 1 to 4. This is because the strong ionic bonds formed between the carboxyl-rich polysaccharide and iron ions, and the restricted drying-induced orientation of fibers under certain conditions and the role of the deep eutectic solvent in promoting the formation of crystal zones in the polymer further enable the formation of more crystal zones in the polymer network, thus increasing the toughness of the hydrogel. On the contrary, Comparative Example 1 lacks the formation of strong ionic bonds, and Comparative Example 2 has no fiber orientation, so its mechanical properties are weaker than those of Examples 1 to 3. In addition, although the traditional freeze-thaw cycle method used in Comparative Example 3 can induce the crystallization of polyvinyl alcohol, it does not induce the orientation of fibers and the deep eutectic solvent does not induce the crystallization of polyvinyl alcohol, resulting in its still low mechanical properties. Therefore, the method of the present invention is remarkable in toughening the hydrogel. The mechanical properties of Comparative Example 4 are better than those of Comparative Examples 1 to 3 but slightly weaker than those of Examples 1 to 3, indicating that the deep eutectic solvent can improve the strength of the hydrogel by inducing the formation of more crystal zones in polyvinyl alcohol.

[0099] The deep eutectic solvent is a "non-solvent" for polysaccharide and polyvinyl alcohol, and can induce the further formation of crystal zones between the two through hydrophobic interaction. Therefore, in addition to the ability to provide low-temperature stability, the role of the deep eutectic solvent in the present invention can also toughen the hydrogel.

[0100] Figure 4 It shows that the total tensile energy, dissipated energy and energy dissipation rate of the gel product prepared in Example 1 increase steadily under cyclic tensile with gradient strain. Among them, Figure 4 in (a) is the tensile curve of the gel product prepared in Example 1 in the cyclic tensile test with strains of 50%, 100%, 150%, 200% and 250% respectively, Figure 4 in (b) is the total tensile energy, dissipated energy and energy dissipation rate of the gel product prepared in Example 1 in the cyclic tensile test with strains of 50%, 100%, 150%, 200% and 250% respectively, Figure 4 in (c) is the cyclic tensile test curve of the gel product prepared in Example 1 when the strain is fixed at 200%, Figure 4 in (d) is the change of strength and dissipated energy of the gel product prepared in Example 1 in the cyclic tensile test when the strain is fixed at 200%. Figure 4 The test results show that in this test, the gel product prepared in Example 1 can maintain good mechanical stability without obvious breakage; the strength remains stable under cyclic tensile with fixed strain, and the dissipated energy only decreases in the first cycle and then remains stable, indicating that the structure of the gel product prepared in Example 1 remains stable without excessive sacrifice of ionic bonds and hydrogen bonds, indicating that the hydrogel prepared by the present invention can maintain stable mechanical properties. Further experimental results are as Figure 10 shown.

[0101] Figure 5 Among them, (a) is the differential scanning calorimetry test image of the hydrogel containing iron ions prepared in Example 1 after being soaked in the eutectic solvent composed of choline chloride and urea (the molar ratio of choline chloride to urea is preferably 1:2) for different times. Figure 5 Among them, (b) is the EIS curve image of the hydrogel product prepared in Example 1 after being soaked in the eutectic solvent for 5 minutes at different temperatures. Figure 5 Among them, (c) is the impedance and ionic conductivity of the hydrogel product prepared in Example 1 after being soaked in the eutectic solvent for 5 minutes at different temperatures. Figure 5 The differential scanning calorimetry image shows that the peaks of the hydrogel during heating and cooling disappear after soaking in the eutectic solution, indicating that the hydrogel does not freeze and melt with temperature changes. In addition, Figure 5 The EIS impedance image in (c) shows that the impedance of Example 1 at room temperature is only 11.42 Ω, and the ionic conductivity is 17.06 mS / cm. As the temperature decreases, the impedance increases, but at -40 °C, the impedance is only 28.07 Ω, and the ionic conductivity is 6.80 mS / cm. Therefore, the hydrogel prepared by the present invention has good low-temperature anti-freezing ability.

[0102] Figure 6 It is the performance test result of the gel product prepared in Example 1 after being assembled into a triboelectric nanogenerator. Figure 6 The specific experimental method is as follows: The tough anti-freezing conductive hydrogel prepared in Example 1 with a size of 5 cm × 5 cm × 1 mm is coated in a 7 cm × 7 cm VHB TM 4905 elastomer, and the open-circuit voltage generated by rubbing with a 7 cm × 7 cm nitrile rubber is as Figure 6 shown in (a), the short-circuit current generated is as Figure 6 shown in (b), and the short-circuit charge generated is as Figure 6 shown in (c). Figure 6 It shows that the open-circuit voltage, short-circuit current, and short-circuit charge generated after Example 1 is assembled into a triboelectric nanogenerator are 20.07 V, 0.34 μA, and 6.55 nC respectively, and remain stable. Therefore, Example 1 has good and stable output performance after being assembled into a device.

[0103] Figure 7 It is the sensor signal image for monitoring the flexion and extension of the human wrist and elbow after Example 1 is assembled into a triboelectric nanogenerator. Figure 8 It is the sensor signal image for monitoring the slow walking and fast walking of the human body after Example 1 is assembled into a triboelectric nanogenerator. Figure 9 It is the sensor signal image for monitoring the jogging, fast running, and jumping of the human body after Example 1 is assembled into a triboelectric nanogenerator. Figure 8 andFigure 9 The assembled triboelectric nanogenerator of Example 1 was installed at the position of the forefoot of the experimenter's shoe sole.

[0104] Figure 7 、 Figure 8 、 Figure 9 The performance of the hydrogel-based flexible triboelectric nanogenerator assembled from Example 1 in signal detection of different movements is shown. For the wrist flexion and extension movements with small tensile stress and the elbow flexion and extension movements with large stress, the nanogenerator provided in Example 1 of the present invention has good periodic signal output, and the signal output under large strain is more obvious. In addition, the generator can not only withstand tensile stress, but also has good electrical signal response under compressive stress. For the three actions of walking, running and jumping, the generator also has stable periodic signal output. In addition, the generator can accurately identify the same action at different frequencies (such as slow walking and fast walking, jogging and running). The electrical signals of low-frequency actions such as slow walking and jogging are weak and the signal interval time is slightly longer, and the signals are weak; while the electrical signals of high-frequency actions such as fast walking and running are significantly enhanced and the interval time is short. Therefore, the triboelectric nanogenerator assembled in the present invention can detect a variety of actions and distinguish the same action at different frequencies, and is a good motion signal detection sensor.

[0105] Figure 10 Figure for comparing the morphology before and after stretching, bending, twisting and curling of the tough anti-freezing conductive hydrogel product prepared in Example 1. From Figure 10 it can be seen that the morphology of the tough anti-freezing conductive hydrogel prepared in the present invention has no obvious change before and after stretching, bending, twisting and curling, indicating that the tough anti-freezing conductive hydrogel provided by the present invention has stable mechanical properties.

[0106] It can be seen from the above examples that the present invention adopts simple solvent exchange, greatly simplifies the material preparation process and operation difficulty, and improves the fiber orientation and induces the formation of hydrogen bonds by the structural design strategy of "fiber rearrangement - introduction of bonding - network reconstruction", thereby enhancing the strength and toughness of the polymer network itself.

[0107] Although the above examples have described the present invention in detail, they are only a part of the embodiments of the present invention, rather than all embodiments. Other embodiments can also be obtained according to this embodiment without creative efforts, and these embodiments all belong to the protection scope of the present invention.

Claims

1. A method for preparing a strong antifreeze conductive hydrogel, characterized in that: The following steps are involved: Mixing a polysaccharide, polyvinyl alcohol and a solvent to obtain a polymer solution, wherein the polysaccharide contains a carboxyl group and the solvent comprises water and an organic solvent; freezing the polymer solution to obtain a pre-organogel; subjecting the pre-organogel to a first solvent replacement to obtain an initial hydrogel; drying the initial hydrogel to obtain a xerogel; The drying is carried out under pre-stretching strain conditions; Treating the xerogel with an inorganic metal salt aqueous solution to obtain a hydrogel containing metal ions; The hydrogel containing metal ions is subjected to second solvent replacement using a low eutectic solvent to obtain the tough antifreeze conductive hydrogel.

2. The preparation method according to claim 1, characterized in that: The polysaccharide includes one or more of carboxymethyl cellulose, carboxylated nanocellulose, carboxymethyl chitosan, sodium alginate and hyaluronic acid.

3. The preparation method according to claim 1 or 2, characterized in that: The weight average molecular weight of the polyvinyl alcohol is 9000 to 205000; The mass ratio of the polysaccharide to the polyvinyl alcohol is 0.5:100 to 20:

100.

4. The preparation method according to claim 1, characterized in that: The pre-stretching strain is 20-200%.

5. The preparation method according to claim 1, characterized in that: The inorganic metal salt in the inorganic metal salt aqueous solution includes one or more of ferric chloride, calcium chloride and copper chloride; The content of the inorganic metal salt in the inorganic metal salt aqueous solution is 0.5-10 wt %.

6. The preparation method according to claim 1, characterized in that: The deep eutectic solvent comprises one or more of a choline chloride-urea deep eutectic solvent, a choline chloride-acrylic acid deep eutectic solvent and a choline chloride-malonic acid deep eutectic solvent; The time for the second solvent replacement is 1 to 30 minutes.

7. The tough antifreeze conductive hydrogel prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The invention comprises a polymer network formed by polysaccharide, polyvinyl alcohol and metal ions and a solvent, wherein the solvent comprises water and a deep eutectic solvent.

8. The tough antifreeze conductive hydrogel according to claim 7, characterized in that: In the tough antifreeze conductive hydrogel, the content of polyvinyl alcohol is 5-15wt%, the content of polysaccharide is 0.025-3wt%, and the content of metal ions is 10-20mg / g.

9. Use of the tough antifreeze conductive hydrogel according to claim 8 or 7 in a hydrogel nanogenerator.

10. A hydrogel friction nanogenerator, characterized in that: It comprises a positive friction layer, an electrode and a negative friction layer, wherein the electrode is wrapped inside the negative friction layer; the electrode is the tough antifreeze conductive hydrogel as described in claim 8 or 7.

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