Anti-freezing water-retaining diode-like composite hydrogel and preparation method thereof

Abstract

The invention discloses an anti-freezing and water-retaining diode-like composite hydrogel and a preparation method thereof. According to the invention, the surface of the diode-like composite hydrogel is treated by using a plasma technology, and (3-aminopropyl) triethoxysilane is used as a coating substrate, so that the tight combination between the coating and the surface of the hydrogel is enhanced; then N-dimethylformamide is used as an anti-freezing agent to be attached to the substrate coating, and a network barrier wrapping the surface of the hydrogel is formed; and soaking in silicone oil to prepare the double-coating hydrogel with ultrahigh water retention and frost resistance. The basic performance of the hydrogel is basically not affected by a polymerization packaging method, and meanwhile, the stability of the hydrogel in the air is enhanced, the service life of the hydrogel is prolonged, and the anti-freezing and water-retaining properties are obtained; therefore, the actual application range of the hydrogel can be expanded.

Description

Technical Field

[0001] The invention belongs to the technical field of functional polymer materials, and particularly relates to an antifreeze and water-retaining diode-like composite hydrogel and a preparation method thereof. Background Art

[0002] Hydrogels are composed of a three-dimensional cross-linked polymer network with a combination of hydrophobic groups and hydrophilic residues. The hydrophilic residues bind to water molecules, connecting them within the network, while the hydrophobic residues swell upon contact with water, forming a cross-linked polymer. Hydrogels are soft, hydrophilic, and biocompatible. These properties make hydrogels suitable for a variety of applications, including flexible electronics, smart wearable devices, and tissue engineering. Despite these advantages, they also face several problems and challenges. Traditional hydrogels are easily dehydrated during long-term use due to long-term exposure to the surrounding environment, resulting in the loss of key properties such as elasticity and conductivity. Similarly, traditional hydrogels lack antifreeze properties and are prone to fracture under low temperature conditions.

[0003] Polyvinyl alcohol (PVA) is an extremely safe organic polymer that is non-toxic, has no side effects, and exhibits excellent biocompatibility. Its aqueous gels are widely used in medical applications such as ophthalmology, wound dressings, and artificial joints. However, because PVA hydrogels contain a large amount of water, nearly all hydrogels inevitably dry in air, reducing their toughness and functionality. Few hydrogels developed to date have demonstrated stability in air and extreme environments, limiting their practical applications. Because drying and freezing are inherent properties of hydrogels, developing hydrogels with cryoresistant and water-retaining properties is a significant challenge. To expand the practical application of hydrogels, it is necessary to develop novel hydrogels that overcome the shortcomings of traditional hydrogels, such as their resistance to drying and freezing in extreme environments.

[0004] In addition, the hydrogels currently produced have disadvantages such as single function. In order to meet the wide range of needs in biomedicine and industry, it is of great significance to research and develop hydrogels with the dual properties of water retention and antifreeze. It is crucial for hydrogels to be used in wearable electronic devices in harsh environments. Summary of the Invention

[0005] In order to overcome the deficiencies and shortcomings of the prior art, the purpose of the present invention is to provide an antifreeze and water-retaining diode-like composite hydrogel and a preparation method thereof. This method, based on the PAP-MCP diode-like composite hydrogel, is based on double polymer coating encapsulation and polymerizes a double coating on the hydrogel surface to form a stable water-retaining and antifreeze barrier.

[0006] The first object of the present invention is to provide a method for preparing an antifreeze and water-retaining diode-like composite hydrogel, comprising the following steps: S1 acrylamide, N, N'- methylenebisacrylamide and initiator were sequentially added to water, heated and stirred until uniformly dispersed to obtain an AAm mixture; S2. Mixing cellulose, NH4HCO3, MXene suspension, and water to obtain a CNF-MXene suspension; S3. The polydimethyldiallylammonium chloride solution was added to the CNF-MXene suspension prepared in step S2 and mixed evenly. Then, polyvinyl alcohol was added and heated with stirring until the polyvinyl alcohol was completely dissolved to obtain a PDAC-MCP composite. S4. Sodium polystyrene sulfonate was added to the CNF-MXene suspension prepared in step S2 and mixed evenly. Polyvinyl alcohol was then added and heated with stirring until the polyvinyl alcohol was completely dissolved to obtain a PSSNa-MCP composite. S5. The PSSNa-MCP complex obtained in step S4 was cryogenically cooled to form a gel to obtain a PSSNa-MCP hydrogel; the AAm mixture obtained in step S1 was applied to the upper surface of the PSSNa-MCP hydrogel, and then irradiated with ultraviolet light to partially polymerize the AAm to obtain a PA-MCP composite gel; S6. The PDAC-MCP complex prepared in step S3 is poured onto the upper surface of the PA-MCP composite gel prepared in step S5, and the AAm is completely polymerized by ultraviolet irradiation to form a PAM layer; the mixture is then cryogenically frozen and thawed to obtain a PAP-MCP diode-like composite hydrogel. S7. Plasma-treated the PAP-MCP diode composite hydrogel to generate hydroxyl groups on the surface. The hydrogel was then immersed in a mixed solution of (3-aminopropyl)triethoxysilane and n-butyl acetate for 0.2-1 h. Excess surface solution was removed and removed to obtain a PAP-MCP diode composite hydrogel coated with a substrate coating. S8. The PAP-MCP diode-like composite hydrogel coated with the base coating was immersed in a mixed solution of N-dimethylformamide and n-butyl acetate for 0.2-1 h. The excess solution on the surface was removed and immersed in silicone oil for 1 h to obtain an antifreeze and water-retaining diode-like composite hydrogel.

[0007] Preferably, the initiator in step S1 is 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone.

[0008] Preferably, the heating and stirring in steps S1, S3 and S4 is stirring at 95°C for 3 hours; the low-temperature cooling to form gel in step S5 is cooling at -10°C to -4°C for 2-5 minutes, the ultraviolet irradiation in step S5 is 254 nm ultraviolet irradiation for 1 hour; the ultraviolet irradiation in step S6 is 254 nm ultraviolet irradiation for 0.5 hours, and the low-temperature freezing in step S6 is freezing at -10°C to -4°C for 10-12 hours.

[0009] Preferably, the plasma surface treatment in step S7 is performed using O2 as the treatment gas and a power of 600 W for 3-5 s.

[0010] Preferably, in step S1, the mass ratio of acrylamide, N,N'-methylenebisacrylamide and initiator is 2:0.01:0.1; in step S2, the amount ratio of cellulose, NH4HCO3, MXene suspension and water is 2.4 g:1 g:30 mL:12 mL; in step S3, the concentration of polydimethyldiallyl ammonium chloride solution is 20% by mass, the volume ratio of polydimethyldiallyl ammonium chloride solution to CNF-MXene suspension is 10:42, and the amount ratio of polydimethyldiallyl ammonium chloride solution to polyvinyl alcohol is 10 mL:12-15 g; in step S4, the amount ratio of sodium polystyrene sulfonate to CNF-MXene suspension is 2.4 g:42 mL, the mass ratio of sodium polystyrene sulfonate to polyvinyl alcohol is 2.4:12-15; the volume ratio of (3-aminopropyl)triethoxysilane to n-butyl acetate in the mixed solution in step S7 is 1:100; and the volume ratio of N-dimethylformamide to n-butyl acetate in the mixed solution in step S8 is 5:4.

[0011] Preferably, the thickness ratio of the PSSNa-MCP hydrogel layer, the PAM layer and the PDAC-MCP hydrogel layer in the PAP-MCP diode composite hydrogel is 1:0.1:1.

[0012] Preferably, the MXene suspension is prepared by the following method: 12.8 g of LiF was added to 284 mL of 15.7% HCl solution and stirred for 20 min. Then, 8 g of Ti3AlC2 powder was added to the LiF / HCl solution and stirred at 35°C for 24 h. The mixture was washed with deionized water until the pH of the suspension was 6. The precipitate was separated and diluted with 400 mL of deionized water, ultrasonically treated in an ice bath for 2 h, and centrifuged at 10,000 rpm for 10 min to obtain a MXene suspension.

[0013] In the above preparation method, the PAP-MCP diode hydrogel is prepared by a freeze-thaw method; in step S5, ultraviolet irradiation causes partial polymerization of AAm, and in step S6, ultraviolet irradiation causes complete polymerization of AAm to form a PAM hydrogel connecting layer, thereby increasing the interfacial adhesion between the PDAC-MCP layer and the PAM layer; the plasma treatment time in step S7 should not be too long, as too long a time will cause wrinkles on the surface of the hydrogel and damage the hydrogel body; in steps S7 and S8, the immersion should be air-dried to remove residual liquid from the previous solution before immersing in the next solution. The immersion time should not be too long or too short, as too long or too short will affect the coating thickness. If too long, the coating will be too thick and easily cracked and easily fall off; if too short, the coating will not be frost-resistant or water-retaining, and the coating will be unevenly distributed.

[0014] The second object of the present invention is to provide an antifreeze and water-retaining diode-like composite hydrogel prepared according to the method.

[0015] The third object of the present invention is to provide a self-generating sensor comprising the antifreeze and water-retaining diode-like composite hydrogel.

[0016] The fourth object of the present invention is to provide the use of the antifreeze and water-retaining diode-like composite hydrogel in the preparation of a self-generating sensor.

[0017] The present invention first prepares a PAP-MCP diode composite hydrogel having a three-layer structure comprising a PSSNa-MCP hydrogel, a PAM hydrogel and a PDAC-MCP hydrogel. On this basis, the present invention uses a plasma surface treatment technology to treat the surface of the PAP-MCP diode composite hydrogel to generate hydroxyl groups on the surface. Then, (3-aminopropyl) triethoxysilane is used as a coating base to enhance the close bonding between the coating and the hydrogel surface. N-dimethylformamide is then used as an antifreeze agent and attached to the base coating to form a network barrier wrapped around the hydrogel surface. Finally, after being soaked in silicone oil, a double-coated diode composite hydrogel with ultra-high water retention and antifreeze properties is prepared.

[0018] The present invention has the following advantages over the prior art: (1) The present invention aims to address the shortcomings of the current diode-like composite hydrogel performance. Based on the PAP-MCP diode-like composite hydrogel, the water-retaining property of the (3-aminopropyl)triethoxysilane bottom layer is used to make the composite hydrogel less likely to lose water. The antifreeze property of the N-dimethylformamide layer is then used to give the composite hydrogel antifreeze performance. The present invention polymerizes a double coating on the surface of the PAP-MCP diode-like composite hydrogel, so that the composite hydrogel has excellent water-retaining and antifreeze properties. The composite hydrogel has a wider range of applications.

[0019] (2) The present invention utilizes a polymerization encapsulation method to leave the basic properties of the composite hydrogel almost unaffected, while at the same time enhancing the stability of the composite hydrogel in the air, extending its lifespan, and obtaining antifreeze and water-retaining properties. Therefore, it can be used as a general method to expand the practical application range of hydrogels.

[0020] (3) The antifreeze and water-retaining diode-like composite hydrogel provided by the present invention provides a new research direction for the use of hydrogels in extreme environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a graph showing the test results of the writing sensing performance of the antifreeze and water-retaining diode-like composite hydrogel.

[0022] Figure 2 This is a graph showing the water retention performance of the antifreeze and water-retaining diode-like composite hydrogel at room temperature; the "uncoated" on the left side of each group represents the PAP-MCP diode-like composite hydrogel, and the "coated" on the right side represents the antifreeze and water-retaining diode-like composite hydrogel with a double surface polymer coating.

[0023] Figure 3 This is the cyclic tensile stress-strain curve of the antifreeze and water-retaining diode-like composite hydrogel.

[0024] Figure 4 This is a graph showing the output voltage of the antifreeze and water-retaining diode-like composite hydrogel in response to bending movements of the fingers, wrists, elbows, and knees.

[0025] Figure 5 This is a graph showing the continuous voltage output performance of the antifreeze and water-retaining diode-like composite hydrogel under low temperature conditions of -60°C.

[0026] Figure 6 The diagram shows the bending states of two hydrogels under low temperature conditions of -80°C; among them: A is the bending state of the PAP-MCP diode composite hydrogel, and B is the bending state of the antifreeze and water-retaining diode composite hydrogel with a surface polymer double coating. DETAILED DESCRIPTION

[0027] The following examples are provided to further illustrate the present invention, but are not intended to limit the present invention.

[0028] The cellulose used in the following examples is TEMPO cellulose nanofiber (manufacturer: Tianjin Mujingling Biotechnology Co., Ltd.; main components: CNF, deionized water, purity >99%). Acrylamide (AR, 99%, 71.08 MW), N,N'-methylenebisacrylamide (AR, 99%, 154.17 MW), polydimethyldiallylammonium chloride (600-900 Cp (25°C)), polyvinyl alcohol (alcoholysis degree: 98%-99% (mol / mol), 44.05 MW), sodium polystyrene sulfonate (average molecular weight 70,000, powder 206.2 MW), and (3-aminopropyl)triethoxysilane (AR, 99%, 221.37 MW).

[0029] The MXene suspension used in the following examples was prepared by the following method: First, 160 mL of deionized water was added to 124 mL of a 36% HCl solution. Then, 12.8 g of LiF was added to the HCl solution and stirred for 20 min. Then, 8 g of Ti3AlC2 powder was added to the mixed solution and stirred at 35°C for 24 h. The mixture was repeatedly washed with deionized water until the pH of the suspension reached 6. Finally, the precipitate was diluted with 400 mL of deionized water, ultrasonicated in an ice bath for 2 h, and centrifuged at 10,000 rpm for 10 min to obtain a MXene suspension.

[0030] Example 1 (1) Preparation of PAP-MCP diode composite hydrogel: ① Add 6 g acrylamide (AAm), 0.03 g N,N'-methylenebisacrylamide (MBAA), and 0.3 g 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (initiator) to 20 mL of deionized water in sequence. Heat and stir at 95°C for 3 h until uniformly dispersed to obtain an AAm mixed solution, which was then placed in a dark environment to cool for later use.

[0031] ② Mix 2.4 g of cellulose, 1 g of NH4HCO3, 30 mL of MXene suspension, and 12 mL of water to obtain 42 mL of CNF-MXene suspension.

[0032] ③ Add 10 mL (20 wt%) of polydimethyldiallyl ammonium chloride (PDADMAC) aqueous solution to the CNF-MXene suspension (42 mL) prepared according to step ② and stir to mix evenly. Then, add 12 g of polyvinyl alcohol (PVA) and stir at 95 °C for 3 h until the PVA is completely dissolved to obtain the PDAC-MCP composite.

[0033] ④ Add 2.4 g of sodium polystyrene sulfonate (PSSNa) to the CNF-MXene suspension (42 mL) prepared according to step ② and stir to mix evenly. Then add 12 g of polyvinyl alcohol (PVA) and stir at 95 °C for 3 h until PVA is completely dissolved to obtain the PSSNa-MCP composite.

[0034] ⑤ Pour the PSSNa-MCP complex prepared in step ④ into a glass mold and cool it at -10°C for 2 min to obtain a PSSNa-MCP hydrogel; then apply the AAm mixture prepared in step ① on the PSSNa-MCP hydrogel and irradiate it with 254 nm ultraviolet light for 1 h to partially polymerize the AAm to obtain a PA-MCP composite hydrogel.

[0035] ⑥ Pour the PDAC-MCP complex prepared in step ③ onto the upper surface of the AAm layer of the PA-MCP composite hydrogel prepared in step ⑤, and irradiate it with 254 nm ultraviolet light for 0.5 h to completely polymerize the AAm to form a PAM hydrogel connecting layer (PAM layer), then freeze it at -10°C for 10 h and thaw it at room temperature to obtain a PAP-MCP diode composite hydrogel, wherein the thickness ratio of the PSSNa-MCP hydrogel layer, the PAM layer, and the PDAC-MCP hydrogel layer is 1:0.1:1.

[0036] (2) Hydrogel surface treatment and preparation of base coating: The PAP-MCP diode composite hydrogel prepared in step (1) was subjected to plasma treatment (output power 600 W for 3 s) using O2 as the treatment gas to generate hydroxyl groups on the surface; then the treated PAP-MCP diode composite hydrogel was immediately immersed in a mixed solution consisting of 0.5 mL (3-aminopropyl) triethoxysilane and 50 mL n-butyl acetate for 0.2 h; the hydrogel was taken out and placed at room temperature, and the excess solution on the surface was removed in a ventilated environment to obtain a PAP-MCP diode composite hydrogel coated with a base coating.

[0037] (3) Preparation of N-dimethylformamide antifreeze layer: The PAP-MCP diode-like composite hydrogel coated with the base coating prepared in step (2) was immersed in a mixed solution consisting of 25 mL of N-dimethylformamide and 20 mL of n-butyl acetate for 0.2 h; taken out and placed at room temperature, surface moisture was removed in a ventilated environment, and finally immersed in silicone oil for 1 h and then taken out to obtain an antifreeze and water-retaining diode-like composite hydrogel with a surface polymerized double coating.

[0038] Example 2 (1) Preparation of PAP-MCP diode composite hydrogel: ① Add 6 g acrylamide (AAm), 0.03 g N,N'-methylenebisacrylamide (MBAA), and 0.3 g 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (initiator) to 20 mL of deionized water in sequence. Heat and stir at 95°C for 3 h until uniformly dispersed to obtain an AAm mixed solution, which was then placed in a dark environment to cool for later use.

[0039] ② Mix 2.4 g of cellulose, 1 g of NH4HCO3, 30 mL of MXene suspension, and 12 mL of water to obtain 42 mL of CNF-MXene suspension; ③ Add 10 mL (20 wt%) of polydimethyldiallyl ammonium chloride (PDADMAC) aqueous solution to the CNF-MXene suspension (42 mL) prepared according to step ② and stir to mix evenly. Then, add 14 g of polyvinyl alcohol (PVA) and stir at 95 °C for 3 h until the PVA is completely dissolved to obtain the PDAC-MCP composite.

[0040] ④ Add 2.4 g of sodium polystyrene sulfonate (PSSNa) to the CNF-MXene suspension (42 mL) prepared according to step ② and stir to mix evenly. Then add 14 g of polyvinyl alcohol (PVA) and stir at 95 °C for 3 h until PVA is completely dissolved to obtain the PSSNa-MCP composite.

[0041] ⑤ Pour the PSSNa-MCP complex prepared in step ④ into a glass mold and cool it at -4°C for 5 min to obtain a PSSNa-MCP hydrogel; then apply the AAm mixture prepared in step ① on the PSSNa-MCP hydrogel and irradiate it with 254 nm ultraviolet light for 1 h to partially polymerize the AAm to obtain a PA-MCP composite hydrogel.

[0042] ⑥ Pour the PDAC-MCP complex prepared in step ③ onto the upper surface of the PA-MCP composite hydrogel prepared in step ⑤ (i.e., the upper surface of the AAm layer therein), and irradiate it with 254 nm ultraviolet light for 0.5 h to completely polymerize the AAm to form a PAM hydrogel connecting layer (PAM layer), then freeze it at -4°C for 12 h and thaw it at room temperature to obtain a PAP-MCP diode composite hydrogel, wherein the thickness ratio of the PSSNa-MCP hydrogel layer, the PAM layer, and the PDAC-MCP hydrogel layer is 1:0.1:1.

[0043] (2) Hydrogel surface treatment and preparation of base coating: The PAP-MCP diode composite hydrogel prepared in step (1) was subjected to plasma treatment (output power 600 W for 5 s) using O2 as the treatment gas to generate hydroxyl groups on the surface; then the treated PAP-MCP diode composite hydrogel was immediately immersed in a mixed solution consisting of 0.5 mL (3-aminopropyl) triethoxysilane and 50 mL n-butyl acetate for 0.6 h, taken out and placed at room temperature, and excess solution on the surface was removed in a ventilated environment to obtain a PAP-MCP diode composite hydrogel coated with a base coating.

[0044] (3) Preparation of N-dimethylformamide antifreeze layer: The PAP-MCP diode-like composite hydrogel coated with the base coating prepared in step (2) was immersed in a mixed solution consisting of 25 mL of N-dimethylformamide and 20 mL of n-butyl acetate for 0.6 h; taken out and placed at room temperature, surface moisture was removed in a ventilated environment, and finally immersed in silicone oil for 1 h and then taken out to obtain an antifreeze and water-retaining diode-like composite hydrogel with a surface polymerized double coating.

[0045] Example 3 (1) Preparation of PAP-MCP diode composite hydrogel: ① Add 6 g acrylamide (AAm), 0.03 g N,N'-methylenebisacrylamide (MBAA), and 0.3 g 2-hydroxy-4'-(2-hydroxyethoxy)-2-methylpropiophenone (I2959) (initiator) to 20 mL of deionized water in sequence. Heat and stir at 95°C for 3 h until uniformly dispersed to obtain an AAm mixed solution, which was then placed in a dark environment to cool for later use.

[0046] ② Mix 2.4 g of cellulose, 1 g of NH4HCO3, 30 mL of MXene suspension, and 12 mL of water to obtain 42 mL of CNF-MXene suspension; ③ Add 10 mL (20 wt%) of polydimethyldiallyl ammonium chloride (PDADMAC) aqueous solution to the nanocellulose-MXene (CNF-MXene) suspension (42 mL) prepared according to step ② and stir to mix evenly. Then, add 15 g of polyvinyl alcohol (PVA) and stir at 95 °C for 3 h until the PVA is completely dissolved to obtain the PDAC-MCP composite.

[0047] ④ Add 2.4 g of sodium polystyrene sulfonate (PSSNa) to the CNF-MXene suspension (42 mL) prepared according to step ② and stir to mix evenly. Then add 15 g of polyvinyl alcohol (PVA) and stir at 95 °C for 3 h until PVA is completely dissolved to obtain the PSSNa-MCP composite.

[0048] ⑤ Pour the PSSNa-MCP complex prepared in step ④ into a glass mold and cool it at -4°C for 5 min to obtain a PSSNa-MCP hydrogel; then apply the AAm mixture prepared in step ① on the PSSNa-MCP hydrogel and irradiate it with 254 nm ultraviolet light for 1 h to partially polymerize the AAm to obtain a PA-MCP composite hydrogel.

[0049] ⑥ The PDAC-MCP complex prepared in step ③ was poured onto the upper surface of the PA-MCP composite hydrogel prepared in step ⑤ (i.e., the upper surface of the Aam layer therein), and irradiated with 254 nm ultraviolet light for 0.5 h to completely polymerize AAm to form a PAM hydrogel connecting layer (PAM layer), which was then frozen at -4°C for 12 h and thawed at room temperature to obtain a PAP-MCP diode composite hydrogel, wherein the thickness ratio of the PSSNa-MCP hydrogel layer, the PAM layer, and the PDAC-MCP hydrogel layer was 1:0.1:1.

[0050] (2) Hydrogel surface treatment and preparation of base coating: The PAP-MCP diode composite hydrogel prepared in step (1) was plasma treated with O2 as the treatment gas (output power 600 W for 5 s) to generate hydroxyl groups on the surface. The treated PAP-MCP diode composite hydrogel was then immediately immersed in a mixed solution consisting of 0.5 mL (3-aminopropyl) triethoxysilane and 50 mL n-butyl acetate for 1 h. The treated PAP-MCP diode composite hydrogel was taken out and placed at room temperature and the excess solution on the surface was removed in a ventilated environment to obtain a PAP-MCP diode composite hydrogel coated with a base coating.

[0051] (3) Preparation of N-dimethylformamide antifreeze layer: The PAP-MCP diode-like composite hydrogel coated with the base coating prepared in step (2) was immersed in a mixed solution consisting of 25 mL of N-dimethylformamide and 20 mL of n-butyl acetate for 1 h, taken out and placed at room temperature, and surface moisture was removed in a ventilated environment. Finally, it was immersed in silicone oil for 1 h and then taken out to obtain an antifreeze and water-retaining diode-like composite hydrogel with a surface polymerized double coating.

[0052] Example 4: Performance Test The PAP-MCP diode-like composite hydrogel and the antifreeze and water-retaining diode-like composite hydrogel with a surface polymer double coating prepared in Example 3 were used as the test objects to test their sensing performance, water retention performance, mechanical properties, antifreeze and electrical output performance.

[0053] (1) Sensing performance: The antifreeze-resistant, water-retaining diode-like composite hydrogel with a double surface polymer coating prepared in Example 3 was cut into a sample measuring 2 cm (length) × 2 cm (width) × 0.1 cm (thickness). This sample was connected to an LCR digital bridge via copper wires for writing sensing performance testing.

[0054] The results are as follows Figure 1 As shown, it can be seen that when the hydrogel is spread on an insulating surface and writing is repeated three times on its surface, the relative resistance of the hydrogel changes regularly, indicating that the hydrogel is very sensitive to changes in external force. Therefore, the hydrogel is very suitable as a new type of ultra-sensitive sensor.

[0055] (2) Water retention performance: At room temperature, observe the water loss of samples with different shapes (square, circle, heart, triangle, and five-pointed star).

[0056] The results are as follows Figure 2 As shown, it can be seen that after 5 days of exposure to the natural environment, the PAP-MCP diode-like composite hydrogel (without coating) on ​​the left is very easy to lose water, dry out and deform, while the antifreeze and water-retaining diode-like composite hydrogel (with coating) with a double surface polymer coating on the right has strong water retention and does not lose water significantly within 5 days, and can still maintain its original shape.

[0057] (3) Mechanical properties: The antifreeze and water-retaining diode-like composite hydrogel (4 cm (length) × 1 cm (width) × 0.5 cm (thickness)) with a double-coated surface polymer coating prepared in Example 3 was subjected to a cyclic tensile test (100%-450% strain). Figure 3 As shown in the figure, it can be seen that with the increase of tensile strain, the tensile strain is stretched to 100%, 150%, 200%, 250%, 300%, 350%, 400% and 450%, respectively. As the maximum tensile strain increases, the stress-strain curve area of ​​the antifreeze and water-retaining diode-like composite hydrogel with a surface polymer double coating becomes larger, indicating that the energy consumed by the dissociation of hydrogen bonds and coordination bonds in the hydrogel during deformation increases. This energy dissipation ability is crucial for the synthesis of hydrogels with high strength and high toughness.

[0058] (4) Antifreeze and electrical output performance: ① The antifreeze and water-retaining diode-like composite hydrogel with a double-coated surface polymer coating prepared in Example 3 was used as the object. It was adhered to joints such as fingers, wrists, elbows, and knees, and the output voltage generated by bending the fingers, wrists, elbows, and knees was detected at a low temperature of -20°C.

[0059] The results are as follows Figure 4The figure shows the output voltages generated by bending the fingers, wrist, elbow, and knee, from left to right. It can be seen that when the hydrogel is adhered to the corresponding joints, the output voltage is generated by squeezing the hydrogel through movement, and the output voltage is stable as the joints move.

[0060] ② Using the antifreeze and water-retaining diode-like composite hydrogel (4 cm (length) × 4 cm (width) × 0.5 cm (thickness)) with a surface polymer double coating prepared in Example 3 as the object, the composite hydrogel was continuously pressed in a harsh environment of -60°C and the output voltage generated was detected.

[0061] The results are as follows Figure 5 As shown in the figure, when the antifreeze and water-retaining diode-like composite hydrogel with a surface polymer double coating is continuously pressed in a harsh environment of -60°C, its output voltage value remains stable, indicating that the hydrogel not only has good water-retaining and antifreeze properties, but also has stable electrical output performance.

[0062] ③ The PAP-MCP diode-like composite hydrogel and the antifreeze and water-retaining diode-like composite hydrogel with a surface polymerized double coating prepared in Example 3 were placed at -80°C for a bending test.

[0063] The results are as follows Figure 6 As shown, the PAP-MCP diode-like composite hydrogel cannot be bent, while the antifreeze and water-retaining diode-like composite hydrogel with a double surface polymer coating can still be bent.

Claims

1. A method for preparing an antifreeze and water-retaining diode-like composite hydrogel, characterized in that: The following steps are involved: S1 acrylamide, N, N'- methylenebisacrylamide and initiator were sequentially added to water, heated and stirred until uniformly dispersed to obtain an AAm mixture; S2. Mixing cellulose, NH4HCO3, MXene suspension, and water to obtain a CNF-MXene suspension; S3. The polydimethyldiallylammonium chloride solution was added to the CNF-MXene suspension prepared in step S2 and mixed evenly. Then, polyvinyl alcohol was added and heated with stirring until the polyvinyl alcohol was completely dissolved to obtain a PDAC-MCP composite. S4. Sodium polystyrene sulfonate was added to the CNF-MXene suspension prepared in step S2 and mixed evenly. Polyvinyl alcohol was then added and heated with stirring until the polyvinyl alcohol was completely dissolved to obtain a PSSNa-MCP composite. S5. The PSSNa-MCP complex obtained in step S4 was cryogenically cooled to form a gel to obtain a PSSNa-MCP hydrogel; the AAm mixture obtained in step S1 was applied to the upper surface of the PSSNa-MCP hydrogel, and then irradiated with ultraviolet light to partially polymerize the AAm to obtain a PA-MCP composite gel; S6. The PDAC-MCP complex prepared in step S3 is poured onto the upper surface of the PA-MCP composite gel prepared in step S5, and the AAm is completely polymerized by ultraviolet irradiation to form a PAM layer; the mixture is then cryogenically frozen and thawed to obtain a PAP-MCP diode-like composite hydrogel. S7. Plasma-treated the PAP-MCP diode composite hydrogel to generate hydroxyl groups on the surface. The hydrogel was then immersed in a mixed solution of (3-aminopropyl)triethoxysilane and n-butyl acetate for 0.2-1 h. Excess surface solution was removed and removed to obtain a PAP-MCP diode composite hydrogel coated with a substrate coating. S8. The PAP-MCP diode-like composite hydrogel coated with the base coating was immersed in a mixed solution of N-dimethylformamide and n-butyl acetate for 0.2-1 h. The excess solution on the surface was removed and immersed in silicone oil for 1 h to obtain an antifreeze and water-retaining diode-like composite hydrogel.

2. The method according to claim 1, characterized in that The initiator in step S1 is 2-hydroxy-4′-(2-hydroxyethoxy)-2-methylpropiophenone.

3. The method according to claim 1, wherein The heating and stirring in steps S1, S3 and S4 is stirring at 95°C for 3 hours; the low-temperature cooling to form gel in step S5 is cooling at -10°C to -4°C for 2-5 minutes, and the ultraviolet irradiation in step S5 is 254 nm ultraviolet irradiation for 1 hour; the ultraviolet irradiation in step S6 is 254 nm ultraviolet irradiation for 0.5 hours, and the low-temperature freezing in step S6 is freezing at -10°C to -4°C for 10-12 hours.

4. The method according to claim 1, wherein The plasma surface treatment in step S7 is performed using O2 as the treatment gas and a power of 600 W for 3-5 s.

5. The method according to claim 1, wherein In the step S1, the mass ratio of acrylamide, N,N'-methylenebisacrylamide and initiator is 2:0.01:0.1; in the step S2, the amount ratio of cellulose, NH4HCO3, MXene suspension and water is 2.4 g:1 g:30 mL:12 mL; in the step S3, the concentration of the polydimethyldiallyl ammonium chloride solution is 20% by mass, the volume ratio of the polydimethyldiallyl ammonium chloride solution to the CNF-MXene suspension is 10:42, and the amount ratio of the polydimethyldiallyl ammonium chloride solution to polyvinyl alcohol is 10 mL:12-15 g; in the step S4, the amount ratio of sodium polystyrene sulfonate to the CNF-MXene suspension is 2.4 g:42 mL, the mass ratio of sodium polystyrene sulfonate to polyvinyl alcohol is 2.4:12-15; the volume ratio of (3-aminopropyl)triethoxysilane to n-butyl acetate in the mixed solution in step S7 is 1:100; and the volume ratio of N-dimethylformamide to n-butyl acetate in the mixed solution in step S8 is 5:

4.

6. The method according to claim 1, characterized in that The thickness ratio of the PSSNa-MCP hydrogel layer, the PAM layer and the PDAC-MCP hydrogel layer in the PAP-MCP diode composite hydrogel is 1:0.1:

1.

7. The method according to claim 1, wherein The MXene suspension was prepared by the following method: 12.8 g of LiF was added to 284 mL of 15.7% HCl solution and stirred for 20 min. Then, 8 g of Ti3AlC2 powder was added to the LiF / HCl solution, stirred at 35°C for 24 h, and washed with deionized water until the pH of the suspension was 6. The precipitate was separated and then diluted with 400 mL of deionized water, ultrasonically treated in an ice bath for 2 h, and centrifuged at 10,000 rpm for 10 min to obtain a MXene suspension.

8. The antifreeze and water-retaining diode-like composite hydrogel prepared according to the method according to any one of claims 1 to 7.

9. A self-generating sensor, characterized in that: It comprises the antifreeze and water-retaining diode-like composite hydrogel according to claim 8.

10. Use of the antifreeze and water-retaining diode-like composite hydrogel according to claim 8 in the preparation of a self-generating sensor.

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