Hydrophobic salt-resistant polymer and preparation method thereof, composite gel, preparation method and application

Abstract

The invention relates to a hydrophobic salt-resistant polymer and a preparation method thereof, a composite gel, a preparation method and application, the hydrophobic salt-resistant polymer has hydrophobic performance, can repel halogen ions and further has salt resistance, the polymer and a gel matrix are compounded to form moisture absorption cooling gel, the stability between the gel and a heat source can be enhanced, and the stability of the gel is improved. The cooling effect is improved.

Description

Technical Field

[0001] The present invention relates to a polymer and a composite gel, belonging to the field of materials. Background Art

[0002] From households, industries to commerce, refrigeration technology is an indispensable part of human daily life. With global warming and energy transformation, the refrigeration demand in all walks of life is also increasing day by day. Traditional active refrigeration technologies usually consume a large amount of energy and emit a large amount of carbon dioxide greenhouse gases, imposing a relatively large burden on the earth's environment and human survival. Evaporative cooling refrigeration is a passive refrigeration method. Its principle is that due to water having the highest evaporation enthalpy among room-temperature liquids, evaporative cooling of water can take away a large amount of heat, thus achieving a cooling effect. However, due to the dependence on liquid water sources during long-term operation, the natural evaporation of water is restricted and affected by climatic conditions. In contrast, regardless of geographical and hydrological conditions, due to the global hydrological cycle, atmospheric humidity is a reliable source of fresh water. The amount of water in the atmosphere is estimated to be 1.29 billion tons, which is six times the total amount of water in global rivers. If water can be extracted from the air (Atmospheric moisture exploitation, AME) through a water vapor adsorbent and used for cooling, it will be a promising method to meet decentralized energy demands and promote the transition to a low-carbon economy, and cold energy can be obtained from the ubiquitous atmospheric humidity anytime and anywhere. In this process, the adsorbent material plays a crucial role, and its inherent properties, such as hygroscopicity, structure, and functionality, will all affect the overall performance of AME. Benefiting from highly adjustable physical structures and chemical properties, composite hygroscopic polymer gels (HPG) can be precisely controlled through gel chemistry to achieve ideal hygroscopic properties. In addition, their rich porous structures, unique swelling characteristics, and easily integrated functional additives enable HPG to obtain a high water absorption capacity at a relatively wide working humidity, making it an ideal material for air water extraction and cooling.

[0003] However, two problems will occur when the HPG cools down: First, during the cooling process, heat is conducted from the surface of the heat source to the HPG through the interface, causing a large amount of water in the HPG to evaporate. Since the water transmission speed in the polymer network of the gel is different, the water transmission speed on the upper surface and the edge is slow. Therefore, as the water evaporates, the water content in the gel is uneven everywhere, resulting in the curling or shrinking of the gel, poor contact with the heat source surface, unstable cooling interface, and thus introducing air with low thermal conductivity to form an interfacial thermal resistance, affecting the cooling effect. Currently, the commonly used solution is to inhibit the curling of the hydrogel by means of iron frames, ropes, etc. However, this method can only form good contact between the bound place and the heat source surface, and there is still a possibility of poor contact in the unbound place. In addition, there is also a way to solve it by chemical bulk modification. For example, the literature (Adv. Mater. 2021, 33, 2103937) selects a hydrophilic polymer network (acrylic acid-c%o-2-acrylamido-2-methylpropanesulfonic acid) (P(AA-co-AMPSA)) to accommodate the hygroscopic liquid of 1-ethyl-3-methylimidazolium acetate ([EMIM][Ac]) and reduced graphene oxide (rGO) additive to obtain a solid rGO / ionic gel (RIG). Benefiting from the addition of [EMIM][Ac], the obtained RIG exhibits strong adhesion mediated by multiple supramolecular forces, thus forming a stable contact interface with the heat source surface. However, this bulk modification method sacrifices the water absorption capacity to a certain extent. Second, HPG usually composits with hygroscopic salts to improve the water absorption capacity. However, hygroscopic salts usually contain halogen atoms. When a hygroscopic salt leaks, the halogen atoms will come into contact with the heat source surface, thus corroding the heat source surface made of some metal materials. The literature (Cell Reports Physical Science 3, 100781, 2022) introduced a layer of PE film between the hydrogel and the heat source surface through physical modification to prevent the halogen atoms from leaking and corroding the metal. However, the PE film has the situation of wrinkling and deformation, affecting the stability of the cooling interface. In addition, the literature (Mater. Horiz., 2021, 8, 1518–1527) replaced the chlorine anions in the common hygroscopic salts with benign anions for ion exchange (including acetate, oxalate, and citrate) through chemical modification, thus reducing the corrosiveness. However, this bulk modification method also sacrifices the water absorption capacity to a certain extent. In summary, how to simultaneously take into account the stability of the cooling interface, the corrosion resistance of the adsorbent, and the water absorption capacity of the HPG to achieve the best effect is the main bottleneck affecting the cooling effect of the HPG.

[0004] Technical content

[0005] In order to solve the above problems, the present invention provides a polymer which, after being compounded with the gel, does not reduce the water absorption of the gel itself, but can improve the bonding strength between the gel and the substrate to be cooled, thereby avoiding the curling of the gel.

[0006] Based on the above scheme, the present invention provides a hydrophobic salt-resistant polymer on the one hand, the structural formula of the polymer is:

[0007] Wherein x, y, and z are all natural numbers greater than 1 or equal to 1.

[0008] In a second aspect, a method for preparing a hydrophobic salt-resistant polymer is provided, comprising the following steps:

[0009] S01: Lithium bis(trifluoromethanesulfonyl)imide is mixed with methacryloyloxyethyltrimethylammonium chloride to undergo ion exchange reaction to obtain TSFI - Compound 1;

[0010] S02 polymerizes compound 1 with a hydrophobic monomer and a flexible monomer to form the hydrophobic salt-resistant polymer.

[0011] As a preferred solution, the specific operation steps of step S01 are:

[0012] a. Mix deionized water, lithium bis(trifluoromethanesulfonylimide) monomer, and methacryloyloxyethyltrimethylammonium chloride monomer, stir thoroughly, and let stand. After the water and oil separate, pour out the supernatant to leave an oily liquid. In this step, lithium bis(trifluoromethanesulfonylimide) monomer and methacryloyloxyethyltrimethylammonium chloride monomer undergo ion exchange to obtain compound 1. The reaction is as follows:

[0013]

[0014] b. Continue to add deionized water to the oily liquid, stir and let it stand for separation of water and oil, leaving the oily liquid. Repeat the same operation 5 times to obtain a clean oily ionic liquid. In this step, the residual LiCl in the compound 1 obtained in a is removed;

[0015] c. The cleaned oily ionic liquid was placed in a vacuum oven and dried at 60° C. for 24 h to remove residual moisture, thereby obtaining the final ionic liquid, namely, compound 1.

[0016] As a preferred solution, step S02 is specifically: mixing compound 1, hydrophobic monomer hexafluorobutyl acrylate, and flexible monomer 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester, adding photoinitiator 2,2-diethoxyacetophenone, and UV light-initiated polymerization at room temperature to obtain a hydrophobic salt-resistant polymer.

[0017] In a third aspect, the present invention provides a composite gel comprising a polymer layer on a gel matrix as a protective layer, which enhances the bonding strength between the gel and the metal matrix and prevents the gel from corroding the metal matrix. The protective layer is the aforementioned hydrophobic and salt-resistant polymer.

[0018] In a fourth aspect, the present invention provides a method for preparing the composite gel, comprising the following steps:

[0019] S01 obtains a gel matrix;

[0020] S02 coating or impregnating the gel matrix with a polymer precursor solution, wherein the polymer precursor solution is a mixture of compound 1, a hydrophobic monomer, a flexible monomer, and 2,2-diethoxyacetophenone;

[0021] S03 uses UV light irradiation to react substances in the polymer precursor solution to form a hydrophobic and salt-resistant polymer on the gel matrix;

[0022] S04: Soaking the gel obtained in step S03 in a hygroscopic inorganic salt for loading, and drying to obtain an integrated double-layer composite atmospheric hygroscopic cooling gel with a hydrophobic protective layer, i.e., a composite gel.

[0023] The present invention utilizes an in-situ polymerization method to generate a hydrophobic, salt-resistant polymer on the surface of a gel matrix. This polymer is then composited onto the gel matrix to form a protective layer. The composite gel is an integrated, double-layered atmospheric moisture-absorbing and cooling gel with a hydrophobic protective layer. The gel layer and the protective layer are mechanically interlocked. Without sacrificing adsorption / desorption performance, the gel stabilizes the cooling interface and prevents halogen atom corrosion of the substrate, enhancing the effectiveness of air moisture extraction and cooling across the entire humidity range.

[0024] As a preferred embodiment, the hydrophobic monomer is hexafluorobutyl acrylate, which has a high glass transition temperature and is conducive to improving the hydrophobic performance. The flexible monomer is 2-methyl-2-acrylate-2-(2-methoxyethoxy)ethyl ester. After the flexible monomer reacts with the compound, it can adjust the elastic modulus of the polymer and form a good bond with the substrate (the substrate to be cooled).

[0025] As one embodiment, compound 1 is an ionic liquid, and the TSFI present in the ionic liquid - It has an electrostatic repulsion effect on halogen ions. Its preparation method is: lithium bis(trifluoromethanesulfonyl)imide and methacryloyloxyethyltrimethylammonium chloride are prepared by ion exchange. The ion exchange reaction formula is:

[0026]

[0027] The specific steps are as follows: Mix deionized water, lithium bis(trifluoromethanesulfonyl)imide monomer, and methacryloyloxyethyl trimethyl ammonium chloride monomer, stir and then let stand. After the water and oil are separated, pour out the upper clear liquid and leave the oily liquid. Subsequently, continue to add deionized water to the oily liquid, stir at the same stirring speed, let stand for water-oil separation, and leave the oily liquid. Repeat the same operation several times to obtain a clean oily ionic liquid, place it in a vacuum oven, dry it at 60 °C to remove residual moisture, and obtain the final ionic liquid. Preferably, the addition ratio of lithium bis(trifluoromethanesulfonyl)imide to methacryloyloxyethyl trimethyl ammonium chloride monomer is 1:1.

[0028] As a preferred embodiment, the gel matrix is formed by cross-linking any one, two or more monomers of sodium acrylate and its derivatives, acrylamide, and acrylic acid. The formed gel has good hydrophilicity and a large water absorption capacity, and the monomer for forming the gel matrix is further preferably acrylamide. Further preferably, the ionic liquid, hexafluorobutyl acrylate hydrophobic monomer, and 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate flexible monomer in the polymer precursor solution are mixed in a mass ratio of (8-14):(45-56):(30-47), and preferably mixed in a mass ratio of 11:51:37.

[0029] As a preferred embodiment, the preparation method of the gel matrix includes the following steps:

[0030] (1) Mix and polymerize the polymer monomer, deionized water, initiator, and cross-linking agent, stir evenly, and then add tetramethylethylenediamine to obtain a precursor solution; the polymer monomer is preferably any one or a combination of two or more of sodium acrylate and its derivatives, acrylamide, and acrylic acid, the initiator is preferably one of potassium persulfate and ammonium persulfate, and further preferably ammonium persulfate. The reaction conditions of ammonium persulfate are mild, and it can initiate a polymerization reaction with the remaining monomers at low temperature; the cross-linking agent is preferably one of ethylene glycol dimethacrylate and N,N'-methylenebisacrylamide, and further preferably N,N'-methylenebisacrylamide. N,N'-methylenebisacrylamide has a low cost and is easy to disperse in an aqueous solution.

[0031] (2) Inject the precursor solution obtained in step (1) into a mold and polymerize to obtain a gel sample;

[0032] (3) Wash the gel sample obtained in step (2) with deionized water 3-4 times, remove the unreacted polymer monomer and cross-linking agent, and then soak it in deionized water to absorb water;

[0033] (4) Freeze the washed gel sample;

[0034] (5) Freeze-dry the frozen gel sample to remove moisture to create pores, and thus obtain the gel matrix;

[0035] The present invention prepares a gel matrix by means of freeze-drying. By removing moisture through freeze-drying, a pore structure is formed, thereby obtaining a porous polymer gel. Due to the existence of the porous structure, the mass transfer of water molecules is significantly accelerated, and a place is provided for loading hygroscopic inorganic salts later, so that the prepared gel has excellent hygroscopic properties.

[0036] During the preparation process of the gel matrix, the content of each component in the precursor solution is preferably as follows: the content of N,N-methylenebisacrylamide is 0.10 wt%, the content of ammonium persulfate in the precursor solution is 0.20 wt%, the content of acrylamide is 9.96 wt%, and the content of tetramethylethylenediamine is 0.06 wt%.

[0037] During the preparation process of the gel matrix, the reaction conditions are preferably as follows: in step (2), the polymerization reaction temperature is room temperature and the time is 1 - 24 h. In step (3), the soaking temperature is room temperature and the time is 1 - 2 h. In step (4), the freezing temperature is -45 °C and the time is 3.5 - 5 h. In step S05, the freeze-drying temperature is 40 - 60 °C and the time is 48 h.

[0038] In the fifth aspect, the present invention provides a method for absorbing moisture and reducing temperature using a composite gel. The side of the composite gel provided with a protective layer is attached to a heat source (or a substrate to be cooled). The composite gel provides an intermittent passive refrigeration method. The working mode is as follows: at high temperature (when working), the evaporation of water in the composite gel can take away a large amount of heat and reduce the temperature of the heat source; at low temperature (when the heat source rests), the hydrogel can automatically absorb moisture in the air for automatic water replenishment and restore the swollen state. The composite gel can be reused and has an automatic circulation ability. This device works without external energy input and has the characteristics of no noise, small volume, low cost, convenient intelligence, adjustable volume, zero noise, and wide application range.

[0039] Furthermore, the composite gel can be used in the fields of electronic devices, construction, automobiles, integrated circuits, data centers, etc.

[0040] The composite gel prepared by the present invention is an integrated double-layer composite atmospheric moisture-absorbing and temperature-reducing gel with a hydrophobic protective layer, which can be automatically regenerated. The principle is as follows: the saturated vapor pressure of the hygroscopic salt is lower than that of pure water. When the composite hydrogel contains a hygroscopic salt, the vapor pressure of the composite hydrogel is controlled by the concentration of the hygroscopic salt. When the vapor pressure of the composite hydrogel is lower than the vapor pressure of the environment, the composite hydrogel can automatically absorb water from the environment; conversely, when the vapor pressure of the composite hydrogel is higher than the vapor pressure of the environment, the water inside the composite hydrogel will evaporate.

[0041] Attach the side of the protective layer of the composite gel prepared by the present invention to the surface of the heat source. When the temperature of the heat source surface is too high, the composite gel desorbs, and water evaporates from the composite gel. Since the latent heat of water is relatively large, a large amount of heat can be carried away, thereby regulating the temperature of the heat source.

[0042] Through the ion exchange process of the present invention, the binding energy between N + and TFSI - is greater than that between N + and CI - . The binding energy between Cl - and Li + is also greater than that between Cl - and N + ions. At the same time, there is also an electrostatic repulsion between TFSI - and CI - . Therefore, the entire protective layer has a certain repulsive effect on Cl - . Secondly, the presence of the protective layer forms a hydrophobic interface physically, hindering LiCl from contacting the metal substrate. In these two aspects, the corrosion resistance of the atmospheric moisture-absorbing and cooling gel is improved.

[0043] The beneficial effects produced by the present invention are as follows: (1) The interface design of the gel in the present invention can be used for cooling electronic devices. This hydrogel combines the functions of moisture absorption, evaporation and heat dissipation, stable refrigeration interface, corrosion resistance, and reusability. It can effectively dissipate heat from the heat source intelligently without external energy input, and has the characteristics of no noise, small volume, low cost, convenient intelligence, adjustable volume, and wide application range. The design strategy of this material has strong scalability and can be extended to other hydrogels.

[0044] (2) The composite gel in the present invention improves the adhesion of the moisture-absorbing and cooling gel without sacrificing the water absorption capacity through the protective layer designed at the interface, thereby improving the cooling effect. At the same time, it can effectively prevent the leakage of hygroscopic salt halogen ions and prevent corrosion of the heat source surface, expanding the application range.

[0045] (3) The present invention forms a protective layer through in-situ polymerization, which can effectively resist the curling caused by interfacial heat transfer, improve the adhesion force, and thus improve the cooling performance. At the same time, in the non-flat state / dynamic state, this advantage is more prominent. When the temperature of the heat source is 70 °C, the maximum adsorption cooling duration can reach 8-9 h, and the maximum average temperature reduction is 8 °C.

[0046] (4) In the present invention, the polymer forming the protective layer is synthesized from a hydrophobic monomer, an ionic liquid, a flexible monomer, and a photoinitiator. Among them, the hydrophobic monomer is hexafluorobutyl acrylate; the ionic liquid is made by ion exchange of lithium bis(trifluoromethanesulfonyl)imide and methacryloyloxyethyl trimethyl ammonium chloride, and is used to repel chloride ions; the flexible monomer is 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate, which adjusts the elastic modulus; the photoinitiator is 2,2-diethoxyacetophenone, which promotes the photocuring of the protective layer precursor liquid. Description of the Drawings

[0047] Figure 1 Polymer synthesis reaction formula in the present invention;

[0048] Figure 2 Schematic diagram of the preparation method of the composite gel in the present invention;

[0049] Figure 3 Scanning electron micrograph of the composite gel in the present invention;

[0050] Figure 4 Graph of the 180° peel test results of the gel in the present invention;

[0051] Figure 5 Gel adsorption-desorption test graphs in Example 2 and Comparative Example 1. In the graph, PAM / LiCl with a protective layer is the test data of the gel prepared in Example 2, and PAM / LiCl is the test data of the gel prepared in Comparative Example 1;

[0052] Figure 6 Graph of the general cooling performance test results of the gels in Example 2 and Comparative Example 1;

[0053] Anti-corrosion performance test after 60 adsorption-desorption cycles in FIGS. 7(a) and 7(b): FIG. 7(a) is the aluminum plate contacted by the gel in Example 2, and FIG. 7(b) is the aluminum plate contacted by the gel in Comparative Example 1. In the graph, the substrate is the aluminum plate;

[0054] Figure 8 Contact angles of the polymer in Example 1 and the gel in Comparative Example 1. Detailed Description of the Invention

[0055] The present invention will be further explained in detail below with reference to the drawings and specific examples. However, it should be understood that the protection scope of the present invention is not limited by the specific examples. The embodiments of the present invention are described by taking polyacrylamide hydrogel as an example, and other hydrogels are also applicable. Similarly, in the application scenario, the aluminum plate is used as the heat source for illustration, and other heat sources are also applicable. The dosages or operation parameters of the substances in the following examples only list the optimal values. According to the conventional knowledge of those skilled in the art, the dosages or parameters can be adjusted to meet specific requirements, and the adjusted solutions are still within the protection scope of the present invention.

[0056] For all the raw materials of the present invention, there are no special restrictions on their purity, and analytically pure ones are preferably used in the present invention. For all the raw materials of the present invention, their sources and abbreviations belong to the conventional sources and abbreviations in the art, and are clear and definite in the fields of their related uses. Those skilled in the art can purchase them from the market or prepare them by conventional methods according to the abbreviations and corresponding uses.

[0057] Example 1

[0058] A preparation method of a hydrophobic salt-resistant polymer, comprising the following steps:

[0059] (1) Mix 20 ml of deionized water, 5.8 g of lithium bis(trifluoromethanesulfonyl)imide monomer, and 5 g of methacryloyloxyethyl trimethylammonium chloride monomer, stir for 1 h at a stirring speed of 300 r / min, then let stand. After the water and oil are separated, pour out the upper clear liquid and leave the oily liquid.

[0060] (2) Continue to add deionized water to the oily liquid, stir for 20 min at the same stirring speed, let stand for water-oil separation, and leave the oily liquid. Repeat the same operation 5 times to obtain a cleaned oily ionic liquid.

[0061] (3) Put the oily ionic liquid into a vacuum oven and bake it at 60 °C for 24 h to remove the residual moisture and obtain the final ionic liquid.

[0062] (4) Mix the ionic liquid, hydrophobic monomer of hexafluorobutyl acrylate, and flexible monomer of 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate to form a mixed solution. The mass percentages of each component in the mixed solution are: ionic liquid 10.85 wt%, hydrophobic monomer of hexafluorobutyl acrylate 50.28 wt%, and flexible monomer of 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate 37 wt%. Add 1.87 wt% of photoinitiator 2,2-diethoxyacetophenone to the mixed solution to obtain a polymer precursor solution.

[0063] (5) Subject the polymer precursor solution to UV light-induced polymerization at room temperature for 20 - 30 min to obtain a hydrophobic salt-resistant polymer.

[0064] Example 2

[0065] A preparation method of a composite gel, as Figure 2 , comprising the following steps:

[0066] Preparation of the gel matrix:

[0067] (1) Ammonium persulfate, N,N'-methylenebisacrylamide, and acrylamide were dissolved in deionized water and stirred evenly to form a mixed solution. The mass ratio of each component in the mixed solution was: 0.20 wt% ammonium persulfate, 0.10 wt% N,N'-methylenebisacrylamide, 9.96 wt% acrylamide solution, 89.68 wt% deionized water. Subsequently, 0.06 wt% of tetramethylethylenediamine was added to the mixed solution to obtain a precursor solution;

[0068] (2) The precursor solution was injected into a 5.0×5.0×2.0 cm 3 polytetrafluoroethylene mold, sealed, and polymerized at room temperature for 1 h to obtain a 5.0×5.0×0.5 cm 3 gel sample;

[0069] (3) The gel sample obtained in step (2) was washed with deionized water and then soaked in deionized water for 1 hour to remove unreacted monomers, crosslinking agents, and initiators and absorb water;

[0070] (4) The gel sample soaked in step (3) was placed in a freezer and frozen in a -45°C freezer for 4 h;

[0071] (5) The completely frozen gel sample in step (4) was placed in a freeze dryer and freeze-dried under the condition of ~-50°C to obtain a gel matrix.

[0072] Preparation of the protective layer part:

[0073] (6) 20 ml of deionized water, 5.8 g of lithium bis(trifluoromethanesulfonyl)imide monomer, and 5 g of methacryloyloxyethyltrimethylammonium chloride monomer were mixed and stirred at a stirring speed of 300 r / min for 1 h, then left to stand. After the water-oil layer separation, the upper clear liquid was poured out, leaving an oily liquid. Subsequently, deionized water was continuously added to the oily liquid, stirred at the same stirring speed for 20 min, left to stand for water-oil separation, and the oily liquid was left. After repeating the same operation 5 times, a clean oily ionic liquid was obtained, placed in a vacuum oven, and dried at 60°C for 24 h to remove residual moisture to obtain the final ionic liquid.

[0074] (7) Each monomer liquid was mixed to form a mixed solution. The mass percentage of each component in the mixed solution was: ionic liquid 10.85 wt%, hexafluorobutyl acrylate hydrophobic monomer 50.28 wt%, 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate flexible monomer 37 wt%. Then, 1.87 wt% of the photoinitiator 2,2-diethoxyacetophenone was added to the mixed solution to obtain a protective layer precursor solution.

[0075] UV curing:

[0076] (8) In the 5.0×5.0×0.5 cm obtained in step (5)3 One side of the gel matrix is evenly coated with the protective layer precursor liquid, with a coating amount of about 0.03-0.05g / cm 2 , UV light initiates polymerization at room temperature for 20 to 30 minutes, the polymerization reaction formula is as follows Figure 1 After the reaction is completed, a gel matrix with a protective layer is obtained.

[0077] Loading LiCl:

[0078] (9) The protective layer side of the gel matrix obtained in step (8) is upward, and the gel below the protective layer is immersed in a 40 wt% LiCl solution, with the protective layer placed above the liquid surface. After soaking at room temperature for 72 hours, it is placed in a forced air drying oven, first at 80°C for 24 hours, and then at 100°C for 12 hours, to obtain an integrated double-layer composite atmospheric moisture-absorbing and cooling gel with a hydrophobic protective layer, i.e., the above-mentioned composite gel.

[0079] The microstructure of the composite gel prepared in Example 2 was observed under a scanning electron microscope. Figure 3 It can be seen that the integrated double-layer composite atmospheric hygroscopic cooling gel with a hydrophobic protective layer consists of a gel layer and a protective layer. The upper layer is a porous gel layer, and the lower layer is a dense protective layer. The thickness of the protective layer is approximately 260 μm.

[0080] Comparative Example 1

[0081] Compared with Example 2, the gel does not have a protective layer, and the preparation method is as follows:

[0082] (1) ammonium persulfate, N,N-methylenebisacrylamide, and acrylamide were dissolved in deionized water and stirred to form a mixed solution, wherein the mass ratio of the components in the mixed solution was: 0.20 wt% ammonium persulfate, 0.10 wt% N,N-methylenebisacrylamide, 9.96 wt% acrylamide solution, and 89.68 wt% deionized water, and then 0.06 wt% tetramethylethylenediamine was added to the mixed solution to obtain a precursor solution;

[0083] (2) Inject the precursor solution into a 5.0×5.0×2.0cm 3 After sealing in a polytetrafluoroethylene mold, polymerization was carried out at room temperature for 1 h to obtain a 5.0×5.0×0.5 cm 3 Gel samples;

[0084] (3) washing the gel sample obtained in step (2) with deionized water 3 to 4 times and then soaking it at room temperature for 1 hour;

[0085] (4) placing the gel sample soaked in step (3) into a freezer and freezing it at -45°C for 4 hours;

[0086] (5) Put the completely frozen gel sample in step (4) into a freeze dryer and conduct freeze drying under the condition of ~ -50 °C;

[0087] (6) Immerse the gel sample obtained in step (5) in a 40wt% LiCl solution, soak it at room temperature for 72 h, then put it into a forced-air oven, bake it at 80 °C for 24 h and then at 100 °C for 12 h to obtain a gel without a hydrophobic protective layer.

[0088] Test the 180° peel test of the composite gel in Test Example 2 and the gel in Comparative Example 1. The results are as Figure 4 It can be seen that the stable platform load of the composite gel prepared in Example 2 is about 50 N m -1 while the stable platform load of the gel prepared in Comparative Example 1 is only about 9 N m -1 indicating that the presence of the protective layer greatly improves the adhesion performance of the composite gel.

[0089] Test the water adsorption - desorption performance of the composite gel in Test Example 2 and the gel in Comparative Example 1 at different humidities. As Figure 5 it can be seen that the moisture absorption capacities of the composite gel prepared in Example 2 at relative humidities of 40%, 60%, and 80% can reach 1.5, 2.1, and 3.4 g g -1 respectively; while at the same humidity, the moisture absorption capacities of the gels prepared in the comparative example are 1.5, 2.1, and 3.4 g g -1 respectively. Their moisture absorption capacities are the same at the same humidity, indicating that the presence of the protective layer does not affect the moisture absorption capacity of the moisture-absorbing gel.

[0090] Test the cooling performance of the composite gel in Test Example 2 and the gel in Comparative Example 1. As Figure 6 it can be seen that under the same moisture absorption humidity and time, within the limited cooling time, the maximum cooling amplitudes of the composite gel prepared in Example 2 and the gel prepared in Comparative Example 1 do not differ much. However, at relative adsorption humidities of 40%, 60%, and 80%, the cooling times of the composite gel prepared in Example 2 are 5.37 h, 6.91 h, and 8.3 h respectively, while the cooling times of the moisture-absorbing and cooling gel without a hydrophobic protective layer prepared in Comparative Example 1 are only 1.21 h, 1.82 h, and 3.36 h respectively, indicating that the presence of the protective layer greatly improves the cooling performance of the gel.

[0091] Test the corrosion of the composite gel in Test Example 2 and the gel in Comparative Example 1 on metal after contacting with the metal. As shown in Figure 7, under the same number of cycles, the aluminum plate contacted by the integrated double-layer composite moisture-absorbing and cooling gel with a hydrophobic protective layer prepared in Example 2 still remains smooth, while the aluminum plate contacted by the moisture-absorbing and cooling gel without a hydrophobic protective layer prepared in Comparative Example 1 shows obvious pitting corrosion.

[0092] The contact angles of the polymer in Test Example 1 and the contact angle of the gel in Comparative Example 1 are as follows Figure 8 , indicating that the hydrophobic salt-resistant polymer (protective layer) is hydrophobic, while the gel PAM / LiCl without a protective layer in Comparative Example 1 is hydrophilic.

[0093] The above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention.

Claims

1. A hydrophobic and salt-resistant polymer, characterized in that: The structural formula is as follows: where x ≥ 1, y ≥ 1, z ≥ 1, and x, y, z are natural numbers.

2. A method for preparing a hydrophobic and salt-resistant polymer, characterized in that: It includes the following steps: S01 Mix lithium bis(trifluoromethanesulfonyl)imide with methacryloyloxyethyl trimethyl ammonium chloride to carry out an ion exchange reaction to obtain Compound 1 containing TSFI - ; S02 Polymerize compound I with a hydrophobic monomer and a flexible monomer to form the hydrophobic salt-resistant polymer.

3. The preparation method according to claim 2, wherein: The structural formula of compound I is as follows:

4. The preparation method according to claim 2, characterized in that: The hydrophobic monomer is hexafluorobutyl acrylate, and the flexible monomer is 2-(2-methoxyethoxy)ethyl 2-methyl-2-propenoate. The polymerization reaction conditions of compound I, the hydrophobic monomer, and the flexible monomer are UV light irradiation. The structural formula of the resulting hydrophobic salt-resistant polymer is as follows: Where x≥1, y≥1, z≥1, and x, y, z are natural numbers.

5. The preparation method according to claim 2, wherein: In step S02, the mixing mass ratio of each component is compound I monomer:hydrophobic monomer:flexible monomer = (8 - 14):(45 - 56):(30 - 47).

6. A preparation method of a composite gel, characterized in that: It includes the following steps: S01 Obtain a gel matrix; S02 Coat at least one side of the gel matrix with a polymer precursor solution. The preparation method of the polymer precursor solution is as follows: a Mix lithium bis(trifluoromethanesulfonyl)imide with methacryloyloxyethyl trimethyl ammonium chloride to carry out an ion exchange reaction to obtain Compound I containing TSFI - ; b Mix compound I, a hydrophobic monomer, and a flexible monomer to obtain a polymer precursor solution; S03 The polymer precursor solution polymerizes on the gel matrix to form a hydrophobic salt-resistant polymer.

7. The preparation method of the composite gel according to claim 6, wherein: The gel matrix is formed by cross-linking any one, two, or more monomers selected from sodium acrylate and its derivatives, acrylamide, and acrylic acid.

8. The preparation method of the composite gel according to claim 6, characterized in that: It further includes step S04 Place the gel matrix composite with the hydrophobic salt-resistant polymer in a hygroscopic salt solution to fill the salt on the gel matrix.

9. A composite gel prepared according to any one of claims 6 - 8.

10. A method for using the composite gel according to claim 9, characterized in that: Attach the side provided with the protective layer to the object to be cooled. The protective layer is a hydrophobic salt-resistant polymer.

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