Low-thickness, macroscopically uniform and stable inorganic hydrated salt phase change gel material and preparation method thereof

Abstract

The invention provides an inorganic hydrated salt phase change gel material which is low in thickness and macroscopically uniform and stable and a preparation method of the inorganic hydrated salt phase change gel material. The inorganic hydrated salt phase change gel material is prepared from the following components in percentage by weight: 70 to 90 percent of hydrated salt, 0 to 6 percent of nucleating agent, 0 to 6 percent of gel thickener, 0 to 18 percent of deionized water, 8 to 30 percent of gel monomer, 0.03 to 0.5 percent of chemical cross-linking agent, 2 to 10 percent of surface modifier, 2 to 10 percent of dispersing agent, 0.03 to 0.5 percent of ionic cross-linking agent, 0.005 to 0.5 percent of initiator and 0.1 to 1 percent of surfactant. The method comprises the following steps: heating inorganic salt in a water bath, stirring and dissolving, sequentially adding a monomer combination and a cross-linking agent to form a uniform solution, adding a solution prepared from an initiator and deionized water into the solution, adding a surfactant, uniformly stirring, and pouring into a specific mold; and standing and heating in a drying oven until the reaction is complete, standing at normal temperature, and demolding to obtain the inorganic hydrated salt phase change gel material. According to the invention, the specific surfactant is introduced to regulate and control the interface characteristics of the hydrated salt gel precursor, so that the macroscopic uniformity that the thickness deviation is less than or equal to 0.1 mm is realized.

Description

Technical Field

[0001] This invention relates to the field of phase change materials technology, and in particular to a low-thickness, macroscopically uniform and stable inorganic hydrated salt phase change gel material and its preparation method. Background Technology

[0002] Phase change materials can absorb and release a large amount of latent heat through a phase transition process. The energy storage efficiency of phase change materials is significantly higher than that of sensible heat energy storage methods that rely solely on temperature changes. Therefore, they have important application value in fields such as building energy conservation, solar energy utilization, industrial waste heat recovery, and battery thermal management.

[0003] Among various phase change materials, inorganic phase change materials, represented by hydrated inorganic salts, have unique advantages over traditional organic phase change materials: lower raw material costs, higher phase change enthalpy, better thermal conductivity, and natural flame-retardant properties, making them a key research focus in the field of medium- and low-temperature energy storage. However, hydrated inorganic salts have inherent defects. They are prone to leakage during solid-liquid phase change, and phase separation may occur after multiple cycles due to density differences. Some salts are also corrosive. These problems limit the direct application of hydrated inorganic salts.

[0004] Hydrogels, as three-dimensional network materials formed by cross-linking of hydrophilic polymer chains, can stably encapsulate liquid hydrated salts through capillary forces and hydrogen bonds in their network pores, achieving "shape-based encapsulation." This encapsulation method can preserve the phase change energy storage characteristics of hydrated salts while effectively overcoming their leakage and phase separation problems. When the pore size of the hydrogel network matches the crystal size of the hydrated salt, a better encapsulation effect can be obtained.

[0005] However, existing research on hydrated salt gels largely focuses on optimizing thermal and mechanical properties, with insufficient attention paid to key morphological parameters (such as thickness and flatness) for practical applications. When using mold casting to prepare low-thickness hydrated salt gels, significant problems arise: the hydrogel precursor solution, containing high concentrations of salt ions and polymer chains, exhibits high surface tension. The significantly increased solid-liquid contact area in the low-thickness mold leads to solution aggregation at the mold center and edge shrinkage, resulting in uneven gel sheet thickness and potentially localized voids lacking material. This macroscopic inhomogeneity disrupts heat flow distribution and induces anisotropy in mechanical properties, severely limiting its application in thickness-sensitive scenarios such as flexible wearables and ultra-thin battery thermal protection.

[0006] While existing patented technologies have made significant strides in the field of phase change gels, they exhibit considerable limitations in controlling the uniformity of low-thickness inorganic hydrated salt gels.

[0007] CN119979127A discloses a high enthalpy phase change gel for cold chain applications, using n-alkanes (25-30 wt%) as the phase change substrate and constructing a network with polyvinyl alcohol and a crosslinking agent to improve stability. While this technology achieves a high enthalpy of 280-310 J / g, it has three limitations: ① The use of organic phase change materials results in poor flame retardancy (oxygen index < 20%) and high cost (raw material cost approximately 10-15 RMB / kg); ② It does not involve low-thickness molding processes, and its mold shaping relies on static cooling at -10℃, making it only suitable for samples with a thickness ≥ 5 mm, and unable to solve the uneven spreading of gels around 1 mm due to surface tension; ③ The system contains a large amount of organic components, resulting in poor compatibility with inorganic hydrated salts, making it difficult to directly apply to inorganic systems.

[0008] CN120289933A proposes a flexible anisotropic conductive hydrated salt gel, which achieves lithium battery thermal management through a semi-interpenetrating structure of hydrophilic modified conductive filler (1-15 parts) and hydrogel network. The core of this technology lies in the balance between conductivity and flexibility, but its impregnation process (impregnation in hydrated salt solution for 24-48 hours) has significant defects: ① Thickness control depends on the swelling degree of the hydrogel, making it difficult to accurately control uniformity below 1 mm, with measured thickness deviation > 0.3 mm; ② It has not been optimized for surface tension, and central agglomeration still exists at low thicknesses; ③ The introduction of conductive filler reduces the phase transition enthalpy (by 10-15% compared to pure hydrated salt), which is inconsistent with the "high enthalpy + low thickness uniformity" goal pursued by this invention.

[0009] CN120349777A employs an organic-inorganic composite phase change material (30-80wt%) and a polyurethane matrix, suppressing leakage through capillary adsorption of porous materials such as foamed graphite. While this technology improves cycle stability, it has key shortcomings in low-thickness applications: ① The addition of porous materials increases the system viscosity, resulting in poor flowability in 1mm molds and a tendency for "insufficient adhesive" at the edges; ② The introduction of organic phase change materials (such as n-octadecane) lowers the total enthalpy (measured at 100-150 J / g), which is lower than that of pure inorganic hydrated salt systems; ③ It relies on complex processes such as crushing and grinding (10-20 mesh) and mold curing (25-70℃), which cannot simplify the low-thickness molding process.

[0010] In summary, existing technologies either focus on the high enthalpy of organic phase change materials or emphasize functional improvements such as conductivity and flexibility, but neither has solved the core contradiction of inorganic hydrated salt gels at a low thickness of about 1 mm: the balance between uneven spreading dominated by surface tension and high enthalpy and ease of processing. Summary of the Invention

[0011] The embodiments of the present invention provide a low-thickness and macroscopically uniform and stable inorganic hydrated salt phase change gel material and its preparation method, so as to achieve the goal of providing a low-thickness and macroscopically uniform and stable inorganic hydrated salt phase change gel material.

[0012] To achieve the above objectives, the present invention adopts the following technical solution.

[0013] According to one aspect of the present invention, a low-thickness and macroscopically uniform and stable inorganic hydrated salt phase change gel material is provided, comprising the following components by weight percentage:

[0014] The composition includes 70-90% hydrated salt, 0-6% nucleating agent, 0-6% gel thickener, 0-18% deionized water, 8-30% gel monomer, 2-10% surface modifier, 2-10% dispersant, 0.03-0.5% chemical crosslinking agent, 0.03-0.5% ionic crosslinking agent, 0.005-0.5% initiator, and 0.1-1% surfactant.

[0015] Preferably, the surfactant is one or more of the following: MS-7100, DuPont FS-3100, Fluorad FC4430, Capstone FS-30, Capstone FS-63, Yumu YM-3016, Superwet-320, MS-8100, fluorosurfactant RP-6100, fluorosurfactant RP-7100, FH3100, fluorocarbon surfactant HT-3100, and fluorosurfactant 1730.

[0016] Preferably, the hydrated salt includes one or more of sodium sulfate decahydrate, magnesium chloride dodecahydrate, calcium nitrate hexahydrate, disodium phosphate dodecahydrate, sodium thiosulfate pentahydrate, sodium acetate trihydrate, potassium dihydrogen phosphate trihydrate, calcium chloride hexahydrate, and magnesium nitrate hexahydrate.

[0017] Preferably, the nucleating agent comprises one or more of the following: sodium tetraborate decahydrate, anhydrous sodium sulfate, anhydrous sodium carbonate, potassium chloride, strontium chloride hexahydrate, alum, silicon dioxide, zinc oxide, magnesium hydroxide, calcium carbonate, nano-carbon powder, and microcrystalline graphite.

[0018] Preferably, the gel thickener includes one or more of sodium carboxymethyl cellulose, xanthan gum, guar gum, sodium alginate, polyvinyl alcohol, sodium polyacrylate, bentonite, and fumed silica.

[0019] Preferably, the gel monomer includes one or more of sodium acrylate, acrylic acid, 2-hydroxyethylacrylamide, and acrylamide.

[0020] According to another aspect of the present invention, a method for preparing an inorganic hydrated salt phase change gel material is provided, comprising:

[0021] Hydrated salt crystals are placed in a container, which is then placed in a constant temperature water bath. A surface modifier is added to the container and the mixture is stirred. A dispersant is then added to the container, which is placed under ultrasound for ultrasonic dispersion. The solution is then heated to a certain temperature and stirred until it is completely dissolved to form a transparent solution A.

[0022] After sequentially adding gel monomer, gel thickener, chemical crosslinking agent and ionic crosslinking agent to the transparent solution A, a uniform pregel solution B is obtained.

[0023] After adding a surfactant to a uniform pregel solution B, the mixture is stirred at high speed. The amphiphilic molecular structure of the surfactant changes the interaction between surface molecules of the solution from strong polar attraction to weak van der Waals forces between fluorocarbon chains, thereby reducing the surface tension of the solution and obtaining a pregel solution C containing the surfactant.

[0024] The initiator is dissolved in a solvent to obtain an initiator solution. The initiator solution is placed under ultrasonic irradiation for ultrasonic dispersion treatment. Under constant temperature conditions, pregel solution C is added dropwise to the initiator solution and stirred until uniformly mixed to obtain mixture D.

[0025] The mixture D is poured into a mold of a specific size that has been treated to prevent sticking, and the mold of the specific size filled with the material is placed in an oven for segmented crosslinking treatment.

[0026] After the segmented cross-linking treatment, the material is subjected to constant temperature standing and low temperature treatment, and then demolded to remove it from the mold of the specific size to obtain a hydrogel of the target thickness.

[0027] Preferably, the amphiphilic molecular structure in the surfactant transforms the surface molecular interactions of the solution from strong polar attraction to weak van der Waals forces between fluorocarbon chains, reducing the surface tension of the solution and obtaining a pre-gel solution C containing the surfactant, comprising:

[0028] In the hydrated salt gel solution system composed of uniform pregel liquid B and surfactant, the molecules in the amphiphilic molecular structure of the fluorinated nonionic surfactant spontaneously migrate to the gas-liquid interface. The hydrophilic ends of the amphiphilic molecular structure combine with water molecules and salt ions in the solution through polar interactions, while the fluorocarbon chains are oriented towards the air phase due to intermolecular forces. This directional arrangement replaces the original highly cohesive molecules on the surface of the solution, changing the interaction between surface molecules of the solution from strong polar attraction to weak van der Waals forces between fluorocarbon chains, thereby reducing the surface tension of the solution.

[0029] The hydrophilic end of the surfactant forms a weak interaction with the polar groups on the mold surface, reducing the solid-liquid interfacial tension, further increasing the spreading coefficient, enhancing wettability, and allowing the solution to adhere more evenly to the mold surface. The resulting liquid film has a uniform thickness, making the thickness of the hydrogel lower than the set size.

[0030] Preferably, the step of pouring the mixture D into a mold of a specific size that has undergone anti-stick treatment, and performing a segmented crosslinking treatment on the mold of the specific size in an oven, includes:

[0031] The segmented crosslinking process includes sequential low-temperature pre-crosslinking and high-temperature deep crosslinking. The low-temperature pre-crosslinking process involves pre-crosslinking a mold of a specific size in an oven at 50–55°C for 30–60 minutes to fix the shape of the mold. The high-temperature deep crosslinking process involves heating the oven to 65–80°C and then deeply crosslinking the mold of a specific size for 30–60 minutes to strengthen and fix the network structure of the mold.

[0032] The mold of a specific size is a cuboid container with internal dimensions of length * width * height. The height direction is the thickness direction of the gel. With a certain bottom area, by adding different volumes of the mixture D, the thickness of the mixture D in the mold is changed, thereby controlling the thickness of the hydrogel. At the same time, the surfactant reduces the surface tension of the hydrogel solution, allowing the hydrogel solution to spread in the mold even when the thickness is lower than the set value.

[0033] Preferably, in the preparation of the transparent solution A, the mass ratio of the hydrated salt, surface modifier, and dispersant is approximately 500:10:1;

[0034] In the preparation of the uniform pregel liquid, the mass ratio of gel monomer: chemical crosslinking agent: gel thickener: ionic crosslinking agent is 60:5:3:12.

[0035] As can be seen from the technical solution provided by the present invention above, the present invention provides a low-thickness and macroscopically uniform and stable inorganic hydrated salt phase change gel material and its preparation method, which can solve the technical problems of uneven spreading and poor morphological stability caused by excessive surface tension in the preparation process of existing low-thickness hydrated salt gels, the need for complex equipment, cumbersome process and high cost of traditional molding methods, and the performance fluctuation caused by uneven thickness in practical applications of materials, while it is difficult to take into account both high phase change enthalpy and certain mechanical strength.

[0036] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and will become apparent from the description or may be learned by practice of the invention. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 The present invention also provides a process flow diagram of the preparation method of the above-mentioned inorganic hydrated salt phase change gel material;

[0039] Figure 2 An image of a sample of a hydrated salt gel with 1 wt‰ surfactant added, provided as an embodiment of the present invention;

[0040] Figure 3 The image shows a phenomenon where a hydrogel without added surfactant agglomerates and is difficult to spread in a 1mm tank, as provided in an embodiment of the present invention.

[0041] Figure 4 This is a photograph of a 1 mm hydrogel with surface pores prepared by the plate pressing method in Comparative Example 2, provided as an embodiment of the present invention.

[0042] Figure 5 A comparison of the contact angles of hydrogel on the surface of a silicone mold before and after adding 1 wt‰ surfactant is provided for an embodiment of the present invention (left: no surfactant added, contact angle 111.1°; right: with 1 wt‰ surfactant added, contact angle 42.2°).

[0043] Figure 6 Tensile stress-strain curves of hydrogels with different surfactant addition amounts (0wt‰, 1wt‰, 2wt‰, 3wt‰, 4wt‰, 5wt‰) provided for embodiments of the present invention;

[0044] Figure 7 A comparison diagram of tensile stress-strain between a hydrogel with 1 wt‰ surfactant and a hydrogel with surface pores, provided for an embodiment of the present invention;

[0045] Figure 8 SEM microstructure images of a PA-10 hydrogel (ac), pure SSD (df), and a hydrogel (gi) with 1 wt‰ surfactant added, provided for embodiments of the present invention;

[0046] Figure 9 This invention provides a DSC temperature rise comparison curve of hydrogel before and after adding 1 wt‰ surfactant, which is provided as an embodiment of the invention. Detailed Implementation

[0047] Embodiments of the present invention are described in detail below, examples of which are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0048] Those skilled in the art will understand that, unless specifically stated otherwise, the singular forms “a,” “an,” “the,” and “the” used herein may also include the plural forms. It should be further understood that the term “comprising” as used in this specification means the presence of the stated features, integers, steps, operations, elements, and / or components, but does not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof. It should be understood that when we say an element is “connected” or “coupled” to another element, it can be directly connected or coupled to the other element, or there may be intermediate elements. Furthermore, “connected” or “coupled” as used herein can include wireless connections or couplings. The term “and / or” as used herein includes any and all combinations of one or more of the associated listed items.

[0049] It will be understood by those skilled in the art that, unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It should also be understood that terms such as those defined in general dictionaries should be understood to have the same meaning as in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless defined as herein.

[0050] To facilitate understanding of the embodiments of the present invention, the following will provide further explanation and description with reference to the accompanying drawings and several specific embodiments. These embodiments do not constitute a limitation on the embodiments of the present invention.

[0051] This invention provides a solution that achieves low-thickness uniform molding without the need for precision equipment by controlling interface characteristics, while maintaining the high phase change enthalpy of inorganic hydrated salts. This solution is key to expanding its application in fields such as flexible wearables and thermal protection of thin batteries.

[0052] This invention provides an inorganic hydrated salt phase change gel material, comprising the following components by weight percentage:

[0053] Hydrated salt 70-90%, nucleating agent 0-6%, gel thickener 0-6%, deionized water 0-18%, gel monomer 8-30%, surface modifier 2-10%, dispersant 2-10%, chemical crosslinking agent 0.03-0.5%, ionic crosslinking agent 0.03-0.5%, initiator 0.005-0.5%, surfactant 0.1-1%.

[0054] Furthermore, the hydrated salt includes one or more of sodium sulfate decahydrate, magnesium chloride dodecahydrate, calcium nitrate hexahydrate, disodium phosphate dodecahydrate, sodium thiosulfate pentahydrate, sodium acetate trihydrate, potassium dihydrogen phosphate trihydrate, calcium chloride hexahydrate, and magnesium nitrate hexahydrate.

[0055] Furthermore, the nucleating agent includes one or more of the following: sodium tetraborate decahydrate, anhydrous sodium sulfate, anhydrous sodium carbonate, potassium chloride, strontium chloride hexahydrate, alum, silicon dioxide, zinc oxide, magnesium hydroxide, calcium carbonate, nano-carbon powder, and microcrystalline graphite.

[0056] The thickener includes one or more of sodium carboxymethyl cellulose, xanthan gum, guar gum, sodium alginate, polyvinyl alcohol, sodium polyacrylate, bentonite, and fumed silica.

[0057] Furthermore, the gel monomer includes one or more of sodium acrylate, acrylic acid, 2-hydroxyethylacrylamide, and acrylamide.

[0058] Furthermore, the chemical crosslinking agent is N,N′-methylenebisacrylamide;

[0059] Furthermore, the surface modifier is a coupling agent KH-550.

[0060] Furthermore, the dispersant is analytical grade ethanol.

[0061] The initiator includes one or more of ammonium persulfate, potassium persulfate, and diisopropyl peroxide.

[0062] Furthermore, the surfactant is one or more of the following: MS-7100, DuPont FS-3100, Fluorad FC4430, Capstone FS-30, Capstone FS-63, Yumu YM-3016, Superwet-320, MS-8100, fluorosurfactant RP-6100, fluorosurfactant RP-7100, FH3100, fluorocarbon surfactant HT-3100, and fluorosurfactant 1730.

[0063] This invention relates to the preparation of thin-film hydrogels. It utilizes specific surfactants to regulate the interfacial properties of hydrated salt gel precursors, and the addition of a small amount of surfactant can improve the spreading performance of the hydrogel.

[0064] A pretreatment process was added to the hydrogel preparation, which involved adding a silane coupling agent and analytical grade ethanol to the hydrated salt solution followed by ultrasonic dispersion. This process removed surface impurities and improved the compatibility with the gel network. This pretreatment process, in conjunction with surfactants, can reduce the repulsion between the hydrated salt and the gel, and regulate the gel surface tension to jointly promote the successful preparation of low-thickness gels.

[0065] This invention also provides a processing flow for the preparation method of the above-mentioned inorganic hydrated salt phase change gel material, as follows: Figure 1 As shown, the mass fractions of each material include: 70-90 parts hydrated salt, 0-6 parts nucleating agent, 0-6 parts thickener, 0-18 parts deionized water, 8-30 parts gel monomer, 2-10 parts surface modifier, 2-10 parts dispersant, 0.03-0.5 parts chemical crosslinking agent, 0.03-0.5% ionic crosslinking agent, 0.005-0.5 parts initiator, and 0.1-1 parts surfactant. The method includes the following processing steps:

[0066] Step S1, Pretreatment of Hydrated Salt: Hydrated salt crystals are placed in a container in a constant-temperature water bath. A surface modifier is added to the hydrated salt, and the mixture is stirred. Then, a dispersant is added to the container, and the container is placed under ultrasonic waves for ultrasonic dispersion. The solution is then heated to a certain temperature and stirred until completely dissolved to form a transparent solution A. The mass ratio of the hydrated salt, surface modifier, and dispersant is approximately 500:10:1.

[0067] Step S1 may specifically include:

[0068] 1.1 Place the hydrated salt crystals in a 50℃ constant temperature water bath, add 0.1g of surface modifier silane coupling agent KH-550, and stir magnetically at 300rpm for 30min;

[0069] 1.2 Add 5 mL of ethanol and sonicate at 300 W for 15 min;

[0070] 1.3 Heat the water bath to 55℃ and wait for 20 minutes to allow the temperature inside the bottle to reach 55℃. At the same time, stir magnetically at 300 rpm until completely dissolved, forming a milky white transparent solution A. The temperature of transparent solution A is 40-80℃.

[0071] Step S2, Pregel preparation: Gel monomer, gel thickener, chemical crosslinking agent and ionic crosslinking agent are added sequentially to transparent solution A to obtain uniform pregel B.

[0072] The specific process includes:

[0073] 2.1 Add gel monomer AAS (sodium acrylate) and chemical crosslinking agent MBA (N,N′-methylenebisacrylamide) to transparent solution A to obtain a mixed solution. Stir the mixed solution at 55℃ and 350rpm for 1.5h.

[0074] 2.2 Add gel thickener SA to the above-mentioned mixed solution after constant temperature stirring, cool to 50℃ and stir for 2 hours to form a primary network precursor;

[0075] 2.3 Add the ionic crosslinking agent CaCl2 to the above primary network precursor, cool down and keep stirring at 50°C for 0.5 h to obtain a uniform pregel solution B. The temperature of the uniform pregel solution B is 40-80°C.

[0076] In this step, the mass ratio of the above materials can be: gel monomer AAS: chemical crosslinking agent MBA: gel thickener SA: ionic crosslinking agent CaCl2 = 60:5:3:12.

[0077] Step S3, surfactant compounding: After adding surfactant to the uniform pregel solution B, the mixture is stirred at high speed. The amphiphilic molecular structure of the surfactant changes the interaction between surface molecules of the solution from strong polar attraction to weak van der Waals forces between fluorocarbon chains, thereby significantly weakening the surface cohesion and directly reducing the surface tension of the solution, resulting in a pregel solution C containing surfactant.

[0078] Add 0.06g of DuPont FS-3100 surfactant to the above homogeneous pregel solution B, and stir at 500rpm for 1.5min to obtain a pregel solution C containing surfactant.

[0079] In hydrated salt gel solution systems, fluorinated nonionic surfactants function due to their amphiphilic molecular structure (hydrophobic ends of fluorocarbon chains and hydrophilic ends of polyoxyethylene, etc.): their molecules spontaneously migrate towards the gas-liquid interface, the hydrophilic ends bind with water molecules and salt ions in the solution through polar interactions, while the fluorocarbon chains, due to extremely low intermolecular forces, face towards the air phase. This directional arrangement replaces the original highly cohesive molecules on the surface (such as clusters of aggregated water molecules and salt ion aggregates), transforming the strong polar attraction between surface molecules into weak van der Waals forces between fluorocarbon chains, thus significantly weakening surface cohesion and directly reducing the surface tension of the solution (from 72 mN / m in pure water to 20-30 mN / m or even lower). This reduction in surface tension further improves the spreading performance of the solution on a flat mold, because the spreading ability of the solution is determined by the spreading coefficient (S = γ). sa -γ sl -γ la ) determines the surface tension (γ) la The decrease of ) directly increases the value of S, making it easier for the solution to overcome its own cohesive force and diffuse to the mold surface.

[0080] Meanwhile, the hydrophilic end of the surfactant can form weak interactions (such as hydrogen bonds and dipole interactions) with the polar groups on the mold surface, reducing the solid-liquid interfacial tension (γ). sl This further amplifies the spreading coefficient and enhances wettability (reducing the contact angle). Furthermore, the low viscosity and dispersing effect of the fluorocarbon chain reduce the aggregation of salt particles or gel precursors, avoiding localized resistance that hinders spreading and allowing the solution to more uniformly "fit" the mold surface. These effects ultimately contribute to the preparation of a 1mm thick material: low surface tension improves the fluidity of the solution in the mold, enabling it to quickly fill the mold cavity under gravity or slight external force, avoiding "edge shrinkage" or "voids"; good wettability ensures close contact between the solution and the mold surface, resulting in a uniform initial liquid film thickness (close to the 1mm gap designed in the mold); and during the curing process of the hydrated salt gel, the stable low surface tension state of the surfactant maintains the liquid film morphology, preventing liquid film shrinkage caused by surface tension rebound before curing, ultimately fixing the 1mm spreading thickness as the finished material thickness.

[0081] Step S4, Initiator Treatment: Dissolve the initiator in a solvent to obtain an initiator solution. The initiator temperature is 20–35°C.

[0082] In practical applications, 0.04g of initiator APS can be dissolved in 3.0g of deionized water to obtain an initiator solution.

[0083] The initiator solution was subjected to ultrasonic dispersion under ultrasonic irradiation. Then, under constant temperature conditions, pregelation solution C was added dropwise to the initiator solution, and the mixture was stirred until homogeneous to obtain mixture D.

[0084] Step S5, mold casting and gel segmented crosslinking: Pour the mixture D into a mold of a specific size that has been treated with an anti-stick coating.

[0085] The aforementioned mold of a specific size is a simple rectangular container with internal dimensions of length * width * height. The height direction corresponds to the thickness direction of the gel. With a given base area, by adding different volumes of hydrogel solution, the thickness within the mold can be altered, thus achieving thickness control. When a thicker layer is desired, the force of gravity in the thickness direction breaks the cohesion of the gel, allowing it to spread and form a gel. However, during the preparation of thinner hydrogels, the gravity in the thickness direction is insufficient to break the surface cohesion, resulting in aggregation, as follows: Figure 3 Therefore, this invention significantly improves the problem of difficulty in molding thin hydrogels and the occurrence of agglomeration by adding surfactants to the gel and performing surface treatment with hydrated salts. Thus, it is a simple and efficient method for preparing thin hydrogels.

[0086] A segmented crosslinking process is performed on a mold of a specific size in an oven. This segmented crosslinking process includes low-temperature pre-crosslinking and high-temperature deep crosslinking. The low-temperature pre-crosslinking process can fix the shape of the mold of a specific size, and the high-temperature deep crosslinking process can strengthen the network structure that fixes the mold of a specific size.

[0087] The materials used for the molds of the specific dimensions mentioned above include, but are not limited to, polytetrafluoroethylene (PTFE), acrylic, glass, and soft silicone. The segmented crosslinking treatment includes sequential low-temperature pre-crosslinking and high-temperature deep crosslinking. The low-temperature pre-crosslinking treatment involves pre-crosslinking the mold of the specific dimensions in an oven at 50–55°C for 30–60 minutes, which fixes the shape of the mold. The high-temperature deep crosslinking treatment involves heating the oven to 65–80°C and then deeply crosslinking the mold of the specific dimensions for 30–60 minutes, which strengthens and fixes the network structure of the mold.

[0088] With a given base area, the thickness of the hydrogel can be controlled by adding different volumes of the mixture D to a mold of a specific size, thereby altering the thickness of the mixture D within the mold. Simultaneously, the surfactant's reduction of the surface tension of the hydrogel solution allows the hydrogel solution to break down the "cohesive force" even at a lower thickness, enabling it to spread well within the mold.

[0089] Step S6, Post-processing and Demolding: After the cross-linked reinforced network structure of the mold of a specific size is kept at a constant temperature and then subjected to low temperature treatment, it is demolded to obtain a hydrogel of the target thickness.

[0090] The above constant temperature resting refers to resting at room temperature, and the low temperature for low temperature treatment is -20 to 5℃.

[0091] Example 1:

[0092] Preparation of low-thickness PAAS / CA / SSD hydrogels with 1 wt‰ surfactant

[0093] Raw material composition (total mass 60g): Sodium sulfate decahydrate (SSD) 44.8g, sodium acrylate (AAS) 6.0g, N,N'-methylenebisacrylamide (MBA) 0.5g, sodium alginate (SA) 0.3g, anhydrous calcium chloride (CaCl2) 1.2g, ammonium persulfate (APS) 0.04g, deionized water 3.0g, sodium hexametaphosphate (SHMP) 0.6g, borax 3.6g, surfactant (DuPont FS-3100) 0.06g (1wt‰); Pretreatment agent: ethanol (analytical grade) 5mL, silane coupling agent KH-550 0.1g.

[0094] Preparation steps:

[0095] (1) SSD pretreatment: Place the SSD crystal in a 50℃ constant temperature water bath, add 0.1g of silane coupling agent KH-550 and stir at 300rpm for 30min, then add 5mL of ethanol and sonicate at 300W for 15min, and heat to 55℃ and stir until completely dissolved into a milky white transparent solution.

[0096] (2) Preparation of pregel solution: AAS and MBA were added to the SSD solution in sequence (stirred at 55℃ and 350rpm for 1.5h), then SA was added (cooled down to 50℃ and stirred for 2h), and finally CaCl2 was added (stirred at 50℃ for 0.5h) to form a uniform pregel solution.

[0097] (3) Initiator treatment: Dissolve APS in 3.0g deionized water, sonicate at 200W for 5min, add the pregel solution at a drop rate of 1mL / min in a constant temperature water bath at 35℃, and stir at 400rpm until the addition is complete.

[0098] (4) Surfactant compounding: After the initiator is mixed, let it stand for 2 minutes, add 0.06g of DuPont FS-3100 surfactant, and stir at 500rpm for 1.5 minutes.

[0099] (5) Mold casting and segmented crosslinking: Pour the above mixture into a 250mm×180mm×1mm polytetrafluoroethylene-coated soft silicone mold. First, pre-crosslink in a 50℃ oven for 30 minutes, then raise the temperature to 65℃ for deep crosslinking for 30 minutes.

[0100] (6) Post-treatment and demolding: After cross-linking, the hydrogel was first kept at 25°C for 6 hours, then transferred to 5°C for 6 hours, and demolded to obtain a 1 mm thick hydrogel.

[0101] Performance test results:

[0102] Macroscopic morphology: The 1mm material obtained by the above method has a uniform thickness (deviation ≤0.1mm), and is free of holes and shrinkage (corresponding to...). Figure 2 Effect), Figure 3 This image illustrates the phenomenon of a hydrogel without added surfactant agglomerating and becoming difficult to spread in a 1mm tank, as provided in an embodiment of the present invention.

[0103] Contact angle: 42.2° (69° lower than the sample without surfactant, corresponding to...) Figure 5 ), Figure 5 This is a comparison diagram of the contact angle of hydrogel on the surface of a silicone mold before and after adding 1 wt‰ surfactant, provided by an embodiment of the present invention. Figure 5 Left image: No surfactant added, contact angle 111.1°; Figure 5 Right figure: With 1 wt‰ surfactant added, the contact angle is 42.2°;

[0104] Mechanical properties: The tensile strength of the crystalline state is 0.08 MPa, and the elongation at break is 12%, which is superior to the pressed sample. Figure 7 , Figure 7 A comparison diagram of tensile stress-strain between a hydrogel with 1 wt‰ surfactant and a hydrogel with surface pores, provided for an embodiment of the present invention;

[0105] Thermal properties: Phase transition temperature 31.88℃, phase transition enthalpy 121.1 J / g, decomposition enthalpy 946.4 J / g (no significant difference from the sample without surfactant). Figure 9 ), Figure 9 This invention provides a DSC temperature rise comparison curve of hydrogel before and after adding 1 wt‰ surfactant, as an embodiment of the invention.

[0106] Microstructure: The hydrogel network is loose but continuous, and the SSD crystals are uniformly dispersed (corresponding to...). Figure 8 in gi), Figure 8 SEM microstructure images of a PA-10 hydrogel (ac), pure SSD (df), and a hydrogel (gi) with 1 wt‰ surfactant added, provided for embodiments of the present invention.

[0107] Example 2:

[0108] Preparation of low-thickness PAAS / CA / SSD hydrogels with the addition of 3 wt‰ surfactant

[0109] Raw material composition: except that the amount of surfactant added is 0.18g (3wt‰), the rest is the same as in Example 1.

[0110] Preparation steps: Same as in Example 1.

[0111] Performance test results:

[0112] Macroscopic appearance: Thickness deviation ±0.15mm, no obvious defects;

[0113] Contact angle: 38.5°;

[0114] Mechanical properties: Tensile strength 0.06 MPa (lower than Example 1, corresponding to...) Figure 6 ), Figure 6 Tensile stress-strain curves of hydrogels with different surfactant addition amounts (0wt‰, 1wt‰, 2wt‰, 3wt‰, 4wt‰, 5wt‰) are provided for embodiments of the present invention.

[0115] Thermal properties: Phase change enthalpy 118.9 J / g, decomposition enthalpy 932.7 J / g.

[0116] Comparative Example 1:

[0117] Low-thickness hydrogels without added surfactants (self-leveling method).

[0118] Raw material composition: except that no surfactant is added, the rest is the same as in Example 1.

[0119] Preparation steps: Same as in Example 1, except for the surfactant addition step.

[0120] Performance test results:

[0121] Macroscopic morphology: Agglomeration after self-leveling prevented the gel from spreading on the mold surface, resulting in a sample with a thickness close to the target value (corresponding to...). Figure 3 ).

[0122] Contact angle: 111.1° (corresponding to) Figure 5 Left).

[0123] Mechanical properties: This method did not produce a hydrated salt gel of the target thickness.

[0124] Comparative Example 2:

[0125] Low-thickness hydrogels were prepared by plate pressing.

[0126] Raw material composition: Same as comparative example 1 (without surfactant).

[0127] Preparation steps:

[0128] (1) Prepare the pregel solution according to steps (1)-(3) of Example 1.

[0129] (2) After pouring into a 1mm mold, press with a flat plate until the thickness meets the standard, and then crosslink and cure at 60℃.

[0130] Performance test results:

[0131] Macroscopic morphology: The surface is covered with holes (corresponding to...) Figure 4 ), Figure 4 This is a photograph of the surface pores of the 1 mm hydrogel prepared by the plate pressing method in Comparative Example 2.

[0132] Mechanical properties: Tensile strength 0.07 MPa, lower than that of Example 1, corresponding to Figure 7 .

[0133] Thermal properties: Phase change enthalpy 115.3 J / g (due to uneven salt distribution caused by porosity).

[0134] A comparison of Examples 1-2 and Comparative Examples 1-2 shows that when the surfactant addition amount is 1 wt‰, the thickness is low.

[0135] The PAAS / CA / SSD hydrogel exhibits the best macroscopic uniformity, the smallest thickness deviation, and excellent balanced thermal and mechanical properties, significantly outperforming traditional methods. This verifies the effectiveness of the present invention in controlling the morphology of low-thickness hydrogels through surfactants.

[0136] In summary, the method of the present invention can achieve the following beneficial effects:

[0137] Interface control and material system synergy overcome the bottleneck of low-thickness molding: This invention fundamentally solves the problems of uneven spreading, edge shrinkage, and porosity caused by excessive surface tension in low-thickness (around 1 mm) hydrated salt gels by introducing specific surfactants to regulate the interfacial properties of the precursor, achieving macroscopic uniformity with a thickness deviation of ≤0.1 mm. This design does not rely on precision coating equipment and can be compatible with conventional mold casting processes simply by optimizing the material system, filling the gap in the existing technology for morphological control of low-thickness inorganic hydrated salt gels.

[0138] Performance-process balance design, preserving high energy storage and structural stability: While solving the molding problem, this invention optimizes the amount of surfactant and the ratio of hydrogel network to fully preserve the high phase change enthalpy (≥119J / g) of inorganic hydrated salts, while ensuring that the material has the mechanical strength (tensile strength ≥0.25MPa) to meet practical applications. This avoids the contradiction in the prior art of "improving moldability at the expense of energy storage or mechanical properties", and achieves a triple synergy of "low thickness uniformity + high enthalpy value + stable mechanical properties".

[0139] Low cost and universality, with potential for large-scale application: The surfactants and raw materials used in this invention are all commercially available conventional chemicals, requiring no special intermediates or expensive equipment. The raw material cost is significantly lower than that of ultrathin hydrogel technology that relies on precision coating. At the same time, by adjusting the mold depth, it can flexibly adapt to thickness requirements of 0.5-2mm, making it suitable for various thickness-sensitive scenarios such as flexible wearables and thermal protection of thin batteries, providing a feasible path for the large-scale promotion of inorganic hydrated salt gels.

[0140] Those skilled in the art will understand that the accompanying drawings are merely schematic diagrams of one embodiment, and the modules or processes shown in the drawings are not necessarily essential for implementing the present invention.

[0141] The various embodiments in this specification are described in a progressive manner. Similar or identical parts between embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for apparatus or system embodiments, since they are basically similar to method embodiments, the description is relatively simple; relevant parts can be referred to the descriptions in the method embodiments. The apparatus and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0142] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A low-thickness and macroscopically uniform and stable inorganic hydrated salt phase change gel material, characterized in that, By weight percentage, it includes the following components: The composition includes 70-90% hydrated salt, 0-6% nucleating agent, 0-6% gel thickener, 0-18% deionized water, 8-30% gel monomer, 2-10% surface modifier, 2-10% dispersant, 0.03-0.5% chemical crosslinking agent, 0.03-0.5% ionic crosslinking agent, 0.005-0.5% initiator, and 0.1-1% surfactant.

2. The inorganic hydrated salt phase change gel material according to claim 1, characterized in that, The surfactant is one or more of the following: MS-7100, DuPont FS-3100, Fluorad FC4430, Capstone FS-30, Capstone FS-63, Yumu YM-3016, Superwet-320, MS-8100, fluorosurfactant RP-6100, fluorosurfactant RP-7100, FH3100, fluorocarbon surfactant HT-3100, and fluorosurfactant 1730.

3. The inorganic hydrated salt phase change gel material according to claim 1, characterized in that, The hydrated salts include one or more of sodium sulfate decahydrate, magnesium chloride dodecahydrate, calcium nitrate hexahydrate, disodium phosphate dodecahydrate, sodium thiosulfate pentahydrate, sodium acetate trihydrate, potassium dihydrogen phosphate trihydrate, calcium chloride hexahydrate, and magnesium nitrate hexahydrate.

4. The inorganic hydrated salt phase change gel material according to claim 1, characterized in that, The nucleating agent includes one or more of the following: sodium tetraborate decahydrate, anhydrous sodium sulfate, anhydrous sodium carbonate, potassium chloride, strontium chloride hexahydrate, alum, silicon dioxide, zinc oxide, magnesium hydroxide, calcium carbonate, nano-carbon powder, and microcrystalline graphite.

5. The inorganic hydrated salt phase change gel material according to claim 1, characterized in that, The gel thickener includes one or more of sodium carboxymethyl cellulose, xanthan gum, guar gum, sodium alginate, polyvinyl alcohol, sodium polyacrylate, bentonite, and fumed silica.

6. The inorganic hydrated salt phase change gel material according to claim 1, characterized in that, The gel monomer includes one or more of sodium acrylate, acrylic acid, 2-hydroxyethylacrylamide, and acrylamide.

7. A method for preparing the inorganic hydrated salt phase change gel material according to any one of claims 1 to 6, characterized in that, include: Hydrated salt crystals are placed in a container, which is then placed in a constant temperature water bath. A surface modifier is added to the container and the mixture is stirred. A dispersant is then added to the container, which is placed under ultrasound for ultrasonic dispersion. The solution is then heated to a certain temperature and stirred until it is completely dissolved to form a transparent solution A. After sequentially adding gel monomer, gel thickener, chemical crosslinking agent and ionic crosslinking agent to the transparent solution A, a uniform pregel solution B is obtained. After adding a surfactant to a uniform pregel solution B, the mixture is stirred at high speed. The amphiphilic molecular structure of the surfactant changes the interaction between surface molecules of the solution from strong polar attraction to weak van der Waals forces between fluorocarbon chains, thereby reducing the surface tension of the solution and obtaining a pregel solution C containing the surfactant. The initiator is dissolved in a solvent to obtain an initiator solution. The initiator solution is placed under ultrasonic irradiation for ultrasonic dispersion treatment. Under constant temperature conditions, pregel solution C is added dropwise to the initiator solution and stirred until uniformly mixed to obtain mixture D. The mixture D is poured into a mold of a specific size that has been treated to prevent sticking, and the mold of the specific size filled with the material is placed in an oven for segmented crosslinking treatment. After the segmented cross-linking treatment, the material is subjected to constant temperature standing and low temperature treatment, and then demolded to remove it from the mold of the specific size to obtain a hydrogel of the target thickness.

8. The method according to claim 7, characterized in that, The amphiphilic molecular structure of the surfactant transforms the surface molecular interactions of the solution from strong polar attraction to weak van der Waals forces between fluorocarbon chains, reducing the surface tension of the solution and yielding a pre-gel solution C containing the surfactant, comprising: In the hydrated salt gel solution system composed of uniform pregel liquid B and surfactant, the molecules in the amphiphilic molecular structure of the fluorinated nonionic surfactant spontaneously migrate to the gas-liquid interface. The hydrophilic ends of the amphiphilic molecular structure combine with water molecules and salt ions in the solution through polar interactions, while the fluorocarbon chains are oriented towards the air phase due to intermolecular forces. This directional arrangement replaces the original highly cohesive molecules on the surface of the solution, changing the interaction between surface molecules of the solution from strong polar attraction to weak van der Waals forces between fluorocarbon chains, thereby reducing the surface tension of the solution. The hydrophilic end of the surfactant forms a weak interaction with the polar groups on the mold surface, reducing the solid-liquid interfacial tension, further increasing the spreading coefficient, enhancing wettability, and allowing the solution to adhere more evenly to the mold surface. The resulting liquid film has a uniform thickness, making the thickness of the hydrogel lower than the set size.

9. The method according to claim 7, characterized in that, The process of pouring the mixture D into a mold of a specific size that has undergone anti-stick treatment, and then performing a segmented crosslinking treatment on the mold of the specific size in an oven, includes: The segmented crosslinking process includes sequential low-temperature pre-crosslinking and high-temperature deep crosslinking. The low-temperature pre-crosslinking process involves pre-crosslinking a mold of a specific size in an oven at 50–55°C for 30–60 minutes to fix the shape of the mold. The high-temperature deep crosslinking process involves heating the oven to 65–80°C and then deeply crosslinking the mold of a specific size for 30–60 minutes to strengthen and fix the network structure of the mold. The mold of a specific size is a cuboid container with internal dimensions of length * width * height. The height direction is the thickness direction of the gel. With a certain bottom area, by adding different volumes of the mixture D, the thickness of the mixture D in the mold is changed, thereby controlling the thickness of the hydrogel. At the same time, the surfactant reduces the surface tension of the hydrogel solution, allowing the hydrogel solution to spread in the mold even when the thickness is lower than the set value.

10. The method according to claim 7, characterized in that, In the preparation of the transparent solution A, the mass ratio of the hydrated salt, surface modifier, and dispersant is approximately 500:10:1; In the preparation of the uniform pregel liquid, the mass ratio of gel monomer: chemical crosslinking agent: gel thickener: ionic crosslinking agent is 60:5:3:12.

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