A surface hydrophobic core-shell structure composite hygroscopic hydrogel, and a preparation method and application thereof

Abstract

This invention belongs to the field of hydrophilic gel and air moisture extraction technology, specifically relating to a core-shell composite hygroscopic hydrogel with a hydrophobic surface, its preparation method, and its application. The specific preparation method involves placing a hydrophilic gel loaded with hygroscopic salts in a hydrophobic polymer solution. Using a phase inversion method, a porous hydrophobic polymer shell is loaded onto the surface of the hydrophilic gel, resulting in a composite hygroscopic hydrogel with the hydrophilic gel loaded with hygroscopic salts as the core and the porous hydrophobic polymer as the shell. The prepared composite hygroscopic hydrogel can prevent hygroscopic salt leakage, has high water absorption performance, good long-term stability, and a simple preparation method. The composite hygroscopic hydrogel prepared by this invention can be widely used in air moisture extraction, humidity control, and agricultural moisture retention.

Description

Technical Field

[0001] This invention belongs to the field of hydrophilic gel and air-based water extraction technology, specifically relating to a core-shell composite hygroscopic hydrogel with a hydrophobic surface, its preparation method, and its application. Background Technology

[0002] Polymer hydrogels are hydrophilic three-dimensional cross-linked networks formed by the swelling of water molecules. Their network structure is formed by polymer chains cross-linking through covalent or non-covalent bonds. Thanks to their excellent swelling properties, hydrogels can store large amounts of water and reduce the enthalpy of vaporization, thus improving desorption efficiency. Therefore, composite adsorbents using hydrogels as a matrix material have attracted widespread attention and are likely to become the next generation of ideal adsorption-based air-to-water materials. Polymer hydrogels with hydrophilic networks and porous structures are considered ideal matrices for loading hygroscopic salts, as their porous structure effectively prevents the aggregation of hygroscopic salts, thereby improving their long-term performance.

[0003] Although composite hygroscopic hydrogels can adsorb large amounts of water vapor through their porous structure and high hydration capacity, the hygroscopic salt solution will still leak from the hydrogel when the equilibrium adsorption capacity exceeds its maximum water retention capacity, resulting in the loss of hygroscopic salt and a subsequent decrease in water vapor adsorption performance. Therefore, how to suppress the leakage of hygroscopic salt while ensuring high hygroscopic capacity, thereby improving the long-term stability of composite hygroscopic hydrogels, remains an urgent problem to be solved.

[0004] To address this issue, researchers have constructed a photothermal hydrophobic shell on the surface of cellulose nanofiber aerogels using a freeze-drying strategy to suppress the leakage of hygroscopic salt solutions. This photothermal hydrophobic shell is composed of polydimethylsiloxane, carbon black, and cellulose nanofibers. The aerogel exhibits good long-term stability and rapid water vapor adsorption under high humidity. However, the preparation process of the polydimethylsiloxane shell is relatively cumbersome and lacks versatility. Furthermore, the hydrophobic shell can inhibit the hygroscopic properties of the hydrogel to some extent. Therefore, developing simpler physical or chemical methods to construct porous hydrophobic shells to suppress the leakage of hygroscopic salt solutions and improve the long-term stability of composite hygroscopic hydrogels is of great significance. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a core-shell composite hygroscopic hydrogel with a hydrophobic surface, its preparation method, and its application, solving the technical problems of hygroscopic salt leakage, poor water absorption performance of the hygroscopic hydrogel, poor long-term stability, and cumbersome preparation methods in existing technologies.

[0006] To achieve the above objectives, according to one aspect of the present invention, a method for preparing a core-shell composite hygroscopic hydrogel with a hydrophobic surface is provided. Specifically, the method includes placing a hydrophilic gel loaded with hygroscopic salts in a hydrophobic polymer solution, and using a phase inversion method to load a porous hydrophobic polymer shell layer on the surface of the hydrophilic gel, thereby obtaining a composite hygroscopic hydrogel with a hydrophilic gel loaded with hygroscopic salts as the core layer and a porous hydrophobic polymer as the shell layer.

[0007] Preferably, the specific preparation steps of the hydrophilic gel loaded with hygroscopic salt are as follows:

[0008] (1) Preparation of hydrophilic gel precursor solution;

[0009] (2) The gel precursor solution is cured by heating or photocuring to obtain a hydrophilic gel;

[0010] (3) Soak the hydrophilic gel in an aqueous solution of hygroscopic salt to load the hygroscopic salt onto the hydrophilic gel, thus obtaining a hydrophilic gel loaded with hygroscopic salt.

[0011] Preferably, the hydrophilic gel is a zwitterionic electrolyte hydrogel, and is preferably one or more of polymethacryloylethyl sulfobetaine, polyvinyl alcohol, polyacrylic acid, sodium polystyrene sulfonate, polyacrylamide, and poly[2(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide.

[0012] Preferably, the hydrophilic gel in step (2) is a microspherical hydrophilic gel, and its specific preparation steps are as follows: the hydrophilic gel precursor solution obtained in step (1) is added dropwise into an oily solution, and then cured by heating or light curing to obtain a microspherical hydrophilic gel. The diameter of the microspherical hydrophilic gel is 5 mm to 25 mm.

[0013] Preferably, the specific preparation steps of the hydrophobic polymer solution are as follows: dissolving the hydrophobic polymer material in a mixture of a good solvent and a poor solvent to obtain the hydrophobic polymer solution;

[0014] Preferably, the hydrophobic polymer is one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, polypropylene, and polyacrylonitrile.

[0015] Preferably, the hygroscopic salt is one or more of potassium chloride, sodium chloride, potassium bromide, magnesium chloride, magnesium bromide, lithium chloride, and lithium bromide.

[0016] Preferably, the concentration of the hygroscopic salt in the aqueous solution is 1M-10M.

[0017] Preferably, the good solvent is one or more of methylene sulfone, N,N-dimethylformamide, and N-methylpyrrolidone, and the bad solvent is water.

[0018] Preferably, the volume ratio of the good solvent to the poor solvent is 0.01-0.06.

[0019] Preferably, the hydrophobic polymer solution contains 1% to 10% by mass; the immersion time of the hydrophilic gel loaded with hygroscopic salt in the hydrophobic polymer solution is 3 to 10 minutes; the phase transition temperature is 20°C to 80°C; and the thickness of the porous hydrophobic polymer shell is 200 μm to 800 μm.

[0020] According to another aspect of the present invention, a method for preparing the aforementioned hydrophobic core-shell structure composite hygroscopic hydrogel is provided.

[0021] According to another aspect of the present invention, the application of the composite hygroscopic hydrogel is provided, which is applied to the fields of air water extraction, humidity control, and agricultural moisturizing.

[0022] In summary, compared with the prior art, the above-described technical solutions conceived by this invention mainly possess the following technical advantages:

[0023] (1) The hydrophilic / hydrophobic core-shell composite hygroscopic hydrogel of the present invention achieves efficient adsorption of water vapor. The core-shell structure consists of a hydrophilic gel core and a hydrophobic shell, respectively, from the inside out. The hydrophilic gel core is responsible for capturing water vapor, while the hydrophobic shell effectively prevents leakage of the hygroscopic salt solution. In addition, the construction of the porous hydrophobic shell enhances the mechanical stability of the hydrogel. This structure ensures the material's efficient hygroscopic performance, long-term stability, and recyclability under various humidity conditions. At the same time, this structural design cleverly balances the high water absorption capacity inside the hydrogel with the moisture retention capacity outside, extending the service life of the material and providing a new strategy for the construction of hydrophilic gels. The composite hygroscopic hydrogel of the present invention exhibits excellent adsorption capacity under high humidity conditions.

[0024] (2) The present invention provides a simple preparation method, which uses a phase inversion method to construct a hydrophobic shell on the surface of a hydrogel. Rapid bidirectional diffusion of good solvent and poor solvent occurs on the surface of the hydrogel, forming a relatively dense surface structure. The poor phase droplet solution composed of good solvent, poor solvent and polymer is dispersed in the continuous polymer-rich phase and continues to increase until the surrounding rich phase solidifies, forming a through-pore structure.

[0025] (3) The core-shell structure design of the present invention also allows for the control of the hygroscopic properties of the hydrogel by changing the thickness and porosity of the shell layer, enabling it to adapt to different environmental conditions and application requirements. The shell layer thickness can be controlled by changing the soaking time, achieving a porous hydrophobic polymer shell layer thickness of 200μm~800μm, and the porosity can be controlled by the volume ratio of good and bad solvents, curing temperature, and shell material concentration. This size control capability provides flexibility for the applicability of the hydrogel in different application scenarios. In applications that require large-scale water vapor capture and multiple cycles, a hydrogel with a thicker shell layer can be selected to reduce the degree of hygroscopic salt leakage and extend the service life; while in environments requiring rapid response or in space-constrained environments, a hydrogel with a thinner shell layer can be selected to improve the reaction speed and adaptability. The controllability of the core-shell size also helps to realize the large-scale production and processing of the hydrogel, enabling it to be customized according to market demand; the porous structure of the hydrophobic polymer shell layer can increase the water vapor throughput, thereby enhancing the water vapor adsorption capacity of the core-shell composite hygroscopic hydrogel.

[0026] (4) The present invention uses hygroscopic salt. After the hygroscopic salt is embedded in the hydrogel, it first captures water vapor and then liquefies water molecules in situ on the surface of the hydrogel. The liquefied water is transferred to the polymer network through the osmotic pressure difference and is stored due to the unique swelling properties of the hydrogel, thereby increasing the interaction between the gel and water in the air and enhancing the adsorption capacity.

[0027] (5) The present invention uses microspherical hydrogels to obtain hydrogels with the smallest surface area of ​​the same volume. After being coated with a hydrophobic shell, the water vapor adsorption performance of the composite hygroscopic hydrogel will decrease. However, using a hydrophobic shell with the smallest surface area can make the inhibiting effect smaller, reducing the inhibitory effect of the subsequent hydrophobic shell on the water adsorption capacity.

[0028] (6) The present invention can select different types of gel precursor solutions as needed to meet different application requirements. The preparation process of the present invention does not require complicated post-processing steps, which not only simplifies the production process and reduces costs, but also makes it easy to scale up production and promotes application. The simple preparation process only requires the energy consumption of polymerization, which overcomes the existing technology that uses grafting chemical methods to fix the shell to the outside of the hydrogel core, which requires heating or photocuring. It has no environmental impact and meets the requirements of green chemistry and sustainable production. Attached Figure Description

[0029] Figure 1 A schematic diagram of the preparation of PSBMA-LiCl@PVDF;

[0030] Figure 2 Leakage test diagrams for (a) PSBMA-LiCl and (b) PSBMA-LiCl@PVDF hygroscopic salt solutions;

[0031] Figure 3 (a) Equilibrium adsorption capacity and (b) percentage of equilibrium adsorption capacity during multiple cycles of PSBMA-LiCl and PSBMA-LiCl@PVDF.

[0032] Figure 4 Thermogravimetric curves of (a) PSBMA-LiCl and (b) PSBMA-LiCl@PVDF after different cycles of moisture absorption. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0034] This invention provides a method for preparing a core-shell composite hygroscopic hydrogel with a hydrophobic surface, comprising the following steps:

[0035] (1) Preparation of hydrophilic gel precursor solution;

[0036] (2) The hydrophilic gel precursor solution is added dropwise into an oily solution, and then cured by heating or photocuring to obtain a hydrophilic gel;

[0037] (3) The hydrophilic gel is immersed in an aqueous solution of hygroscopic salt to load the hygroscopic salt onto the hydrophilic gel, thereby obtaining a hydrophilic gel loaded with hygroscopic salt.

[0038] (4) Dissolve the hydrophobic polymer material in a mixture of a good solvent and a bad solvent to obtain a hydrophobic polymer solution;

[0039] (5) The hydrophilic gel loaded with hygroscopic salt is immersed in the hydrophobic polymer solution and then undergoes phase inversion to obtain a composite hygroscopic hydrogel with the hydrophilic gel loaded with hygroscopic salt as the core layer and the porous hydrophobic polymer as the shell layer.

[0040] In some embodiments, the hydrophilic gel is a zwitterionic electrolyte hydrogel, preferably one or more of polymethacryloylethyl sulfobetaine, polyvinyl alcohol, polyacrylic acid, sodium polystyrene sulfonate, polyacrylamide, and poly[2(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide.

[0041] In some embodiments, the hydrophobic polymer is one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, polypropylene, and polyacrylonitrile.

[0042] In some embodiments, the hygroscopic salt is one or more of potassium chloride, sodium chloride, potassium bromide, magnesium chloride, magnesium bromide, lithium chloride, and lithium bromide.

[0043] In some embodiments, the concentration of the hygroscopic salt is 1M-10M.

[0044] In some embodiments, the good solvent is one or more of methylene sulfone, N,N-dimethylformamide, and N-methylpyrrolidone, the bad solvent is water, and the volume ratio of the good solvent to the bad solvent is 0.01-0.06.

[0045] In some embodiments, the hydrophobic polymer solution contains 1% to 10% by mass of the hydrophobic polymer.

[0046] In some embodiments, the immersion time of the hydrophilic gel loaded with hygroscopic salt in the hydrophobic polymer solution is 3-10 minutes, and the phase transition temperature is 20°C-80°C.

[0047] In some embodiments, the thickness of the porous hydrophobic polymer shell is 200 μm to 800 μm.

[0048] In some embodiments, the oily solution is one or more of chloromethane, dichloromethane, and chlorobenzene.

[0049] In some embodiments, microfluidics, needles, pipettes, or droppers are used to dropwise add the gel precursor solution into the oily solution.

[0050] Example 1

[0051] (1) Dissolve 2.79 g of methacryloyl ethyl sulfobetaine (SBMA) monomer and 15 mg of N,N′-methylenebisacrylamide (BIS) in 5 mL of water to obtain a monomer concentration of 2 M. Add 20 µL of photoinitiator 1173 and mix well. Pour the solution into a plastic petri dish with a diameter of 35 mm and cure it under ultraviolet light at a wavelength of 365 nm for 10 min. Then, soak the PSBMA hydrogel in water to wash away unreacted reagents.

[0052] (2) The polymethacryloyl ethyl sulfobetaine (PSBMA) hydrogel, which has been thoroughly washed with water, is immersed in an 8M LiCl aqueous solution for 12 hours to load LiCl.

[0053] (3) Preparation of porous hydrophobic polyvinylidene fluoride (PVDF) shell by phase inversion method: 5% PVDF by mass fraction was dissolved in a mixed solution of dimethyl sulfoxide (DMSO) and water with a volume ratio of 5:95. The prepared PSBMA-LiCl hydrogel was immersed in the PVDF solution for 1 min to coat the surface with a layer of PVDF. Then, the PSBMA-LiCl hydrogel coated with PVDF was immersed in deionized water at 65℃ for 10 min to exchange solvent and form the PVDF shell, thus obtaining PSBMA-LiCl@PVDF. The preparation flow chart is shown below. Figure 1 As shown.

[0054] Example 2

[0055] The PSMBA in Example 1 was modified to include polyacrylamide (PAM), poly[2(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide, poly[2(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (PSA), polyvinyl alcohol (PVA), polyacrylic acid (PAA), and sodium polystyrene sulfonate (PSS).

[0056] Example 3

[0057] The concentrations of the LiCl solution in Example 1 were adjusted to 2M, 4M, 6M, and 10M.

[0058] Example 4

[0059] The aqueous solution of LiCl in Example 1 was adjusted to contain MgCl2, KCl, NaCl, and MgBr2.

[0060] Example 5

[0061] The PVDF in Example 1 was changed to polytetrafluoroethylene (PTFE), polyvinyl butyral (PVB), polypropylene (PP), and polyacrylonitrile (PAN).

[0062] Example 6

[0063] The mass fraction of PVDF in Example 1 was adjusted to 3%, 5%, and 10%.

[0064] Example 7

[0065] The DMSO and water in Example 1 were adjusted to N,N-dimethylformamide (DMF) and water.

[0066] Example 8

[0067] The volume ratio of DMSO and water in Example 1 was adjusted to 0.02, 0.03, and 0.04.

[0068] Example 9

[0069] The curing shell temperature in Example 1 was adjusted to 20°C, 40°C, and 60°C.

[0070] Comparative Example 1

[0071] (1) Dissolve 2.79 g of methacryloyl ethyl sulfobetaine (SBMA) monomer and 15 mg of N,N′-methylenebisacrylamide (BIS) in 5 mL of water to obtain a monomer concentration of 2 M. Add 20 µL of photoinitiator 1173 and mix well. Pour the solution into a plastic petri dish with a diameter of 35 mm and cure it under ultraviolet light at a wavelength of 365 nm for 10 min. Then, soak the PSBMA hydrogel in water to wash away unreacted reagents.

[0072] (2) The polymethacryloyl ethyl sulfobetaine (PSBMA) hydrogel, which has been thoroughly washed with water, is immersed in an 8M LiCl aqueous solution for 12 hours to load LiCl, thus obtaining PSBMA-LiCl.

[0073] Results analysis:

[0074] Figure 2 (a) shows the leakage test diagram of the PSBMA-LiCl hygroscopic salt solution in Comparative Example 1, and (b) shows the leakage test diagram of the PSBMA-LiCl@PVDF hygroscopic salt solution in Example 1. Figure 2 As shown, at 4 h, neither the PSBMA-LiCl@PVDF hydrogel prepared in Example 1 nor the PSBMA-LiCl hydrogel prepared in Comparative Example 1 showed leakage of hygroscopic salt solution. However, at 8 h, the PSBMA-LiCl hydrogel without PVDF coating showed obvious leakage of hygroscopic salt solution. The PSBMA-LiCl@PVDF hydrogel coated with PVDF did not show leakage of hygroscopic salt solution until 12 h. These results indicate that PVDF coating has a significant effect on inhibiting leakage of hygroscopic salt solution and can reduce leakage of hygroscopic salt solution by 100%.

[0075] Figure 3(a) represents the equilibrium adsorption capacity of PSBMA-LiCl and PSBMA-LiCl@PVDF during multiple cycles, and (b) represents the percentage of equilibrium adsorption capacity of PSBMA-LiCl and PSBMA-LiCl@PVDF during multiple cycles. The cyclic stability of the composite hygroscopic hydrogel before and after PVDF coating was studied under a relative humidity (RH) of 90%. Although the water vapor adsorption performance of the composite hygroscopic hydrogel decreased after PVDF coating, the PVDF shell can suppress the leakage of relative salt solution and prevent the degradation of water vapor adsorption performance caused by the decrease in salt content under high humidity conditions. It still has significant advantages in long-term use. Therefore, suppressing the leakage of hygroscopic salt solution by coating with PVDF is of great significance for the long-term use of composite hygroscopic hydrogels in high humidity environments.

[0076] Figure 4 (a) shows the thermogravimetric curves of PSBMA-LiCl after 0, 1, and 5 cycles of adsorption. Figure 4 Table (b) shows the thermogravimetric curves of PSBMA-LiCl@PVDF after 0, 1, and 5 cycles of adsorption. The weight loss test (TGA) revealed a significant decrease in salt content in the uncoated PSBMA-LiCl hydrogel after the first cycle, decreasing from 52% to 37%, with no further decrease after the fifth cycle. This is consistent with the observed leakage of hygroscopic salt solution; significant leakage occurred during the first water vapor adsorption process, but no leakage was observed in subsequent cycles. In contrast, the PSBMA-LiCl@PVDF hydrogel coated with a hydrophobic PVDF shell did not show a decrease in salt content after five cycles. The above results further demonstrate that leakage of the hygroscopic salt solution leads to a decrease in the salt content inside the hydrogel, while the hydrophobic PVDF shell can effectively inhibit the leakage of the hygroscopic salt solution, thereby ensuring that the salt content inside the composite hygroscopic hydrogel does not decrease during the water vapor adsorption process, and improving the stability of the composite hygroscopic hydrogel during long-term use.

[0077] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a core-shell composite hygroscopic hydrogel with a hydrophobic surface, characterized in that, A hydrophilic gel loaded with hygroscopic salts is placed in a hydrophobic polymer solution. A porous hydrophobic polymer shell is loaded onto the surface of the hydrophilic gel using a phase inversion method, thereby obtaining a composite hygroscopic hydrogel with a hydrophilic gel loaded with hygroscopic salts as the core layer and a porous hydrophobic polymer as the shell layer; the hydrophilic gel is a polyzwitterionic electrolyte hydrogel. The specific preparation steps for the hydrophilic gel loaded with hygroscopic salt are as follows: (1) Preparation of hydrophilic gel precursor solution; (2) The gel precursor solution is cured by heating or photocuring to obtain a hydrophilic gel; (3) Soak the hydrophilic gel in an aqueous solution of hygroscopic salt to load the hygroscopic salt onto the hydrophilic gel to obtain a hydrophilic gel loaded with hygroscopic salt; the hydrophilic gel in step (2) is a microspherical hydrophilic gel, and its specific preparation steps are as follows: the hydrophilic gel precursor solution obtained in step (1) is added dropwise into an oily solution, and then cured by heating or photocuring to obtain a microspherical hydrophilic gel.

2. The method for preparing a hydrophobic core-shell composite hygroscopic hydrogel according to claim 1, characterized in that, The zwitterionic electrolyte hydrogel is one or more of polymethacryloylethyl sulfobetaine and poly[2(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide.

3. The method for preparing a hydrophobic core-shell composite hygroscopic hydrogel according to claim 2, characterized in that, The diameter of the microspherical hydrophilic gel is 5 mm to 25 mm.

4. The method for preparing a hydrophobic core-shell composite hygroscopic hydrogel according to claim 3, characterized in that, The specific preparation steps of the hydrophobic polymer solution are as follows: dissolve the hydrophobic polymer material in a mixture of a good solvent and a poor solvent to obtain the hydrophobic polymer solution.

5. The method for preparing a hydrophobic core-shell composite hygroscopic hydrogel according to claim 4, characterized in that, The hydrophobic polymer is one or more of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl butyral, polypropylene, and polyacrylonitrile; the hygroscopic salt is one or more of potassium chloride, sodium chloride, potassium bromide, magnesium chloride, magnesium bromide, lithium chloride, and lithium bromide, and the concentration of the hygroscopic salt in the aqueous solution is 1 mol / L-10 mol / L.

6. The method for preparing a hydrophobic core-shell composite hygroscopic hydrogel according to claim 4, characterized in that, The good solvent is one or more of methylene sulfone, N,N-dimethylformamide, N-methylpyrrolidone, and dimethyl sulfoxide, and the bad solvent is water. The volume ratio of the good solvent to the bad solvent is 0.01-0.

06.

7. The method for preparing a hydrophobic core-shell composite hygroscopic hydrogel according to claim 6, characterized in that, The hydrophobic polymer solution contains 1% to 10% by mass of the hydrophobic polymer; the hydrophilic gel loaded with hygroscopic salt is immersed in the hydrophobic polymer solution for 3 to 10 minutes; the phase transition temperature is 20°C to 80°C; and the porous hydrophobic polymer shell thickness is 200 μm to 800 μm.

8. The composite hygroscopic hydrogel prepared by the method for preparing a surface-hydrophobic core-shell structure composite hygroscopic hydrogel according to any one of claims 1-7.

9. The application of the composite hygroscopic hydrogel according to claim 8, characterized in that, It can be applied to air water intake and humidity control.

10. The application of the composite hygroscopic hydrogel according to claim 9, characterized in that, The humidity control specifically refers to the field of agricultural moisture retention.

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