A high-strength biomimetic shell structure TOCNF / MXene / PEG phase change composite film, a preparation method and application thereof

Abstract

The application discloses a high-strength biomimetic shell structure TOCNF / MXene / PEG phase change composite film and a preparation method and application thereof. 2+ The interaction between the one-dimensional nanocellulose TOCNF and the two-dimensional nanosheet MXene, such as hydrogen bond, etc., realizes uniform and stable stacking of the two in the film, and Ca 2+ The ion crosslinking network formed between the carboxyl of the TOCNF and the oxygen-containing functional groups of the MXene can be used as a bridge to enhance the interlayer bonding force, so that the mechanical strength of the composite film is significantly improved, and the interlayer slip is effectively inhibited.

Description

Technical Field

[0001] This invention relates to the field of phase change energy storage materials and nanocomposite materials, and particularly to a high-strength biomimetic shell-like structure TOCNF / MXene / PEG phase change composite film, its preparation method, and its applications. Background Technology

[0002] Phase change materials (PCMs) hold significant promise for applications in wearable thermal management and smart fabrics, with polyethylene glycol (PEG) being a commonly used PCM material. However, in practical applications, PEG exhibits a noticeable solid-liquid phase change leakage problem, and its intrinsic strength is extremely low, making it highly susceptible to breakage under frequent bending or stretching in flexible environments. To address these issues, researchers have commonly employed biomass porous scaffolds to physically confine PEG, effectively suppressing PCM leakage and improving the structural stability of the composite system to some extent. However, due to the porous structure of the biomass scaffold itself, the improvement in its mechanical properties is limited, and the tensile strength of the composite material is typically still in the kPa range, making it difficult to meet the requirements for use under high-strength tensile or complex deformation conditions.

[0003] To further enhance mechanical properties, some studies have constructed mechanically reinforcing structures through chemical modification or the introduction of cross-linked networks, effectively improving the strength of materials. However, excessive chemical cross-linking often introduces internal stress concentration, leading to decreased flexibility and deteriorated cyclic stability during repeated bending or stretching, thus limiting its reliability in long-term dynamic service environments.

[0004] In recent years, inspired by the structure of natural seashells and nacre, the self-assembly of TEMPO oxidized cellulose nanofibers (TOCNF) and MXene to construct biomimetic layered structures has been considered an effective way to enhance mechanical strength. These materials significantly improve the overall strength and toughness of the composite system through the synergistic effect of highly oriented two-dimensional sheets. However, existing biomimetic layered structures mostly rely on weak interactions such as hydrogen bonds for interfacial bonding, making them prone to interlayer slippage under external forces. Therefore, achieving long-term shape stability of flexible phase change composite films under complex mechanical environments remains a key challenge for phase change energy storage materials in the field of wearable thermal management. Summary of the Invention

[0005] The present invention aims to at least partially solve one of the technical problems in the related art.

[0006] Therefore, this invention proposes a high-strength biomimetic shell-like structure TOCNF / MXene / PEG phase change composite film, its preparation method, and its application.

[0007] In a first aspect, this invention proposes a method for preparing a high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite thin film, comprising the following steps:

[0008] (1) Mix the TOCNF dispersion with the MXene dispersion, stir and sonicate to obtain a TOCNF / MXene mixed dispersion;

[0009] (2) The mixed dispersion is vacuum filtered to deposit a TOCNF / MXene skeleton film with a shell-like layered structure on the filter membrane;

[0010] (3) The skeleton film is immersed in a calcium salt aqueous solution for reaction, inducing Ca 2+ Ion crosslinking yields a reinforced framework film;

[0011] (4) The reinforced skeleton film is completely immersed in a polyethylene glycol aqueous solution, and then dried to obtain a TOCNF / MXene / PEG phase change film;

[0012] (5) The TOCNF / MXene / PEG phase change film is immersed in a hydrophobic modification solution for surface coating, and then dried to obtain a high-strength biomimetic shell-like phase change composite film.

[0013] Further, in step (1), the concentration of the TOCNF dispersion is 1.13~1.35wt%, and the concentration of the MXene dispersion is 0.5~1wt%.

[0014] Further, in step (1), the mass ratio of TOCNF to MXene in the TOCNF / MXene mixed dispersion is 3:1 to 1:1.

[0015] Furthermore, in step (1), the ultrasonic treatment adopts a pulse mode, the ultrasonic power is 300~600W, and the ultrasonic time is 0.5~1h.

[0016] Furthermore, the concentration of the calcium salt aqueous solution is 0.005~0.5M.

[0017] Furthermore, the calcium salt aqueous solution is a soluble calcium salt aqueous solution, which includes at least one of calcium chloride solution, calcium gluconate solution, or calcium acetate solution.

[0018] Furthermore, in step (3), the time for immersing the skeleton film in the calcium salt aqueous solution is 0.5~5h.

[0019] Furthermore, the average molecular weight of the polyethylene glycol is 1000~4000.

[0020] Furthermore, the mass concentration of the polyethylene glycol aqueous solution is 30% to 70%.

[0021] Furthermore, in step (4), the drying process involves standing at 25-40°C for 12-24 hours.

[0022] Furthermore, the hydrophobic modification solution includes at least one of the following: 1708 type PVDF fluorocarbon resin solution, PDMS solution, and stearic acid ethanol solution.

[0023] Furthermore, in step (5), the time for immersing the TOCNF / MXene / PEG phase change film in the hydrophobic modification solution for surface coating is 0.5~5 min.

[0024] Furthermore, in step (5), the drying process is carried out at 25-40°C for 0.5-2 hours.

[0025] Secondly, this invention proposes a high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite film prepared by the method proposed in the first aspect above. The phase change composite film is a three-dimensional framework structure, wherein TOCNF and MXene are bonded together via Ca2+. 2+ A shell-like layered structure constructed by ion crosslinking, with polyethylene glycol phase change units loaded within the nanolayer confinement space of the three-dimensional framework.

[0026] Thirdly, this invention proposes the application of the high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite film prepared by the method proposed in the first aspect above, or the high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite film proposed in the second aspect above, in the field of wearable human thermal management and solar photothermal conversion devices.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] This invention utilizes the interactions, such as hydrogen bonds, between one-dimensional cellulose nanofiber TOCNF and two-dimensional nanosheets MXene to achieve uniform and stable stacking of the two within a thin film. 2+ It can form an ionic crosslinking network between the carboxyl groups of TOCNF and the oxygen-containing functional groups of MXene, which acts as a bridge to enhance the interlayer bonding force, thereby significantly improving the mechanical strength of the composite film and effectively suppressing interlayer slippage.

[0029] This invention uses the biomass material TOCNF in combination with two-dimensional MXene to construct a layered framework, and polyethylene glycol (PEG) as the phase change functional component. The raw materials are widely available and environmentally friendly. By utilizing the interlayer confinement effect of the shell-like structure, combined with the hydrophobic layer on the surface, the liquid leakage problem of phase change materials at high temperatures is solved, ensuring the chemical stability of the material in complex environments.

[0030] The TOCNF / MXene / PEG phase change film prepared by this invention can maintain shape stability and exhibit no liquid leakage under heating conditions of 80°C, demonstrating excellent performance. Thanks to hydrogen bonding and the shell-like structure of ionic crosslinking, the film has a tensile strength of up to 50~70MPa and a latent heat of phase change of not less than 118.4J / g. In addition, the film surface contact angle is maintained at about 106°, and it can maintain stable performance in various harsh environments such as human perspiration or high humidity, demonstrating strong environmental adaptability. Attached Figure Description

[0031] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings, wherein:

[0032] Figure 1 Flowchart of a high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite thin film and its preparation method;

[0033] Figure 2 A process diagram illustrating the high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite thin film and its preparation method;

[0034] Figure 3 Here is a SEM image of the phase change thin film, where... Figure 3 Image (a) is a SEM image of the phase change film of Example 1. Figure 3 Image (b) is a SEM image of the phase change film of Example 2. Figure 3 Image (c) is a SEM image of the phase change film of Example 3. Figure 3 Image (d) is a SEM image of the phase change film in Comparative Example 2;

[0035] Figure 4 Here is a SEM image of the phase change thin film, where... Figure 4 Image (a) is a SEM image of the phase change film in Comparative Example 4. Figure 4 (b) is a SEM image of the phase change film of Comparative Example 8;

[0036] Figure 5 XPS test images of MXene and the TOCNF / MXene / Ca thin film in Example 2 are shown below. Figure 5 (a) shows the C 1s XPS spectrum of MXene. Figure 5 (b) shows the C 1s XPS spectra of TOCNF / MXene / Ca. Figure 5 (c) shows the Ti 2p XPS spectrum of MXene. Figure 5 (d) shows the Ti 2p XPS spectrum of TOCNF / MXene / Ca;

[0037] Figure 6XPS test images of MXene, TOCNF, and the TOCNF / MXene and TOCNF / MXene / Ca films in Example 2 are shown. Figure 6 (a) shows the XPS full spectrum of TOCNF, MXene, TOCNF / MXene, and TOCNF / MXene / Ca films. Figure 6 (b) shows the Ca 2p high-resolution XPS spectrum of TOCNF / MXene / Ca;

[0038] Figure 7 The images show the FT-IR test results of the phase change films in Examples 1-3.

[0039] Figure 8 The figures shown are tensile test diagrams of phase change films from Examples 1-3 and Comparative Examples 3-10. Figure 8 (a) shows the tensile test results of the phase change films in Comparative Examples 7-10. Figure 8 (b) shows the tensile test results of the phase change films in Comparative Examples 3-6. Figure 8 (c) shows the tensile test results of the phase change films in Examples 1-3;

[0040] Figure 9 The figures show DSC test results for pure PEG and the phase change films of Examples 1-3. Figure 9 (a) shows the DSC heating and melting curve. Figure 9 (b) is the DSC cooling crystallization curve. Figure 9 (c) shows the DSC comparison curves of the TMP-2 film before and after 200 thermal cycles;

[0041] Figure 10 Leakage test results for the phase change film and PEG in Example 2;

[0042] Figure 11 The stability test results for the phase change film and PEG in Example 2 are shown.

[0043] Figure 12 The water contact angle test diagrams are shown for the phase change films in Example 2 and Comparative Example 1.

[0044] Figure 13 The image shown is an infrared thermal imaging test image of the phase change thin film in Example 2. Figure 13 (a) is an infrared thermogram of a human body model with a TMP-2 film attached under simulated solar radiation. Figure 13 (b) is an infrared thermogram of a human model with a thin film attached, showing the gradual release of heat energy after solar radiation is removed. Detailed Implementation

[0045] Embodiments of the present invention are described in detail below, examples of which are illustrated 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 intended to explain the present invention, and should not be construed as limiting the present invention.

[0046] The following description, in conjunction with the accompanying drawings, describes the high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite thin film, its preparation method, and its applications.

[0047] like Figure 1 and Figure 2 As shown, the preparation method of the high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite film of the present invention includes the following steps:

[0048] (1) Mix the TOCNF dispersion with the MXene dispersion, stir and sonicate to obtain a TOCNF / MXene mixed dispersion;

[0049] (2) The mixed dispersion is vacuum filtered to deposit a TOCNF / MXene skeleton film with a shell-like layered structure on the filter membrane;

[0050] (3) The skeleton film is immersed in a calcium salt aqueous solution for reaction, inducing Ca 2+ Ion crosslinking yields a reinforced framework film;

[0051] (4) The reinforced skeleton film is completely immersed in a polyethylene glycol aqueous solution, and then dried to obtain a TOCNF / MXene / PEG phase change film;

[0052] (5) The TOCNF / MXene / PEG phase change film is immersed in a hydrophobic modification solution for surface coating, and then dried to obtain a high-strength biomimetic shell-like phase change composite film.

[0053] Step (1) involves the blending and uniform dispersion of TOCNF and MXene, wherein the concentration of the TOCNF dispersion is 1.13~1.35wt%, the concentration of the MXene dispersion is 0.5~1wt%, and the MXene nanosheets are transition metal carbides, preferably titanium carbide (Ti3C2T). x The mass ratio of TOCNF to MXene in the obtained TOCNF / MXene mixed dispersion was 3:1 to 1:1.

[0054] After mixing the TOCNF dispersion and the MXene dispersion, the mixture was placed in an ice-water bath for stirring and ultrasonic treatment. The ultrasonic power was set to 300-600W, and the ultrasonic time was 0.5-1h. A pulse mode was used during the ultrasonic process, alternating between continuous and intermittent ultrasonic treatment, to effectively prevent localized overheating and oxidation of the MXene.

[0055] Step (2) is a vacuum filtration-assisted directional assembly process. Using vacuum filtration technology, TOCNF and MXene are deposited on the filter membrane surface, inducing the self-assembly of one-dimensional fibers and two-dimensional nanosheets to form a highly ordered biomimetic shell-like layered structure. This structure provides a stable confined space for subsequent PEG filling and lays the foundation for the high strength of the film.

[0056] Step (3) is Ca² + The induced non-covalent crosslinking strengthening process involves a calcium salt aqueous solution with a concentration of 0.005–0.5 M. This calcium salt aqueous solution is a soluble calcium salt solution, comprising at least one of calcium chloride, calcium gluconate, or calcium acetate solutions. The skeleton film is immersed in the calcium salt aqueous solution for 0.5–5 hours. During this process, calcium ions form a non-covalent ionic crosslinking network with the carboxyl groups on the TOCNF surface and the active groups on the MXene surface. This crosslinking force significantly enhances the mechanical strength of the skeleton.

[0057] Step (4) is the phase change material loading process, in which the ion-crosslinked reinforced film is completely immersed in a polyethylene glycol (PEG) aqueous solution with a mass fraction of 30% to 70%. The average molecular weight of the PEG is 1000 to 4000, preferably 2000. The drying process involves standing at 25 to 40°C for 12 to 24 hours, using a concentration gradient to drive PEG molecules into the nanolayers of the framework.

[0058] Step (5) is a surface hydrophobic modification process. The TOCNF / MXene / PEG phase change film obtained in step (4) is immersed in a hydrophobic modification solution for surface coating. After removal and drying, a high-strength biomimetic shell-like phase change composite film is obtained. The hydrophobic layer not only improves the weather resistance of the material, but also further helps to lock in the internal phase change components. The hydrophobic modification solution includes at least one of 1708 type PVDF fluorocarbon resin solution, PDMS solution, and stearic acid ethanol solution. The time for immersing the TOCNF / MXene / PEG phase change film in the hydrophobic modification solution for surface coating is 0.5~5 min. The drying in step (5) is carried out at 25~40°C for 0.5~2 h to form a film on the surface.

[0059] The high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite film of the present invention is prepared by the method of the present invention. The phase change composite film is a three-dimensional skeleton structure, wherein the three-dimensional skeleton structure is formed by TOCNF and MXene through Ca. 2+ A shell-like layered structure constructed by ion crosslinking is formed, with polyethylene glycol phase transition units loaded within the confined nanolayer space of the three-dimensional framework. The film exhibits a biomimetic shell-like alternating layered stacked structure, where two-dimensional MXene nanosheets act as supporting "building blocks," and one-dimensional TOCNF fibers and PEG molecules act as filling "mortar." The following synergistic forces exist within the film: a multi-layered hydrogen bond network formed by functional groups among TOCNF, MXene, and PEG; Ca... 2+ Ionic coordination bonds are formed with the carboxyl groups on the surface of TOCNF and the oxygen-containing functional groups on the surface of MXene; these ionic coordination bonds constitute a non-covalent cross-linked network, which is used to constrain the interlayer slip of MXene sheets.

[0060] The present invention will now be described in detail with reference to specific embodiments.

[0061] Example 1

[0062] Weigh 3.32 g of a 1.13 wt% TOCNF dispersion and mix it with 1.25 g of a 1 wt% MXene dispersion (solid content mass ratio 3:1). Add 5 ml of water and stir at 500 rpm for 1 hour using a magnetic stirrer. Then, use a probe-type ultrasonic processor at 600 W in pulse mode (on for 3 seconds, off for 2 seconds) for 30 minutes to obtain a uniform TOCNF / MXene dispersion.

[0063] The above mixed dispersion was poured into a vacuum filtration device and filtered using a mixed cellulose membrane with a pore size of 0.22 μm. The vacuum was maintained at -0.09 MPa. After the solvent passed through the filter membrane, a TOCNF / MXene wet membrane with a biomimetic shell-like oriented stacked structure was formed on the surface of the filter membrane.

[0064] Prepare a 0.01M CaCl2 aqueous solution. Immerse the wet membrane with the filter membrane into the calcium salt solution and allow it to stand at room temperature (25°C) for 1 hour to induce Ca2+ absorption. 2+ It undergoes a coordination reaction with the carboxyl groups of TOCNF and the surface functional groups of MXene. After removal, it is rinsed with a small amount of deionized water to obtain a TOCNF / MXene / Ca film.

[0065] The cross-linked reinforced skeleton film was completely immersed in a 50% (w / w) aqueous solution of polyethylene glycol (PEG, Mn=2000) and allowed to stand at room temperature for 12 hours to allow solvent exchange, enabling PEG molecules to fully penetrate into the confined space between the nanolayers. The film was then removed and allowed to air dry at room temperature for 24 hours until constant weight was achieved.

[0066] The dried film was immersed in a 1708 type PVDF fluorocarbon resin solution using an impregnation method. After removal, it was dried in a 30°C oven for 30 minutes. This resulted in a high-strength, biomimetic shell-like TMP-1 phase change composite film.

[0067] Example 2

[0068] Weigh 2.65 g of a 1.13 wt% TOCNF dispersion and mix it with 2 g of a 1 wt% MXene dispersion (solid content mass ratio 3:2). Add 5 ml of water and stir at 500 rpm for 1 hour using a magnetic stirrer. Then, use a probe-type ultrasonic processor at 600 W in pulse mode (on for 3 seconds, off for 2 seconds) for 30 minutes to obtain a uniformly mixed TOCNF / MXene dispersion.

[0069] The above mixed dispersion was poured into a vacuum filtration device and filtered using a mixed cellulose membrane with a pore size of 0.22 μm. The vacuum was maintained at -0.09 MPa. After the solvent passed through the filter membrane, a TOCNF / MXene wet membrane with a biomimetic shell-like oriented stacked structure was formed on the surface of the filter membrane.

[0070] Prepare a 0.01M CaCl2 aqueous solution. Immerse the wet membrane with the filter membrane into the calcium salt solution and allow it to stand at room temperature (25°C) for 1 hour to induce Ca2+ absorption. 2+ It undergoes a coordination reaction with the carboxyl groups of TOCNF and the surface functional groups of MXene. After removal, it is rinsed with a small amount of deionized water to obtain a TOCNF / MXene / Ca film.

[0071] The cross-linked reinforced skeleton film was completely immersed in a 50% (w / w) aqueous solution of polyethylene glycol (PEG, Mn=2000) and allowed to stand at room temperature for 12 hours to allow solvent exchange, enabling PEG molecules to fully penetrate into the confined space between the nanolayers. The film was then removed and allowed to air dry at room temperature for 24 hours until constant weight was achieved.

[0072] The dried film was rapidly immersed in a 1708 type PVDF fluorocarbon resin solution using an impregnation method. After removal, it was dried in a 30°C oven for 30 minutes. This resulted in a high-strength, biomimetic shell-like TMP-2 phase change composite film.

[0073] Example 3

[0074] Weigh 2.21 g of a 1.13 wt% TOCNF dispersion and mix it with 2.5 g of a 1 wt% MXene dispersion (solid content mass ratio 1:1). Add 5 ml of water and stir at 500 rpm for 1 hour using a magnetic stirrer. Then, use a probe-type ultrasonic processor at 600 W in pulse mode (on for 3 seconds, off for 2 seconds) for 30 minutes to obtain a uniform TOCNF / MXene dispersion.

[0075] The above mixed dispersion was poured into a vacuum filtration device and filtered using a mixed cellulose membrane with a pore size of 0.22 μm. The vacuum was maintained at -0.09 MPa. After the solvent passed through the filter membrane, a TOCNF / MXene wet membrane with a biomimetic shell-like oriented stacked structure was formed on the surface of the filter membrane.

[0076] Prepare a 0.01M CaCl2 aqueous solution. Immerse the wet membrane with the filter membrane into the calcium salt solution and allow it to stand at room temperature (25°C) for 1 hour to induce Ca2+ absorption. 2+ It undergoes a coordination reaction with the carboxyl groups of TOCNF and the surface functional groups of MXene. After removal, it is rinsed with a small amount of deionized water to obtain a TOCNF / MXene / Ca film.

[0077] The cross-linked reinforced skeleton film was completely immersed in a 50% (w / w) aqueous solution of polyethylene glycol (PEG, Mn=2000) and allowed to stand at room temperature for 12 hours to allow solvent exchange, enabling PEG molecules to fully penetrate into the confined space between the nanolayers. The film was then removed and allowed to air dry at room temperature for 24 hours until constant weight was achieved.

[0078] The dried film was rapidly immersed in a 1708 type PVDF fluorocarbon resin solution using an impregnation method. After removal, it was dried in a 30°C oven for 30 minutes. This resulted in a high-strength, biomimetic shell-like TMP-3 phase change composite film.

[0079] Comparative Example 1

[0080] Weigh 3.32 g of a 1.13 wt% TOCNF dispersion and mix it with 1.25 g of a 1 wt% MXene dispersion (solid content mass ratio 3:1). Add 5 ml of water and stir at 500 rpm for 1 hour using a magnetic stirrer. Then, use a probe-type ultrasonic processor at 600 W in pulse mode (on for 3 seconds, off for 2 seconds) for 30 minutes to obtain a uniform TOCNF / MXene dispersion.

[0081] The above mixed dispersion was poured into a vacuum filtration device and filtered using a mixed cellulose membrane with a pore size of 0.22 μm. The vacuum was maintained at -0.09 MPa. After the solvent passed through the filter membrane, a TOCNF / MXene wet membrane with a biomimetic shell-like oriented stacked structure was formed on the surface of the filter membrane.

[0082] Prepare a 0.01M CaCl2 aqueous solution. Immerse the wet membrane with the filter membrane into the calcium salt solution and allow it to stand at room temperature (25°C) for 1 hour to induce Ca2+ absorption. 2+ It undergoes a coordination reaction with the carboxyl groups of TOCNF and the surface functional groups of MXene. After removal, it is rinsed with a small amount of deionized water to obtain a TOCNF / MXene / Ca film.

[0083] The cross-linked reinforced skeleton film was completely immersed in a 50% (w / w) aqueous solution of polyethylene glycol (PEG, Mn=2000) and allowed to stand at room temperature for 12 hours for solvent exchange, allowing PEG molecules to fully penetrate into the confined space between the nanolayers. The film was then removed and allowed to air dry at room temperature for 24 hours until constant weight was achieved. This yielded the TMP-1 phase change composite film without a hydrophobic coating.

[0084] Comparative Example 2

[0085] Weigh 4.42 g of a 1.13 wt% TOCNF dispersion, add 5 ml of water, and stir at 500 rpm for 1 h using a magnetic stirrer. Then, use a probe-type ultrasonic processor at 600 W in pulse mode (on for 3 seconds, off for 2 seconds) for 30 min to obtain a uniform TOCNF dispersion.

[0086] The dispersion was poured into a vacuum filtration apparatus and filtered using a mixed cellulose membrane with a pore size of 0.22 μm. The vacuum was maintained at -0.09 MPa, and after the solvent had completely permeated through the filter membrane, a TOCNF wet membrane was formed on the surface of the filter membrane.

[0087] Prepare a 0.01M CaCl2 aqueous solution. Immerse the wet membrane with the filter membrane into the calcium salt solution and allow it to stand at room temperature (25°C) for 1 hour to induce Ca2+ absorption. 2+ It undergoes a coordination reaction with the carboxyl group of TOCNF. After removal, it is rinsed with a small amount of deionized water to obtain a TOCNF / Ca film.

[0088] The cross-linked reinforced backbone film was completely immersed in a 50% (w / w) aqueous solution of polyethylene glycol (PEG, Mn=2000) and allowed to stand at room temperature for 12 hours for solvent exchange, allowing PEG molecules to fully penetrate into the confined space between the nanolayers. The film was then removed and allowed to air dry at room temperature for 24 hours until constant weight was achieved. The TP-4 phase change composite film was finally obtained.

[0089] Comparative Example 3

[0090] Weigh 3.32 g of a 1.13 wt% TOCNF dispersion and mix it with 1.25 g of a 1 wt% MXene dispersion (solid content mass ratio 3:1). Add 5 ml of water and stir at 500 rpm for 1 hour using a magnetic stirrer. Then, use a probe-type ultrasonic processor at 600 W in pulse mode (on for 3 seconds, off for 2 seconds) for 30 minutes to obtain a uniform TOCNF / MXene dispersion.

[0091] The above mixed dispersion was poured into a vacuum filtration device and filtered using a mixed cellulose membrane with a pore size of 0.22 μm. The vacuum was maintained at -0.09 MPa, and after the solvent had completely permeated through the filter membrane, a TOCNF / MXene wet membrane with a biomimetic shell-like oriented stacked structure was formed on the surface of the filter membrane.

[0092] The framework film was completely immersed in a 50 wt% aqueous solution of polyethylene glycol (PEG, Mn=2000) and allowed to stand at room temperature for 12 h to allow solvent exchange, enabling PEG molecules to fully penetrate into the confined space between the nanolayers. The film was then removed and allowed to air dry at room temperature for 24 h until constant weight was achieved.

[0093] The dried film was immersed in a 1708 type PVDF fluorocarbon resin ethanol solution using an impregnation method. After removal, it was dried in a 30°C oven for 30 minutes to form a film. The final FTMP-1 phase change composite film was obtained.

[0094] Comparative Example 4

[0095] Weigh 2.65 g of a 1.13 wt% TOCNF dispersion and mix it with 2 g of a 1 wt% MXene dispersion (solid content mass ratio 3:2). Add 5 ml of water and stir at 500 rpm for 1 hour using a magnetic stirrer. Then, use a probe-type ultrasonic processor at 600 W in pulse mode (on for 3 seconds, off for 2 seconds) for 30 minutes to obtain a uniformly mixed TOCNF / MXene dispersion.

[0096] The above mixed dispersion was poured into a vacuum filtration device and filtered using a mixed cellulose membrane with a pore size of 0.22 μm. The vacuum was maintained at -0.09 MPa, and after the solvent had completely permeated through the filter membrane, a TOCNF / MXene wet membrane with a biomimetic shell-like oriented stacked structure was formed on the surface of the filter membrane.

[0097] The skeleton film was completely immersed in a 50 wt% aqueous solution of polyethylene glycol (PEG, Mn=2000) and allowed to stand at room temperature for 12 h to allow solvent exchange, enabling PEG molecules to fully penetrate into the confined space between the nanolayers. The film was then removed and allowed to air dry at room temperature for 24 h until constant weight was achieved.

[0098] The dried film was immersed in a 1708 type PVDF fluorocarbon resin ethanol solution using an impregnation method. After removal, it was dried in a 30°C oven for 30 minutes to form a film. The final FTMP-2 phase change composite film was obtained.

[0099] Comparative Example 5

[0100] Weigh 2.21 g of a 1.13 wt% TOCNF dispersion and mix it with 2.5 g of a 1 wt% MXene dispersion (solid content mass ratio 1:1). Add 5 ml of water and stir at 500 rpm for 1 hour using a magnetic stirrer. Then, use a probe-type ultrasonic processor at 600 W in pulse mode (on for 3 seconds, off for 2 seconds) for 30 minutes to obtain a uniform TOCNF / MXene dispersion.

[0101] The above mixed dispersion was poured into a vacuum filtration device and filtered using a mixed cellulose membrane with a pore size of 0.22 μm. The vacuum was maintained at -0.09 MPa, and after the solvent had completely permeated through the filter membrane, a TOCNF / MXene wet membrane with a biomimetic shell-like oriented stacked structure was formed on the surface of the filter membrane.

[0102] The skeleton film was completely immersed in a 50 wt% aqueous solution of polyethylene glycol (PEG, Mn=2000) and allowed to stand at room temperature for 12 h for solvent exchange, allowing PEG molecules to fully penetrate into the confined space between the nanolayers. The film was then removed and allowed to air dry at room temperature for 24 h until constant weight was achieved.

[0103] The dried film was immersed in a 1708 type PVDF fluorocarbon resin ethanol solution using an impregnation method. After removal, it was dried in a 30°C oven for 30 minutes to form a film. The final FTMP-3 phase change composite film was obtained.

[0104] Comparative Example 6

[0105] Weigh 4.42 g of a 1.13 wt% TOCNF dispersion, add 5 ml of water, and stir at 500 rpm for 1 h using a magnetic stirrer. Then, use a probe-type ultrasonic processor at 600 W in pulse mode (on for 3 seconds, off for 2 seconds) for 30 min to obtain a uniform TOCNF dispersion.

[0106] The above mixed dispersion was poured into a vacuum filtration device and filtered using a mixed cellulose membrane with a pore size of 0.22 μm. The vacuum was maintained at -0.09 MPa, and after the solvent had completely passed through the filter membrane, a TOCNF wet membrane was formed on the surface of the filter membrane.

[0107] The framework film was completely immersed in a 50 wt% aqueous solution of polyethylene glycol (PEG, Mn=2000) and allowed to stand at room temperature for 12 hours for solvent exchange, allowing PEG molecules to fully penetrate into the confined space between the nanolayers. The film was then removed and allowed to air dry at room temperature for 24 hours until constant weight was achieved. The FTP-4 phase change composite film was finally obtained.

[0108] Comparative Example 7

[0109] Weigh 3.32 g of a 1.13 wt% TOCNF dispersion and mix it with 1.25 g of a 1 wt% MXene dispersion (solid content mass ratio 3:1). Add 5 ml of water, and add polyethylene glycol (PEG2000) in the same amount as in Example 1 under magnetic stirring. Stir at 500 rpm for 1 h using a magnetic stirrer, followed by probe-type ultrasonic treatment for 30 min to obtain a uniformly mixed dispersion. Pour the dispersion directly into a petri dish and allow it to dry naturally at room temperature to form a film, ultimately obtaining the BTMP-1 phase change composite film.

[0110] Comparative Example 8

[0111] Weigh 2.26 g of a 1.13 wt% TOCNF dispersion and mix it with 2 g of a 1 wt% MXene dispersion (solid content mass ratio 3:2). Add 5 ml of water and, under magnetic stirring, add the same amount of polyethylene glycol (PEG2000) as in Example 2. Place the mixture in an ice-water bath and stir at 500 rpm for 1 h using a magnetic stirrer, followed by probe-type ultrasonic treatment for 30 min to obtain a uniformly mixed dispersion. Pour the dispersion directly into a petri dish and allow it to dry naturally at room temperature to form a film, ultimately obtaining the BTMP-2 phase change composite film.

[0112] Comparative Example 9

[0113] Weigh 2.21 g of a 1.13 wt% TOCNF dispersion and mix it with 2.5 g of a 1 wt% MXene dispersion (TOCNF to MXene solid content mass ratio of 1:1). Add 5 ml of water and, under magnetic stirring, add the same amount of polyethylene glycol (PEG2000) as in Example 3. Place the mixture in an ice-water bath and stir at 500 rpm for 1 h using a magnetic stirrer, followed by probe-type ultrasonic treatment for 30 min to obtain a uniformly mixed dispersion. Pour the dispersion directly into a petri dish and allow it to dry naturally at room temperature to form a film, ultimately obtaining the BTMP-3 phase change composite film.

[0114] Comparative Example 10

[0115] Weigh 4.42 g of a 1.13 wt% TOCNF dispersion, add 5 ml of water, and add the same amount of polyethylene glycol (PEG2000) as in Example 4 under magnetic stirring. Place the mixture in an ice-water bath and stir at 500 rpm for 1 h using a magnetic stirrer, followed by probe-type sonication for 30 min to obtain a uniformly mixed dispersion. Pour the dispersion directly into a petri dish and allow it to dry naturally at room temperature to form a film, ultimately obtaining the BTP-4 phase change composite film.

[0116] Experimental Example 1

[0117] SEM tests were performed on the phase change films of Examples 1-3 and Comparative Examples 2, 4, and 8. The test results are as follows: Figure 3 and Figure 4 .in, Figure 3 Image (a) is a SEM image of the phase change film of Example 1. Figure 3 Image (b) is a SEM image of the phase change film of Example 2. Figure 3 Image (c) is a SEM image of the phase change film of Example 3. Figure 3 Image (d) is a SEM image of the phase change film in Comparative Example 2. Figure 4 Image (a) is a SEM image of the phase change film in Comparative Example 4. Figure 4 (b) is a SEM image of the phase change film of Comparative Example 8.

[0118] from Figure 3 It can be seen that TMP-1 begins to form a layered structure, while TMP-2 and TMP-3 both exhibit a complete layered structure. In contrast, the phase change film in Comparative Example 2 has a smooth and dense surface, consistent with its internal ordered structure. Since there is no MXene in Comparative Example 2, a layered structure cannot be formed.

[0119] from Figure 4 It can be seen that FTMP-2 did not undergo Ca... 2+ Crosslinking retains some layered features but the interlayer stacking is loose. It can be seen that ionic crosslinking is the key to suppressing lamellar slip and achieving qualitative changes in strength. BTMP-2, on the other hand, is made by direct mixing without vacuum filtration, and only exhibits weak layered features and a loose overall structure. It can be seen that vacuum filtration is the basis for constructing an ordered biomimetic skeleton and ensuring shape stability.

[0120] Experimental Example 2

[0121] XPS tests were performed on MXene and the TOCNF / MXene / Ca film from Example 2. The test results are as follows: Figure 5 As shown, where, Figure 5 (a) shows the C 1s XPS spectrum of MXene. Figure 5(b) shows the C 1s XPS spectra of TOCNF / MXene / Ca. Figure 5 (c) shows the Ti 2p XPS spectrum of MXene. Figure 5 (d) shows the Ti 2p XPS spectrum of TOCNF / MXene / Ca. From... Figure 5 It can be seen that, compared with the original MXene, the C in MXene / TOCNF / Ca O peak (286.6 / 287.4 eV) and Ti The O peaks (458.3 / 459.1 eV) both shifted to higher binding energies, indicating that multiple hydrogen bonds were formed between the MXene nanosheets and TOCNF.

[0122] Experimental Example 3

[0123] XPS tests were performed on the TOCNF, MXene, TOCNF / MXene, and TOCNF / MXene / Ca films in Example 2. The test results are as follows: Figure 6 ,in, Figure 6 (a) shows the XPS full spectrum of TOCNF, MXene, TOCNF / MXene, and TOCNF / MXene / Ca films. Figure 6 (b) is the high-resolution XPS spectrum of Ca 2p for TOCNF / MXene / Ca.

[0124] from Figure 6 As can be seen, compared with MXene / TOCNF in Example 2, new Ca 2p3 / 2 (346.0 eV) and Ca 2p1 / 2 (349.6 eV) peaks were observed in the MXene / TOCNF / Ca sample, further confirming the presence of Ca. 2+ Induced ion modification.

[0125] Test Example 4

[0126] FT-IR tests were performed on the phase change thin films in Examples 1-3, and the test results are as follows: Figure 7 As shown. From Figure 7 It can be seen that, compared with pure PEG, the composite film contains The shift of the OH absorption peak to lower wavenumbers indicates an interaction between TOCNF and PEG, which may help limit PEG leakage.

[0127] Experimental Example 5

[0128] Tensile tests were performed on the phase change films of Examples 1-3 and Comparative Examples 3-10, and the test results are as follows: Figure 8 As shown, where, Figure 8 (a) shows the tensile test results of the phase change films in Comparative Examples 7-10. Figure 8 (b) shows the tensile test results of the phase change films in Comparative Examples 3-6. Figure 8 (c) shows the tensile test results of the phase change thin films in Examples 1-3.

[0129] from Figure 8 It can be seen that the phase change films obtained by direct mixing (Comparative Examples 7-10) exhibit tensile strengths below 37 MPa. The mother-of-pearl biomimetic phase change films (Comparative Examples 3-6) formed by vacuum filtration after mixing achieved the highest tensile strength of 46 MPa. After vacuum filtration, the Ca²⁺ of the TOCNF / MXene network… + Coordination crosslinking (Examples 1-3) further improved the mechanical properties, with the films exhibiting tensile strengths exceeding 50 MPa. These results indicate that the mechanical properties of phase change films depend on the preparation process, and are influenced by vacuum filtration and Ca... 2+ The films treated with coordination crosslinking exhibited significantly enhanced mechanical properties.

[0130] Experimental Example 6

[0131] DSC tests were performed on pure PEG and the phase change films of Examples 1-3. The test results are as follows: Figure 9 As shown in Table 1, where, Figure 9 (a) shows the DSC heating and melting curve. Figure 9 (b) is the DSC cooling crystallization curve. Figure 9 (c) shows the DSC comparison curves of the TMP-2 film before and after 200 thermal cycles.

[0132] from Figure 9 As shown in Table 1, the enthalpy of melting (ΔHm) of pure PEG is 177.7 J / g, and the enthalpy of crystallization (ΔHc) is 170.5 J / g. In contrast, the phase transition enthalpy of the composite film is significantly reduced, with ΔHm and ΔHc values ​​falling in the ranges of 118.4–120.4 J / g and 116.8–121.4 J / g, respectively. The latent heat of the film is approximately 66.6–67.8% of that of the original PEG. This reduction is consistent with the relative content of PEG in the composite film, as the presence of MXene nanosheets and TOCNF does not participate in latent heat storage. The cyclic thermal reliability of TMP-2 was further evaluated, and the differential scanning calorimetry curve remained stable after 200 melt-solidification cycles, almost perfectly matching the original curve.

[0133] Table 1:

[0134]

[0135] Experimental Example 7

[0136] Leakage tests were performed on the TMP-2 phase change film in Example 2. The test method involved placing the sample on an 80°C constant temperature heating stage and observing changes in the sample's morphology and whether any liquid seeped through. The test results are as follows: Figure 10 As shown. From Figure 10 It can be seen that pure polyethylene glycol melts into a liquid rapidly within 3 minutes at 80°C, while no liquid leakage was observed in TMP-2 even after 30 minutes.

[0137] The stability of the TMP-2 phase change film in Example 2 under a 100-gram compressive load was tested. The test method involved placing the sample on an 80°C constant-temperature heating platform and observing changes in morphology and any liquid seepage. The test results are as follows: Figure 11 As shown, from Figure 11 It can be seen that TMP-2 maintains its shape stability under a 100g compressive load (approximately 2000 times its own weight), confirming its shape-stable phase transition properties. In contrast, pure PEG completely melts into a liquid state at 80°C, and liquid substances cannot maintain a fixed shape under a 100g load and will leak under pressure. Therefore, the experiment does not require specific measurements to prove the deformation of pure PEG, but directly uses it as the benchmark for losing shape stability, thus highlighting the excellent structural strength of the TMP-2 film, which can support 2000 times its own weight without leakage under the same conditions.

[0138] Experimental Example 8

[0139] The water contact angle of the phase change films in Example 2 and Comparative Example 1 was tested, and the test results are as follows: Figure 12 As shown. From Figure 12 As can be seen, the thin film material of Example 2 exhibits a water contact angle of 106°, which is much higher than that of the uncoated film in Comparative Example 1, indicating that the construction of the hydrophobic surface in Example 2 has been successful.

[0140] Experimental Example 9

[0141] Infrared thermal imaging tests were performed on the TMP-2 phase change thin film in Example 2, and the test results are as follows: Figure 13 As shown, where, Figure 13 (a) is an infrared thermogram of a human body model with a TMP-2 film attached under simulated solar radiation. Figure 13 (b) is an infrared thermogram of a human model with a thin film attached, showing the gradual release of heat energy after solar radiation is removed.

[0142] To verify the actual wearable performance, a phase change film was attached to the body of a human model, and infrared thermal imaging was performed. Figure 13As can be seen, under solar radiation, the chest temperature rose to 54°C, significantly higher than the surrounding area. After solar radiation was turned off, the temperature stabilized at 37.2°C, while the surrounding background temperature had dropped to room temperature (approximately 25°C), indicating that heat energy was gradually dissipating. These results highlight the potential of this film for achieving all-weather, continuous thermal regulation in wearable devices.

[0143] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms may refer to different embodiments or examples. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0144] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0145] Although embodiments of the invention have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the claims and their equivalents.

Claims

1. A method for preparing a high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite thin film, characterized in that, Includes the following steps: (1) The TOCNF dispersion and the MXene dispersion are mixed, stirred and ultrasonically treated to obtain the TOCNF / MXene mixed dispersion. The mass ratio of TOCNF to MXene in the TOCNF / MXene mixed dispersion is 3:1 to 1:1, and the MXene is titanium carbide. (2) The mixed dispersion is vacuum filtered to deposit a TOCNF / MXene skeleton film with a shell-like layered structure on the filter membrane; (3) The skeleton film is immersed in a calcium salt aqueous solution for reaction, inducing Ca 2+ Ion crosslinking yields a reinforced framework film; (4) The reinforced skeleton film is completely immersed in a polyethylene glycol aqueous solution, and then dried to obtain a TOCNF / MXene / PEG phase change film; (5) The TOCNF / MXene / PEG phase change film is immersed in a hydrophobic modification solution for surface coating, and then dried to obtain a high-strength biomimetic shell-like phase change composite film.

2. The method as described in claim 1, characterized in that, In step (1), the concentration of the TOCNF dispersion is 1.13~1.35wt%, and the concentration of the MXene dispersion is 0.5~1wt%.

3. The method as described in claim 1, characterized in that, In step (1), the ultrasonic treatment adopts pulse mode, the ultrasonic power is 300~600W, and the ultrasonic time is 0.5~1h.

4. The method as described in claim 1, characterized in that, The concentration of the calcium salt aqueous solution is 0.005~0.5M; And / or, the calcium salt aqueous solution is a soluble calcium salt aqueous solution, which includes at least one of calcium chloride solution, calcium gluconate solution or calcium acetate solution; And / or, in step (3), the time for immersing the skeleton film in the calcium salt aqueous solution is 0.5~5h.

5. The method as described in claim 1, characterized in that, The average molecular weight of the polyethylene glycol is 1000~4000; And / or, the mass concentration of the polyethylene glycol aqueous solution is 30%~70%; And / or, in step (4), drying is performed by standing at 25~40°C for 12~24 hours.

6. The method as described in claim 1, characterized in that, The hydrophobic modification solution includes at least one of PDMS solution and stearic acid ethanol solution.

7. The method as described in claim 1, characterized in that, In step (5), the time for immersing the TOCNF / MXene / PEG phase change film in the hydrophobic modification solution for surface coating is 0.5~5 min; And / or, in step (5), the drying is performed at 25~40°C for 0.5~2h.

8. A high-strength biomimetic shell-like structure TOCNF / MXene / PEG phase change composite film, characterized in that, The phase change composite film prepared by the method according to any one of claims 1 to 7 has a three-dimensional framework structure, wherein the three-dimensional framework structure is formed by TOCNF and MXene through Ca 2+ A shell-like layered structure constructed by ion crosslinking, with polyethylene glycol phase change units loaded within the nanolayer confinement space of the three-dimensional framework.

9. The application of the high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite film prepared by the method according to any one of claims 1 to 7, or the high-strength biomimetic shell-like TOCNF / MXene / PEG phase change composite film according to claim 8, in the field of wearable human thermal management and solar photothermal conversion devices.

Images