Radiation refrigeration coupled evaporation cooling composite material, preparation method and application

Abstract

The application discloses a radiation refrigeration coupling evaporation cooling composite material, a preparation method and application, and belongs to the technical field of high polymer composite materials. The application solves the problems of the existing radiation refrigeration coupling evaporation cooling composite material, such as complex preparation steps, insufficient interlayer bonding stability and the like. The application comprises the following steps: S1, preparing a polyvinyl alcohol aqueous solution; S2, treating hexagonal boron nitride by using a surfactant to obtain a hexagonal boron nitride dispersion liquid; S3, mixing a hygroscopic substance, the polyvinyl alcohol aqueous solution and the hexagonal boron nitride dispersion liquid to obtain a hygroscopic substance / PVA / BN composite material; and S4, preparing an alkaline trigger solution, and making the alkaline trigger solution contact and react with the hygroscopic substance / PVA / BN composite material obtained in S3 to obtain the radiation refrigeration coupling evaporation cooling composite material. The application has good flexibility, moisture responsiveness, rapid film forming property, infrared radiation heat dissipation capacity, evaporation cooling capacity and heat buffering performance, and can be applied to the field of passive thermal management.

Description

Technical Field

[0001] This invention belongs to the field of polymer composite materials technology, specifically relating to a composite material with radiation-cooled coupled evaporative cooling, its preparation method, and its application. Background Technology

[0002] With the continuous increase in energy consumption and the growing demand for thermal management, fields such as building cooling, outdoor equipment heat dissipation, electronic device thermal control, photovoltaic module cooling, and cold chain transportation are placing higher demands on passive cooling materials that require low energy consumption and no external power. Traditional active cooling methods typically rely on external energy inputs such as compressors, fans, or circulating pumps, which not only have high energy consumption but also suffer from problems such as complex equipment, high maintenance costs, and limited applicability in outdoor, mobile, or distributed applications. Therefore, developing passive thermal management materials that require no additional energy input or operate with low energy consumption is of great significance.

[0003] Radiation cooling is a typical passive cooling technology. Its basic principle is that materials emit mid-infrared thermal radiation into a cold source in outer space through an atmospheric window of 8–13 μm, thereby releasing heat to the outside world in the form of electromagnetic waves, achieving passive cooling of the object's surface. In recent years, radiation cooling films, coatings, and porous materials with high solar reflectivity and high-mid-infrared emissivity have received widespread attention. However, existing radiation cooling materials still have certain shortcomings in practical applications:

[0004] The cooling capacity of a single radiative cooling mechanism is easily limited by environmental conditions. In environments with high solar irradiance, high heat flux density, low wind speed, or partial semi-enclosed spaces, relying solely on infrared radiation for heat dissipation often fails to quickly dissipate instantaneous heat, and the material surface may still experience significant temperature increases. Moisture is widely present in the natural environment, and the evaporation of water absorbs a large amount of latent heat, making it a highly efficient passive cooling method. Therefore, to address this issue, introducing a moisture absorption-retention-release function into the radiative cooling film, allowing the film to further remove heat through water evaporation under heat flux or light irradiation, could significantly improve the material's cooling capacity and thermal buffering performance in complex environments. However, existing coupled radiative and evaporative cooling materials typically require the construction of multilayer structures, water storage layers, hydrogel layers, or hydrophilic / hydrophobic gradient structures. The preparation steps for such materials are complex, the interlayer bonding stability is insufficient, and structural damage, loss of functional components, or degradation of cooling performance are prone to occur during long-term cyclic moisture absorption-evaporation processes, hindering large-scale preparation and practical applications. Summary of the Invention

[0005] To address the problems of complex preparation steps, insufficient interlayer bonding stability, and structural damage, functional component loss, or cooling performance degradation during long-term cyclic hygroscopic-evaporative cooling coupling materials in existing technologies, which hinder large-scale preparation and practical applications, this invention provides a composite material, preparation method, and application of radiative cooling coupled with evaporative cooling. The purpose of this invention is to: construct a continuous and stable PVA film-forming network using polyvinyl alcohol (PVA) as a flexible film-forming matrix; introduce hygroscopic substances into a PVA aqueous solution in a one-step process, ensuring uniform distribution of the hygroscopic substances within the PVA film-forming network, thereby improving the film's moisture absorption and water retention capacity and evaporative cooling stability; introduce and pre-disperse hexagonal boron nitride (BN) particles to form a uniformly dispersed lamellar filler network within the PVA matrix, which plays a synergistic role in infrared radiation heat dissipation, thermal conductivity diffusion, and alkaline-triggered rapid shaping; and employ an alkaline trigger agent to in-situ trigger the wet film, establishing a preparation strategy of "one-step introduction of hygroscopic substances, BN pre-dispersion, wet film construction, and alkaline-triggered rapid shaping," thereby achieving coupled cooling of radiative cooling and evaporative cooling.

[0006] The technical solution adopted in this invention is as follows:

[0007] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0008] S1: Prepare an aqueous solution of polyvinyl alcohol;

[0009] S2: Hexagonal boron nitride is treated with a surfactant to obtain a hexagonal boron nitride dispersion;

[0010] S3: Mix the hygroscopic material, the polyvinyl alcohol aqueous solution obtained in S1, and the hexagonal boron nitride dispersion obtained in S2 to obtain the hygroscopic material / PVA / BN composite material.

[0011] S4: Prepare an alkaline trigger solution, and bring the alkaline trigger solution into contact with and react with the hygroscopic material / PVA / BN composite material obtained in S3 to obtain a composite material with radiation cooling coupled with evaporative cooling;

[0012] S1 and S2 have no order.

[0013] After adopting this technical solution, polyvinyl alcohol forms a continuous flexible film-forming network; the hygroscopic substance is added to the polyvinyl alcohol aqueous solution in one step and is uniformly distributed within the polyvinyl alcohol film-forming network; the hexagonal boron nitride particles are distributed in the polyvinyl alcohol film-forming network to enhance the infrared radiation heat dissipation capability, thermal conductivity and diffusion capability of the film, as well as the rapid wet film setting capability under alkaline triggering conditions; the polyvinyl alcohol-based radiation cooling coupled evaporative cooling film can achieve coupled cooling of radiation cooling and evaporative cooling through the infrared radiation heat dissipation effect of the polyvinyl alcohol matrix and hexagonal boron nitride particles, as well as the moisture absorption and evaporative cooling effect induced by the hygroscopic substance.

[0014] As a preferred embodiment, the amounts of each component, by mass, are as follows: polyvinyl alcohol: 10-60 parts; hygroscopic substance: 1-50 parts; hexagonal boron nitride particles: 1-70 parts; surfactant: 0.1-10 parts; water: 40-300 parts.

[0015] Preferably, the hygroscopic substance is one or more of lithium chloride, calcium chloride, magnesium chloride, lithium bromide, lithium nitrate, potassium acetate, and potassium carbonate.

[0016] Furthermore, the hygroscopic substance is lithium chloride.

[0017] Preferably, the mass ratio of the hygroscopic substance to polyvinyl alcohol is 0.02 to 6.00, the mass of the hygroscopic substance is 0.10 to 0.80 times the mass of the total water in the system, the mass ratio of hexagonal boron nitride, water and surfactant in the hexagonal boron nitride dispersion in S2 is 5 to 20: 10 to 40: 0.5 to 3, and the water activity of the system is 0.40 to 0.80.

[0018] Further, the mass ratio of the hygroscopic substance to polyvinyl alcohol is 0.50 to 5.50, more preferably 2.00 to 5.50; the mass of the hygroscopic substance is 0.20 to 0.50 times the total mass of water in the system, more preferably 0.28 to 0.35 times; the mass ratio of hexagonal boron nitride, water, and surfactant is 10:20:1, and the water activity of the system is 0.50 to 0.70, more preferably 0.55 to 0.65.

[0019] Preferably, the alkaline triggering agent is one or more of sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, and borax aqueous solution.

[0020] Preferably, the pH value of the alkaline trigger is 9 to 14.

[0021] Preferably, the concentration of the alkaline trigger is 0.00001–5 mol / L; more preferably 0.001–1 mol / L; and even more preferably 0.01–0.5 mol / L.

[0022] Preferably, the particle size or flake size of the hexagonal boron nitride particles is 0.05–10 μm; more preferably, it is 0.1–1 μm.

[0023] Preferably, the polyvinyl alcohol is one or more of PVA1750, PVA1788, PVA1799, and PVA2488.

[0024] Preferably, the surfactant is one or more of Tween 80, Tween 20, Span 80, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and polyvinylpyrrolidone; more preferably, the surfactant is Tween 80.

[0025] Preferably, the polyvinyl alcohol aqueous solution has a mass fraction of 3–25 wt%; more preferably 5–20 wt%; and even more preferably 8–15 wt%.

[0026] Preferably, the mass fraction of the hexagonal boron nitride particles in the composite material of radiation-cooled coupled evaporative cooling is 1-30 wt%; more preferably 1-15 wt%; and even more preferably 1 wt%, 3 wt%, 6 wt%, 9 wt%, 12 wt% or 15 wt%.

[0027] Preferably, the surfactant is one or more of Tween 80, Tween 20, Span 80, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and polyvinylpyrrolidone; more preferably, the surfactant is Tween 80.

[0028] Preferably, the hexagonal boron nitride dispersion in S2 is prepared by one or more of mechanical stirring, magnetic stirring, ultrasonic dispersion, and high-speed shear dispersion; more preferably, the mechanical stirring time is 5-10 min and the ultrasonic dispersion time is 5-10 min.

[0029] Preferably, the dissolution temperature of polyvinyl alcohol in S1 is 70–98 °C, and the stirring time is 0.5–6 h; more preferably, the dissolution temperature is 90–95 °C, and the stirring time is 1–3 h.

[0030] Preferably, the hygroscopic substance in S3 is added in the form of solid powder, granules, aqueous solution or dispersion; the stirring time after addition is 5 to 10 minutes.

[0031] Furthermore, the hygroscopic substance in S3 is lithium chloride, which is added in the form of solid powder, granules, lithium chloride aqueous solution or lithium chloride dispersion.

[0032] Preferably, the order of adding the hygroscopic substance and the boron nitride dispersion in S3 is as follows: first add the hygroscopic substance to the polyvinyl alcohol aqueous solution, and then add the boron nitride slurry; or first add the boron nitride dispersion to the polyvinyl alcohol aqueous solution, and then add the hygroscopic substance; or add the hygroscopic substance and the boron nitride dispersion to the polyvinyl alcohol aqueous solution simultaneously.

[0033] Preferably, the alkaline trigger in S4 is brought into contact with the hygroscopic material / PVA / BN composite material by one of the following methods: dripping, spraying, impregnation, atomization, roller coating, scraping, or atmospheric treatment.

[0034] Preferably, the composite material obtained in S4 with radiation-cooled coupled evaporative cooling is in the form of a composite film or a gelled part.

[0035] Preferably, the steps for preparing the composite membrane include:

[0036] Step A: The moisture-absorbing material / PVA / BN composite material obtained in S3 is coated onto the substrate by one of the following methods: casting, blade coating, or dip coating to form a wet film;

[0037] Step B: The alkaline trigger is brought into contact with the wet film obtained in Step A and reacted and shaped by one of the following methods: dripping, spraying, dipping, atomizing, roller coating, scraping, or atmospheric treatment.

[0038] Step C: Wash and dry at room temperature to obtain the composite membrane;

[0039] When preparing gelled parts, an alkaline triggering agent solution is directly added to the hygroscopic material / PVA / BN composite material obtained by S3 to form a mixture. The mixture is then pressed, cut, or re-molded to obtain gelled parts of the desired shape.

[0040] Preferably, water is used for washing in step C to remove residual alkaline triggering agents on the film surface and to regulate the content of hygroscopic substances in the film.

[0041] Preferably, the drying temperature in step C is 20–35 °C and the drying time is 0.1–1 h; more preferably, the drying temperature is 25–30 °C.

[0042] A composite material prepared by a method for preparing a composite material using radiation-cooled coupled evaporative cooling.

[0043] Application of a radiation-cooled coupled-evaporative cooling composite material or a radiation-cooled coupled-evaporative cooling composite material prepared by a method thereof as a passive thermal management material.

[0044] With this technical solution, the composite material with radiative cooling coupled with evaporative cooling achieves synergistic cooling through infrared radiation heat dissipation in the 8–13 μm atmospheric window band, the enhanced infrared radiation and thermal conductivity diffusion of hexagonal boron nitride particles, and the heat absorption effect of water evaporation generated after the hygroscopic material absorbs and retains moisture. Under conditions of sunlight, heat flow impact, or high temperature, the composite material reduces surface temperature fluctuations and improves the thermal buffering capacity of the covered material through the adsorption and release of moisture within the film.

[0045] Preferably, the passive thermal management material is used in one or more of the following: building exterior walls, roofs, tents, cold chain packaging, outdoor electronic equipment, photovoltaic module backsheets, communication base station housings, vehicle exterior surfaces, wearable cooling materials, energy storage equipment housings, and industrial equipment thermal insulation and cooling.

[0046] In summary, due to the adoption of the above technical solution, the beneficial effects of the present invention are:

[0047] 1. This invention constructs a process path of "PVA, hygroscopic material, surfactant, BN composite system\alkaline triggering", which enables rapid shaping and film formation of PVA-based wet films under normal temperature or mild conditions. It effectively overcomes the problems of long film formation cycle, poor wet film stability, component migration and uneven thickness caused by the reliance on natural drying of traditional PVA films. It is suitable for rapid prototyping, in-situ curing and continuous preparation.

[0048] 2. This invention introduces a one-step method to add hygroscopic substances into a polyvinyl alcohol aqueous solution, ensuring that the hygroscopic substances are in full contact with the PVA molecular chains before film formation and are uniformly distributed within the PVA network during film formation. Compared with surface coating or post-impregnation methods, this invention reduces the risk of local accumulation, precipitation, and migration of hygroscopic substances, and improves the stability of the film's moisture absorption-water retention-water release cycle and the durability of evaporative cooling.

[0049] 3. In this invention, hexagonal boron nitride particles, after pre-dispersion with a surfactant, are combined with a PVA and hygroscopic material system. In the film, they serve both as infrared radiation heat dissipation and thermal conductivity diffusion enhancement units, and also participate in network construction through interfacial interactions with PVA segments and ions and water molecules in the system. Compared to systems without BN or with unevenly dispersed BN, the film obtained by this invention exhibits better thermal diffusivity, structural stability, and film uniformity.

[0050] 4. This invention establishes and utilizes a "BN particle synergistic alkaline-triggered rapid wet film formation" strategy. After the wet film is formed, in-situ treatment with an alkaline trigger agent enables the PVA segments, BN particle interfaces, and the hydrated ion environment of the hygroscopic material to work synergistically. This locks in the distribution of functional components inside the film in a short time, reduces structural defects caused by filler sedimentation, salt migration, and drying shrinkage, and facilitates the formation of a uniform and stable composite cooling material.

[0051] 5. The film obtained by this invention can simultaneously utilize the infrared radiation heat dissipation effect of the polyvinyl alcohol matrix and hexagonal boron nitride particles, the thermal conductivity and diffusion effect of the hexagonal boron nitride particles, and the moisture absorption and water retention and water evaporation heat absorption effects induced by the hygroscopic material, thereby achieving enhanced coupling between radiative cooling and evaporative cooling. Compared with single radiative cooling films, the film of this invention has better cooling capacity and thermal buffering performance under strong light, high heat flux, or environmental humidity changes.

[0052] 6. This invention uses polyvinyl alcohol, hygroscopic substances, hexagonal boron nitride particles, conventional surfactants and common alkaline triggers as raw materials. The preparation process is carried out in an aqueous phase, at normal pressure and mild temperature. It does not require complex multilayer structures, long-term natural drying or high-temperature sintering processes. The process is simple and the conditions are mild, making it suitable for large-scale production and industrial application. It can be widely used in building exterior surfaces, outdoor equipment, electronic devices, photovoltaic modules, cold chain packaging, wearable cooling materials and other passive thermal management fields. Attached Figure Description

[0053] Figure 1 The above are FTIR characterization images of the raw materials and products prepared in Example 5 of this invention;

[0054] Figure 2 These are SEM images of the product from Example 5 of this invention at different magnifications;

[0055] Figure 3 This is a diagram showing the elemental surface distribution of the product in Example 5 of this invention;

[0056] Figure 4 These are images showing the film formation effect in Example 5 of this invention and under different raw material compositions;

[0057] Figure 5 This is a graph showing the test results of the mechanical properties and flexibility of the product in Example 5 of this invention;

[0058] Figure 6 This is a diagram showing the rapid film formation process of the product in Example 5 of this invention and the test results of the flexibility of the resulting film;

[0059] Figure 7 This is a temperature control test diagram of the product of Example 5 in this invention under a heat flow of 1000 W / m².

[0060] Figure 8 This is a cooling test diagram of the commercial thin film in this invention under simulated sunlight at 1000 W / m².

[0061] Figure 9 This is a cooling test diagram of Example 5 of the present invention under simulated sunlight at 1000W / m².

[0062] Figure 10 This is a product diagram of Comparative Example 1 in this invention;

[0063] Figure 11 This is a product diagram of Comparative Example 2 in this invention;

[0064] Figure 12 A product diagram of Comparative Example 3 in this invention. Detailed Implementation

[0065] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0066] To enhance the moisture absorption and water retention properties of the film, lithium chloride was introduced into the original film formation process.

[0067] Example 1

[0068] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0069] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0070] S2: Weigh hexagonal boron nitride particles with a flake size of 100 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0071] S3: At room temperature, 2.80 g of lithium chloride and 1.33 g of BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 3 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0072] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 3 wt%.

[0073] Example 2

[0074] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0075] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0076] S2: Weigh hexagonal boron nitride particles with a flake size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0077] S3: At room temperature, 2.80 g of lithium chloride and 1.33 g of the BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 3 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0078] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 3 wt%.

[0079] Example 3

[0080] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0081] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0082] S2: Weigh hexagonal boron nitride particles with a flake size of 1 μm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0083] S3: At room temperature, 2.80 g of lithium chloride and 1.33 g of BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 3 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0084] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 3 wt%.

[0085] Example 4

[0086] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0087] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0088] S2: Weigh hexagonal boron nitride particles with a sheet size of 10μm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0089] S3: At room temperature, 2.80 g of lithium chloride and 1.33 g of BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 3 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0090] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 3 wt%.

[0091] Example 5

[0092] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0093] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0094] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0095] S3: At room temperature, 2.80 g of lithium chloride and 3.04 g of BN dispersion prepared in S2 were slowly added simultaneously to the PVA solution in S1, so that the mass percentage of BN in the film was 6 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0096] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 6 wt%.

[0097] Example 6

[0098] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0099] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0100] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0101] S3: At room temperature, 3.76 g of lithium chloride and 5.32 g of BN dispersion prepared in S2 were slowly added simultaneously to the PVA solution in S1, so that the mass percentage of BN in the film was 9 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system to obtain a hygroscopic material / PVA / BN composite material.

[0102] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 9 wt%.

[0103] Example 7

[0104] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0105] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0106] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0107] S3: At room temperature, 4.38 g of lithium chloride and 8.50 g of the BN dispersion prepared in S2 were slowly added simultaneously to the PVA solution in S1, so that the mass percentage of BN in the film was 12 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0108] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 12 wt%.

[0109] Example 8

[0110] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0111] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0112] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Span 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Span 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0113] S3: At room temperature, 3.31 g of lithium chloride and 3.04 g of the BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 6 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0114] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 6 wt%.

[0115] Example 9

[0116] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0117] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0118] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0119] S3: At room temperature, 3.31 g of lithium chloride and 3.04 g of the BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 6 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0120] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L KOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 6 wt%.

[0121] Example 10

[0122] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0123] S1: Weigh 1 g of PVA (PVA1788), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved to obtain a 10 wt% PVA aqueous solution, and cool to room temperature for later use.

[0124] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0125] S3: At room temperature, 3.31 g of lithium chloride and 3.04 g of the BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 6 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0126] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 6 wt%.

[0127] Example 11

[0128] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0129] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0130] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0131] S3: At room temperature, 3.31 g of lithium chloride and 3.04 g of the BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 6 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0132] S4: Under slight stirring, slowly add a small amount of NaOH aqueous solution with a concentration of 0.1 mol / L to the above hygroscopic material / PVA / BN composite material. The system will rapidly change from a flowable state to a non-flowable gel block within about 5 to 15 seconds. Then, press, cut or reshape the gel to obtain the desired shape.

[0133] Example 12

[0134] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0135] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0136] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0137] S3: At room temperature, 3.31 g of CaCl2 and 3.04 g of BN dispersion prepared by S2 were simultaneously and slowly added to the PVA solution of S1, so that the mass percentage of BN in the film was 6 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system to obtain a hygroscopic material / PVA / BN composite material.

[0138] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaOH aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 6 wt%.

[0139] Comparative Example 1

[0140] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0141] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0142] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0143] S3: At room temperature, 3.31 g of lithium chloride and 3.04 g of the BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 6 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0144] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L NaCl aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 6 wt%.

[0145] Comparative Example 2

[0146] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0147] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0148] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0149] S3: At room temperature, 3.31 g of lithium chloride and 3.04 g of the BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 6 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0150] S4: Prepare a wet film from the hygroscopic material / PVA / BN composite material according to the desired morphology, and spray a 0.1 mol / L HCl aqueous solution onto the surface of the wet film at a spraying rate of 0.1 mL / cm². 2 The wet film changed from a flowable state to a non-flowable state within 5 minutes; the shaped film was washed and dried to obtain a polyvinyl alcohol-based radiation-cooled coupled evaporative cooling film with a BN content of 6 wt%.

[0151] Comparative Example 3

[0152] A method for preparing a composite material with radiation-cooled coupled evaporative cooling includes the following steps:

[0153] S1: Weigh 1 g of PVA (PVA1799), add 9 g of deionized water, stir at 95 ℃ for 2 h until PVA is completely dissolved, and obtain a PVA aqueous solution with a mass fraction of 10 wt%. Cool to room temperature for later use.

[0154] S2: Weigh hexagonal boron nitride particles with a sheet size of 500 nm, add Tween 80 and deionized water, wherein the mass ratio of hexagonal boron nitride particles, water and Tween 80 is 10:20:1, mechanically stir for 5 min, and ultrasonically disperse for 5 min to obtain a stable hexagonal boron nitride dispersion.

[0155] S3: At room temperature, 3.31 g of lithium chloride and 3.04 g of the BN dispersion prepared in S2 were simultaneously and slowly added to the PVA solution in S1, so that the mass percentage of BN in the film was 6 wt%. At the same time, the mixture was stirred at 100-300 r / min for 5 min until the lithium chloride was completely dissolved and the hexagonal boron nitride particles were uniformly dispersed in the PVA and lithium chloride system, thus obtaining a hygroscopic material / PVA / BN composite material.

[0156] S4: Prepare a wet film by absorbing the hygroscopic material / PVA / BN composite material in the desired form, without treatment with an alkaline triggering agent, let it stand for 5 min, and observe whether the wet film can quickly solidify and form a film.

[0157] The parameter changes in Examples 1-12 and Comparative Examples 1-3 are shown in Table 1 below:

[0158] Table 1

[0159]

[0160] Examples 1-4 investigated the effects of boron nitride (BN) particle size on film uniformity, infrared radiation heat dissipation, and thermal conductivity by varying the particle size or flake size. Examples 5-7 investigated the effects of different filler contents on the film's radiation-cooling coupled evaporative cooling performance by varying the BN content. Example 8 investigated the effects of surfactants on BN dispersion stability and film structural uniformity by varying the type of surfactant. Example 9 investigated the effects of different alkaline triggers on the rapid setting behavior of wet films by varying the type of alkaline trigger. Example 10 investigated the effects of different polyvinyl alcohol (PVA) matrices on film formation, flexibility, and cooling performance by varying the type of PVA. Example 11 was used to verify the applicability of the triggering method within the system in the preparation of gel parts, thick films, or irregular structures. Example 12 was used to verify the effects of different hygroscopic substances.

[0161] Comparative Examples 1-3 were prepared using neutral salt solution, acidic solution, and no triggering agent, respectively, to illustrate the importance of alkaline triggering conditions for the rapid setting of PVA, lithium chloride, and BN wet films. The above examples and comparative examples collectively demonstrate that introducing lithium chloride as a hygroscopic substance into the PVA / BN system in a one-step process, followed by in-situ surface triggering using an alkaline triggering agent after wet film formation, is beneficial for simultaneously achieving uniform distribution of functional components, rapid wet film setting, and enhanced coupling between radiative cooling and evaporative cooling.

[0162] It should be noted that Example 5 is a preferred embodiment of the present invention. To further illustrate the technical effects achievable by the present invention, the following description is based on the relevant characterization results of the product obtained in Example 5.

[0163] The FTIR characterization results of the polyvinyl alcohol-based radiation-cooled coupled evaporative cooling thin film obtained in Example 5 of this invention are as follows: Figure 1 As shown. By Figure 1 It can be seen that, from Figure 1 It can be seen that PVA is approximately 3300–3500 cm. -1 The broad peak at approximately 1080–1140 cm⁻¹ is attributed to the –OH stretching vibration. -1 The absorption peak at 1360–1380 cm⁻¹ is attributed to the C–O stretching vibration; the absorption peak at 1360–1380 cm⁻¹ in BN is at 1360–1380 cm⁻¹. -1 Approximately 780–820 cm -1 The positions at these points correspond to the B–N stretching vibration and the B–N–B bending vibration, respectively. The characteristic peaks related to –OH, C–O, and BN in the composite film show certain peak position shifts, peak shapes, or intensity changes, indicating that the PVA, BN, and salt components are not simply physically mixed, but rather interact at the interface. Specifically, the alkaline environment of NaOH promotes the interaction between the boron-containing active sites on the BN surface and the PVA hydroxyl groups, resulting in a change in peak position at approximately 1000–1200 cm⁻¹. -1 The change in C–O / B–O related absorption in the region suggests the possible formation of B–O–C bonds, boron-oxygen coordination structures, or related boron-oxygen bonding structures. The introduction of LiCl alters the broad –OH peak in PVA, indicating that Li… + There may be coordination between Cl and the hydroxyl oxygen atom. - Hydrogen bonds or ion-dipole interactions may exist between the PVA and hydroxyl groups, thereby regulating the hydrogen bond network between PVA segments and endowing the film with moisture absorption and water retention capabilities. These multiple effects work together to promote the formation of a stable network structure within the composite film, which is beneficial to improving the structural stability of the film and the ability to rapidly solidify and form a wet film, and provides a basis for its synergistic cooling through radiation and evaporation.

[0164] The SEM cross-sectional morphology and elemental distribution results of the thin film obtained in Example 5 of this invention are as follows: Figure 2 and Figure 3 As shown. By Figure 2 It can be seen that the cross-section of the composite film exhibits a continuous three-dimensional porous network structure, with the PVA matrix forming a through skeleton. Pore structures, filamentous bridging structures, and lamellar filler embedded morphology can be observed in the cross-section, indicating that the PVA matrix undergoes network construction during film formation and can play a role in fixing and bridging hexagonal boron nitride particles. Figure 3The elemental distribution results show that C and O elements are continuously distributed in the cross-sectional area, indicating that PVA forms a continuous phase; B and N elements correspond to hexagonal boron nitride particles and are relatively uniformly distributed in the film; Cl element mainly comes from lithium chloride, and it is continuously distributed inside the film, indicating that lithium chloride can be uniformly introduced into the PVA network in one step; Na element comes from the residue or related sodium salt components after NaOH triggering treatment, indicating that the alkaline triggering agent participates in the wet film setting process. These results indicate that the PVA / lithium chloride / BN composite film obtained in this invention forms a composite network structure of a continuous PVA framework, a uniformly dispersed BN phase, and a hygroscopic lithium chloride phase, which is beneficial for achieving enhanced coupling between radiative cooling and evaporative cooling.

[0165] The film-forming process of Example 5 and related control systems of the present invention is as follows: Figure 4 As shown. By Figure 4 It is known that without the addition of an alkaline trigger, the PVA, lithium chloride, and BN composite system still possesses a certain degree of fluidity and is difficult to stabilize and solidify on its own within a short period of time; the PVA and BN system also primarily exhibits a flowable or weakly stabilized state. When an aqueous NaOH solution is introduced onto the surface of the PVA, lithium chloride, and BN composite wet film, the system can rapidly transition from a flowable state to a non-flowable state, forming a continuous and complete film structure. Compared to the PVA and BN system, the lithium chloride, BN, and alkaline trigger in this invention exhibit a synergistic effect. Lithium chloride provides hygroscopic and water-retaining properties and moisture regulation, BN provides structural support and interfacial enhancement, and NaOH promotes rapid network formation, thereby achieving rapid film stabilization and formation of the wet film. Figure 4 It can also be seen that the obtained film has a uniform appearance, with no obvious cracking, powdering or delamination, and has good integrity and shape retention.

[0166] The mechanical properties and flexibility of the thin film obtained in Example 5 of this invention are as follows: Figure 5 As shown. By Figure 5 It can be seen that the film exhibits good ductility and fracture resistance in the tensile test. The stress-strain curve shows that the film can still maintain a continuous structure in a large strain range, indicating that it has good tensile toughness. Figure 5 The photographs of the bending, stretching, and rolling processes further demonstrate that the film can withstand various deformations such as manual stretching, bending, folding, and rolling, without any obvious cracking, powdering, delamination, or breakage observed after deformation. These results indicate that the film of this invention possesses excellent flexibility, resistance to bending fatigue, and shape adaptability, meeting the application requirements of complex surfaces such as building exteriors, equipment housings, cold chain packaging, tent fabrics, and wearable substrates.

[0167] Example 5 of the present invention describes a rapid film-forming process in a liquid state and the resulting film's flexibility. Figure 6 As shown. By Figure 6 It can be seen that when the PVA, lithium chloride, and BN composite solution is placed on the substrate surface, the system remains a wet slurry without contact with the alkaline trigger. When the alkaline trigger is introduced, the system can change from a fluid state to a peelable film structure in a short time. The peeled film maintains its intact morphology and does not show obvious breakage, pulverization, or severe cracking. Figure 6 The right side further shows that the obtained film can withstand deformations such as stretching, bending, torsion, and folding, indicating that it has good flexibility and deformation adaptability. This result demonstrates that the process route of "PVA, lithium chloride, BN composite solution, alkaline triggering, and rapid film formation" adopted in this invention can effectively shorten the natural drying time of traditional PVA-based films and improve the problems of strong wet film flowability, easy migration of functional components, and difficulty in controlling film morphology.

[0168] The temperature control test results of the thin film obtained in Example 5 of this invention under a heat flux of 1000 W / m² are as follows: Figure 7 As shown. By Figure 7 It can be seen that under continuous heat flow, the film of the present invention can effectively reduce the surface temperature of the covered object, exhibiting good passive thermal management capabilities. This effect mainly comes from the infrared radiation heat dissipation and thermal diffusion effect enhanced by BN, as well as the moisture absorption and water retention and water evaporation endothermic effect induced by lithium chloride.

[0169] The test results under xenon lamps in Examples 2, 5, 6, and 7 are shown in Table 2:

[0170] Table 2

[0171]

[0172] The test results for the heating elements in Examples 2, 5, 6, and 7 are shown in Table 3.

[0173] Table 3

[0174]

[0175] Temperature control performance tests were conducted on different thin film samples for one hour under simulated heat flux of 1000 W / m². The test process included a continuous heating phase from 0 to 1800 seconds and a natural cooling phase from 1800 to 3600 seconds, with the ambient temperature maintained at approximately 14.5°C during the test. The results showed that during continuous heating, the surface temperature of the blank sample rose rapidly, reaching approximately 49.5°C at 1800 seconds, indicating its weak ability to suppress external heat input and difficulty in achieving effective heat dissipation. The commercial thin film showed a relatively lower temperature rise, with a maximum temperature of approximately 45.5°C, demonstrating a certain degree of temperature control. In contrast, the composite thin film containing 6 wt% filler (Example 5) exhibited a significantly slower temperature rise, with the surface temperature eventually stabilizing at approximately 39.0°C, significantly lower than the blank sample and the commercial thin film. Compared to the two control samples mentioned above, this composite thin film achieved temperature reductions of approximately 10.5°C and 6.5°C, respectively, indicating that the introduction of filler can effectively enhance the infrared radiation heat dissipation capability of the thin film, thereby suppressing the accumulation of heat on the material surface. After 1800 seconds, when the heat source was removed, all samples entered a natural cooling phase, with their surface temperatures gradually decreasing towards ambient temperature. The blank sample cooled relatively quickly, reaching approximately 16.0°C at the end of the test; while the composite film containing 6 wt% filler experienced a more gradual cooling process, with a final temperature of approximately 19.0°C, slightly higher than the other samples. This phenomenon indicates that the addition of filler not only enhances the passive cooling capability of the film under photothermal effects but may also alter the thermal capacity and back heat transfer resistance of the material system, resulting in stronger thermal buffering capacity and temperature stability of the composite film during changes in external heat flow.

[0176] To evaluate the thermal management performance and humidity response behavior of the thin film under prolonged strong light exposure, a continuous 360-minute temperature control test was conducted on both the commercial radiation-cooled thin film and the thin film in Example 5. The light intensity was also 1000 W / m². The results are as follows: Figure 8 and Figure 9As shown in the figure, during the initial 0-30 minutes of the test, the surface temperature of the films increased rapidly with the light exposure, but the temperature response of the commercial film was more pronounced, with its surface temperature rising from approximately 17°C to approximately 28°C. In contrast, the composite film of Example 5 showed a smaller temperature increase, only reaching approximately 24°C, indicating that it effectively reduced the impact of heat input on surface temperature in the initial heating stage, exhibiting better initial thermal barrier and heat dissipation capabilities. As the test time increased, the samples gradually reached thermodynamic steady state. The surface temperature of the commercial film eventually stabilized at approximately 31°C, while the composite film of Example 5 maintained a steady-state temperature of approximately 27.5-28°C. Under continuous high-intensity heat flow for 6 hours, the composite film of Example 5 maintained a temperature advantage of approximately 3-3.5°C over the commercial film, indicating that it can maintain superior temperature control and thermal management stability even under long-term strong light exposure. Furthermore, the humidity change results further revealed the differences in the cooling mechanisms of the two films. The relative humidity of the environment corresponding to the commercial film remained relatively stable after decreasing to approximately 51%, while the relative humidity of the environment corresponding to the composite film of Example 5 remained at approximately 53%, exhibiting continuous and dense sawtooth-like fluctuations. This humidity fluctuation indicates the presence of relatively active moisture adsorption, desorption, or moisture response processes within the composite film. Therefore, the cooling effect of the composite film of Example 5 not only originates from infrared radiation heat dissipation but may also be accompanied by latent heat loss during moisture evaporation. The synergistic effect between infrared radiation heat dissipation and moisture evaporation cooling is a key reason why this composite film achieves a low steady-state temperature and excellent temperature control performance under high-intensity light irradiation. Figure 8 and 9 It is known that, compared with commercial films, the film of the present invention has better cooling effect and heat buffering capacity, and can reduce the temperature rise and delay heat accumulation under light conditions, making it suitable for long-term passive thermal management applications outdoors.

[0177] The wet film state of Comparative Example 1 is as follows Figure 10 As shown. This comparative example uses a neutral NaCl solution instead of an alkaline trigger. (From...) Figure 8 It can be seen that the system is difficult to solidify quickly under the action of neutral salt solution, and it mainly remains in a flowing state and cannot form a stable film.

[0178] The wet film state of Comparative Example 2 is as follows Figure 11 As shown. This comparative example uses acidic HCl solution instead of an alkaline trigger. (From...) Figure 9 It can be seen that the system is also difficult to form a stable film quickly under acidic conditions, indicating that the acidic environment is not conducive to the rapid stabilization of the PVA, lithium chloride, and BN composite system.

[0179] The wet film state of Comparative Example 3 is as follows Figure 12 As shown. This comparative example did not include a triggering agent. (By...) Figure 10It is known that, without a triggering agent, the system remains in a flowable state and it is difficult to form a stable membrane structure in a short time.

[0180] In conclusion, Figures 1-12 The characterization and testing results show that the PVA, lithium chloride, and BN composite film obtained in Example 5 of this invention can be rapidly shaped and formed under alkaline triggering conditions, creating a composite network structure with uniform structure, good flexibility, and passive thermal management function. Compared with the comparative example, the film of this invention can simultaneously achieve uniform distribution of functional components, rapid wet film sizing, and enhanced coupling of radiative cooling and evaporative cooling, making it suitable for building exterior surfaces, outdoor equipment, electronic devices, cold chain packaging, wearable cooling materials, and other passive thermal management applications.

[0181] The embodiments described above merely illustrate specific implementation methods of this application, and while the descriptions are detailed and specific, they should not be construed as limiting the scope of protection of this application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the technical solution of this application, and these modifications and improvements all fall within the scope of protection of this application.

Claims

1. A method for preparing a composite material with radiation-cooled coupled evaporative cooling, characterized in that: Includes the following steps: S1: Prepare an aqueous solution of polyvinyl alcohol; S2: Hexagonal boron nitride is treated with a surfactant to obtain a hexagonal boron nitride dispersion; S3: Mix the hygroscopic material, the polyvinyl alcohol aqueous solution obtained in S1, and the hexagonal boron nitride dispersion obtained in S2 to obtain the hygroscopic material / PVA / BN composite material. S4: Prepare an alkaline trigger solution, and bring the alkaline trigger solution into contact with and react with the hygroscopic material / PVA / BN composite material obtained in S3 to obtain a composite material with radiation cooling coupled with evaporative cooling; S1 and S2 have no order.

2. The method for preparing a composite material with radiation-cooled coupled evaporative cooling according to claim 1, characterized in that: The amounts of each component, by mass, are as follows: polyvinyl alcohol: 10-60 parts; hygroscopic substance: 1-50 parts; hexagonal boron nitride particles: 1-70 parts; surfactant: 0.1-10 parts; Water: 40-300 parts.

3. The method for preparing a composite material with radiation-cooled coupled evaporative cooling according to claim 1, characterized in that: The hygroscopic substance is one or more of lithium chloride, calcium chloride, magnesium chloride, lithium bromide, lithium nitrate, potassium acetate, and potassium carbonate.

4. A method for preparing a composite material with radiation-cooled coupled evaporative cooling according to any one of claims 1-3, characterized in that: The mass ratio of the hygroscopic substance to polyvinyl alcohol is 0.02 to 6.00, and the mass of the hygroscopic substance is 0.10 to 0.80 times the total mass of water in the system. In the hexagonal boron nitride dispersion in S2, the mass ratio of hexagonal boron nitride, water, and surfactant is 5 to 20: 10 to 40: 0.5 to 3, and the water activity of the system is 0.40 to 0.

80.

5. A method for preparing a composite material with radiation-cooled coupled evaporative cooling according to any one of claims 1-3, characterized in that: The alkaline trigger has a pH value of 9 to 14, and the alkaline trigger is one or more of sodium hydroxide, potassium hydroxide, barium hydroxide, calcium hydroxide, sodium carbonate, sodium bicarbonate, ammonia, and borax aqueous solution.

6. A method for preparing a composite material with radiation-cooled coupled evaporative cooling according to any one of claims 1-3, characterized in that: The particle size or flake size of the hexagonal boron nitride particles is 0.05–10 μm; the polyvinyl alcohol is one or more of PVA1750, PVA1788, PVA1799, and PVA2488, and the surfactant is one or more of Tween 80, Tween 20, Span 80, sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, and polyvinylpyrrolidone.

7. A method for preparing a composite material with radiation-cooled coupled evaporative cooling according to any one of claims 1-3, characterized in that: The composite material obtained in S4 with radiation-cooled coupled evaporative cooling is in the form of a composite film or a gelled part.

8. The method for preparing a composite material with radiation-cooled coupled evaporative cooling according to claim 7, characterized in that: The steps for preparing the composite membrane include: Step A: The moisture-absorbing material / PVA / BN composite material obtained in S3 is coated onto the substrate by one of the following methods: casting, blade coating, or dip coating to form a wet film; Step B: Add or spray an alkaline solution to the wet film, or immerse the wet film directly in the alkaline solution to form it; Step C: Wash and dry at room temperature to obtain the composite membrane; When preparing gelled parts, an alkaline triggering agent solution is directly added to the hygroscopic material / PVA / BN composite material obtained by S3 to form a mixture. The mixture is then pressed, cut, or re-molded to obtain gelled parts of the desired shape.

9. A composite material prepared by the method for preparing a composite material with radiation cooling coupled with evaporative cooling according to any one of claims 1-8.

10. The application of a composite material of radiation-cooled coupled evaporative cooling as described in claim 9, or a composite material of radiation-cooled coupled evaporative cooling prepared by the method of any one of claims 1-8, as a passive thermal management material.

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