Directional water delivery radiation refrigeration phase change material membrane and preparation method and application thereof

Abstract

The invention relates to the technical field of heat storage and energy saving functional composite materials, in particular to a directional water delivery radiation refrigeration phase change material film and a preparation method and application thereof. The method comprises the following steps: carrying out first electrostatic spinning on a spinning solution prepared by emulsifying a polymer, a phase change material and radiation refrigeration particles to prepare a water conveying layer; carrying out secondary electrostatic spinning on the water delivery layer by adopting the spinning solution to form a water-resisting layer; and a radiation refrigeration layer is deposited on the water-resisting layer in situ, and the directional water delivery radiation refrigeration phase change material film is obtained. According to the invention, the three-layer gradient structure of the water delivery layer, the water-resisting layer and the radiation refrigeration layer is subjected to same-component different-parameter one-time forming for the first time; the prepared directional water delivery radiation refrigeration phase-change material film can quickly and directionally deliver sweat or moisture from one side to the other side and evaporate the sweat or moisture, has efficient daytime radiation refrigeration capacity and heat energy storage and release functions, overcomes the defects of single function, interface stripping and optical blind area in the prior art, and has wide application prospects. The problem that three requirements of dryness, coolness and constant temperature cannot be considered is solved.

Description

Technical Field

[0001] This invention relates to the field of thermal energy storage and energy-saving composite materials, specifically to a directional water conveyance radiation cooling phase change material membrane, its preparation method, and its application. Background Technology

[0002] With global warming and rising living standards, the demand for personal thermal management technologies and energy-efficient building materials is becoming increasingly urgent. Traditional cooling methods, such as air conditioning systems, consume large amounts of energy and exacerbate the urban heat island effect. Therefore, passive cooling technologies that do not require external energy input have become a research hotspot. Radiative cooling technology optimizes the optical properties of materials to efficiently reflect sunlight (0.3µm~2.5µm wavelength) and radiate heat into the cold outer space through atmospheric windows (8µm~13µm), thereby achieving a cooling effect below ambient temperature.

[0003] Currently, in practical applications, especially in wearable devices or building exteriors, the management of human sweat or environmental humidity is crucial. If moisture cannot be drained and evaporated in a timely manner, it will not only cause discomfort, but the heat absorption process during evaporation will also affect the efficiency of radiative cooling. In addition, radiative cooling technology does not have the capacity to store heat, and cannot absorb excess heat to ensure the continuous operation of the cooling process.

[0004] However, in existing technologies, most studies focus only on single radiative cooling or thermal storage functions. Although some directional water-transporting radiative cooling phase change material membranes have been applied to the field of radiative cooling, the following problems still exist: First, poor structural compatibility: some studies directly mix radiative cooling particles with phase change matrix to prepare directional water-transporting radiative cooling phase change material membranes. However, the large differences in density and polarity between the two lead to the formation of optical blind zones inside the material, resulting in a decrease in solar reflectivity. Second, lack of water-transporting structural adaptation: in pursuit of high thermal storage density, the directional water-transporting radiative cooling phase change material membranes prepared by existing methods have a simple porosity structure and no through-pores, making it impossible to achieve water transport. Third, low interfacial bonding strength: when applying directional water-transporting radiative cooling phase change material membranes to the field of radiative cooling, a multi-layer composite structure is used. Due to the material differences between layers, adhesives are needed for bonding. However, due to the differences and low bonding strength, interfacial delamination easily occurs during thermal cycling due to differences in thermal expansion coefficients. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a directional water-transporting radiation-cooling phase change material membrane, its preparation method, and its applications. The directional water-transporting radiation-cooling phase change material membrane of this invention combines dryness, coolness, and temperature control. It consists of a water-transporting layer, a water-barrier layer, and a radiation-cooling layer, which are stacked sequentially from bottom to top along the thickness direction. The radiation-cooling layer is formed by directly depositing pure radiation-cooling particles onto the surface of the water-barrier layer via electrostatic spraying, resulting in a three-layer structure formed in a single step, reducing optical blind spots and significantly improving solar reflectivity. Simultaneously, a differentiated electrospinning process achieves an asymmetric network structure between the water-transporting and water-barrier layers, enabling unidirectional water transport from the water-transporting layer to the water-barrier layer. Furthermore, the electrospinning uses consistent raw materials, ensuring no material differences between layers and guaranteeing efficient bonding without interfacial delamination.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: The first objective of this invention is to provide a method for preparing a directional water transport radiation cooling phase change material membrane, comprising the following steps: S1. The polymer, phase change material, and radiative cooling particles are dissolved together in a solvent and emulsified to obtain a spinning solution. The mass fractions of each component in the spinning solution are as follows: polymer 20%~30%, radiative cooling particles 10%~20%, and phase change material 50%~70%. The polymer is selected from cellulose acetate, polylactic acid, or polycaprolactone. The polymer is characterized by easy solubility, good film-forming properties, and good thermal stability, and is a non-strongly hydrophilic polymer, which can both ensure water transport and reduce water erosion. The phase change material membrane can undergo a phase change within a specific temperature range, absorbing or releasing a large amount of latent heat during this process, acting as a thermal buffer, effectively prolonging the duration of comfortable temperature, and improving the cooling effect. It is selected from one or more alkanes, fatty acids, or fatty alcohols. In addition to its high energy storage density, adjustable phase change temperature, and stable chemical properties, it is hydrophobic and has good compatibility with membrane materials. The radiation-cooling particles are selected from one or more of alumina, silicon dioxide, titanium dioxide, or barium sulfate, and the particle size of the radiation-cooling particles is 0.1 μm to 1 μm; more preferably, the particle size of the radiation-cooling particles is 0.2 μm to 0.4 μm. They exhibit high light reflectivity (strong radiation-cooling performance), and the particle size is controllable during the particle preparation process.

[0007] S2. Perform electrospinning on the spinning solution for the first time to form a water-carrying layer; continue electrospinning on the water-carrying layer using the spinning solution for the second time, and attach a water-proof layer on the water-carrying layer.

[0008] S3. A dispersion of radiation-cooling particles is deposited in situ on the water-proof layer to form a radiation-cooling layer. After drying, a directional water-transporting radiation-cooling phase change material membrane is obtained.

[0009] Preferably, in the spinning solution, the mass fraction of polymer is 18%~25%, the mass fraction of radiation cooling particles is 15%, and the mass fraction of phase change material is 60%.

[0010] Preferably, the mass fraction of the radiation-cooling particles in the dispersion is 3% to 10%; more preferably, the mass fraction of the radiation-cooling particles is 5% to 10%.

[0011] Preferably, the dispersion of the radiation-cooling particles is prepared by the following steps: dispersing the radiation-cooling particles in a dispersant and ultrasonically dispersing them at 100W for 10 to 30 minutes to obtain a dispersion of the radiation-cooling particles. The dispersant is volatile and has low toxicity, and is preferably at least one of ethanol, isopropanol, or methanol.

[0012] Preferably, the polymer has a mass fraction of 10% to 30%, and more preferably, the polymer has a mass fraction of 18% to 25%.

[0013] Preferably, when preparing the water transport layer, the voltage of the first electrospinning is 20kV~25kV, the propulsion rate is 0.8mL / h~2mL / h, and the receiving distance is 15cm~20cm; more preferably, when preparing the water transport layer, the voltage of the first electrospinning is 22kV~25kV, the propulsion rate is 1.2mL / h~1.5mL / h, and the receiving distance is 18cm~20cm.

[0014] Preferably, when preparing the water-proof layer, the electrospinning voltage is 12kV~18kV, the propulsion rate is 1mL / h~2mL / h, and the receiving distance is 10cm~15cm; and the voltage difference between the first electrospinning and the second electrospinning is ≥5kV and the receiving distance difference is ≥3cm, so as to achieve the interlayer pore-hydrophobic gradient.

[0015] More preferably, during the second preparation of the water-proof layer, the electrospinning voltage is 12kV~15kV, the feed rate is 1mL / h~1.5mL / h, and the receiving distance is 10cm~12cm.

[0016] Preferably, the radiation cooling layer is prepared by electrostatic spraying, with the electrostatic spraying voltage being 15kV~20kV, the spraying rate being 0.3mL / min~1mL / min, and the spraying time being 5min~15min.

[0017] Preferably, the water contact angle of the water conveying layer is 10°~90°, and the water contact angle of the water-proof layer is 10°~30°.

[0018] Preferably, the solvent is selected from one or more of dimethylformamide, acetone or tetrahydrofuran.

[0019] Preferably, the drying conditions are: drying at 60℃~80℃ for 1h~2h to remove residual solvent.

[0020] Preferably, the polymer is dissolved under the following conditions: the polymer is placed in a solvent and dissolved at 60°C to 100°C for 2 to 6 hours; more preferably, it is dissolved at 60°C to 80°C for 4 to 5 hours.

[0021] Preferably, the emulsification conditions are: high-speed shearing at 10000 rpm to 20000 rpm for 10 min to 40 min; more preferably, high-speed shearing at 12000 rpm to 15000 rpm for 15 min to 25 min.

[0022] A second objective of this invention is to provide a directional water-transporting radiation-cooling phase change material membrane prepared by the above-described method.

[0023] Preferably, the directional water-carrying radiation-cooling phase change material membrane is formed by stacking a water-carrying layer, a water-resistant layer, and a radiation-cooling layer sequentially from bottom to top along the thickness direction; the interfaces of the water-carrying layer and the water-resistant layer are naturally integrated; both the water-carrying layer and the water-resistant layer have penetrating micropores, and the porosity of the water-resistant layer is less than that of the water-carrying layer; the fiber diameter of the water-resistant layer is greater than that of the water-carrying layer. In this invention, the porosity of the water-carrying layer is 70%~90%, and the pore size is 0.1μm~2μm; the porosity of the water-resistant layer is 50%~70%, and the pore size is 1μm~10μm. The small pore size results in high capillary action, allowing water to easily pass through.

[0024] Preferably, the thickness of the directional water-carrying radiation cooling phase change material film is 80μm~300μm, it can be bent 180° without cracking, and its unidirectional water-carrying rate is ≥10μL / cm. 2 s.

[0025] A third objective of this invention is to provide the application of the above-mentioned directional water-transporting radiation-cooling phase change material membrane in the preparation of smart wearable clothing, building energy-saving coatings, or zero-energy personal thermal management devices.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. This invention provides a method for preparing a directional water-transporting radiation-cooled phase change material membrane. A polymer, a phase change material, and radiation-cooled particles are dissolved together in a solvent to obtain a spinning solution. In the spinning solution, the mass fraction of the polymer is 20%–30%, the mass fraction of the radiation-cooled particles is 10%–20%, and the mass fraction of the phase change material is 50%–70%. The spinning solution is subjected to a first electrospinning process to form a water-transporting layer. A second electrospinning process is then performed on the water-transporting layer using the same spinning solution, and a water-resistant layer is attached to the water-transporting layer. A dispersion of radiation-cooled particles is deposited in situ on the water-resistant layer to form a radiation-cooled layer. After drying, the directional water-transporting radiation-cooled phase change material membrane is obtained. This invention uses polymers, phase change materials, and radiation-cooled particles in the same proportion to co-dissolve and emulsify a homogeneous spinning solution. Through a differentiated electrospinning process, a water-transporting layer and a water-resistant layer are constructed sequentially, and radiation-cooled particles are deposited in situ on the surface of the water-resistant layer, achieving an integrated three-layer structure. The preparation method of the present invention successfully decouples the material composition and functional structure, synergistically integrating the three major functions of directional water conveyance, radiative cooling and phase change thermal storage, while endowing the water conveyance layer-water barrier layer interface with natural fusion characteristics, and achieving high-strength interlayer bonding without adhesives.

[0027] Compared with existing technologies, this invention effectively avoids the defects of material films prepared by existing technologies, such as single function, interface peeling and optical blind spots, and simultaneously meets the triple requirements of dryness, coolness and constant temperature, providing an innovative solution for zero-energy passive thermal management.

[0028] Among these advancements, a differentiated electrospinning technique achieves an asymmetric wettability structure of a high-porosity water-conveying layer and a low-porosity water-barrier layer. This structure allows water molecules to permeate unidirectionally from the water-conveying layer to the water-barrier layer through capillary forces, thus achieving directional water transport, efficient solar reflection and mid-infrared emission, and excellent thermal energy storage and regulation capabilities. This has significant scientific importance and immense application value. Furthermore, the directional water-conveying radiation-cooling phase change material membrane of this invention exhibits differential hydrophilicity and hydrophobicity. The water contact angle on the water-conveying layer side does not exceed 90°, and the water contact angle on the water-barrier layer side does not exceed 30°. This enables unidirectional water permeation from the water-conveying layer direction to the water-barrier layer direction, while water cannot permeate from the water-barrier layer to the water-conveying layer direction and remains on the surface.

[0029] 2. The directional water-transporting radiation-cooling phase change material membrane of the present invention consists of a water-transporting layer, a water-insulating layer, and a radiation-cooling layer, which are stacked sequentially from bottom to top along the thickness direction, providing a triple function of dryness, coolness, and constant temperature: First, directional water transport: The asymmetrical structure of the water-transporting layer and the water-insulating layer generates a strong unidirectional capillary force, which can quickly pump water from the water-transporting layer to the water-insulating layer, resulting in a high evaporation rate and keeping the contact surface dry. Second, efficient cooling: Nanoparticles on the network skeleton of the water-transporting layer and the water-insulating layer, as well as in the high-concentration radiation layer, give the material high solar reflectivity (>90%) and high-to-medium infrared thermal emissivity (>90%). Third, intelligent temperature regulation: The phase change material is filled in the skeleton, absorbing excess heat and effectively extending the cooling time, with a phase change enthalpy greater than 120 J / g and a heat loss rate of less than 5% after 500 thermal cycles.

[0030] 3. The directional water-transporting radiation cooling phase change material membrane of the present invention has good flexibility and can be bent more than 180° while still maintaining its shape without breaking.

[0031] 4. The directional water conveyance radiation cooling phase change material membrane of the present invention has excellent heat storage capacity, with a phase change enthalpy greater than 110 J / g, and a heat loss rate of no more than 5% after 500 thermal cycles.

[0032] 5. The directional water conveyance radiation cooling phase change material membrane of the present invention has high solar reflectivity (>90%) and high-to-medium infrared thermal emissivity (>90%).

[0033] 6. This invention also provides a method for preparing a directional water-transporting radiation-cooled phase change material membrane. A polymer solution, the directional water-transporting radiation-cooled phase change material membrane, and radiation-cooling particles are dissolved together in a solvent and emulsified to obtain a spinning solution. A layer of spinning solution is deposited on a substrate to obtain a water-transporting layer. A layer of spinning solution is electrospun on the water-transporting layer to obtain a water-barrier layer. A layer of ethanol dispersion of radiation-cooling particles is deposited in situ on the water-barrier layer, and then dried to obtain the directional water-transporting radiation-cooled phase change material membrane. The electrospinning / spraying technology used in this invention is mature and can precisely control parameters (such as voltage, flow rate, and solution concentration) to regulate fiber diameter, porosity, and interlayer structure, achieving performance optimization and facilitating large-scale production. Attached Figure Description

[0034] Figure 1 This is a schematic diagram illustrating the structure and principle of the directional water conveyance radiation cooling phase change material membrane in Example 1.

[0035] Figure 2 This is a differential scanning calorimetry curve of the directional water conveyance radiation cooling phase change material membrane of Example 1.

[0036] Figure 3The diagrams show the water permeation of the directional water-carrying radiation cooling phase change material membrane of Example 1 at different times. In the diagram, a is the water permeation on the water-proof layer side, b is the water permeation on the water-carrying side, a1 and b1 are both 0s, a2 and b2 are both 10s, and a3 and b3 are both 300s. Detailed Implementation

[0037] The technical solution of the present invention will be clearly and completely described below with reference to the data in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0038] It should be noted that the technical terms used in this invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of this invention. Unless otherwise specified, all raw materials, reagents, instruments and equipment used in the following embodiments of this invention can be purchased on the market or prepared by existing methods.

[0039] In existing technologies, most studies focus only on single radiative cooling or thermal storage functions. Although some phase change materials have been applied to the field of radiative cooling, the following problems still exist: First, radiative cooling particles are prone to agglomeration when directly mixed with the phase change matrix, resulting in optical blind spots and reduced reflectivity; second, the material has a simple pore structure, making it impossible to achieve directional water transport; and third, the interfacial bonding strength of the multilayer structure is low, making it easy to peel off.

[0040] This invention avoids agglomeration problems by employing a layered design of high-concentration radiation-cooling particles plus an intermediate layer of dispersed radiation-cooling particles, thereby increasing reflectivity to over 90%. Through differentiated structures between layers, this invention incorporates through-holes while ensuring the energy load of the directional water-carrying radiation-cooling phase change material membrane, thus balancing thermal storage and water transport functions. Furthermore, this invention utilizes an integrated multi-step electrospinning and electrospraying process, resulting in a naturally fused three-layer structure with high bonding strength and no peeling.

[0041] To enable those skilled in the art to more clearly understand the technical solution of the present invention, the following will provide a detailed description in conjunction with specific embodiments: Example 1 A method for preparing a directional water conveyance radiation cooling phase change material membrane includes the following steps: S1. Dissolve 2g of cellulose acetate in 8g of dimethylformamide and stir at 80℃ for 5h to obtain a cellulose acetate solution; add 6g of docosane and 2g of silica (particle size 0.3μm) to the cellulose acetate solution, and emulsify at a high speed of 15000 rpm for 15min to form a spinning solution; use electrospinning technology to spin the spinning solution at a voltage of 22kV and a feed rate of 1.2mL / h, with a receiving distance of 18cm to obtain a water transport layer.

[0042] S2. Using electrospinning technology, the spinning solution is spun on the water transport layer at a voltage of 15kV and a feed rate of 1mL / h, with a receiving distance of 12cm, to obtain a water-proof layer.

[0043] S3. Add 0.5g of silica (0.3µm particle size) to 9.5g of ethanol and sonicate at 100W for 30min to obtain a spraying solution. Apply the solution via electrostatic spraying at 15kV and a spray rate of 0.5ml / h for 2h to obtain a water-resistant layer surface, i.e., a high-concentration radiation layer. Then dry at 60℃ for 2h to remove residual solvent, obtaining a directional water-transporting radiation-cooling phase change material film, the structure of which is as follows: Figure 1 As shown.

[0044] The directional water-transporting radiation-cooling phase change material membrane prepared by this invention has good flexibility, and can be bent more than 180° while maintaining its shape without breaking; the phase change enthalpy value is 130 J / g (e.g., ...). Figure 2 As shown), the phase transition enthalpy after 500 thermal cycles is 126 J / g (as shown). Figure 2 As shown), the loss rate is approximately 3%. The solar reflectance is 93% and the high-mid-infrared thermal emissivity is 92%. The porosity of the water-conveying layer is 80% with a pore size of 2 μm, while the porosity of the water-impermeable layer is 60% with a pore size of 8 μm. The water contact angle on the water-conveying layer side is 60°, and on the water-impermeable layer side it is 30°, enabling unidirectional water permeation from the water-conveying layer direction to the water-impermeable layer direction. Water cannot permeate from the water-impermeable layer to the water-conveying layer direction and remains on the surface, such as... Figure 3 As shown. The thermal cycle in this invention consists of raising the temperature from 0°C to 100°C as one cycle.

[0045] Example 2 A method for preparing a directional water conveyance radiation cooling phase change material membrane includes the following steps: S1. Dissolve 2.5g of polylactic acid in 8g of dimethylformamide and stir at 80℃ for 4h to obtain a polylactic acid solution; add 5g of octadecylane and 2.5g of barium sulfate (particle size 0.3μm) to the polylactic acid solution, and emulsify at a high speed of 12000 rpm for 20min to form a spinning solution; use electrospinning technology to spin the spinning solution at a voltage of 25kV and a feed rate of 1.5mL / h, with a receiving distance of 20cm to obtain a water transport layer.

[0046] S2. Using electrospinning technology, at a voltage of 12kV and a feed rate of 1.5mL / h, the spinning solution is spun on the water transport layer, with a receiving distance of 12cm, to obtain a water-proof layer.

[0047] S3. Add 1g of barium sulfate (0.3µm particle size) to 9g of ethanol and sonicate at 100W for 30min to obtain a spraying solution; spray electrostatically at 18kV and a spray rate of 0.5ml / h for 1h to obtain a water-proof layer surface, i.e., a high-concentration radiation layer; then dry at 60℃ for 2h to remove residual solvent and obtain a directional water-transporting radiation-cooling phase change material film.

[0048] The directional water-transporting radiation-cooling phase change material membrane prepared by this invention has good flexibility, and can be bent more than 180° while maintaining its shape without breaking; the phase change enthalpy is 120 J / g, and after 500 thermal cycles, the phase change enthalpy is about 114 J / g, with a loss rate of 5%; the solar reflectivity is 95% and the high-mid infrared thermal emissivity is 95%; the porosity of the water-transporting layer is 90% with a pore size of 1 μm, and the porosity of the water-proof layer is 50% with a pore size of 10 μm; the water contact angle on the water-transporting layer side is 70°, and the water contact angle on the water-proof layer side is 25°; it can achieve unidirectional water permeation from the water-transporting layer direction to the water-proof layer direction; water cannot permeate from the water-proof layer to the water-transporting layer direction and remains on the surface.

[0049] Example 3 A method for preparing a directional water conveyance radiation cooling phase change material membrane includes the following steps: S1. Dissolve 2g of polycaprolactone in 8g of dimethylformamide and stir at 60℃ for 5h to obtain a polycaprolactone solution; add 7g of octadecylane and 1g of barium sulfate (particle size 0.3μm) to the polycaprolactone solution and emulsify at a high speed of 15000 rpm for 20min to form a spinning solution; use electrospinning technology to spin the spinning solution at a voltage of 22kV and a feed rate of 1.2mL / h, with a receiving distance of 15cm to obtain a water transport layer.

[0050] S2. Using electrospinning technology, the spinning solution is spun on the water transport layer at a voltage of 12kV and a feed rate of 1mL / h, with a receiving distance of 15cm, to obtain a water-proof layer.

[0051] S3. Add 0.8g of alumina (0.4μm particle size) particles to 9.2g of ethanol and sonicate at 100W for 30min to obtain a spraying liquid; spray electrostatically at 16kV and a spraying rate of 0.5ml / h for 2h to obtain a water-proof layer surface, i.e., a high-concentration radiation layer; then dry at 60℃ for 2h to remove residual solvent and obtain a directional water-transporting radiation cooling phase change material film.

[0052] The directional water-transporting radiation-cooling phase change material membrane prepared by this invention has good flexibility, and can be bent more than 180° while maintaining its shape without breaking; the phase change enthalpy is 140 J / g, and after 500 thermal cycles, the phase change enthalpy is about 133 J / g, with a loss rate of 5%; the solar reflectivity is 93% and the high-mid infrared thermal emissivity is 92%; the porosity of the water-transporting layer is 85% with a pore size of 0.1 μm, and the porosity of the water-proof layer is 65% with a pore size of 1 μm; the water contact angle on the water-transporting layer side is greater than 80°, and the water contact angle on the water-proof layer side is 20°; it can achieve unidirectional water permeation from the water-transporting layer direction to the water-proof layer direction; water cannot permeate from the water-proof layer to the water-transporting layer direction and remains on the surface.

[0053] Comparative Example 1 A method for preparing a directional water-conveying radiation-cooling phase change material membrane, wherein the electrospinning conditions for the water-conveying layer and the water-resistant layer are the same, both being water-conveying layer conditions, includes the following steps: S1. Dissolve 2g of cellulose acetate in 8g of dimethylformamide and stir at 80℃ for 5h to obtain a cellulose acetate solution; add 6g of docosane and 2g of silica (particle size 0.3μm) to the cellulose acetate solution, and emulsify at a high speed of 15000 rpm for 15min to form a spinning solution; use electrospinning technology to spin the spinning solution at a voltage of 22kV and a feed rate of 1.2mL / h, with a receiving distance of 18cm to obtain a water transport layer.

[0054] S2. Using electrospinning technology, at a voltage of 22kV and a feed rate of 1.2mL / h, the spinning solution is spun on the water transport layer, with a receiving distance of 18cm, to obtain a water-resistant layer.

[0055] S3. Add 0.5g of silica (0.3µm particle size) particles to 9.5g of ethanol and sonicate at 100W for 30min to obtain a spraying liquid; spray electrostatically at 15kV and a spraying rate of 0.5ml / h for 2h to obtain a water-proof layer surface, i.e., a high-concentration radiation layer; then dry at 60℃ for 2h to remove residual solvent and obtain a directional water-transporting radiation-cooling phase change material film.

[0056] The directional water-transporting radiation-cooling phase change material membrane prepared by this invention has good flexibility, and can be bent more than 180° while maintaining its shape without breaking; the phase change enthalpy is 130 J / g, and after 500 thermal cycles, the phase change enthalpy is 126 J / g, with a loss rate of 3%; the solar reflectivity is 93% and the high-mid infrared thermal emissivity is 92%; the porosity of the water-transporting layer is 80% with a pore size of 2 μm, and the porosity of the water-proof layer is 80% with a pore size of 2 μm; the water contact angle on the water-transporting layer side is 60°, and the water contact angle on the water-proof layer side is 55°; water droplets can be absorbed on both sides of the water-transporting layer and the water-proof layer, and unidirectional water permeation from the direction of the water-transporting layer to the direction of the water-proof layer cannot be achieved.

[0057] Comparative Example 2 A method for preparing a directional water-conveying radiation-cooling phase change material membrane, wherein the electrospinning conditions for both the water-conveying layer and the water-resistant layer are the same, both being water-resistant layer conditions, includes the following steps: S1. Dissolve 2g of cellulose acetate in 8g of dimethylformamide and stir at 80℃ for 5h to obtain a cellulose acetate solution; add 6g of docosane and 2g of silica (particle size 0.3μm) to the cellulose acetate solution, and emulsify at a high speed of 15000 rpm for 15min to form a spinning solution; use electrospinning technology to spin the spinning solution at a voltage of 15kV and a feed rate of 1mL / h, with a receiving distance of 12cm to obtain a water transport layer.

[0058] S2. Using electrospinning technology, the spinning solution is spun on the water transport layer at a voltage of 15kV and a feed rate of 1mL / h, with a receiving distance of 12cm, to obtain a water-proof layer.

[0059] S3. Add 0.5g of silica (0.3µm particle size) particles to 9.5g of ethanol and sonicate at 100W for 30min to obtain a spraying liquid; spray electrostatically at 15kV and a spraying rate of 0.5ml / h for 2h to obtain a water-proof layer surface, i.e., a high-concentration radiation layer; then dry at 60℃ for 2h to remove residual solvent and obtain a directional water-transporting radiation-cooling phase change material film.

[0060] The directional water-transporting radiation-cooling phase change material membrane prepared by this invention has good flexibility, and can be bent more than 180° while maintaining its shape without breaking; the phase change enthalpy is 130 J / g, and after 500 thermal cycles, the phase change enthalpy is 126 J / g, with a loss rate of 3%; the solar reflectivity is 93% and the high-mid infrared thermal emissivity is 92%; the porosity of the water-transporting layer is 60% with a pore size of 1 μm, and the porosity of the water-proof layer is 60% with a pore size of 1 μm; the water contact angle on the water-transporting layer side is 35°, and the water contact angle on the water-proof layer side is 30°; water droplets can stay on both sides of the water-transporting layer and the water-proof layer, and unidirectional water permeation from the water-transporting layer direction to the water-proof layer direction cannot be achieved.

[0061] Comparative Example 3 A method for preparing a directional water conveyance radiation cooling phase change material membrane includes the following steps: S1. Dissolve 2g of thermoplastic polyurethane in 8g of dimethylformamide and stir at 80℃ for 5h to obtain a thermoplastic polyurethane solution; add 6g of docosane and 2g of silica (particle size 0.3μm) to the thermoplastic polyurethane solution and emulsify at a high speed of 15000 rpm for 15min to form a spinning solution; use electrospinning technology to spin the spinning solution at a voltage of 22kV and a feed rate of 1.2mL / h, with a receiving distance of 18cm to obtain a water transport layer.

[0062] S2. Using electrospinning technology, the spinning solution is spun on the water transport layer at a voltage of 15kV and a feed rate of 1mL / h, with a receiving distance of 12cm, to obtain a water-proof layer.

[0063] S3. Add 0.5g of silica (0.3µm particle size) particles to 9.5g of ethanol and sonicate at 100W for 30min to obtain a spraying liquid; spray electrostatically at 15kV and a spraying rate of 0.5ml / h for 2h to obtain a water-proof layer surface, i.e., a high-concentration radiation layer; then dry at 60℃ for 2h to remove residual solvent and obtain a directional water-transporting radiation-cooling phase change material film.

[0064] The directional water-transporting radiation-cooling phase change material membrane prepared by this invention has good flexibility, and can be bent more than 180° while maintaining its shape without breaking; after 500 thermal cycles, the phase change enthalpy is 126 J / g, with a loss rate of 3%; the solar reflectivity is 90% and the high-mid infrared thermal emissivity is 91%; the porosity of the water-transporting layer is 80% with a pore size of 5 μm, and the porosity of the water-proof layer is 60% with a pore size of 10 μm; the water contact angle on the water-transporting layer side is 120°, and the water contact angle on the water-proof layer side is 110°; water droplets can stay on both sides of the water-transporting layer and the water-proof layer, and unidirectional water permeation from the water-transporting layer direction to the water-proof layer direction cannot be achieved.

[0065] It should be noted that when numerical ranges are involved in this invention, it should be understood that both endpoints of each numerical range, as well as any value between the two endpoints, can be selected. Since the steps and methods used are the same as in the embodiments, preferred embodiments are described here to avoid redundancy. Although preferred embodiments of the invention have been described, those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of this invention.

Claims

1. A method for preparing a directional water conveyance radiation cooling phase change material membrane, characterized in that, Includes the following steps: The polymer, phase change material, and radiation-cooled particles are dissolved together in a solvent and emulsified to obtain a spinning solution. In the spinning solution, the mass fraction of polymer is 20%~30%, the mass fraction of radiation-cooled particles is 10%~20%, and the mass fraction of phase change material is 50%~70%. The polymer is selected from cellulose acetate, polylactic acid, or polycaprolactone; The phase change material is selected from at least one of alkanes, fatty acids, and fatty alcohols; The radiation-cooling particles are selected from at least one of alumina, silicon dioxide, titanium dioxide, and barium sulfate; The spinning solution is subjected to electrospinning for the first time to form a water-carrying layer; On the water transport layer, a second electrospinning process is carried out using spinning solution, and a water-proof layer is attached to the water transport layer. A dispersion of radiation-cooling particles is deposited in situ on the water-resistant layer to form a radiation-cooling layer. After drying, a directional water-transporting radiation-cooling phase change material membrane is obtained.

2. The method for preparing the directional water conveyance radiation cooling phase change material membrane according to claim 1, characterized in that, In the spinning solution, the mass fraction of polymer is 18%~25%, the mass fraction of radiation-cooled particles is 15%, and the mass fraction of phase change material is 60%.

3. The method for preparing the directional water conveyance radiation cooling phase change material membrane according to claim 1, characterized in that, In the dispersion of radiation-cooled particles, the mass fraction of radiation-cooled particles is 3% to 10%.

4. The method for preparing the directional water conveyance radiation cooling phase change material membrane according to claim 1, characterized in that, The radiation cooling layer was prepared by electrostatic spraying. The electrostatic spraying voltage was 15kV~20kV, the spraying rate was 0.3mL / min~1mL / min, and the spraying time was 5min~15min.

5. The method for preparing the directional water conveyance radiation cooling phase change material membrane according to claim 1, characterized in that, The voltage for the first electrospinning was 20kV~25kV, the feed rate was 0.8mL / h~2mL / h, and the receiving distance was 15cm~20cm.

6. The method for preparing the directional water conveyance radiation cooling phase change material membrane according to claim 4, characterized in that, The voltage for the second electrospinning is 12kV~18kV, the feed rate is 1mL / h~2mL / h, and the receiving distance is 10cm~15cm; The voltage difference between the first and second electrospinning processes is ≥5kV, and the receiving distance difference is ≥3cm.

7. A directional water-transporting radiation-cooling phase change material membrane prepared by the preparation method according to any one of claims 1 to 6, characterized in that, The directional water-carrying radiation-cooling phase change material membrane is composed of a water-carrying layer, a water-insulating layer, and a radiation-cooling layer stacked sequentially from bottom to top along the thickness direction; both the water-carrying layer and the water-insulating layer have penetrating micropores, and the porosity of the water-insulating layer is less than that of the water-carrying layer.

8. The method for preparing the directional water conveyance radiation cooling phase change material membrane according to claim 7, characterized in that, The water contact angle of the aquifer is 10°~90°, and the water contact angle of the impermeable layer is 10°~30°.

9. The directional water conveyance radiation cooling phase change material membrane according to claim 7, characterized in that, The thickness of the phase change material film for directional water conveyance and radiation cooling is 80μm~300μm.

10. The application of the directional water-transporting radiation-cooling phase change material membrane of claim 7 in the preparation of smart wearable clothing, building energy-saving coatings, or zero-energy personal thermal management devices.

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