Preparation method of self-assembled multilayer radiation refrigeration film

Abstract

The invention relates to the technical field of energy-saving materials, and discloses a preparation method of a self-assembled multilayer radiation refrigeration film, the self-assembled multilayer radiation refrigeration film comprises: a surface coating composed of a super-hydrophobic coating and used for providing anti-fouling and self-cleaning functions; the top layer is composed of titanium dioxide nanoparticles and has high sunlight reflectivity; the middle layer is a polytetrafluoroethylene layer with a hierarchical porous structure and provides thermal insulation and efficient mid-infrared emission; the bottom layer is composed of graphene oxide, has high heat conduction performance and promotes heat transfer; and the substrate is a flexible polyester film PET and is used as a supporting structure. Through the titanium dioxide nano-particle design of the top layer and the graded porous structure of the middle layer, the film achieves the reflectivity exceeding 90% in the sunlight band (400-2500nm), meanwhile, the film has the radiance exceeding 85% in the middle infrared band (8-13mu m), and due to the optical performance, surface heat absorption can be remarkably reduced under the intense sunlight condition.

Description

Technical Field

[0001] The invention relates to the technical field of energy-saving materials, and in particular to a method for preparing a self-assembled multilayer radiation refrigeration film. Background Art

[0002] Radiative cooling technology is a technology that uses the thermal radiation of an object to dissipate heat to the outside world. By reflecting solar radiation and emitting mid-infrared radiation, passive cooling can be achieved without consuming external energy. In recent years, this technology has received widespread attention in the fields of building energy conservation, agricultural greenhouses, and electronic equipment heat dissipation. As an important carrier of radiative cooling technology, multilayer radiative cooling film has become the key to achieving efficient heat dissipation with its hierarchical functional distribution and optimized optical properties of materials.

[0003] Existing radiative cooling films usually adopt simple single-layer or double-layer structures. These films often have low reflectivity in the solar band and insufficient radiation efficiency in the mid-infrared band, and cannot achieve significant cooling effects in high-temperature environments. In addition, traditional preparation methods such as coating and thermal evaporation technology make it difficult to ensure the uniformity of film thickness and the accuracy of functional distribution, resulting in a significant reduction in overall optical and thermal performance. These shortcomings limit the application scope of radiative cooling films, especially in areas with strong demand for efficient passive cooling. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for preparing a self-assembled multilayer radiative cooling film, which solves the problem that traditional preparation methods are difficult to ensure the uniformity of film thickness and the accuracy of functional distribution, resulting in a significant reduction in overall optical and thermal properties.

[0005] To achieve the above objectives, the present invention is implemented through the following technical solutions: a self-assembled multilayer radiation cooling film, comprising:

[0006] Surface coating, consisting of a superhydrophobic coating, is used to provide anti-fouling and self-cleaning functions;

[0007] The top layer, made of titanium dioxide nanoparticles, has high solar reflectivity;

[0008] The middle layer is a polytetrafluoroethylene layer with a graded porous structure, which provides thermal insulation and efficient mid-infrared emission;

[0009] The bottom layer, composed of graphene oxide, has high thermal conductivity and promotes heat transfer;

[0010] The substrate is a flexible polyester film PET, which serves as a supporting structure;

[0011] The multilayer radiation cooling film is composed of a surface coating, a top layer, a middle layer, a bottom layer and a substrate in sequence.

[0012] Preferably, the method comprises the following steps:

[0013] S1. Surface coating preparation: spraying a super hydrophobic coating composed of siloxane and fluorocarbon compound on the top surface, with a coating thickness of 2-5 μm;

[0014] S2, top layer preparation: preparing a titanium dioxide suspension, and forming a top layer on the substrate surface by electrostatic spraying technology;

[0015] S3, preparation of the middle layer: preparing a porous polytetrafluoroethylene emulsion, using electrostatic spraying to form an middle layer on the top layer, and forming a hierarchical porous structure through volatilization of the pore-forming agent;

[0016] S4, bottom layer preparation: preparing a graphene oxide solution, using electrostatic spraying to form a bottom layer on the middle layer, and enhancing thermal conductivity by low-temperature reduction;

[0017] S5. Self-assembly and curing: The sprayed multilayer film is placed in an electrostatic field of 100-200 V / cm for 20-40 minutes, and then cured at 80-120° C. for 1-2 hours to complete the self-assembly of the multilayer structure.

[0018] Preferably, the top layer is composed of titanium dioxide nanoparticles with a particle size of 20-30 nm, and the thickness of the top layer is 5-10 μm.

[0019] Preferably, the intermediate layer has a hierarchical porous structure, the micropore diameter ranges from 1 to 5 μm, the nanopore diameter ranges from less than 200 nm, and the thickness of the intermediate layer is 20 to 50 μm.

[0020] Preferably, the bottom layer is prepared from a graphene oxide solution having a mass concentration of 3-8 wt %, and is subjected to a low-temperature reduction treatment using ascorbic acid, and the thickness of the bottom layer is 10-15 μm.

[0021] Preferably, the surface coating is composed of siloxane and fluorocarbon, wherein the mass fraction of siloxane is 8-12%, and the mass fraction of fluorocarbon is 0.3-1%.

[0022] Preferably, the mass concentration of the titanium dioxide suspension is 5-15wt%, and the spraying speed during the spraying process is 5-10cm / s.

[0023] Preferably, the polytetrafluoroethylene emulsion contains 1-5% by mass of a pore-forming agent, the pore-forming agent is toluene or methanol, and after spraying, the pore-forming agent is volatilized by low-temperature drying at 50°C.

[0024] Preferably, the graphene oxide solution is reduced by ascorbic acid, and the spraying distance of the electrostatic spraying is 10-15 cm.

[0025] The present invention provides a method for preparing a self-assembled multilayer radiation cooling film, which has the following beneficial effects:

[0026] 1. Through the titanium dioxide nanoparticle design of the top layer and the graded porous structure of the middle layer, the film achieves a reflectivity of more than 90% in the solar band (400-2500nm) and an emissivity of more than 85% in the mid-infrared band (8-13μm). This optical property can significantly reduce surface heat absorption under strong sunlight conditions and efficiently dissipate heat through mid-infrared radiation, so that the surface temperature of the film can be 5-10°C lower than the ambient temperature.

[0027] 2. The present invention adopts electrostatic spraying technology combined with electrostatic field self-assembly process to achieve orderly arrangement of materials at the molecular scale, making the bonding between film layers tighter and enhancing the overall performance of the multilayer film. Compared with the traditional multilayer film preparation process, this method significantly improves the uniformity of the film layer, thickness controllability and stability of functional distribution, ensuring the best performance of each layer of functional material in optical and thermal properties.

[0028] 3. The present invention reduces environmental pollution by introducing environmentally friendly ascorbic acid as a reducing agent for graphene oxide to replace traditional strong reducing agents (such as hydrazine). In addition, the temperature of the curing stage of the entire process is relatively low (80-120°C), and energy consumption is significantly reduced. The raw materials selected in the preparation process, such as polylactic acid (PLA) and polytetrafluoroethylene, also have high environmental protection properties. This low-energy consumption and environmentally friendly preparation method makes it more suitable for large-scale industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 is a cross-sectional view of the self-assembled multi-layer radiation cooling film of the present invention;

[0030] Figure 2 The present invention is a flow chart of a method for preparing a self-assembled multilayer radiation cooling film.

[0031] Among them, 1. surface coating; 2. top layer; 3. middle layer; 4. bottom layer; 5. base. DETAILED DESCRIPTION

[0032] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0033] Please refer to the attached Figure 1 The embodiment of the present invention provides a self-assembled multilayer radiation cooling film, comprising:

[0034] Surface coating 1, consisting of a super hydrophobic coating, for providing anti-fouling and self-cleaning functions;

[0035] Top layer 2, composed of titanium dioxide nanoparticles, has high solar reflectivity;

[0036] The middle layer 3 is a polytetrafluoroethylene layer with a graded porous structure, which provides thermal insulation and efficient mid-infrared emission;

[0037] The bottom layer 4, composed of graphene oxide, has high thermal conductivity and promotes heat transfer;

[0038] Substrate 5, which is a flexible polyester film PET, serving as a supporting structure;

[0039] The multilayer radiative cooling film consists of a surface coating, a top layer, an intermediate layer, a bottom layer and a substrate.

[0040] Specifically, the multi-layer radiative cooling film achieves high-efficiency characteristics of sunlight reflection and mid-infrared radiation through the combination of multiple functional film layers. The surface coating can significantly reduce the adhesion of pollution particles and moisture, and improve the stability of long-term use. The top layer is responsible for reflecting sunlight and reducing the surface temperature of the film. The middle layer uses a material with a graded porous structure, which can not only reduce heat transfer, but also achieve efficient radiation heat dissipation in the mid-infrared band. The bottom layer is designed with high thermal conductivity materials to accelerate the conduction and radiation of heat from the substrate. The substrate provides overall flexible support, making the film suitable for installation on complex curved surfaces and large-area laying.

[0041] A method for preparing a self-assembled multilayer radiation cooling film comprises the following steps:

[0042] S1, preparation of surface coating 1: spraying a super hydrophobic coating composed of siloxane and fluorocarbon compound on the surface of the top layer 2, with a coating thickness of 2-5 μm;

[0043] S2, preparation of top layer 2: preparing titanium dioxide suspension, and forming top layer 2 on the surface of substrate 5 by electrostatic spraying technology;

[0044] S3, preparation of the middle layer 3: preparing a porous polytetrafluoroethylene emulsion, and forming the middle layer 3 on the top layer 2 by electrostatic spraying, and forming a hierarchical porous structure by volatilization of the pore-forming agent;

[0045] S4, preparation of bottom layer 4: preparing a graphene oxide solution, forming bottom layer 4 on middle layer 3 by electrostatic spraying, and enhancing thermal conductivity by low temperature reduction;

[0046] S5. Self-assembly and curing: The sprayed multilayer film is placed in an electrostatic field of 100-200 V / cm for 20-40 minutes, and then cured at 80-120°C for 1-2 hours to complete the self-assembly of the multilayer structure.

[0047] Specifically, the preparation method relies on electrostatic spraying technology to build the membrane structure layer by layer, and by precisely controlling the concentration, distance, speed and spraying environment parameters of the spraying material, the thickness of each layer is ensured to be uniform and the functionality is outstanding. Before the preparation of each layer of material, it is necessary to disperse or emulsify it to form a uniform suspension or emulsion. Through electrostatic field-assisted spraying and subsequent curing treatment, the orderly arrangement and combination of each layer of material can be achieved at the molecular level, constructing a multilayer membrane structure with excellent optical and thermal properties.

[0048] The top layer 2 is composed of titanium dioxide nanoparticles having a particle size of 20-30 nm, and the thickness of the top layer 2 is 5-10 μm.

[0049] Specifically, the top layer material is based on titanium dioxide nanoparticles. By adjusting the particle size and dispersant ratio, films with different optical properties can be obtained. Particles with a particle size of 20-30nm can achieve high reflectivity in the visible and near-infrared bands. During the spraying process, the thickness and surface finish of the top layer can be precisely controlled by adjusting the concentration of the suspension and the number of spray layers. The prepared top layer has excellent resistance to UV aging and can maintain a stable reflective effect under long-term sunlight.

[0050] The intermediate layer 3 has a hierarchical porous structure, the micropore diameter ranges from 1 to 5 μm, the nanopore diameter ranges from less than 200 nm, and the thickness of the intermediate layer 3 is 20 to 50 μm.

[0051] Specifically, the middle layer forms a hierarchical porous structure with micrometer and nanometer pore sizes through the introduction of pore-forming agents. This structure can achieve efficient thermal radiation in the mid-infrared band (8–13μm), and the presence of air in the pores significantly reduces the thermal conductivity, thereby effectively reducing the transfer of heat to the substrate. During the preparation process, the pore size and porosity can be precisely controlled by controlling the type and content of the pore-forming agent and the drying speed of the emulsion.

[0052] The bottom layer 4 is prepared from a graphene oxide solution with a mass concentration of 3-8wt% and is subjected to low-temperature reduction treatment by ascorbic acid. The thickness of the bottom layer 4 is 10-15 μm.

[0053] Specifically, the bottom layer is based on graphene oxide, and its thermal conductivity is improved by reduction treatment with ascorbic acid. Compared with untreated graphene oxide, the graphene layer reduced at low temperature has higher thermal conductivity and stability. During the spraying process, multiple thin layers are sprayed and superimposed to ensure that the thickness of the bottom layer is uniform and has excellent interface bonding performance. The bottom layer can quickly diffuse the heat transferred from the substrate to the surface of the entire film, thereby improving the overall heat dissipation efficiency.

[0054] The surface coating 1 is composed of siloxane and fluorocarbon, wherein the mass fraction of siloxane is 8-12% and the mass fraction of fluorocarbon is 0.3-1%.

[0055] Specifically, the surface coating is prepared with a mixed solution of siloxane and fluorocarbon compounds. After spraying and low-temperature curing, a membrane surface with super-hydrophobic properties is formed. Its water contact angle can reach more than 150°, which can effectively prevent water droplets from spreading and dirt from adhering. In addition, the coating has a micro-nano rough surface in structure, so that dust and other pollutant particles can be removed under the action of slight airflow or water flow, thereby keeping the surface clean and the long-term performance of the membrane.

[0056] The mass concentration of the titanium dioxide suspension is 5-15wt%, and the spraying speed during the spraying process is 5-10cm / s.

[0057] Specifically, the dispersion treatment of the top layer material is a key step to ensure the quality of spraying. By adding an appropriate amount of dispersant (such as polyvinyl pyrrolidone) and dispersing the nanoparticles under ultrasonic conditions, a stable suspension can be formed. During the spraying process, adjusting the spraying speed to 5-10cm / s and keeping the spraying distance between 10-15cm can achieve uniform coverage and appropriate adhesion thickness.

[0058] The polytetrafluoroethylene emulsion contains a pore-forming agent with a mass fraction of 1-5%, and the pore-forming agent is toluene or methanol. After spraying, the pore-forming agent is volatilized by low-temperature drying at 50°C.

[0059] Specifically, the hierarchical porous structure of the middle layer is achieved by precise control of the pore former. Toluene or methanol is added to the emulsion as a pore former, and the pore former is dried at 50°C to form a uniform pore size distribution during the slow volatilization process. In this process, the control of the humidity and air flow velocity of the drying environment has a significant impact on the final porosity, and stable conditions need to be maintained.

[0060] The graphene oxide solution was reduced by ascorbic acid and electrostatically sprayed at a spray distance of 10–15 cm.

[0061] Specifically, in the spraying of the graphene oxide bottom layer, the spraying distance is controlled at 10-15cm, which can effectively reduce the problems of droplet dispersion and uneven spraying. The bottom layer after spraying needs to be treated with ascorbic acid solution to partially convert the graphene oxide into reduced graphene through a reduction reaction, thereby improving its thermal conductivity. The reduction process needs to be carried out slowly at room temperature to ensure the integrity of the film.

[0062] The following is a detailed description of the materials used in the multi-layer radiative cooling film technology solution, including the purpose, performance characteristics and role of each material in the preparation process:

[0063] 1. Titanium dioxide (TiO2) nanoparticles

[0064] Purpose: Main material for the top layer, giving it high solar reflectivity.

[0065] Performance characteristics:

[0066] Particle size: 20-30nm, ensuring optical performance while enhancing film uniformity.

[0067] High refractive index: Excellent reflectivity (>90%) in the visible and near-infrared bands.

[0068] Strong chemical stability: It can be exposed to ultraviolet rays and high temperature environments for a long time without performance degradation.

[0069] Function: Through the dispersion and uniform spraying of nanoparticles, a smooth top layer is formed to effectively reflect sunlight and reduce surface heat absorption.

[0070] 2. Polytetrafluoroethylene (PTFE)

[0071] Application: Used in the middle layer to form a thermal insulation layer with a graded porous structure.

[0072] Performance characteristics:

[0073] Low thermal conductivity: reduces the transfer of heat downward through the middle layer.

[0074] Chemically inert: Excellent corrosion and oxidation resistance.

[0075] Easy to form pores: Combining with pore-forming agents can form micron and nanometer pores.

[0076] Function: Through the hierarchical porous structure design, PTFE can not only block heat conduction, but also achieve efficient thermal radiation in the mid-infrared band (8-13μm).

[0077] 3. Graphene oxide (GO)

[0078] Application: Used in the base layer to enhance thermal conductivity.

[0079] Performance characteristics:

[0080] High thermal conductivity: Graphene oxide after reduction treatment has a high thermal conductivity.

[0081] Layered structure: able to form a tight bond with the middle layer and substrate.

[0082] Good processability: Graphene oxide solution is easy to disperse and suitable for spraying to prepare thin films.

[0083] Function: By quickly transferring the heat from the base, the heat is efficiently guided to the surface for radiation.

[0084] 4. Siloxane

[0085] Application: Main component of surface coatings, providing super hydrophobic properties.

[0086] Performance characteristics:

[0087] Low surface energy: significantly reduces the adhesion of water and dirt on the membrane surface.

[0088] Good elasticity: able to withstand slight mechanical deformation without damaging the surface coating.

[0089] Strong weather resistance: It can maintain the hydrophobic effect for a long time in outdoor environment.

[0090] Function: Provides self-cleaning and anti-fouling functions by forming a micro-nanoscale surface roughness structure and a low surface energy layer.

[0091] 5. Fluorocarbons

[0092] Uses: Used in combination with siloxane in surface coating to further enhance hydrophobic properties.

[0093] Performance characteristics:

[0094] Excellent anti-pollution ability: can effectively repel water, grease and other substances.

[0095] UV resistance: not easily degraded by UV radiation.

[0096] High chemical stability: strong resistance to corrosion and chemical attack.

[0097] Function: Works synergistically with siloxane to optimize the hydrophobicity and durability of surface coatings.

[0098] 6. Polyvinylpyrrolidone (PVP)

[0099] Uses: Dispersant for titanium dioxide suspension.

[0100] Performance characteristics:

[0101] Good dispersibility: can effectively prevent the agglomeration of titanium dioxide nanoparticles.

[0102] Good solubility: easily soluble in water, convenient for preparing uniform suspension.

[0103] Function: In the preparation of the top layer material, ensure that the titanium dioxide particles are evenly dispersed and improve the flatness and reflective properties of the film after spraying.

[0104] 7. Pore-forming agent (toluene, methanol)

[0105] Application: Used in middle layer materials to form hierarchical porous structure.

[0106] Performance characteristics:

[0107] High volatility: It can evaporate at low temperatures, making it easier to control the pore formation process.

[0108] Good compatibility with PTFE: can be evenly distributed in the emulsion without affecting other properties of the material.

[0109] Function: During the drying process, it evaporates and leaves micron and nanometer pores in the PTFE layer, improving the heat dissipation and insulation performance of the middle layer.

[0110] 8. Ascorbic Acid

[0111] Application: Used for low temperature reduction treatment of graphene oxide.

[0112] Performance characteristics:

[0113] Strong reduction ability: It can reduce part of graphene oxide to graphene, improving its thermal conductivity.

[0114] Highly environmentally friendly: Compared with chemically stronger reducing agents (such as hydrazine), ascorbic acid is safer and more environmentally friendly.

[0115] Function: Through the low-temperature reduction process, the thermal conductivity of the bottom layer is optimized to ensure the overall heat dissipation efficiency of the film.

[0116] 9. Flexible polyester film (PET)

[0117] Application: As a substrate for multilayer films, providing support and flexibility.

[0118] Performance characteristics:

[0119] Excellent mechanical strength: able to withstand the load and installation pressure of multi-layer membranes.

[0120] Good flexibility: suitable for laying on complex curved surfaces or large areas.

[0121] High temperature resistance: Able to maintain structural stability during the curing stage.

[0122] Function: As the bottom support material, it ensures the overall structural integrity of the multilayer film and provides mechanical and thermal stability.

[0123] Material Overview

[0124] The above materials play their respective roles in the design of the multilayer radiative cooling film: titanium dioxide and polytetrafluoroethylene realize optical and thermal functions, graphene oxide enhances thermal conductivity, siloxane and fluorocarbon compounds provide self-cleaning ability, and the base PET provides structural support. The rational selection and optimized combination of these materials together give the film excellent heat dissipation performance and multifunctionality.

[0125] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A self-assembled multilayer radiative cooling film, characterized in that: include: The surface coating (1) is composed of a super hydrophobic coating for providing anti-fouling and self-cleaning functions; The top layer (2) is composed of titanium dioxide nanoparticles, which have high solar reflectivity; The middle layer (3) is a polytetrafluoroethylene layer with a hierarchical porous structure, which provides thermal insulation and efficient mid-infrared emission; A bottom layer (4), composed of graphene oxide, has high thermal conductivity and promotes heat transfer; The substrate (5) is a flexible polyester film PET, which serves as a supporting structure; The multilayer radiation cooling film is composed of a surface coating (1), a top layer (2), an intermediate layer (3), a bottom layer (4) and a substrate (5) in sequence.

2. A method for preparing a self-assembled multilayer radiation cooling film, characterized in that: The self-assembled multilayer radiative cooling film according to claim 1 comprises the following steps: S1. Preparation of surface coating (1): spraying a super hydrophobic coating composed of siloxane and fluorocarbon compound on the surface of the top layer (2), with a coating thickness of 2-5 μm; S2, preparation of the top layer (2): preparing a titanium dioxide suspension, and forming a top layer (2) on the surface of the substrate (5) by electrostatic spraying technology; S3, preparation of the middle layer (3): preparing a porous polytetrafluoroethylene emulsion, and using electrostatic spraying to form the middle layer (3) on the top layer (2), and forming a hierarchical porous structure through volatilization of the pore-forming agent; S4, preparation of the bottom layer (4): preparing a graphene oxide solution, using electrostatic spraying to form a bottom layer (4) on the middle layer (3), and enhancing the thermal conductivity by low-temperature reduction; S5. Self-assembly and curing: The sprayed multilayer film is placed in an electrostatic field of 100-200 V / cm for 20-40 minutes, and then cured at 80-120°C for 1-2 hours to complete the self-assembly of the multilayer structure.

3. The method for preparing a self-assembled multilayer radiative cooling film according to claim 2, characterized in that: The top layer (2) is composed of titanium dioxide nanoparticles with a particle size of 20-30 nm, and the thickness of the top layer (2) is 5-10 μm.

4. The method for preparing a self-assembled multilayer radiative cooling film according to claim 2, characterized in that: The intermediate layer (3) has a hierarchical porous structure, the diameter of the micropores is in the range of 1-5 μm, the diameter of the nanopores is in the range of less than 200 nm, and the thickness of the intermediate layer is in the range of 20-50 μm.

5. The method for preparing a self-assembled multilayer radiative cooling film according to claim 2, characterized in that: The bottom layer (4) is prepared from a graphene oxide solution with a mass concentration of 3-8wt% and is subjected to low-temperature reduction treatment using ascorbic acid. The thickness of the bottom layer is 10-15 μm.

6. The method for preparing a self-assembled multilayer radiative cooling film according to claim 2, characterized in that: The surface coating (1) is composed of siloxane and fluorocarbon compounds, wherein the mass fraction of siloxane is 8-12% and the mass fraction of fluorocarbon compounds is 0.3-1%.

7. The method for preparing a self-assembled multilayer radiative cooling film according to claim 2, characterized in that: The mass concentration of the titanium dioxide suspension is 5-15wt%, and the spraying speed during the spraying process is 5-10cm / s.

8. The method for preparing a self-assembled multilayer radiative cooling film according to claim 2, characterized in that: The polytetrafluoroethylene emulsion contains 1-5% by mass of a pore-forming agent, which is toluene or methanol. After spraying, the pore-forming agent is volatilized by low-temperature drying at 50°C.

9. The method for preparing a self-assembled multilayer radiative cooling film according to claim 2, characterized in that: The graphene oxide solution is reduced by ascorbic acid, and the spraying distance of the electrostatic spraying is 10-15 cm.

Images