A high-efficiency passive radiative cooling material based on liquid metal and a preparation method thereof

Abstract

This invention discloses a passive radiative cooling material based on liquid metal and its preparation method. The material consists of a substrate layer, a liquid metal thermally conductive layer, and an encapsulation layer. The liquid metal thermally conductive layer, utilizing its high thermal conductivity, can rapidly conduct heat from the human body or device to the external environment, improving the efficiency of passive radiative cooling, maximizing the scattering of solar radiation, and achieving a highly efficient natural cooling effect. Experimental results show that the passive radiative cooling material based on liquid metal prepared in this invention not only has excellent cooling performance but also good flexibility and durability. Using liquid metal as the thermally conductive layer material, leveraging its fluidity and the spontaneously formed nanoscale oxide film on its surface, enhances the bonding force between the liquid metal and the substrate layer, allowing it to adhere well to the substrate layer and improving its stability and flexibility. Therefore, it has broad application prospects in wearable devices, electronic device heat dissipation, and building exterior wall insulation.

Description

Technical Field

[0001] This invention belongs to the field of materials technology, specifically relating to a highly efficient passive radiation cooling material based on liquid metal and its preparation method. Background Technology

[0002] Traditional cooling methods mostly rely on external energy sources, which are not only energy-intensive but also environmentally unfriendly. Passive radiative cooling (PRC) is a cooling technology that does not rely on external energy sources. It utilizes the high emissivity of materials within an atmospheric transparency window (8–13 μm) to radiate heat into outer space, while simultaneously using the material's high reflectivity to reduce the absorption of solar radiation. These advantages demonstrate the broad application prospects of PRC technology, which is expected to provide green and energy-efficient cooling solutions for numerous fields. However, the application of PRC technology in clothing and wearable devices is still in its early stages. Products using traditional solid metal materials as thermal conductive layers suffer from numerous problems, including easy breakage under deformation, complex manufacturing processes, and poor compatibility with flexible polymer substrates. Liquid metal thermal conductive layers, on the other hand, possess enormous application potential due to their excellent fluidity, thermal conductivity, and superior bonding ability with flexible polymer substrates. Therefore, developing a novel passive radiative cooling material based on liquid metal is of great significance. Summary of the Invention

[0003] In view of the technical problems existing in the background art, the purpose of this invention is to provide a highly efficient passive radiation cooling material based on liquid metal and its preparation method.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] The first aspect of this invention provides a method for preparing a highly efficient passive radiation cooling material of liquid metal, comprising the following steps:

[0006] S1. Mix the polymer material, dopant material and organic solvent to obtain a homogeneous mixed solution, and then process it to obtain the base layer;

[0007] S2. A patterned structure is formed on the substrate layer obtained in step S1 by composite liquid metal to obtain a liquid metal thermal conductive layer;

[0008] S3. Using an encapsulation method, an encapsulation layer is constructed using the mixed solution in S1 to encapsulate the surface of the liquid metal thermal conductive layer;

[0009] S4. Drying, curing, and molding yield the passive radiation cooling material.

[0010] Preferably, in step S1, the processing method is any one of electrospinning, solution casting, spraying, roller coating, dip coating, spin coating, dry spinning, wet spinning, and casting film formation. In step S1, the ratio of the polymer material to the dopant material is 1:1×10⁻⁶. -2 ~1×10 2 .

[0011] Preferably, the polymer used to prepare the substrate layer is one or a combination of two or more of TPU, PC, PDMS, PAA, PI, PVDF, PTFE, PET, and PVC; the dopant material is one or a combination of two or more of glass microspheres, titanium dioxide, zirconium dioxide, magnesium oxide, aluminum oxide, and zinc oxide; and the organic solvent is one or a combination of two or more of DMF, DMAc, NMP, acetonitrile, dichloromethane, chloroform, and THF.

[0012] Preferably, in step S2, the method of forming a patterned structure by laminating liquid metal onto the substrate layer is any one of stencil printing, screen printing, direct writing printing, direct coating, laser-induced patterning, double-layer spinning, and oxygen-containing functional group induced wetting; the liquid metal in the liquid metal thermal conductive layer is one or a combination of two or more of Ga-Sn alloy, Ga-In alloy, Ga-In-Sn alloy, and Ga-In-Bi alloy.

[0013] Preferably, in step S3, the encapsulation method is any one of electrospinning, dry spinning, solution casting, spin coating, spraying, dip coating, casting film formation, and roll coating.

[0014] The second aspect of the present invention provides the application of the passive radiation cooling material of the first aspect in the preparation of wearable biological products, energy-saving building products, vehicle cooling products, and environmental protection products.

[0015] A third aspect of the present invention provides a fabric woven from the passive radiation cooling material described in the first aspect, or woven in combination with other materials. The present invention comprises the following:

[0016] Beneficial effects:

[0017] (1) This invention provides a passive radiative cooling material based on liquid metal, which consists of a base layer, a liquid metal thermally conductive layer, and an encapsulation layer. The liquid metal thermally conductive layer utilizes the high thermal conductivity of liquid metal to rapidly conduct heat from the human body or equipment to the external environment, improving the efficiency of passive radiative cooling, maximizing the scattering of solar radiation, achieving a highly efficient natural cooling effect, and reducing energy consumption. Experimental results show that the passive radiative cooling material based on liquid metal prepared in this invention not only has excellent cooling performance but also good flexibility and durability, while also reducing energy consumption and effectively alleviating the climate warming problem caused by traditional cooling methods.

[0018] (2) This invention uses liquid metal as the thermally conductive layer material. Utilizing its fluidity and the spontaneously formed nanoscale oxide film on its surface, the bonding force between the liquid metal and the substrate is enhanced, allowing it to adhere well to the substrate and improving the stability and flexibility of the device. Simultaneously, the fabrication process is simplified, making it suitable for large-scale production. This technology has broad application prospects in wearable devices, electronic device heat dissipation, and building exterior wall insulation. Attached Figure Description

[0019] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0020] Figure 1 A schematic diagram of the structure of a passive radiative cooling material based on liquid metal provided by the present invention;

[0021] Figure 2 A process flow diagram of a method for preparing a passive radiative cooling material based on liquid metal provided by the present invention;

[0022] Figure 3 The image shows the structure of the passive radiation cooling material prepared in Example 1, as characterized by scanning electron microscopy (SEM).

[0023] Figure 4 The graph shows the mechanical cycle performance test curves of the passive radiative cooling material substrate / encapsulation layer prepared in Example 1.

[0024] Figure 5 The conductivity stability of the passive radiative cooling material prepared in Example 1 under different stretching and torsion conditions is shown in the following figures: (a) original state; (b) 150% stretching; (c) 200% stretching; (d) torsion; (e) resistance test graph after returning to the original state.

[0025] Figure 6The graphs show the cooling performance test results of the passive radiation cooling materials prepared in Example 1 and Comparative Examples 1 and 2 (LM in the graphs indicates that the thermal conductive layer is made of liquid metal, Silicone indicates that the thermal conductive layer is made of silicone, and Glassmicrosphere indicates that no thermal conductive layer is added). Detailed Implementation

[0026] In the following description, specific details such as particular system architectures and techniques are set forth for illustrative purposes and not for limitation, in order to provide a thorough understanding of the embodiments of the invention. However, those skilled in the art will understand that the invention may be implemented in other embodiments without these specific details.

[0027] Example 1

[0028] See Figure 1-2 A method for preparing a passive radiative cooling material based on liquid metal includes the following steps:

[0029] S1. Mix 16.8g TPU, 38.4ml DMF, 43.1ml THF and 1.7g glass microspheres, sonicate until the polyurethane is completely dissolved, stir to obtain a uniform mixed solution, and then perform electrospinning. The electrospinning parameters are: high voltage 12KV, spinning distance 15cm, spinning speed 1mL / h, spinning time 2h to obtain a flexible polyurethane fiber substrate layer.

[0030] S2. A patterned structure is formed by bonding Ga-In-Sn alloy onto a substrate layer using a template printing method to obtain a liquid metal thermal conductive layer.

[0031] Among them, the Ga-In-Sn alloy is made by fully mixing Ga, In and Sn in a mass ratio of 68.5:21.5:10;

[0032] S3. Using the same mixed solution and spinning parameters as in S1, the surface of the liquid metal thermally conductive layer is encapsulated by electrospinning to obtain an encapsulation layer.

[0033] S4. The material is dried and cured in a forced-air oven at 60℃ to ensure stable performance, resulting in a passive radiation cooling material. The scanning electron microscope (SEM) characterization results are shown below. Figure 3 .

[0034] The structure of the prepared passive radiative cooling material was characterized by SEM, and the results are shown in the figure. Figure 3 .

[0035] like Figure 3The diagram shows the distribution of hollow glass microspheres within polyurethane fibers and the morphology of the liquid metal thermally conductive layer, demonstrating the successful fabrication of the passive radiative cooling material. The uniform distribution of the hollow glass microspheres within the polyurethane fibers indicates successful preparation of the substrate / encapsulation layer. Furthermore, the liquid metal adheres uniformly and well to the polymer fiber surface, indicating good compatibility with the polymer material.

[0036] The mechanical properties of the prepared substrate / encapsulation layer material were tested using a universal tensile testing machine. The results are shown in the figure. Figure 4 .

[0037] like Figure 4 As shown, the good overlap of the multiple cycle curves indicates that the substrate / encapsulation layer material has good mechanical resilience and flexibility. This property, combined with the room temperature fluidity of liquid metal, ensures that the prepared passive radiation cooling material has good structural stability, flexibility, and durability.

[0038] The conductivity of the prepared passive radiative cooling material under different deformation states was tested using a multimeter. The results are as follows: Figure 5 As shown.

[0039] Figure 5 The results showed that the passive radiative cooling material prepared in Example 1 had a resistance of approximately 0 under pristine, tensile, and torsional conditions. This excellent electrical conductivity stability indicates that the liquid metal thermally conductive layer maintains good structural stability within the passive radiative cooling material under various deformation states, demonstrating a strong bond between the liquid metal and the substrate layer. It also indicates that the prepared passive radiative cooling material possesses excellent flexibility and durability. This strong bond primarily stems from two aspects: firstly, the electrospun fibrous polymer composite material has a porous structure, while the liquid metal exhibits a certain degree of fluidity. When the two are combined, the pressure applied during the transfer process allows the liquid metal to penetrate into the porous fibrous structure. Secondly, there is the bonding force between the gallium oxide thin layer spontaneously formed on the surface of the liquid metal in air and the polar functional groups of the substrate polymer.

[0040] Example 2

[0041] A method for preparing a highly efficient passive radiative cooling material based on liquid metal includes the following steps:

[0042] S1. Preparation of the substrate layer: Mix 5g PAA, 50ml DMF and 100mg magnesium oxide thoroughly to form a homogeneous mixed solution. Use casting to prepare a film with a thickness in the range of 0.1 to 5mm to obtain the substrate layer.

[0043] S2. A pattern is formed on the substrate by transferring the Ga-In-Bi alloy to obtain a liquid metal thermal conductive layer.

[0044] S3. Spray the same mixed solution from S1 onto the surface of the liquid metal thermal conductive layer. After drying, press the entire material to firmly bond the different functional layers and complete the encapsulation on the surface of the liquid metal thermal conductive layer to form an encapsulation layer.

[0045] S4. Place it in a 60℃ forced-air oven to dry, cure, and shape it to ensure stable performance, thus obtaining a passive radiation cooling material.

[0046] Example 3

[0047] A method for preparing a highly efficient passive radiative cooling material based on liquid metal includes the following steps:

[0048] S1. Preparation of the substrate layer: 5g PDMS, 35ml chloroform and 200mg zirconium dioxide are thoroughly mixed, a thin film is prepared by spray deposition, and then dried and cured in a forced-air oven to complete the preparation of the substrate layer;

[0049] S2. The Ga-Sn alloy is patterned and composited onto the substrate layer by screen printing to form a liquid metal thermal conductive layer.

[0050] S3. The same mixed solution in S1 is deposited onto the surface of the liquid metal thermal conductive layer by dip coating to encapsulate the surface of the liquid metal thermal conductive layer and form an encapsulation layer.

[0051] S4. Place it in a 60℃ forced-air oven to dry, cure, and shape it to obtain a passive radiation cooling material.

[0052] Example 4

[0053] A method for preparing a highly efficient passive radiative cooling material based on liquid metal includes the following steps:

[0054] S1. Preparation of the substrate layer: After thoroughly mixing 5g PDMS, 35ml DMF, 25ml acetone and 150mg zirconium dioxide, a thin film is prepared by spray deposition and then dried and cured in an oven to complete the preparation of the substrate layer.

[0055] S2. The Ga-In alloy is patterned on the substrate layer by direct coating to form a liquid metal thermally conductive layer.

[0056] S3. The mixed solution in S1 is dry-spun onto the surface of the liquid metal thermal conductive layer to encapsulate the surface of the liquid metal thermal conductive layer and form an encapsulation layer.

[0057] S4. Place it in a 60℃ forced-air oven to dry, cure, and shape it to obtain a passive radiation cooling material.

[0058] Comparative Example 1

[0059] The steps are basically the same as in Example 1, except that the liquid metal thermally conductive layer in the passive radiative cooling material is replaced with a commercially available thermally conductive silicone layer.

[0060] To test the passive radiative cooling performance of the two materials, the passive radiative cooling materials prepared in Example 1 and Comparative Example 1 were placed outdoors from 12:30 PM to 2:30 PM at 28°C, and temperature changes were monitored in real time. The results are as follows: Figure 6 As shown, both materials exhibit some passive radiative cooling performance, but the passive radiative cooling material prepared in Example 1 demonstrates superior cooling performance. This is primarily because Example 1 uses gallium indium tin liquid metal as the thermally conductive layer, while Comparative Example 1 uses thermally conductive silicone. The metallic bond structure in liquid metal allows free electrons to move rapidly, resulting in efficient heat transfer and the rapid conduction of infrared radiation generated by the object to the outside environment, thus reducing the object's temperature. Silicone, as a polymer material, is bound by van der Waals forces between its molecular chains, and heat conduction mainly relies on molecular chain vibrations; therefore, its thermal conductivity is lower than that of liquid metal. Consequently, when sunlight irradiates both materials, both can utilize the porous fiber composite glass microsphere structure of the outer encapsulation layer to reflect and scatter sunlight. However, Example 1, due to the excellent thermal conductivity of the liquid metal thermally conductive layer, can quickly dissipate the infrared radiation heat generated by the object, exhibiting superior cooling performance.

[0061] Comparative Example 2

[0062] The steps are basically the same as in Example 1, except that no thermally conductive layer is added in Comparative Example 2.

[0063] To test the passive radiative cooling performance of the two materials, the passive radiative cooling materials prepared in Example 1 and Comparative Example 2 were placed outdoors from 12:30 PM to 2:30 PM at 28°C, and temperature changes were monitored in real time. The results are as follows: Figure 6 As shown, due to the porous fiber composite glass microsphere structure of the outer encapsulation layer, sunlight can be reflected and scattered. Both materials prepared in Example 1 and Comparative Example 2 exhibit certain cooling performance. However, the passive radiation cooling material prepared in Example 1 shows superior cooling performance. The main reason is that Example 1 uses Ga-In-Sn liquid metal as a heat-conducting layer, while Comparative Example 2 does not add a heat-conducting layer. The metallic bond structure in the liquid metal allows free electrons to move rapidly, resulting in efficient heat transfer. It can quickly conduct the infrared radiation heat generated by the object to the outside world to further reduce the object's temperature. Comparative Example 2, without adding a heat-conducting layer, can only achieve cooling through the reflection and scattering of sunlight by the encapsulation layer, resulting in poor cooling effect. Therefore, when sunlight irradiates the two materials, Example 1 shows superior cooling performance due to the good thermal conductivity of the liquid metal heat-conducting layer.

[0064] This invention is not limited to the specific embodiments described above. Any modifications made by those skilled in the art based on the above concept without creative effort are within the scope of protection of this invention.

Claims

1. A method for preparing a high-efficiency passive radiative cooling material based on liquid metal, characterized in that, Includes the following steps: S1. Mix the polymer material, dopant material and organic solvent to obtain a mixed solution, and then process it to obtain the base layer; S2. A patterned structure is formed on the substrate layer obtained in step S1 by composite liquid metal to obtain a liquid metal thermal conductive layer; S3. Using an encapsulation method, an encapsulation layer is constructed using the mixed solution in S1 to encapsulate the surface of the liquid metal thermal conductive layer; S4. Drying, curing, and molding to obtain passive radiation cooling material; The polymer material used to prepare the substrate layer is one or a combination of two or more of the following: polyurethane (TPU), polycarbonate (PC), polydimethylsiloxane (PDMS), polymethyl methacrylate (PAA), polyimide (PI), polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyethylene terephthalate (PET), and polyvinyl chloride (PVC). The liquid metal in the liquid metal thermal conductive layer is one or a combination of two or more of the following: gallium (Ga)-tin (Sn) alloy, gallium (Ga)-indium (In) alloy, gallium (Ga)-indium (In)-tin (Sn) alloy, and gallium (Ga)-indium (In)-bismuth (Bi) alloy.

2. The method for preparing a high-efficiency passive radiative cooling material based on liquid metal according to claim 1, characterized in that, In step S1, the processing method is any one of electrospinning, solution casting, spraying, roller coating, dip coating, spin coating, dry spinning, wet spinning, and casting film formation.

3. The method for preparing a highly efficient passive radiative cooling material based on liquid metal according to claim 1, characterized in that, In step S1, the polymer material and the doping material are used in a ratio of 1:1 x 10 -2 ~1 x 10 2 .

4. The method for preparing a high-efficiency passive radiative cooling material based on liquid metal according to claim 1, characterized in that, The doping material is one or a combination of two or more of glass microspheres, titanium dioxide, zirconium dioxide, magnesium oxide, aluminum oxide, and zinc oxide; the organic solvent is one or a combination of two or more of N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMac), N-methylpyrrolidone (NMP), acetonitrile, dichloromethane, chloroform, and tetrahydrofuran (THF).

5. The method for preparing a highly efficient passive radiative cooling material based on liquid metal according to claim 1, characterized in that, In step S2, the method of forming a patterned structure by compositing liquid metal on the substrate layer is any one of stencil printing, direct writing printing, direct coating, laser-induced patterning, double-layer spinning, and oxygen-containing functional group induced wetting.

6. The method for preparing a highly efficient passive radiative cooling material based on liquid metal according to claim 1, characterized in that, In step S3, the encapsulation method is any one of electrospinning, dry spinning, solution casting, spin coating, spraying, dip coating, casting film formation, and roll coating.

7. The application of the high-efficiency passive radiation cooling material based on liquid metal prepared by the preparation method according to any one of claims 1-6 in the preparation of wearable biological products, energy-saving building products, vehicle cooling products, and environmental protection products.

8. A fabric, characterized in that, The fabric is woven from the passive radiative cooling material as described in claim 7 or blended with other materials.

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