1. The utility model provides a flexible composite film of liquid metal which characterized in that includes from top to bottom in proper order:

a high-emissivity layer;

a liquid metal layer;

and packaging the protective layer.

2. The liquid metal flexible composite film according to claim 1, wherein the material of the high radiation layer is selected from any one of PDMS, PE, PVF, PVC and TPX; or the like, or, alternatively,

the material of the high-radiation layer is prepared by compounding high-radiation micro-nano particles and a transparent high polymer material, the high-radiation micro-nano particles are selected from one or more of cordierite, transition metal oxide, silicon carbide, titanium dioxide, silicon dioxide, aluminum oxide and hafnium dioxide, and the transparent high polymer material is selected from any one of PDMS, polyethylene, cellulose, PVF, PVC, TPX and PVA; preferably, the particle size of the high-radiation micro-nano particles is 1 nm-500 μm.

3. A liquid metal flexible composite film according to claim 2, characterized in that the thickness of the high radiation layer is 1 μm to 2mm, preferably 10 μm to 500 μm.

4. A liquid metal flexible composite film according to any one of claims 1 to 3, wherein the liquid metal layer is made of one or more materials selected from gallium, gallium-indium alloy, gallium-indium-tin-zinc alloy, and bismuth-indium-tin-zinc alloy.

5. A liquid metal flexible composite film according to claim 4, wherein the thickness of the liquid metal layer is 1nm to 500 μm, preferably 50nm to 200 μm.

6. A liquid metal flexible composite film according to any one of claims 1 to 5, wherein the material of the encapsulation protection layer is any base material that can be coated with liquid metal, preferably any one of PDMS, polyethylene, PVF, PVC, glass, wood board and metal sheet;

and/or the surface roughness of the packaging protective layer is less than Ra 6.3.

7. The liquid metal flexible composite film according to claim 6, wherein the thickness of the encapsulation protection layer is 100 μm to 10 mm.

8. A method for preparing a liquid metal flexible composite film as claimed in any one of claims 1 to 7, comprising the steps of:

1) forming a liquid metal layer on one surface of the high-radiation layer/the packaging protective layer by liquid-phase magnetron sputtering or spin-coating adhesion transfer printing;

2) and forming an encapsulation protective layer/a high-radiation layer on one surface of the liquid metal layer, which is far away from the high-radiation layer/the encapsulation protective layer.

9. The method for preparing a liquid metal flexible composite film according to claim 8, wherein in step 2), an encapsulation protective layer/high-radiation layer is formed on the side of the liquid metal layer away from the high-radiation layer/encapsulation protective layer in a bonding or adhesion sealing manner.

10. Use of the liquid metal flexible composite film according to any one of claims 1 to 7 for passive radiation refrigeration.

Background

Passive refrigeration is a technique for reducing the temperature of a passively refrigerated space without the use of an external driving force. In contrast to conventional cooling techniques, such as air conditioning or evaporative cooling, compressors and fans are operated mechanically or electrically to forcibly cool a space. The source of this external driving force is mostly from the combustion of fossil fuels. The passive cooling technology does not need external driving force, reduces the absorption of illumination and increases the radiation to the outer space by designing a building structure or an external coating and the like, so that the heat absorption capacity of the passive refrigerating space is smaller than the heat release capacity, and the passive cooling of the passive refrigerating space is realized. The interior of the passively cooled space remains comfortable by reducing unnecessary heat from sunlight directly striking the passively cooled space.

The basic principle of radiation refrigeration can be simply summarized as follows under the condition of neglecting the influence of secondary factors such as non-radiation items and the like: emitting enough infrared radiation energy to a cosmic space with the temperature close to absolute zero through an atmospheric window (mainly 8-13 mu m) to release heat; meanwhile, the energy from the solar spectrum wave band is reflected or scattered as much as possible (mainly studied 0.2-4 μm, because the wave band accounts for more than 98% of the whole solar energy), so as to achieve the purpose of cooling the object itself. Since passive refrigeration research can be partially or completely avoided, the energy savings strategy of the cost of cooling technology driven by power plants such as fans or compressors can also reduce the combustion of environmentally harmful waste byproducts by reducing the need to burn non-renewable fuels. The development of high performance passive refrigeration materials or structures has been actively engaged by many researchers.

Liquid metal, as a unique advanced material with high fluidity, high conductivity and low toxicity, has been extensively and deeply studied in the fields of 3D printing, printed electronics, wearable skin electronics, biomedical devices, etc. due to its flexibility and stretchability. The liquid metal has extremely high reflection performance to full-band electromagnetic waves, the application of the liquid metal in the aspect of energy is generally limited in the aspects of heat conduction and heat convection heat dissipation at present, and the application of the liquid metal in the field of heat dissipation is rarely researched.

In view of this, the invention is particularly proposed.

Disclosure of Invention

The invention aims to provide a liquid metal flexible composite film and a preparation method and application thereof.

Specifically, the invention provides the following technical scheme:

the invention provides a liquid metal flexible composite film, which sequentially comprises the following components from top to bottom:

a high-emissivity layer;

a liquid metal layer;

and packaging the protective layer.

The invention finds that the high-radiation layer can transmit electromagnetic waves with visible light and near infrared wavelength, and has high radiation characteristic to the thermal infrared band of the atmospheric window. The liquid metal layer has high reflectivity to visible light and near infrared wavelength electromagnetic waves, so that the visible light and near infrared wavelength electromagnetic waves transmitted from the high radiation layer are reflected to the high radiation layer, and the high transmissivity of the high radiation layer can ensure that the visible light and near infrared wavelength electromagnetic waves reflected from the liquid metal layer are reflected to the atmosphere. Meanwhile, the liquid metal layer also has good heat conduction property, and can transfer the heat of the passive refrigeration space to the high radiation layer so as to radiate the space. By compounding the liquid metal layer and the high-radiation layer, the high-reflection characteristic and the high-radiation property of the liquid metal can be fully exerted, and the high-heat-conduction characteristic of the liquid metal can be exerted, so that an excellent passive refrigeration effect is realized.

Further, the material of the high-radiation layer is selected from any one of PDMS (polydimethylsiloxane), PE (polyethylene), PVF (polyvinyl fluoride), PVC (polyvinyl chloride), and TPX (poly 4-methylpentene-1).

Or the high-radiation layer is made of high-radiation micro-nano particles and transparent high polymer materials in a composite mode, and the high-radiation micro-nano particles are selected from cordierite, transition metal oxides, silicon carbide, titanium dioxide and silicon dioxideThe transparent polymer material is selected from any one of PDMS, polyethylene, cellulose, PVF, PVC, TPX and PVA (polyvinyl alcohol). As an example, the transition metal oxide may be ZnMn₂O₄、NiCr₂O₄、CoFeO₄、NiFe₂O₄And the like. Further, the particle size of the high-radiation micro-nano particles is 1 nm-500 mu m. The high-radiation micro-nano particles have high absorption characteristics on electromagnetic waves in an atmospheric window waveband, namely, the electromagnetic waves with more multi-wavelength in the atmospheric window can be radiated, so that the radiation performance of a high-radiation layer in the atmospheric window can be greatly improved by mixing the high-radiation micro-nano particles in a transparent high polymer material.

Further, the thickness of the high-radiation layer is 1 mu m-2 mm; preferably 10 to 500. mu.m.

Furthermore, the material of the liquid metal layer is selected from one or more of gallium, gallium-indium alloy, gallium-indium-tin-zinc alloy and bismuth-indium-tin-zinc alloy.

Further, the thickness of the liquid metal layer is 1 nm-500 μm; preferably 50nm to 200. mu.m.

The invention also finds that the thickness of the high-radiation layer has great influence on the reflectivity of the liquid metal flexible composite film in visible light and near infrared bands and the emissivity of the liquid metal flexible composite film in an atmospheric window, the reflectivity of the liquid metal flexible composite film in the visible light and near infrared bands is lowered due to the excessive thickness, and the emissivity of the liquid metal flexible composite film in the atmospheric window is lowered due to the too small thickness. Meanwhile, the thickness of the liquid metal layer has a great influence on the reflectivity of the liquid metal flexible composite film in visible light and near infrared bands, and the excessively thin thickness of the liquid metal can cause the electromagnetic waves in the visible light and near infrared bands to directly penetrate through the liquid metal film and cannot be reflected back to the high-radiation layer. Through a great deal of experimental research, the inventor finds that when the thicknesses of the high-radiation layer and the liquid metal layer are both in the preferred range, the obtained liquid metal flexible composite film has higher reflectivity for visible light and near infrared bands, and has lower reflectivity for an atmospheric window, namely higher emissivity, so that a more excellent passive refrigeration effect is realized.

Furthermore, the material of the sealing and protecting layer is any base material which can be coated by liquid metal, and preferably any one of PDMS, polyethylene, PVF, PVC, glass, wood board and metal sheet. The packaging protective layer mainly plays a role in protecting the liquid metal layer from overflowing and transferring heat of the passive refrigeration space to the liquid metal layer.

Further, the surface roughness of the packaging protective layer is less than Ra 6.3. Therefore, the liquid metal layer with more uniform thickness is obtained, and the liquid metal layer has higher reflectivity for the full-wave-band light wave.

Further, the thickness of the packaging protective layer is 100 mu m-10 mm. The encapsulation protective layer, the high-radiation layer and the liquid metal layer which are matched with the encapsulation protective layer in the thickness range have the advantages that the obtained liquid metal flexible composite film has more excellent passive refrigeration effect.

The invention also provides a preparation method of the liquid metal flexible composite film, which comprises the following steps:

1) forming a liquid metal layer on one surface of the high-radiation layer/the packaging protective layer by liquid-phase magnetron sputtering or spin-coating adhesion transfer printing;

2) and forming an encapsulation protective layer/a high-radiation layer on one surface of the liquid metal layer, which is far away from the high-radiation layer/the encapsulation protective layer.

Further, in step 2), an encapsulation protection layer/high-radiation layer is formed on the side, away from the high-radiation layer/encapsulation protection layer, of the liquid metal layer in a bonding or adhesion sealing manner.

Specifically, the preparation method of the liquid metal flexible composite film comprises the following steps:

1) adding liquid metal into an acid solution to remove a surface oxidation film, wherein the acid solution can be hydrochloric acid, sulfuric acid and the like, and the concentration of the acid solution is 0.1-2 mol/L;

2) immersing one surface of the processed conventional metal target material into an acid solution to contact with liquid metal, wherein the conventional metal target material can be iron, nickel, copper, silver, gold and the like, soaking for 1 min-2 h, and then taking out the metal target material to obtain the metal target material with the surface coated with a layer of liquid metal;

3) placing the metal target material with the surface coated with the liquid metal on a spin coater for spin coating, wherein the rotation speed of the spin coater is 50 r/min-10000 r/min, the running time of the spin coating is 10 s-10 min, and after the spin coating is finished, the liquid phase magnetron sputtering metal target material with the surface coated with the uniform liquid metal can be obtained, and the thickness of the liquid metal layer on the liquid phase magnetron sputtering metal target material after the spin coating is 200 nm-500 mu m;

4) placing the liquid-phase magnetron sputtering metal target material obtained in the step 3) in a magnetron sputtering instrument, taking the high-radiation layer (or the packaging protective layer) which is protected by the outermost adhesive tape and left white as a sputtering substrate, and obtaining the high-radiation layer (or the packaging protective layer) with a liquid metal layer with a certain uniform thickness, wherein the magnetron sputtering time is 10 min-24 h;

5) and removing the protective white tape on the outermost side of the high-radiation layer (or the packaging protective layer) with the liquid metal layer with a certain uniform thickness, and bonding or adhering and sealing the protective white tape with the packaging protective layer (or the high-radiation layer) to obtain the liquid metal flexible composite film. Wherein, the bonding adopts a plasma treatment process, and the bonding time is 5-60 s; the adhesion sealing adopts a glue joint mode, and the glue can be instant glue, epoxy resin bonding, anaerobic glue, UV glue (ultraviolet light curing), hot melt glue, pressure-sensitive glue, latex glue and the like.

Or, the preparation method of the liquid metal flexible composite film comprises the following steps:

1) preparing PDMS mixed solution, pouring the PDMS mixed solution into a container which is placed with a polished silicon wafer in advance, then placing the container on a heating plate at the temperature of 60-85 ℃ for baking for 2.5-0.5 h, and stripping the PDMS from the silicon wafer after PMDS is cured to obtain PDMS with an extremely smooth surface;

2) placing PDMS in a plasma processor for surface treatment, directly dipping the PDMS with the surface treated liquid metal, placing the PDMS with the liquid metal surface facing upwards on a spin coater, and performing spin coating for 10 s-10 min at the rotating speed of 50 r/min-10000 r/min to obtain a liquid metal film with the thickness of 1 mu m-5 mm;

3) the PDMS with the surface coated with the liquid metal film is attached to the high radiation layer (or the packaging protective layer), so that a uniform liquid metal layer with a thickness reduced by half can be obtained on the high radiation layer (or the packaging protective layer).

4) And removing the protective white tape on the outermost side of the high-radiation layer (or the packaging protective layer) with the liquid metal layer with a certain uniform thickness, and bonding or adhering and sealing the protective white tape with the packaging protective layer (or the high-radiation layer) to obtain the liquid metal flexible composite film. Wherein, the bonding adopts a plasma treatment process, and the bonding time is 5-60 s; the adhesion sealing adopts a glue joint mode, and the glue can be instant glue, epoxy resin bonding, anaerobic glue, UV glue (ultraviolet light curing), hot melt glue, pressure-sensitive glue, latex glue and the like.

The invention also provides the application of the liquid metal flexible composite film in the aspect of passive radiation refrigeration.

The invention has the beneficial effects that:

the liquid metal flexible composite film provided by the invention not only reflects a great part of sunlight and near infrared waves back to the atmosphere, but also can exchange heat with outer space (the average temperature in the space is-270.3 ℃) through high radiation of an atmospheric window, thereby realizing the refrigeration effect of a passive refrigeration space. The liquid metal flexible composite film provided by the invention can be applied to the surfaces of refrigerating spaces of various house buildings and the like, and has a great application space for the fields of building energy conservation and the like.

Drawings

Fig. 1 is a schematic structural diagram of a liquid metal flexible composite film provided by the invention.

Fig. 2 shows the principle of radiation refrigeration of the liquid metal flexible composite film provided by the invention.

Fig. 3 shows the basic principle of passive radiation cooling.

Reference numerals: 1. a high-emissivity layer; 2. a liquid metal layer; 3. and packaging the protective layer.

Detailed Description

The terms "upper" and "lower" are used in an orientation or positional relationship shown in the drawings only for convenience in describing the present invention and for simplicity in description, and do not indicate or imply that the referenced devices or elements must have a particular orientation, be constructed and operated in a particular orientation, and thus should not be construed as limiting the present invention. The examples do not indicate any specific techniques or conditions, and the reagents or apparatuses used are not indicated by manufacturers in the literature of the art or by the specifications of the products, and are all conventional products commercially available.

The following examples are intended to illustrate the invention but are not intended to limit the scope of the invention.

The liquid metal is prepared according to the following technical scheme, taking GaIn24.5 as an example:

(a) the method comprises the following steps of mixing metal gallium with purity of 99.9% and indium according to a mass ratio of 75.5: 24.5 weighing and then putting into a beaker;

(b) placing the beaker on a heating constant-temperature magnetic stirrer, setting the heating temperature to 80 ℃, setting the rotating speed to 200r/min, and simultaneously placing a magnetic stirrer;

(c) after the indium block is dissolved, the metal liquid is continuously stirred for 10min, so that the indium block and the metal liquid are completely mixed into a homogeneous phase.

Other liquid metal alloys can be prepared by the same operation by changing the mass ratio of the metal gallium to the metal indium.

Example 1

A liquid metal flexible composite film is composed of a sandwich structure of an upper high-radiation layer 1, a middle liquid metal layer 2 and a lower packaging protective layer 3.

Wherein, the high radiation layer: PDMS with a thickness of 100 μm;

liquid metal layer: liquid metal GaIn24.5 with the thickness of 50 nm;

packaging a protective layer: PDMS with a thickness of 200 μm.

The preparation method of the liquid metal flexible composite film comprises the following steps:

1) adding liquid metal GaIn24.5 into an acid solution to remove a surface oxide film, wherein the acid solution is hydrochloric acid solution with the concentration of 1 mol/L;

2) immersing one surface of the processed copper target material into a hydrochloric acid solution to contact with liquid metal, and taking out the copper target material after immersing for 10min to obtain the copper target material with the surface coated with a layer of liquid metal;

3) placing the copper target material with the surface coated with the liquid metal on a spin coater for spin coating, wherein the rotation speed of the spin coater is 500r/min, the running time of the spin coating is 60s, obtaining a liquid-phase magnetron sputtering copper target material with the surface coated with uniform liquid metal after the spin coating is finished, and the thickness of a liquid metal layer on the liquid-phase magnetron sputtering metal target material after the spin coating is 50 microns;

4) placing the liquid-phase magnetron sputtering copper target material obtained in the step 3) in a magnetron sputtering instrument, taking the PDMS packaging protective layer protected by the outermost side adhesive tape and left white as a sputtering substrate, and performing magnetron sputtering for 20min to obtain a packaging protective layer with a liquid metal layer with the thickness of 50 nm;

5) and removing the protective tape on the outermost side of the packaging protective layer, bonding and sealing the protective tape and PDMS of the high-radiation layer, wherein the bonding adopts a plasma treatment process, and the bonding time is 20s, so that the liquid metal flexible composite film can be obtained.

The composite reflectivity of the liquid metal flexible composite film of the embodiment to visible light and near infrared wave band is more than 85%, the radiance to thermal infrared wave band of an atmospheric window is more than 85%, and the overall refrigeration power is about 50W/m under the outdoor environment at 25 DEG C²。

Example 2

A liquid metal flexible composite film is composed of a sandwich structure of an upper high-radiation layer 1, a middle liquid metal layer 2 and a lower packaging protective layer 3.

Wherein, the high radiation layer: polyethylene having a thickness of 50 μm;

liquid metal layer: liquid metal Ga having a thickness of 250 nm;

packaging a protective layer: polyethylene having a thickness of 100 μm.

The preparation method of the liquid metal flexible composite film comprises the following steps:

1) weighing 50g of polyethylene particles, adding the polyethylene particles into a stainless steel container, then putting the container into a heating box at 120 ℃, and heating for 1 hour until the particles are completely melted;

2) after polyethylene particles are melted, pouring the melted polyethylene into a polished silicon wafer, putting the polished silicon wafer on a spin coater for spin coating, wherein the rotation speed of the spin coater is 5000r/min, and the spin coating is operated for 1min, so that a polyethylene film with the thickness of 50 mu m can be obtained and used as an upper high-radiation layer;

3) then after the polyethylene is completely solidified, peeling the polyethylene film from the silicon wafer to obtain the polyethylene film with the thickness of 50 mu m and two uniform and smooth surfaces;

4) repeating the step 2) and the step 3), wherein the rotating speed of a spin coater is 2000r/min, and the spin coating is carried out for 1min, so that a polyethylene film with the thickness of 100 mu m can be obtained and used as a lower packaging protective layer;

5) preparing PDMS mixed solution, pouring the PDMS mixed solution into a container which is placed with a polished silicon wafer in advance, then placing the container on a heating plate at 75 ℃ for baking for about 1.5h, and stripping the PDMS from the silicon wafer after PMDS is cured to obtain PDMS with uniform and smooth two surfaces;

6) placing PDMS in a plasma processor for surface treatment, directly dipping the PDMS with the surface treated liquid metal, placing the PDMS with the liquid metal surface facing upwards on a spin coating machine, and performing spin coating for 5min at the rotating speed of 10000r/min to obtain a liquid metal film with the thickness of 2 μm;

7) adhering PDMS with the surface coated with the liquid metal film and a lower packaging protective layer polyethylene film for 3 times to obtain a lower packaging protective layer with the surface having a 250nm thick liquid metal film;

8) and removing the protective white tape on the outermost side of the lower packaging protective layer with the surface having the liquid metal film with the thickness of 250nm, and bonding or bonding and sealing the protective white tape and the upper high-radiation layer by using polyethylene glue to obtain the liquid metal flexible composite film.

The composite reflectivity of the liquid metal flexible composite film of the embodiment to visible light and near infrared wavelength bands is more than 80%, and the radiance to thermal infrared band of an atmospheric window is more than 85%. Under the outdoor environment of 25 ℃, the integral refrigeration power is about 40W/m²。

Example 3

The liquid metal flexible composite film of the present embodiment is different from embodiment 1 only in that the thickness of the liquid metal layer is different. In this embodiment, the thickness of the liquid metal layer is 10nm, and other parameters and materials are not changed.

The composite reflectivity of the liquid metal flexible composite film of the embodiment to visible light and near infrared wave band is more than 40%, the radiance to thermal infrared wave band of an atmospheric window is more than 85%, and the overall refrigeration power is about 1W/m under the outdoor environment at 25 DEG C²。

Example 4

The liquid metal flexible composite film of the present embodiment is different from embodiment 1 only in the thickness of the high radiation layer. The thickness of the high-radiation layer in this example is 1 mm. Other parameters and materials are unchanged.

The composite reflectivity of the liquid metal flexible composite film of the embodiment to visible light and near infrared wavelength bands is larger than 50%, and the radiance to thermal infrared band of an atmospheric window is larger than 90%. The overall refrigeration power is about 3W/m under the outdoor environment at 25 DEG C²。

The above examples are only for describing the preferred embodiments of the present invention, and are not intended to limit the scope of the present invention, and various modifications and improvements made to the technical solution of the present invention by those skilled in the art without departing from the spirit of the present invention should fall within the protection scope defined by the claims of the present invention.