CN114688905A - Flexible thermal diode, and preparation method and application thereof - Google Patents
Flexible thermal diode, and preparation method and application thereof Download PDFInfo
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F28—HEAT EXCHANGE IN GENERAL
- F28D—HEAT-EXCHANGE APPARATUS, NOT PROVIDED FOR IN ANOTHER SUBCLASS, IN WHICH THE HEAT-EXCHANGE MEDIA DO NOT COME INTO DIRECT CONTACT
- F28D15/00—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies
- F28D15/02—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes
- F28D15/04—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure
- F28D15/046—Heat-exchange apparatus with the intermediate heat-transfer medium in closed tubes passing into or through the conduit walls ; Heat-exchange apparatus employing intermediate heat-transfer medium or bodies in which the medium condenses and evaporates, e.g. heat pipes with tubes having a capillary structure characterised by the material or the construction of the capillary structure
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- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
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Abstract
The invention discloses a flexible thermal diode, a preparation method and application thereof. The flexible thermal diode comprises a first phase change composite film and a second phase change composite film which have different thermal conductivity temperature coefficients, wherein the first phase change composite film and the second phase change composite film are in thermal contact with each other, the first phase change composite film and the second phase change composite film are stable in shape and flexible before and after phase change, the thermal conductivity of the first phase change composite film and the thermal conductivity of the second phase change composite film are opposite to each other along with the temperature change, and the phase change temperature difference value of the first phase change composite film and the second phase change composite film is less than 10 ℃; the surface wettability of the first phase change composite film is opposite to that of the second phase change composite film, and the interface is incompatible. Compared with the traditional thermal diode, the flexible thermal diode provided by the invention can be conformally attached to a curved surface or an irregular surface needing thermal management, the application field of the phase change film is expanded, and meanwhile, the practicability of the thermal diode is improved.
Description
Technical Field
The invention belongs to the technical field of heat management materials, and particularly relates to a flexible thermal diode, and a preparation method and application thereof.
Background
Thermal diodes, like electronic diodes, also have two poles, a temperature input and a temperature output, respectively. When one pole is connected with the hot end and the other pole is connected with the cold end, the heat flow is JfAfter the positions of the cold end and the hot end are exchanged, the heat flow is JrIf J isfAnd JrNumber ofEquality, breaking the fourier law, this phenomenon is called thermal rectification and this component is called thermal diode (see patent CN 111895827A). Although the current thermal management material can simultaneously have the functions of heat conduction and energy storage (CN111439001A), the thermal rectification function of the thermal diode can better control heat transfer, and the thermal diode has wide application prospects in many fields.
The thermal diode can realize thermal rectification, the thermal conductivity and temperature coefficient of two pole materials are required to be different, preferably, the trend of the thermal conductivity changing along with the temperature is opposite, the heat transfer of one pole material is good in a high-temperature state, and the heat transfer of the other pole material is poor in a low-temperature state; the other pole has good heat transfer at low temperature and poor heat transfer at high temperature. Thus, heat transfer in the forward direction and the reverse direction is asymmetric, and heat rectification is generated. Bipolar materials meeting the above requirements are the key to building thermal diodes. The thermal conductivity of alloy materials and metal oxides generally changes along with the change of temperature (Sci.Technol.adv.Mater.2014,15,064801; appl.Phys.Lett.2009,95,171905), and can be used for preparing thermal diodes, however, the change of the thermal conductivity of the materials needs a large temperature range to be realized, the working temperature range is also an extreme temperature, and the materials cannot be widely applied to actual production and life.
The electronic component can be subjected to heat management by utilizing the characteristic that the phase change material absorbs or releases a large amount of latent heat during phase transition (CN109449131A), meanwhile, the heat conductivity of the phase change material is suddenly changed in the phase transition process (adv. Mater.2019,31,1806518), and the temperature interval of the transition is narrow, so that two phase change materials with the phase transition temperatures close to each other and the heat conductivity opposite to the temperature change are selected to be assembled into the thermal diode, the working temperature difference is small, and the thermal rectification ratio is large. However, the phase change thermal diodes reported at present are all made by encapsulating phase change materials in plastic tubes, and the assembled thermal diodes are all rigid (mater. horiz.,2015,2, 125-.
Disclosure of Invention
The invention mainly aims to provide a flexible thermal diode, a preparation method and application thereof, so as to overcome the defects of the prior art.
In order to achieve the purpose, the technical scheme adopted by the invention comprises the following steps:
the embodiment of the invention provides a flexible thermal diode, which comprises a first phase change composite film and a second phase change composite film with different thermal conductivity temperature coefficients, wherein the first phase change composite film and the second phase change composite film are in thermal contact with each other, the first phase change composite film and the second phase change composite film are stable in shape and flexible before and after phase change, the thermal conductivity of the first phase change composite film and the thermal conductivity of the second phase change composite film are opposite to each other along with the temperature change, and the phase change temperature difference value of the first phase change composite film and the second phase change composite film is less than 10 ℃; the surface wettability of the first phase change composite film is opposite to that of the second phase change composite film, and the interface is incompatible.
The embodiment of the present invention further provides a method for preparing the flexible thermal diode, which includes:
loading the negative temperature coefficient phase change material and the positive temperature coefficient phase change material into the aerogel film respectively so as to prepare a first phase change composite film and a second phase change composite film respectively;
and assembling the first phase change composite film and the second phase change composite film to form the flexible thermal diode.
The embodiment of the invention also provides application of the flexible thermal diode in the field of thermal management.
Compared with the prior art, the invention has the beneficial effects that:
(1) the flexible thermal diode provided by the invention has good flexibility, the rigidity tradition of the traditional thermal diode is subverted, and meanwhile, the flexible thermal diode has small working temperature difference and large thermal rectification ratio;
(2) the flexible thermal diode provided by the invention has the advantages that the preparation method and the assembly process are simple, and the large-scale production is easy to carry out;
(3) the flexible thermal diode provided by the invention has wide application prospect, and can be conformally attached to a curved surface or an irregular surface needing thermal management.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only some embodiments described in the present invention, and for those skilled in the art, other drawings can be obtained according to the drawings without creative efforts.
FIG. 1 is an optical photograph of the flexible thermal diode in an exemplary embodiment of the invention;
FIG. 2 is a schematic view showing the structure of a flexible thermal diode obtained in example 1 of the present invention;
FIG. 3 is a stress-strain curve of the flexible thermal diode obtained in example 2 of the present invention in a tensile mode;
FIGS. 4a to 4b are graphs showing the variation of thermal conductivity with temperature of the C20/PI phase change composite film and the PNIPAM/PI phase change composite film obtained in example 4 of the present invention, respectively;
FIGS. 5 a-5 b are photographs of the hydrophobic corners of the C20/Cellulose phase change composite film and the PNIPAM/Cellulose phase change composite film obtained in example 5 of the present invention;
FIG. 6 is a graph showing the variation of the heat flux in the forward and reverse directions of the flexible thermal diode according to example 9 of the present invention with the temperature difference;
FIG. 7 is a schematic diagram showing the thermal rectification ratio of the flexible thermal diode obtained in example 10 of the present invention;
fig. 8 is a schematic view of an application of the flexible thermal diode in embodiment 11 of the present invention.
Detailed Description
In view of the defects of the prior art, the inventor of the present invention has made long-term research and extensive practice to provide the technical scheme of the present invention, wherein the thermal conductivity of the phase change material in a narrow temperature interval is changed greatly near the phase change temperature, when two phase change materials are screened out, the phase change temperature is close to that of the two phase change materials, the thermal conductivity temperature coefficients are opposite, and the two phase change materials are respectively encapsulated in two high-strength flexible aerogel films with opposite surface wettability. The two phase-change composite films are assembled into a thermal diode, and the thermal diode has good flexibility, small working temperature difference and excellent thermal rectification performance. Therefore, the phase change film can be conformally attached to a curved surface or an irregular surface needing heat management, the application field of the phase change film is expanded, and meanwhile the practicability of the thermal diode is improved.
The technical solutions of the present invention will be described clearly and completely below, and it should be apparent that the described embodiments are some, but not all, embodiments of the present invention. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
One aspect of the embodiments of the present invention provides a flexible thermal diode, which includes a first phase change composite film and a second phase change composite film having different thermal conductivity temperature coefficients, wherein the first phase change composite film and the second phase change composite film are in thermal contact with each other, the first phase change composite film and the second phase change composite film are stable in shape and flexible before and after phase change, the thermal conductivity of the first phase change composite film and the second phase change composite film is in an opposite trend along with temperature change, and the phase change temperature difference between the first phase change composite film and the second phase change composite film is less than 10 ℃; the surface wettability of the first phase change composite film is opposite to that of the second phase change composite film, and the interface is incompatible.
Furthermore, the working temperature difference of the flexible thermal diode is small.
Further, the phase transition temperatures of the first phase transition composite film and the second phase transition composite film are close to each other.
In some more specific embodiments, the thermal rectification ratio of the flexible thermal diode is 1.5-3.0.
In some more specific embodiments, the interface of the first phase change composite film and the second phase change composite film in the flexible thermal diode is incompatible.
Further, the first phase-change composite film is obtained by loading an aerogel film with a negative temperature coefficient phase-change material.
Furthermore, the load capacity of the negative temperature coefficient phase change material in the first phase change composite film is 30 wt% -98 wt%.
Further, the second phase change composite film is obtained by loading a positive temperature coefficient phase change material on an aerogel film.
Furthermore, the loading amount of the positive temperature coefficient phase change material in the second phase change composite film is 30-98 wt%.
Further, the contact angle between the surface of the first phase-change composite film and water is 100-180 degrees.
Further, the contact angle between the surface of the second phase change composite film and water is 0-80 degrees. Further, the thickness ratio of the first phase change composite film to the second phase change composite film is 1: 10-10: 1.
In some more specific embodiments, the thermal conductivities of the negative temperature coefficient phase change material and the positive temperature coefficient phase change material at the phase change point have opposite trends along with the change of the temperature.
Further, the thermal conductivity of the negative temperature coefficient phase change material is reduced along with the increase of the temperature.
Further, the negative temperature coefficient phase change material includes any one or a combination of two or more of paraffin (paraffin), hexadecane (C16), octadecane (C18), eicosane (C20), and Polyethylene (PE), and is not limited thereto.
Further, the thermal conductivity of the positive temperature coefficient phase change material increases with the increase of the temperature.
Further, the positive temperature coefficient phase change material comprises poly (N-isopropylacrylamide) (PNIPAM) aqueous solution and/or vanadium dioxide (VO)2)。
Further, the concentration of the poly (N-isopropylacrylamide) (PNIPAM) aqueous solution is 10 wt% to 50 wt%.
In some more specific embodiments, the aerogel film is a flexible self-supporting aerogel film.
Further, the aerogel film has a tensile strength of 1MPa or more.
Further, the aerogel film has a porosity of 60% or more.
Further, the thermal conductivity of the aerogel film is below 0.1W/m.K.
Further, the aerogel film includes any one or a combination of two or more of a Kevlar (Kevlar) aerogel film, a Polyimide (PI) aerogel film, a Cellulose (Cellulose) aerogel film, and a poly-p-Phenylene Benzobisoxazole (PBO) aerogel film, but is not limited thereto.
In some more specific embodiments, referring to fig. 1, the flexible thermal diode includes a first phase change composite film and a second phase change composite film having different thermal conductivity temperature coefficients; the two phase-change composite films are respectively obtained by loading a negative temperature coefficient phase-change material and a positive temperature coefficient phase-change material on a high-strength flexible aerogel film.
Another aspect of the present invention also provides a method for manufacturing the flexible thermal diode, including:
loading the negative temperature coefficient phase change material and the positive temperature coefficient phase change material into the holes of the aerogel film respectively so as to prepare a first phase change composite film and a second phase change composite film respectively;
and assembling the first phase change composite film and the second phase change composite film to form the flexible thermal diode.
Further, the aerogel film is a high strength, flexible, self-supporting aerogel film.
In some more specific embodiments, the preparation method specifically comprises: and loading the molten or solution-state negative temperature coefficient phase change material into the aerogel film by utilizing capillary action to prepare the first phase change composite film.
In some more specific embodiments, the preparation method specifically comprises: and loading the molten or liquid positive temperature coefficient phase change material into the aerogel film by utilizing capillary action, or compounding the positive temperature coefficient phase change material and the aerogel film by adopting an in-situ growth mode, thereby obtaining a second phase change composite film.
In some more specific embodiments, the preparation method comprises: and jointing the first phase change composite film and the second phase change composite film to form the flexible thermal diode.
Further, the preparation method specifically comprises the following steps: and enabling the first phase change composite film and the second phase change composite film to be in thermal contact with each other, and further assembling to form the flexible thermal diode.
In some more specific embodiments, the preparation method further comprises: firstly, densifying the aerogel film.
Further, the densification processing method includes any one of a hot pressing method and a cold pressing method, and is not limited thereto.
Further, the densification process may improve the strength and flexibility of the aerogel film.
Another aspect of an embodiment of the present invention also provides a use of the aforementioned flexible thermal diode in the field of thermal management.
The flexible thermal diode provided by the invention is simple in preparation and assembly processes and easy for large-scale production.
Further, use of the flexible thermal diode in thermal management of curved or irregularly shaped surfaces.
By the technical scheme, the flexible thermal diode provided by the invention is formed by mutually thermally contacting two flexible phase change composite films with different thermal conductivity temperature coefficients. The two phase-change composite films are respectively obtained by loading a phase-change material on an aerogel film with excellent mechanical property, and have stable forms and flexibility before and after phase change; the phase transition temperature is close; the thermal conductivity has opposite trend along with the temperature; the surface wetting properties are reversed. Compared with the traditional thermal diode, the flexible thermal diode provided by the invention can be conformally attached to a curved surface or an irregular surface needing thermal management, the application field of the phase change film is expanded, and meanwhile, the practicability of the thermal diode is improved.
The technical solutions of the present invention are further described in detail below with reference to several preferred embodiments and the accompanying drawings, which are implemented on the premise of the technical solutions of the present invention, and a detailed implementation manner and a specific operation process are provided, but the scope of the present invention is not limited to the following embodiments.
The experimental materials used in the examples used below were all available from conventional biochemical reagents companies, unless otherwise specified.
Example 1
Paraffin (paraffin) and PNIPAM aqueous solution are respectively selected as a negative temperature coefficient phase change material and a positive temperature coefficient phase change material with opposite thermal conductivity and temperature coefficients, then the negative temperature coefficient phase change material and the positive temperature coefficient phase change material are respectively loaded into Kevlar aerogel films with different thicknesses, a paraffin/Kevlar phase change composite film and a PNIPAM/Kevlar phase change composite film are respectively obtained, the thickness ratio of the paraffin/Kevlar phase change composite film to the PNIPAM/Kevlar phase change composite film is 1:10, the paraffin/Kevlar phase change composite film and the PNIPAM/Kevlar phase change composite film are cut into the same size, and are bonded together to form the flexible thermal diode. Fig. 2 shows a schematic diagram of the flexible thermal diode structure obtained in this embodiment, and other parameters are shown in table 1.
Example 2
Paraffin (paraffin) and PNIPAM aqueous solution are respectively selected as a negative temperature coefficient phase change material and a positive temperature coefficient phase change material with opposite thermal conductivity and temperature coefficients, then the negative temperature coefficient phase change material and the positive temperature coefficient phase change material are respectively loaded into a densified Kevlar aerogel film, a paraffin/D-Kevlar phase change composite film and a PNIPAM/D-Kevlar phase change composite film are respectively obtained, the thickness ratio of the paraffin/D-Kevlar phase change composite film to the PNIPAM/D-Kevlar phase change composite film is 1:5, the paraffin/D-Kevlar phase change composite film and the PNIPAM/D-Kevlar phase change composite film are cut into the same size, and are attached together to be assembled into the flexible thermal diode. See table 1 for details of the parameters.
Example 3
C20 and PNIPAM aqueous solutions are selected as a negative temperature coefficient phase change material and a positive temperature coefficient phase change material with opposite thermal conductivity temperature coefficients respectively, and then the materials are loaded into a densified Kevlar aerogel film and an undensified Kevlar aerogel film respectively to obtain a C20/D-Kevlar phase change composite film and a PNIPAM/Kevlar phase change composite film respectively, wherein the thickness ratio of the two is 1: 6. Cutting the two into the same size, sticking them together, assembling them into flexible thermal diode. Fig. 3 shows the tensile strength curve of the flexible thermal diode obtained in this example, and other parameters are shown in table 1.
Example 4
C20 and PNIPAM aqueous solutions are selected as a negative temperature coefficient phase change material and a positive temperature coefficient phase change material with opposite thermal conductivity and temperature coefficients respectively, and then the materials are loaded into PI aerogel films with different thicknesses respectively to obtain a C20/PI phase change composite film and a PNIPAM/PI phase change composite film, wherein the thickness ratio of the C20/PI phase change composite film to the PNIPAM/PI phase change composite film is 1: 6. Cutting the two into the same size, attaching the two together, and assembling the flexible thermal diode. Fig. 4 shows the thermal conductivity curves of the C20/PI phase change composite film and the PNIPAM/PI phase change composite film with temperature in the flexible thermal diode obtained in this example, and other parameters are shown in table 1.
Example 5
Selecting C20 and PNIPAM aqueous solutions as a negative temperature coefficient phase change material and a positive temperature coefficient phase change material with opposite thermal conductivity and temperature coefficients, respectively loading the materials into Cellulose aerogel films with different thicknesses to respectively obtain a C20/Cellulose phase change composite film and a PNIPAM/Cellulose phase change composite film, wherein the thickness ratio of the C20/Cellulose phase change composite film to the PNIPAM/Cellulose phase change composite film is 1:6, cutting the two into the same size, pasting the two together, and assembling the two into a flexible thermal diode. Fig. 5 shows the surface wettability of the bipolar material C20/Cellulose phase change composite film and PNIPAM/Cellulose phase change composite film of the flexible thermal diode obtained in the present embodiment, and other parameters are shown in table 1.
Example 6
Selecting C18 and PNIPAM aqueous solutions as a negative temperature coefficient phase change material and a positive temperature coefficient phase change material with opposite thermal conductivity and temperature coefficients, respectively loading the materials into a densified Kevlar aerogel film and an undensified Kevlar aerogel film to respectively obtain a C18/D-Kevlar phase change composite film and a PNIPAM/Kevlar phase change composite film with a thickness ratio of 1:6, cutting the two into the same size, pasting the two together, and assembling the two into a flexible thermal diode. See table 1 for other parameters.
Example 7
Selection of PE and VO2Respectively as heat conductionNegative temperature coefficient phase change material and positive temperature coefficient phase change material with opposite temperature coefficient of rate, PE is loaded into PBO aerogel film by solution filling method, VO2Loading the mixture into a PBO aerogel film by an in-situ growth method to respectively obtain a PE/PBO phase-change composite film and VO2The thickness ratio of the/PBO phase-change composite film to the PBO phase-change composite film is 10:1, the PBO phase-change composite film and the PBO phase-change composite film are cut into the same size, and are attached together to assemble the flexible thermal diode. See table 1 for parameters.
Example 8
Selection of PE and VO2Respectively as a negative temperature coefficient phase-change material and a positive temperature coefficient phase-change material with opposite thermal conductivity and temperature coefficients, loading PE into the PBO aerogel film by a solution filling method, and VO2Loading the mixture into a PBO aerogel film by an in-situ growth method to respectively obtain a PE/PBO phase-change composite film and VO2The thickness ratio of the/PBO phase-change composite film to the PBO phase-change composite film is 2.5:1, the PBO phase-change composite film and the PBO phase-change composite film are cut into the same size, and the PBO phase-change composite film are attached together to assemble the flexible thermal diode. See table 1 for parameters.
Example 9
Selecting C18 and PNIPAM aqueous solutions as a negative temperature coefficient phase change material and a positive temperature coefficient phase change material with opposite thermal conductivity and temperature coefficients, respectively loading the materials into a densified Kevlar aerogel film and a densified Cellulose aerogel film to respectively obtain a C18/D-Kevlar phase change composite film and a PNIPAM/Cellulose phase change composite film with a thickness ratio of 1:6, cutting the two into the same size, pasting the two together, and assembling the flexible thermal diode. Fig. 6 shows the variation curve of the heat flux in the forward and reverse directions of the flexible thermal diode obtained in this embodiment with the temperature difference between the two poles, and other parameters are shown in table 1.
Example 10
Selecting C16 and PNIPAM aqueous solutions as a negative temperature coefficient phase change material and a positive temperature coefficient phase change material with opposite thermal conductivity temperature coefficients, and then respectively loading the materials into PI aerogel films and Cellulose aerogel films with different thicknesses to respectively obtain a C20/PI phase change composite film and a PNIPAM/Cellulose phase change composite film, wherein the thickness ratio of the two films is 1: 6. Cutting the two into the same size, bonding together, and assembling into the thermal diode. Fig. 7 shows the thermal rectification ratio of the flexible thermal diode obtained in the present embodiment, and other parameters are shown in table 1.
TABLE 1 Structure and Performance parameters of the flexible thermal diode obtained in examples 1-10
Example 11
C20/D-Kevlar is used as a first phase change composite film, PNIPAM/Kevlar is used as a second phase change composite film, the thickness ratio of the first phase change composite film to the second phase change composite film is 1:6, the first phase change composite film and the second phase change composite film are cut into the same size, and the first phase change composite film and the second phase change composite film are bonded together to form the flexible thermal diode. The second phase change composite film is outside, and including the first phase change composite film, attached to the water pipe surface, when ambient temperature is higher than the temperature of water pipe normal water, can heat water, when ambient temperature is less than the temperature of water pipe normal water, can keep warm to water, realizes the function of thermal management. Fig. 8 shows a schematic diagram of an application of the flexible thermal diode in the present embodiment.
Through the embodiments 1 to 11, it can be found that the thermal diode obtained by the technical scheme of the invention has good flexibility, smaller working temperature difference and excellent thermal rectification performance, is simple in preparation and assembly process, is easy for large-scale production, and can be conformally attached to a curved surface or an irregular surface needing thermal management.
In addition, the inventors of the present invention have also made experiments with other raw materials, process operations, and process conditions described in the present specification with reference to the above examples, and have obtained preferable results.
The aspects, embodiments, features and examples of the present invention should be considered as illustrative in all respects and not intended to be limiting of the invention, the scope of which is defined only by the claims. Other embodiments, modifications, and uses will be apparent to those skilled in the art without departing from the spirit and scope of the claimed invention.
The use of headings and chapters in this disclosure is not meant to limit the disclosure; each section may apply to any aspect, embodiment, or feature of the disclosure.
Throughout this specification, where a composition is described as having, containing, or comprising specific components or where a process is described as having, containing, or comprising specific process steps, it is contemplated that the composition of the present teachings also consist essentially of, or consist of, the recited components, and the process of the present teachings also consist essentially of, or consist of, the recited process steps.
It should be understood that the order of steps or order in which certain actions are performed is not critical, so long as the present teachings remain operable. Further, two or more steps or actions may be performed simultaneously.
While the invention has been described with reference to illustrative embodiments, it will be understood by those skilled in the art that various other changes, omissions and/or additions may be made and substantial equivalents may be substituted for elements thereof without departing from the spirit and scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from its scope. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, unless specifically stated any use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.
Claims (10)
1. A flexible thermal diode is characterized by comprising a first phase change composite film and a second phase change composite film which have different thermal conductivity temperature coefficients, wherein the first phase change composite film and the second phase change composite film are in thermal contact with each other, the first phase change composite film and the second phase change composite film are stable in shape and flexible before and after phase change, the thermal conductivity of the first phase change composite film and the thermal conductivity of the second phase change composite film are opposite to each other along with the temperature change, and the phase change temperature difference of the first phase change composite film and the second phase change composite film is less than 10 ℃; the surface wettability of the first phase change composite film is opposite to that of the second phase change composite film, and the interface is incompatible.
2. The flexible thermal diode of claim 1, wherein: the thermal rectification ratio of the flexible thermal diode is 1.5-3.0;
and/or the first phase-change composite film is obtained by loading an aerogel film with a negative temperature coefficient phase-change material; preferably, the loading amount of the negative temperature coefficient phase change material in the first phase change composite film is 30-98 wt%;
and/or the second phase change composite film is obtained by loading a positive temperature coefficient phase change material on an aerogel film, preferably, the loading amount of the positive temperature coefficient phase change material in the second phase change composite film is 30-98 wt%;
and/or the contact angle between the surface of the first phase-change composite film and water is 100-180 degrees;
and/or the contact angle of the surface of the second phase change composite film and water is 0-80 degrees;
and/or the thickness ratio of the first phase change composite film to the second phase change composite film is 1: 10-10: 1.
3. The flexible thermal diode of claim 2, wherein: the heat conductivity of the negative temperature coefficient phase change material and the positive temperature coefficient phase change material at a phase change point is in an opposite trend along with the temperature change;
and/or the negative temperature coefficient phase change material comprises any one or the combination of more than two of paraffin, hexadecane, octadecane, eicosane and polyethylene;
and/or the positive temperature coefficient phase change material comprises a poly (N-isopropylacrylamide) aqueous solution and/or vanadium dioxide; preferably, the concentration of the aqueous solution of poly (N-isopropylacrylamide) is 10 wt% to 50 wt%.
4. The flexible thermal diode of claim 2, wherein: the aerogel film is a flexible self-supporting aerogel film;
and/or the aerogel film has a tensile strength of 1MPa or more, a porosity of 60% or more, and a thermal conductivity of 0.1W/m.K or less.
5. The flexible thermal diode of claim 2, wherein: the aerogel film comprises any one or the combination of more than two of Kevlar aerogel film, polyimide aerogel film, cellulose aerogel film and poly-p-phenylene benzobisoxazole aerogel film.
6. A method of manufacturing a flexible thermal diode according to any of claims 1 to 5, comprising:
loading the negative temperature coefficient phase change material and the positive temperature coefficient phase change material into the holes of the aerogel film respectively so as to prepare a first phase change composite film and a second phase change composite film respectively;
and assembling the first phase change composite film and the second phase change composite film to form the flexible thermal diode.
7. The preparation method according to claim 6, characterized by specifically comprising:
loading a molten or liquid-state negative temperature coefficient phase change material into the aerogel film by utilizing capillary action to prepare a first phase change composite film;
and/or the preparation method specifically comprises the following steps: and loading the molten or liquid positive temperature coefficient phase change material into the aerogel film by utilizing capillary action, or compounding the positive temperature coefficient phase change material and the aerogel film by adopting an in-situ growth mode, thereby obtaining a second phase change composite film.
8. The production method according to claim 6, characterized by comprising: the first phase change composite film and the second phase change composite film are attached to form the flexible thermal diode;
and/or the preparation method specifically comprises the following steps: and thermally contacting the first phase change composite film and the second phase change composite film with each other, and further assembling to form the flexible thermal diode.
9. The method of claim 6, further comprising: firstly, densifying the aerogel film, wherein the densifying method comprises a hot pressing method and/or a cold pressing method.
10. Use of a flexible thermal diode according to any one of claims 1 to 5 in the field of thermal management; preferably the use of said flexible thermal diode in thermal management of curved or irregularly shaped surfaces.
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