Intelligent light-heat film with both sunlight reflection and adjustable heat emission characteristics and application thereof

Abstract

The application provides a novel intelligent light-heat film with both sunlight reflection and adjustable heat emission characteristics and an application thereof, and a film layer structure of the film comprises four parts of a sunlight reflection layer, a heat emission modulation layer, a gel electrolyte and a counter electrode. The sunlight reflection layer is mainly an infrared transparent polymer or a composite film layer of the infrared transparent polymer and inorganic fillers, the heat emission modulation layer is carbon materials such as carbon nanotubes, graphene and conductive carbon black coated on a porous polymer film, the gel electrolyte is a polymer gel based on an ionic liquid, and the counter electrode has the same structure as the heat emission modulation layer. The film is mainly prepared by using inexpensive and large-area preparation processes such as spraying and blade coating, and on the basis of high sunlight reflection, the emissivity can be controlled and modulated according to different requirements of the environment, and the film can be applied to fields such as building surface energy saving, radiant cooling and infrared camouflage. The film has fast response speed, simple preparation mode and can realize preparation of low-cost and large-area films.

Description

Technical Field

[0001] This invention belongs to the field of new materials technology, specifically relating to a novel intelligent photothermal film with both solar reflection and adjustable thermal emission characteristics and its applications. This film can achieve controllable modulation of emissivity based on high solar reflection and different environmental requirements, and can be applied to fields such as building surface energy conservation, radiation cooling, and infrared camouflage. Background Technology

[0002] Global warming is ongoing, impacting not only human lives but also the balance of natural ecosystems. Traditional thermal control technologies, such as air conditioning, consume approximately 15% of global electricity. The current massive consumption of non-renewable energy and the demands of sustainable development urgently necessitate the development of novel thermal control technologies to reduce the energy consumption and global environmental impact of cooling and heating. In recent years, radiative cooling has become a field of great interest. Traditional radiative cooling technologies achieve this by increasing solar reflection and infrared thermal radiation from object surfaces or coatings. However, simple radiative cooling films can easily cause overcooling in summer and winter, increasing heating costs. Therefore, this invention considers using materials with adjustable emissivity to regulate thermal radiation and address a wider range of climatic conditions.

[0003] Thermal radiation is a ubiquitous phenomenon in nature; all objects with temperatures above absolute zero (−273.15 K) emit or absorb thermal radiation. To measure the intensity of an object's radiated energy, the concept of emissivity is introduced. Emissivity is defined as the ratio of the energy radiated by an object at a given temperature to the energy radiated by a blackbody (an idealized physical body that absorbs all incident electromagnetic radiation) at the same temperature. In human life, different scenarios have different requirements for the infrared radiation intensity of objects. For example, radiative cooling requires high infrared radiation, while infrared stealth requires low infrared radiation. However, the thermal radiation properties of most materials are fixed, making dynamic modulation challenging. Research shows that external stimuli such as electricity, heat, stress, and humidity can control the emissivity of objects. Among these stimuli, electric field-induced variable emissivity devices have attracted considerable attention. Materials that can be induced to change different optical states by external electric field stimulation are called electrochromic materials. Electrochromic devices made from electrochromic materials not only change color in the visible and infrared regions but some can even alter the thermal radiation state in the mid- and far-infrared regions. Compared to other methods, electrochromism offers advantages such as flexible control, simple structure, and excellent performance. Currently, electroemission modulation materials mainly consist of transition metal oxides, represented by WO3, and conductive polymers, represented by polyaniline (PANI). Transition metal oxides are prone to brittle fracture, resulting in poor processability and reduced flexibility. PANI promotes ion insertion and extraction through redox reactions, thus slowing down the device's response speed.

[0004] Based on this, this application was developed. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a novel intelligent photothermal film with fast response speed, large-area fabrication capability, and both solar reflection and adjustable thermal emission characteristics. Based on high solar reflectivity, its emissivity can be controllably modulated according to different environmental requirements. Due to its high solar reflectivity, this film can be used for radiative cooling in buildings; adjusting it to a high emissivity state can achieve further cooling effects, while its low emissivity can prevent overcooling in winter or at night. Furthermore, the film's emissivity modulation capability gives it infrared camouflage capabilities, and its low solar absorption provides a certain degree of heat dissipation, making it suitable for outdoor military camouflage applications.

[0006] The present invention also provides a method for preparing and applying a novel intelligent photothermal film with fast response speed and large-area fabrication capability, which combines solar light reflection and tunable thermal emission characteristics.

[0007] To achieve the above objectives, the present invention provides the following technical solution: A smart photothermal film with both solar reflection and tunable thermal emission characteristics, wherein the smart photothermal film comprises, from top to bottom: a solar reflection layer, a thermal emission modulation layer, a gel electrolyte layer, and a counter electrode; The solar reflective layer is mainly an infrared transparent polymer or a composite layer made of it and inorganic fillers; The thermal emission modulation layer is mainly made of carbon material coated on a porous polymer membrane; The gel electrolyte layer is mainly composed of a polymer backbone and an ionic liquid mixture; The counter electrode is the same as the thermal emission modulation layer.

[0008] Specifically, the infrared transparent polymer can be one or more of polyacrylonitrile (PAN), polyamide (PA), polyethylene (PE), polymethyl methacrylate (PMMA), etc. The inorganic filler can be one or more of the following: calcium fluoride, zinc sulfide, zinc oxide, iron oxide, Prussian blue, etc.

[0009] Specifically, the carbon material can be one or more of the following: single-walled carbon nanotubes, multi-walled carbon nanotubes, conductive carbon black, graphene, etc.; wherein, preferably, the single-walled carbon nanotubes have a diameter of 1~5nm and a length of ≤30μm; the multi-walled carbon nanotubes have a diameter of 10~50nm and a length of 10~50μm; the conductive carbon black has a particle size of 1~50nm; and the graphene has 1~30 layers and a sheet diameter of 1~10μm.

[0010] The porous polymer can be one or more of porous nylon, porous polyethylene (PE), porous polypropylene (PP), etc., with a pore size of 1~5000nm, preferably with a pore size of 10~1000nm.

[0011] Furthermore, the polymer backbone in the gel electrolyte layer can be one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polymethyl methacrylate (PMMA), polyetheramine (PEA), etc.

[0012] Specifically, the ionic liquid in the gel electrolyte layer can be one or more of the following: 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine salt (EMIM:TFSI), 1-butyl-3-methylimidazoline trifluoromethanesulfonate (EMIM:PF6), 1-ethyl-3-methylimidazoline hexafluorophosphate (EMIM:BF4), 1-ethyl-3-methylimidazoline tetrafluoroborate (HMIM:TFSI), and 1-butyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine salt (HMIM:OTF).

[0013] Furthermore, the thickness of the solar reflective layer is 1~100μm, the thickness of the thermal emission modulation layer is 0.5~5μm, the thickness of the porous polymer film is 10~200μm, the thickness of the gel electrolyte layer is 5~500μm, and the thickness of the counter electrode is 0.5~5μm.

[0014] This invention provides a method for preparing the above-mentioned smart photothermal thin film with both solar reflection and tunable thermal emission characteristics, which includes the following steps: 1) Prepared by electrospinning, rapid phase inversion, etc. Specifically, an infrared transparent polymer or it is mixed with an inorganic filler and a solvent to obtain a spinning solution or phase inversion solution, which is then subjected to electrospinning or phase inversion (such as phase inversion after coating), and dried to obtain a solar reflective layer. 2) A carbon-containing slurry is coated onto a porous polymer membrane used as a diaphragm using methods such as spraying, scraping, or roller coating, and then dried to obtain a thermal emission modulation layer; 3) Mix the polymer backbone, ionic liquid and solvent evenly to obtain a gel electrolyte solution, and dry it to obtain a gel electrolyte layer; 4) The fabrication method of the counter electrode is the same as that of the thermal emission modulation layer. That is, the thin film consists of a solar reflective layer, a thermal emission modulation layer, a gel electrolyte layer, and a counter electrode from top to bottom. The solar reflective layer is placed on top of the thermal emission modulation layer, and the gel electrolyte layer and counter electrode are placed sequentially below the thermal emission modulation layer. After adding an encapsulation protective layer, a novel intelligent photothermal thin film with both solar reflection and tunable thermal emission characteristics is obtained. To ensure close contact between each layer, conductive copper foil is preferably adhered to the carbon material of the thermal emission modulation layer and the counter electrode to facilitate voltage application.

[0015] More preferably, in step 1), the concentration of the spinning solution or phase inversion solution is 0.1~0.5g / ml; preferably, the drying is carried out in a drying oven at 30~100℃, and the solvent can be one or more of N,N-dimethylformamide (DMF), water, acetone, formic acid, etc.

[0016] Further preferably, in step 2), the solid content of the carbon-containing slurry is 0.1% to 40%, more preferably, the solid content of the carbon-containing slurry is 0.3% to 20%. The carbon-containing slurry can be obtained by mixing it with N-methylpyrrolidone (NMP) or similar substances.

[0017] More preferably, in step 3), the concentration of the gel electrolyte solution is 5% to 30%, and drying is preferably carried out in a vacuum drying oven at 20 to 100°C. The solvent can be N,N-dimethylformamide (DMF), etc.

[0018] This invention provides a smart photothermal thin film with both solar light reflection and tunable thermal emission characteristics, prepared by the above-described method.

[0019] The present invention also provides applications of the above-mentioned intelligent photothermal film with both solar reflection and adjustable heat emission characteristics in fields such as building energy conservation, personal thermal control, radiative cooling and infrared camouflage.

[0020] The Fermi level and carrier density of carbon materials such as graphene and carbon nanotubes can be tuned through electrolyte gating or doping processes, influencing interband transitions and thus achieving tunable emissivity. Ion migration in carbon materials occurs on the surface, as all host carbon atoms are exposed, significantly shortening device response time. Carbon materials can be fabricated over large areas using simple coating methods such as spraying, blade coating, and roll coating; therefore, this invention selects carbon materials as emissivity modulation materials. Traditional liquid electrolytes are prone to leakage, and their self-absorption can affect the optical state of the thin film. Therefore, this invention uses a gel electrolyte, which improves modulation performance while significantly enhancing the cycling stability of the thin film. This invention uses carbon materials as emissivity modulation materials, combined with a solar reflective layer, a gel electrolyte, and a counter electrode. This structure exhibits low emissivity under positive pressure (2.6V) and high emissivity under negative pressure (−0.7V), consistently reflecting sunlight. This achieves modulation of mid-infrared emissivity while reducing solar radiation absorption, and can actively adjust thermal control according to climatic conditions.

[0021] This invention focuses on a thin film that reflects solar radiation while also modulating mid-infrared light. It is constructed using a solar reflective layer, a thermal emission modulation layer, a gel electrolyte, and a counter electrode, aiming to develop a novel intelligent photothermal thin film that combines solar reflection and tunable thermal emission characteristics. This novel intelligent photothermal thin film possesses radiative cooling capabilities, and due to the infrared transmittance of the solar reflective film, it exhibits tunable blackbody radiative thermal emission characteristics at room temperature. It displays low emissivity under positive pressure (2.6V) and high emissivity under negative pressure (−0.7V). Compared to existing radiative cooling thin films, this invention's film has tunable infrared emissivity, preventing overcooling and adapting to more suitable climatic environments. Furthermore, this film offers advantages such as large modulation amplitude, fast response speed, and large-area fabrication capabilities, making it widely applicable in energy-efficient buildings, radiative cooling, and infrared camouflage.

[0022] Compared with the prior art, the present invention has the following beneficial effects: 1) The thin film preparation method of the present invention is simple, has low requirements for the precision of experimental equipment, and the experimental raw materials are inexpensive and readily available, enabling large-area preparation; 2) The film of this invention has relatively high solar reflectance and a large mid-infrared modulation amplitude, which can realize dynamic intelligent control of infrared based on the applied voltage; the ultraviolet-visible-near-infrared reflectance spectrum and the mid-far-infrared reflectance spectrum show that the film's solar reflectance reaches 80%, and the infrared emissivity modulation in the 8~13μm band of the atmospheric transparency window reaches 0.42; for building energy conservation applications, it can reflect solar radiation while achieving high emissivity in summer, further realizing cooling and heat dissipation, and in winter, by adjusting to a low emissivity state, it achieves the effects of heat preservation and prevention of overcooling; for infrared camouflage applications, the infrared emissivity can be dynamically modulated as needed, and the low solar absorption can reduce the film temperature when used outdoors, and when applied to clothing, it can realize heat dissipation function; 3) The response time of the thin film of the present invention is only 1.1s and 2.1s when switching between high emission and low emission states, respectively, which has a fast response speed; the maximum change in emissivity of the thin film of the present invention reaches 0.42, demonstrating the adjustable thermal emission characteristics of the thin film. 4) This invention, from the perspective of energy conservation, environmental protection and camouflage applications, prepares a radiation cooling film with adjustable emissivity. The emissivity of the film can be precisely adjusted by adjusting the voltage, making it possible to actively and dynamically adjust building heat dissipation and insulation. It can be applied to energy-saving buildings, military infrared camouflage and radiation cooling. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of a novel smart photothermal thin film structure with both solar light reflection and tunable thermal emission characteristics prepared in Example 1 of the present invention. Figure 2 The solar reflectivity of the novel smart photothermal film with both solar reflection and tunable thermal emission characteristics prepared in Example 1 of this invention has a wavelength range of 300~2500nm. As can be seen from the figure, the film has high reflectivity in the visible and near-infrared bands. Figure 3 The reflection spectra of the novel smart photothermal film with both solar reflection and tunable thermal emission characteristics prepared in Example 1 of this invention are shown in the wavelength range of 5~20μm when applied voltages of −0.7V (black line) and 2.6V (red line). Figure 4 The figure shows the emissivity change of the novel smart photothermal film with both solar reflection and tunable thermal emission characteristics prepared in Example 1 of this invention between -3V and 3V. As can be seen from the figure, the emissivity of the film can be obtained with different voltages. Figure 5 The figure shows the current-time curve of the novel smart photothermal film with both solar reflection and tunable thermal emission characteristics prepared in Example 1 of this invention. It can be seen from the figure that the film has a fast response speed. Detailed Implementation

[0024] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art are within the scope of protection of the present invention. Meanwhile, the present invention will be described in detail below with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0025] In the following examples, all raw materials used are ordinary commercially available products that can be purchased directly.

[0026] Single-walled carbon nanotubes have a diameter of 1–5 nm and a length of ≤30 μm; multi-walled carbon nanotubes have a diameter of 10–50 nm and a length of 10–50 μm; conductive carbon black has a particle size of 1–50 nm; graphene has 1–30 layers and a sheet diameter of 1–10 μm. Porous polymers have a pore size of 50–500 nm. Porous polymer films have a thickness of 30–100 μm.

[0027] Example 1 A novel smart photothermal thin film with both solar reflection and tunable thermal emission properties (structure as follows) Figure 1 As shown in the figure, from top to bottom, it consists of a solar reflective layer, a thermal emission modulation layer, a gel electrolyte layer, and a counter electrode. The solar reflective layer is mainly an infrared transparent polymer or a composite layer made of it and an inorganic filler. The thermal emission modulation layer is mainly made of carbon material coated on a porous polymer membrane; The gel electrolyte layer is mainly composed of a polymer backbone and an ionic liquid mixture; The counter electrode is the same as the thermal emission modulation layer. The specific fabrication method includes the following steps: 1) Weigh 0.5g of PAN and 0.5g of calcium fluoride, pour them into 5ml of N,N-dimethylformamide (DMF), place the solution in a 60℃ water bath, and magnetically stir at 1500rpm for 4h to promote dissolution and dispersion, obtaining a spinning solution with a concentration of 0.2g / ml. Take 5ml of the spinning solution and electrospin it on an aluminum foil substrate for 3h, with a spinning voltage of 10kV and a spinning solution flow rate of 0.5ml / h. After spinning, dry it in a 40℃ drying oven. After removing it from the substrate, a PAN / calcium fluoride porous fiber membrane with a thickness of 13μm is prepared, which is the solar reflective layer. 2) Select the spraying method and spray a slurry of carbon-containing material with a solid content of 5% (obtained by dispersing single-walled carbon nanotubes in NMP) onto the porous nylon diaphragm at the maximum air flow rate. Dry it in a drying oven at 45°C to form a thermal emission modulation layer with a thickness of 3μm. 3) Add 0.5g of PVDF-HFP, 0.5g of PMMA and 0.5g of EMIM:TFSI to 5ml of DMF, place in a 60℃ water bath, and magnetically stir at 1500rpm for 3h to form a transparent viscous solution. Dry in a vacuum drying oven at 80℃ to prepare a gel electrolyte layer with a thickness of 210μm. 4) The electrode is fabricated in the same way as the thermal emission modulation layer.

[0028] Sprayed single-walled carbon nanotubes and nylon form a thermoelectric emission modulation layer, with a PAN / calcium fluoride porous fiber membrane placed on top as a sunlight reflector. Similarly, sprayed single-walled carbon nanotubes and nylon serve as the counter electrode. A gel electrolyte layer based on PVDF-HFP, PMMA, and EMIM:TFSI is placed between the thermoelectric emission modulation layer and the counter electrode. Conductive copper foil is adhered to the single-walled carbon nanotubes of the thermoelectric emission modulation layer and the counter electrode. The entire film is encapsulated by a transparent PE film to form a protective layer.

[0029] Figure 2 The solar reflectivity of the novel smart photothermal thin film with both solar reflection and tunable thermal emission characteristics prepared in Example 1 of this invention is shown, with a wavelength range of 300~2500nm. As can be seen from the figure, the thin film has a high reflectivity of 80% in the visible and near-infrared bands, indicating that the thin film can reflect most of the solar radiation energy and has good solar reflection performance.

[0030] Figure 3 The reflection spectra of the novel smart photothermal thin film prepared in Example 1 of this invention, which combines solar reflection and tunable thermal emission characteristics, are presented at applied voltages of −0.7V (black line) and 2.6V (red line), with a wavelength range of 5–20 μm. The figures show a significant difference in reflectance between −0.7V and 2.6V within the atmospheric window range of 8–13 μm. When a negative voltage is applied, cations migrate towards the thermal emission modulation layer, altering their electron concentration and causing a change in emissivity. Within the atmospheric transparency window of 8–13 μm, the maximum emissivity (0.73) is obtained when the voltage is −0.7V. Conversely, applying a positive voltage causes anions to migrate towards the thermal emission modulation layer, resulting in a decrease in emissivity. The lowest emissivity (0.31) is obtained when the voltage is 2.6V, with a maximum emissivity change of 0.42, demonstrating the tunable thermal emission characteristics of the thin film.

[0031] Figure 4The emissivity variation of the novel smart photothermal thin film prepared in Example 1 of this invention, which combines solar reflection and tunable thermal emission characteristics, is shown between -3V and 3V. As can be seen from the figure, the thin film exhibits different emissivities with varying voltages, and the voltage can be actively adjusted to obtain different emissivities as needed. For example, a high emissivity can be achieved during radiative cooling, while a low emissivity can be achieved during thermal camouflage.

[0032] Figure 5 The "current-time" curve of the novel smart photothermal film with both solar reflection and tunable thermal emission characteristics prepared in Example 1 of this invention is given. The time required for the film current to change by 90% is defined as the response time. As can be seen from the figure, the response time of the film is only 1.1s and 2.1s when switching to the high emission and low emission states, respectively, indicating that the film has a fast response speed.

[0033] Example 2 A novel intelligent photothermal film with both solar reflection and tunable thermal emission characteristics comprises, from top to bottom, a solar reflection layer, a thermal emission modulation layer, a gel electrolyte layer, and a counter electrode. The solar reflection layer is mainly an infrared transparent polymer or a composite layer made of it and inorganic fillers. The thermal emission modulation layer is mainly made of carbon material coated on a porous polymer membrane; The gel electrolyte layer is mainly composed of a polymer backbone and an ionic liquid mixture; The counter electrode is the same as the thermal emission modulation layer. The fabrication method specifically includes the following steps: 1) Dissolve 0.2g PMMA and 0.2g zinc oxide powder in a mixed solution of 0.1g water and 2ml acetone to obtain a PMMA solution. Coat the PMMA solution onto an aluminum foil substrate by roller coating. Due to the rapid evaporation of acetone, the solution quickly forms a porous film. Then place it in a drying oven at 60℃ to dry the remaining moisture. After removing it from the substrate, a PMMA / zinc oxide porous film with a thickness of 23μm is prepared, which is the solar reflective layer. 2) Select the scraping method, scrape a slurry of carbon-containing material with a solid content of 8% (obtained by dispersing multi-walled carbon nanotubes in NMP) onto the porous PE membrane, dry it in a 45℃ drying oven, and spray it to form a 5μm thick thermal emission modulation layer. 3) Add 1g of PMMA and 0.5g of EMIM:PF6 to 5ml of DMF, place in a 60℃ water bath, and magnetically stir at 1500rpm for 3h to form a transparent and viscous solution. Dry in a vacuum drying oven at 80℃ to prepare a gel electrolyte layer with a thickness of 305μm. 4) The electrode is fabricated in the same way as the thermal emission modulation layer.

[0034] A heat emission modulation layer is composed of multi-walled carbon nanotubes and porous PE coated by a blade, with a PMMA / zinc oxide porous membrane placed on top of the heat emission modulation layer as a sunlight reflector. Similarly, multi-walled carbon nanotubes and porous PE are coated by a blade as the counter electrode. A gel electrolyte layer based on PMMA and EMIM:PF6 is placed between the heat emission modulation layer and the counter electrode. Conductive copper foil is adhered to the multi-walled carbon nanotubes of the heat emission modulation layer and the counter electrode. The entire film is covered by a transparent PE film to form a protective layer.

[0035] Example 3 A novel intelligent photothermal film with both solar reflection and tunable thermal emission characteristics comprises, from top to bottom, a solar reflection layer, a thermal emission modulation layer, a gel electrolyte layer, and a counter electrode. The solar reflection layer is mainly an infrared transparent polymer or a composite layer made of it and inorganic fillers. The thermal emission modulation layer is mainly made of carbon material coated on a porous polymer membrane; The gel electrolyte layer is mainly composed of a polymer backbone and an ionic liquid mixture; The counter electrode is the same as the thermal emission modulation layer. The fabrication method specifically includes the following steps: 1) Weigh 0.5g of polyamide and 0.5g of iron oxide, pour them into 5ml of formic acid, place them in a 60℃ water bath, and magnetically stir at 1500rpm for 4h to promote dissolution and dispersion, obtaining a spinning solution (polyamide solution) with a concentration of 0.2g / ml. Take 5ml of the spinning solution for electrospinning, spinning time is 2h, spinning voltage is 15kV, and spinning solution flow rate is 0.5ml / h. After spinning, dry in a 40℃ drying oven, and remove from the substrate to prepare a PA / iron oxide porous fiber membrane with a thickness of 18μm, which is the solar reflective layer; 2) Select the roller coating method and use a 20μm wire rod to roll a slurry containing carbon material with a solid content of 5% (obtained by dispersing conductive carbon black in NMP) onto the porous PP diaphragm. Dry it in a drying oven at 45℃ and spray it to form a thermal emission modulation layer with a thickness of 3μm. 3) Add 1g of PVDF-HFP and 0.5g of EMIM:BF4 to 5ml of DMF, place in a 60℃ water bath, and magnetically stir at 1500rpm for 3h to form a transparent and viscous solution. Dry in a vacuum drying oven at 80℃ to prepare a 225μm gel electrolyte layer. 4) The electrode is fabricated in the same way as the thermal emission modulation layer.

[0036] A heat emission modulation layer is composed of roller-coated conductive carbon black and porous PP. A PA / iron oxide porous fiber membrane is placed on top of the heat emission modulation layer as a sunlight reflector. Similarly, roller-coated conductive carbon black and porous PP serve as the counter electrode. A gel electrolyte based on PVDF-HFP and EMIM:BF4 is placed between the heat emission modulation layer and the counter electrode. Conductive copper foil is adhered to the conductive carbon black of the heat emission modulation layer and the counter electrode. The entire film is covered by a transparent PE film to form a protective layer.

[0037] Example 4 A novel intelligent photothermal film with both solar reflection and tunable thermal emission characteristics comprises, from top to bottom, a solar reflection layer, a thermal emission modulation layer, a gel electrolyte layer, and a counter electrode. The solar reflection layer is mainly an infrared transparent polymer or a composite layer made of it and inorganic fillers. The thermal emission modulation layer is mainly made of carbon material coated on a porous polymer membrane; The gel electrolyte layer is mainly composed of a polymer backbone and an ionic liquid mixture; The counter electrode is the same as the thermal emission modulation layer. The fabrication method specifically includes the following steps: 1) A porous PE film with a thickness of 30~40 μm is directly used as a solar reflective layer; 2) Select the spraying method and spray a slurry containing carbon material with a solid content of 5% (obtained by dispersing graphene in NMP) onto the porous nylon diaphragm at the maximum air flow rate. Dry it in a drying oven at 45°C to form a thermal emission modulation layer with a thickness of 3μm. 3) Add 1g of PVDF and 0.5g of HMIM:TFSI to 5ml of DMF, place in a 60℃ water bath, and magnetically stir at 1500rpm for 3h to form a transparent and viscous solution. Dry in a vacuum drying oven at 80℃ to prepare a gel electrolyte layer with a thickness of 208μm. 4) The electrode is fabricated in the same way as the thermal emission modulation layer.

[0038] Sprayed graphene and nylon form the thermal emission modulation layer, and a porous PE film is placed directly on top of the thermal emission modulation layer as a sunlight reflector. Similarly, sprayed graphene and nylon serve as the counter electrode. A gel electrolyte layer based on PVDF and HMIM:TFSI is placed between the thermal emission modulation layer and the counter electrode. Conductive copper foil is adhered to the graphene of the thermal emission modulation layer and the counter electrode. The entire film is covered by a transparent PE film to form a protective layer.

[0039] Example 5 A novel intelligent photothermal film with both solar reflection and tunable thermal emission characteristics comprises, from top to bottom, a solar reflection layer, a thermal emission modulation layer, a gel electrolyte layer, and a counter electrode. The solar reflection layer is mainly an infrared transparent polymer or a composite layer made of it and inorganic fillers. The thermal emission modulation layer is mainly made of carbon material coated on a porous polymer membrane; The gel electrolyte layer is mainly composed of a polymer backbone and an ionic liquid mixture; The counter electrode is the same as the thermal emission modulation layer. The fabrication method specifically includes the following steps: 1) Weigh 0.5g of PAN and 0.5g of Prussian blue, pour them into 5ml of DMF, place the solution in a 60℃ water bath, and magnetically stir at 1500rpm for 4h to promote dissolution and dispersion, obtaining a spinning solution with a concentration of 0.2g / ml. Take 5ml of the spinning solution and electrospin it on a porous PE substrate for 3h, with a spinning voltage of 10kV and a spinning solution flow rate of 0.5ml / h. After spinning, dry it in a 40℃ drying oven. After removing it from the substrate, a PAN / Prussian blue composite fiber membrane with a thickness of 27μm is prepared, which is the solar reflective layer. 2) Select the spraying method and spray a slurry of carbon-containing material with a solid content of 5% (obtained by dispersing single-walled carbon nanotubes in NMP) onto the porous nylon diaphragm at the maximum air flow rate. Dry it in a drying oven at 45°C to form a thermal emission modulation layer with a thickness of 3μm. 3) Dissolve 0.5g of PVDF, 0.5g of PMMA and 0.5g of HMIM:OTF in 5ml of DMF, place in a 60℃ water bath, and magnetically stir at 1500rpm for 3h to form a transparent and viscous solution. Dry in a vacuum drying oven at 80℃ to prepare a 208μm gel electrolyte layer. 4) The electrode is fabricated in the same way as the thermal emission modulation layer.

[0040] A thermal emission modulation layer is composed of sprayed single-walled carbon nanotubes and nylon, with a PAN / Prussian blue composite fiber membrane placed on top as a sunlight reflector. Similarly, a sprayed single-walled carbon nanotube membrane and nylon serve as the counter electrode. A gel electrolyte layer based on PVDF, PMMA, and HMIM:OTF is placed between the thermal emission modulation layer and the counter electrode. Conductive copper foil is adhered to the single-walled carbon nanotubes of the thermal emission modulation layer and the counter electrode. The entire film is encapsulated by a transparent PE film to form a protective layer.

[0041] Furthermore, the visible and near-infrared reflectance spectra, as well as the infrared reflectance spectra, of the thin film samples prepared in Examples 2 to 5 were tested. The test results showed that all samples exhibited effects comparable to those in Example 1, achieving both reflection of most solar radiation and significant modulation of infrared emissivity. This novel intelligent photothermal thin film, possessing both solar reflection and tunable thermal emission characteristics, demonstrates improved practical application capabilities due to its simple preparation method and fast response time, enabling its use in energy-efficient buildings, radiative cooling, and infrared camouflage.

Claims

1. A smart photothermal thin film possessing both solar light reflection and tunable thermal emission characteristics, characterized in that, The intelligent photothermal film consists of, from top to bottom: a solar reflective layer, a thermal emission modulation layer, a gel electrolyte layer, and a counter electrode; The solar reflective layer is a porous fiber membrane formed of polyacrylonitrile and calcium fluoride. The thermal emission modulation layer is composed of a single-walled carbon nanotube coating applied to the surface of a porous nylon membrane and the porous nylon membrane together. The gel electrolyte layer is a gel layer formed by vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate and 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine salt, and is disposed as an independent layer between the thermal emission modulation layer and the counter electrode. The counter electrode adopts the same single-walled carbon nanotube coating / porous nylon membrane composite structure as the thermal emission modulation layer.

2. The intelligent photothermal film as described in claim 1, characterized in that, The single-walled carbon nanotubes have a diameter of 1–5 nm and a length of no more than 30 μm; the porous nylon membrane has a pore size of 50–500 nm and a thickness of 30–100 μm.

3. The intelligent photothermal film as described in claim 1, characterized in that, The thickness of the solar reflective layer is 1~100 μm, and the thickness of the gel electrolyte layer is 5~500 μm.

4. The intelligent photothermal film as described in claim 1, characterized in that, The mass ratio of polyacrylonitrile to calcium fluoride in the solar reflective layer is 1:1; the mass ratio of vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, and 1-ethyl-3-methylimidazoline bis(trifluoromethylsulfonyl)imine salt in the gel electrolyte layer is 1:1:

1.

5. The method for preparing the intelligent photothermal thin film according to any one of claims 1 to 4, characterized in that, Includes the following steps: 1) Polyacrylonitrile, calcium fluoride and solvent are mixed to obtain a spinning solution, which is then electrospun and dried to obtain a polyacrylonitrile / calcium fluoride porous fiber solar reflective layer. 2) Spray a slurry containing single-walled carbon nanotubes onto the surface of a porous nylon membrane and dry it, so that the single-walled carbon nanotube coating and the porous nylon membrane together form a thermal emission modulation layer. 3) Mix vinylidene fluoride-hexafluoropropylene copolymer, polymethyl methacrylate, 1-ethyl-3-methylimidazoline bis(trifluoromethanesulfonyl)imine salt with solvent until uniform, and dry to obtain gel electrolyte layer; 4) Prepare the counter electrode in the same way as in step 2), place the solar reflective layer above the thermal emission modulation layer, and then encapsulate the gel electrolyte layer and the counter electrode below the thermal emission modulation layer.

6. The preparation method according to claim 5, characterized in that, The concentration of the spinning solution in step 1) is 0.1–0.5 g / mL; the solid content of the slurry containing single-walled carbon nanotubes in step 2) is 0.1%–40%; and the concentration of the gel electrolyte solution in step 3) is 5%–30%.

7. A smart photothermal film with both solar reflection and tunable thermal emission characteristics prepared by the preparation method described in claim 5 or 6.

8. The application of the intelligent photothermal film of claim 7 in the fields of building energy conservation, personal thermal control, radiative cooling and infrared camouflage.

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