Preparation method and application of Janus structure PDMS film

Abstract

This invention belongs to the field of flexible functional thin film preparation technology, specifically relating to a method for preparing Janus-structured PDMS thin films and their applications. This method uses PDMS as a flexible substrate, and controls the preparation of titanium dioxide with different morphologies through evaporation-driven hydrothermal methods. Polypyrrole is then composited via in-situ polymerization. An asymmetric interface is constructed by coating two functional fillers: conical titanium dioxide and cracked spherical titanium dioxide, with polypyrrole. The functional layer is then prepared by casting, and finally cured to obtain the desired product. This invention utilizes the high absorption of sunlight by polypyrrole and the special morphology of conical titanium dioxide to improve the absorption rate of sunlight. Furthermore, the high reflectivity of titanium dioxide in the visible and near-infrared range enables passive energy-saving cooling and efficient de-icing and defrosting. While optimizing the spectral control performance of the thin film, it also solves the problems of poor weather resistance and limited functionality.

Description

Technical Field

[0001] This invention belongs to the field of flexible functional thin film preparation technology, specifically relating to a method for preparing a Janus-structured PDMS thin film and its application in radiative cooling and photothermal de-icing. This method can balance the film's efficient radiative cooling performance with excellent photothermal de-icing capability, while simultaneously improving the film's poor structural stability and weak environmental adaptability. This achieves all-weather intelligent thermal regulation and meets the practical needs of outdoor facilities for temperature control, anti-freezing, and energy-saving cooling. Background Technology

[0002] Janus-structured PDMS films are functional thin-film materials designed based on an asymmetric interface structure, possessing both bidirectional optical control and flexible substrate adaptability. While most conventional PDMS-based films can achieve single-function temperature control after modification, they suffer from narrow spectral control ranges, poor environmental adaptability, weak service stability, cumbersome preparation processes, insufficient outdoor weather resistance, and limited functionality. As a classic flexible matrix material, polydimethylsiloxane (PDMS) possesses excellent properties such as good flexibility, high ductility, hydrophobicity and moisture resistance, easy molding, and stable chemical properties, and is widely used in many fields such as building energy conservation, outdoor equipment, aerospace, transportation facilities, and photovoltaic modules. However, pure PDMS-based films have low radiative heat dissipation efficiency, weak photothermal conversion capacity, and poor deformation adaptability under hot and cold environments when used alone.

[0003] Functionally modified fillers are the core functional carriers for constructing Janus asymmetric functional films. In the early years, researchers at home and abroad successively developed various inorganic optical control fillers, mainly including titanium dioxide, silicon dioxide, carbon-based fillers, metal-based micro and nano particles, etc. Some fillers have been successfully applied in the field of temperature control films. However, these traditional modified fillers not only have limited spectral response ranges and significant functional decay under high and low temperature environments, but also have obvious drawbacks such as poor composite compatibility, high raw material costs, and insufficient long-term durability.

[0004] Radiative cooling performance refers to a material's ability to spontaneously radiate infrared heat to achieve passive cooling. It is generally evaluated using infrared emissivity and solar spectral absorptivity. Excellent radiative cooling can achieve energy-free cooling, playing a significant role in building insulation, equipment heat dissipation, and photovoltaic temperature control. Photothermal de-icing performance represents a material's ability to absorb visible and near-infrared light energy and rapidly convert it into heat energy, achieving surface de-icing and defrosting. Thin films with good photothermal de-icing properties can quickly break up ice and snow in low-temperature icy and snowy environments, ensuring the normal operation of outdoor facilities and significantly reducing manual de-icing costs and maintenance losses. Summary of the Invention

[0005] This invention aims to overcome the shortcomings of existing technologies and provide a method for preparing Janus-structured PDMS films that is simple to operate, low in cost, long in service life, and can achieve passive energy-saving cooling, efficient de-icing and defrosting. It also optimizes spectral modulation performance and solves the problems of poor weather resistance, single function, and weak environmental adaptability of thin films.

[0006] Another objective of this invention is to provide an application of the product obtained by the Janus structure PDMS thin film preparation method in radiation cooling and photothermal de-icing.

[0007] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0008] In a first aspect, the present invention provides a method for preparing a Janus-structured PDMS film. Conical and cracked spherical rutile titanium dioxide can be controlled by an evaporation-driven hydrothermal method. Cracked spherical titanium dioxide is used as the cooling-side base material, and polypyrrole-coated conical titanium dioxide is used as the de-icing-side base material. The two base materials are dispersed in a mixture of PDMS prepolymer and tetrahydrofuran, respectively. A casting method is used, firstly, the PDMS mixture dispersed with cracked spherical titanium dioxide is cast into a mold. After the film is formed and cured, a PDMS mixture dispersed with polypyrrole-coated conical titanium dioxide is cast on top. The mixture is then dried to remove the tetrahydrofuran solvent and cured to obtain the Janus-structured PDMS film.

[0009] As a preferred embodiment, the method for preparing the PDMS thin film includes the following steps:

[0010] (1) After mixing tetrahydrofuran (THF), concentrated hydrochloric acid and glacial acetic acid, add poloxamer (F-127) and stir to dissolve, then add tetrabutyl titanate (TBOT).

[0011] (2) Place the solution obtained in step 1 in an oven for evaporation. After evaporation, a titanium dioxide (TiO2) precursor solution is obtained.

[0012] (3) The precursor solution obtained in step 2 was placed in a reaction vessel and subjected to hydrothermal treatment at different hydrothermal temperatures.

[0013] (4) Centrifuge the products obtained in step 3, then wash them twice with anhydrous ethanol and distilled water respectively and centrifuge them. After that, dry and grind the centrifuged products to obtain cracked spherical titanium dioxide (1-TiO2) and conical titanium dioxide (2-TiO2).

[0014] (5) Disperse the 2-TiO2 obtained in step 4 in deionized water, perform ultrasonic dispersion, and add hydrochloric acid (HCl), ammonium persulfate and pyrrole monomer to the solution in sequence, and carry out in-situ polymerization in an ice-water bath;

[0015] (6) The product obtained in step 5 is centrifuged, then washed twice with anhydrous ethanol and distilled water respectively and centrifuged again. After that, the centrifuged product is dried and ground to obtain polypyrrole-coated cone titanium dioxide (2-TiO2@Ppy).

[0016] (7) Disperse the 1-TiO2 and 2-TiO2@Ppy obtained in steps 4 and 6 into a mixed solution of PDMS prepolymer and THF, and add a curing agent;

[0017] (8) The mixed solution of 1-TiO2 and PDMS from step 7, 1-TiO2 / PDMS, is poured into a mold, dried, and cured to obtain a cracked sphere titanium dioxide / PDMS film, also known as 1-TiO2 / PDMS.

[0018] (9) The mixed solution of 2-TiO2@Ppy and PDMS obtained in step 7 is poured onto the film cured in step 8, and then dried and cured to obtain the target product.

[0019] Preferably: In step (1), 30 mL THF, 3 mL 1.2 mol / L concentrated hydrochloric acid and 2 mL glacial acetic acid are mixed, and 1.6 g F-127 is added. The mixture is stirred at 700 r / min for 1 h until the solid dissolves. After dissolution, 3.4 mL TBOT is added, and the mixture is stirred at 700 r / min for 1 h until the solution turns wine red.

[0020] Preferably, in step (2), the obtained mixed solution is placed in a 50 °C oven for 5 h until the solution becomes semi-gelatinous, thus obtaining a titanium dioxide precursor solution.

[0021] Preferably, in step (3), the precursor solution is divided into two portions, which are placed in two 50 ml polytetrafluoroethylene liners respectively, and the two liners are placed in different reaction vessels and hydrothermally heated at 80 ℃ and 120 ℃ for 24 h.

[0022] Preferably, in step (4), the product obtained in step (3) is centrifuged, then washed twice with anhydrous ethanol and deionized water respectively, and dried in an 80°C oven for 12 hours. After grinding the dried product, 1-TiO2 and 2-TiO2 are obtained.

[0023] Preferably, in step (5), 2.5 g of 2-TiO2 is dispersed in 100 mL of deionized water and sonicated for 30 min. Then, 2 mL of 1 mol / L hydrochloric acid solution, 20 mL of 0.01 mol / L ammonium persulfate solution, and 0.1 mL of pyrrole monomer are added to the solution in sequence, and the mixture is stirred at 700 r / min for 6 h in a water bath at a temperature maintained at 0-5 ℃.

[0024] Preferably, in step (6), the product obtained in step (5) is centrifuged, then washed twice with anhydrous ethanol and deionized water respectively, and dried in an 80°C oven for 12 hours. After grinding the dried product, 2-TiO2@Ppy is obtained.

[0025] Preferably, in step (7), THF and PDMS prepolymer are mixed at a ratio of 3 ml: 10 g, and the 1-TiO2 and 2-TiO2@Ppy obtained in steps (4) and (6) are respectively dispersed in the mixed liquid with the corresponding PDMS prepolymer at a mass ratio of 1:10. Curing agent is added at a mass ratio of 10:1 between the prepolymer and the curing agent. The PDMS prepolymer, officially named PDMS siloxane, is purchased from McLean Corporation; the curing agent is polymethylhydrosiloxane.

[0026] Preferably, in step (8), the 1-TiO2 / PDMS mixed solution of 1-TiO2 and PDMS from step (7) is poured into a mold and placed in an oven at 40 °C for 4 h to obtain a 1-TiO2 / PDMS film with a thickness of 0.3~1.0 mm.

[0027] Preferably, in step (9), the mixed solution of 2-TiO2@Ppy obtained in step (7) and PDMS is poured onto the film cured in step (8), and then dried at 40°C for 6 h to obtain the target product with a top layer thickness of 0.3~1.0 mm.

[0028] Secondly, the present invention provides a Janus-structured PDMS thin film prepared by the preparation method described above.

[0029] Thirdly, the present invention provides the application of the Janus structure PDMS thin film described above in radiative cooling and photothermal de-icing.

[0030] The PDMS film prepared above is obtained by drying and demolding.

[0031] Compared with the prior art, the present invention has the following characteristics:

[0032] 1. This invention mainly adopts an evaporation-driven hydrothermal method to controllably prepare titanium dioxide with different morphologies. Different effects can be achieved simply by controlling the hydrothermal temperature. No high-end and complex preparation equipment is required. The operation is simple, the material price is low, and it is suitable for industrial production.

[0033] 2. This invention introduces two special functional fillers, 2-TiO2@Ppy and 1-TiO2, to be used in combination to synergistically optimize solar spectrum reflectivity and infrared radiation heat dissipation efficiency. This overcomes the shortcomings of traditional PDMS films, such as weak temperature control performance, single function, and insufficient environmental weather resistance. It can efficiently complete passive cooling and surface de-icing and defrosting, improving the temperature control protection and all-weather service performance of outdoor facilities.

[0034] 3. This invention uses PDMS as a flexible substrate to construct an asymmetric Janus structure, which can precisely control the optical and thermal properties on both sides of the film, adapt to outdoor day and night temperature differences and ice and snow conditions, and at the same time enhance the stability of the interface bonding, so as to achieve a two-way synergistic control effect of efficient radiative cooling during the day and rapid photothermal de-icing in low-temperature environments.

[0035] 4. The titanium dioxide prepared in this invention is in the rutile phase (only the anatase phase has photocatalytic effect), and its photocatalytic activity is extremely low. More importantly, the TiO2 in this invention does not act directly on the organic polymer matrix in the form of exposed particles with high photocatalytic activity, but is modified by polypyrrole coating and forms a composite interface structure with the PDMS matrix. This structure synergistically ensures the long-term weather resistance of the film from multiple dimensions: First, the composite interface can promote the interfacial transfer of TiO2 photogenerated charge carriers, reducing the attack of strongly oxidizing species on PDMS and polypyrrole segments; second, TiO2, as an inorganic filler, can absorb and scatter ultraviolet light, reducing the penetration of ultraviolet light into the organic phase inside the coating; third, the hydrophobic siloxane network formed by PDMS can block moisture and oxygen, slowing down the aging of polypyrrole in a photo-oxidative environment. The above mechanisms fundamentally solve the problem of easy photodegradation of traditional TiO2 / polymer composite materials, endowing the film with excellent outdoor weather resistance and long-term service stability. Attached Figure Description

[0036] Figure 1 This is a SEM image of the cracked spherical titanium dioxide (1-TiO2) of the present invention.

[0037] Figure 2 This is a SEM image of the cone-shaped titanium dioxide (2-TiO2) of the present invention.

[0038] Figure 3 This is a SEM image of the polypyrrole-coated cone-shaped titanium dioxide (2-TiO2@Ppy) of the present invention.

[0039] Figure 4The images show the absorption and reflectance spectra of the Janus thin film prepared in Example 1 of this invention, obtained by testing the absorption and reflectance of sunlight on both sides.

[0040] Figure 5 This is the temperature change curve of the sample of the present invention under simulated light irradiation.

[0041] Figure 6 This is the temperature change curve of the sample of this invention under real outdoor testing.

[0042] Figure 7 These are de-icing photographs of Example 1 (a, upper image) and Comparative Example 2 (b, lower image) under illumination.

[0043] Figure 8 The reflection and absorption retention rates under light after UV aging for different times in Example 1 are shown.

[0044] Figure 9 This is a 180° peel strength curve of the Janus film in Example 1.

[0045] Figure 10 X-ray diffraction (XRD) patterns of cracked spherical titanium dioxide (1-TiO2) and conical titanium dioxide (2-TiO2). Detailed Implementation

[0046] The present invention will now be described in detail through specific embodiments. These embodiments are provided to enable a more thorough understanding of the invention and to fully convey the scope of the invention to those skilled in the art. As used throughout the specification and claims, the terms "comprising" or "including" are open-ended and are interpreted as "comprising but not limited to". The following description is a preferred embodiment for carrying out the invention; however, this description is intended to illustrate the general principles of the specification and is not intended to limit the scope of the invention. The scope of protection of the invention is determined by the appended claims. Unless otherwise specified, all reagents and materials used in the present invention are commercially available.

[0047] Example 1: Preparation of Janus-structured PDMS thin films

[0048] (1) Take 3 mL of concentrated hydrochloric acid, 2 mL of glacial acetic acid, 1.6 g of F-127 and 30 mL of THF; first add concentrated hydrochloric acid and glacial acetic acid to THF, then add 1.6 g of F-127, stir with a magnetic stirrer at 700 r / min for 1 h.

[0049] Take 3.4 mL of TBOT and add it to the previously stirred solution. Continue stirring at a speed of 700 r / min for 1 h. The solution turns wine red.

[0050] (2) Collect the solution from step (1), place the solution in a 50 mL beaker, place it in an oven, and use it to evaporate THF. The temperature is set to 50 °C and the evaporation time is 5 h.

[0051] (3) Collect the solution from step (2), divide the solution into two equal parts, place them in two 50 ml polytetrafluoroethylene liners, and place the two liners into two independent reaction vessels, and hydrothermally heat them at 80 ℃ and 120 ℃ for 24 h.

[0052] (4) The solid products obtained in step (3) are centrifuged and washed twice with anhydrous ethanol and distilled water respectively. They are then placed in an oven and dried at 80°C for 12 hours to obtain cracked spherical titanium dioxide (1-TiO2) and conical titanium dioxide (2-TiO2).

[0053] (5) Disperse 2.5 g of 2-TiO2 obtained in step (4) in 100 mL of deionized water and sonicate for 30 min. Then add 2 mL of 1 mol / L hydrochloric acid solution, 20 mL of 0.01 mol / L ammonium persulfate solution and 0.1 mL of pyrrole monomer to the solution in sequence, and stir at 700 r / min for 6 h in a water bath at 4 ℃.

[0054] (6) Centrifuge the solid product obtained in step (5) and wash it twice with anhydrous ethanol and distilled water, respectively. Place it in an oven and dry it at 80°C for 12 hours to obtain polypyrrole-coated cone titanium dioxide (2-TiO2@Ppy).

[0055] (7) Take 3 mL of THF and 10 g of PDMS prepolymer and mix them. Add 1 g of curing agent (polymethylhydrosiloxane) and 1 g of 1-TiO2 obtained in step (4) to the mixture. Stir with a magnetic stirrer at a speed of 800 r / min for 1 h to obtain a mixture of 1-TiO2 and PDMS.

[0056] Take 3 mL of THF and 10 g of PDMS prepolymer and mix them. Add 1 g of curing agent (polymethylhydrosiloxane) and 1 g of the solid product obtained in step (6). Stir with a magnetic stirrer at 800 r / min for 1 h to obtain a mixture of 2-TiO2@Ppy and PDMS.

[0057] (8) The mixture of 1-TiO2 and PDMS obtained in step (7) is poured into a mold with a depth of 0.5 mm and dried in an oven at 40 °C for 4 h to obtain a 1-TiO2 / PDMS film.

[0058] (9) The mixed solution of 2-TiO2@Ppy and PDMS obtained in step (7) is poured onto the film cured in step (8), the pouring thickness is controlled to be 0.5 mm, and then dried at 40°C for 6 h to obtain the target product.

[0059] Comparative Example 1: Preparation of a single-layer radiation-cooling thin film

[0060] (1) Take 3 mL of concentrated hydrochloric acid, 2 mL of glacial acetic acid, 1.6 g of F-127 and 30 mL of THF; first add concentrated hydrochloric acid and glacial acetic acid to THF, then add 1.6 g of F-127, stir with a magnetic stirrer at a speed of 700 r / min for 1 h.

[0061] Take 3.4 mL of TBOT and add it to the previously stirred solution. Continue stirring at a speed of 700 r / min for 1 h. The solution turns wine red.

[0062] (2) Collect the solution from step (1), place the solution in a 50 mL beaker, place it in an oven, and use it to evaporate THF. The temperature is set to 50 °C and the evaporation time is 5 h.

[0063] (3) Collect the solution from step (2), place the solution in a 50 ml polytetrafluoroethylene liner, put the liner into the reactor, and hydrothermally heat it at 80 °C for 24 h.

[0064] (4) Centrifuge the solid product obtained in step (3) and wash it twice with anhydrous ethanol and distilled water, and dry it in an oven at 80°C for 12 hours to obtain cracked spherical titanium dioxide (1-TiO2).

[0065] (5) This step (in-situ polymerization step) is not required in this embodiment;

[0066] (6) This step (the coating material acquisition step) is not required in this embodiment;

[0067] (7) Take 3 mL of THF and mix with 10 g of PDMS prepolymer, add 1 g of curing agent (polymethylhydrosiloxane) and 1 g of the solid product obtained in step (4), stir with a magnetic stirrer at 800 r / min for 1 h.

[0068] (8) The mixture obtained in step (7) is poured into a mold with a depth of 0.5 mm and dried in an oven at 40 °C for 4 h to obtain 1-TiO2 / PDMS film.

[0069] (9) This step (double-layer composite step) is not required in this embodiment.

[0070] Comparative Example 2: Preparation of a single-layer photothermal de-icing film

[0071] (1) Take 3 mL of concentrated hydrochloric acid, 2 mL of glacial acetic acid, 1.6 g of F-127 and 30 mL of THF; first add concentrated hydrochloric acid and glacial acetic acid to THF, then add 1.6 g of F-127, stir with a magnetic stirrer at 700 r / min for 1 h.

[0072] Take 3.4 mL of TBOT and add it to the previously stirred solution. Continue stirring at a speed of 700 r / min for 1 h. The solution turns wine red.

[0073] (2) Collect the solution from step (1), place the solution in a 50 mL beaker, place it in an oven, and use it to evaporate THF. The temperature is set to 50 °C and the evaporation time is 5 h.

[0074] (3) Collect the solution from step (2), place the solution in a 50 ml polytetrafluoroethylene liner, put the liner into the reactor, and hydrothermally heat it at 120 °C for 24 h.

[0075] (4) Centrifuge the solid product obtained in step (3) and wash it twice with anhydrous ethanol and distilled water, and dry it in an oven at 80°C for 12 hours to obtain conical titanium dioxide (2-TiO2).

[0076] (5) Disperse 2.5 g of the solid obtained in step (4) in 100 mL of deionized water and sonicate for 30 min. Then add 2 mL of 1 mol / L hydrochloric acid solution, 20 mL of 0.01 mol / L ammonium persulfate solution and 0.1 mL of pyrrole monomer to the solution in sequence, and stir at 700 r / min for 6 h in a water bath at a temperature of 4 ℃.

[0077] (6) Centrifuge the solid product obtained in step (5) and wash it twice with anhydrous ethanol and distilled water, respectively. Place it in an oven and dry it at 80°C for 12 hours to obtain polypyrrole-coated cone titanium dioxide (2-TiO2@Ppy).

[0078] (7) Take 3 mL of THF and 10 g of PDMS prepolymer and mix them. Add 1 g of curing agent (polymethylhydrosiloxane) and 1 g of the solid product obtained in step (6). Stir with a magnetic stirrer at 800 r / min for 1 h.

[0079] (8) This step (the bottom cooling layer pouring step) is not required in this embodiment;

[0080] (9) The mixture obtained in step (7) is poured into a mold with a depth of 0.5 mm and dried in an oven at 40 °C for 4 h to obtain 2-TiO2@Ppy / PDMS film.

[0081] Performance Testing and Comparison

[0082] 1. Morphological and spectral characterization

[0083] The 1-TiO2 prepared in Comparative Example 1 was examined by scanning electron microscopy, and the results are as follows: Figure 1 As shown in the figure, the TiO2 prepared under hydrothermal conditions at 80 ℃ exhibits micron-sized spherical shapes with open crack structures. These crack structures effectively increase the scattering path of incident light and improve reflectivity. Scanning electron microscopy (SEM) analysis of the 2-TiO2 prepared in Comparative Example 2 yielded the following results: Figure 2 As shown in the figure, the prepared TiO2 exhibits a cone-shaped morphology, which is conducive to constructing light traps and reducing light reflection and escape.

[0084] The 2-TiO2@Ppy prepared in Comparative Example 2 was examined by scanning electron microscopy, and the results are as follows: Figure 3 As shown in the figure, the prepared composite material contains conical TiO2 particles coated with Ppy, and the coating effect is good.

[0085] X-ray diffraction (XRD) pattern analysis was performed on cracked spherical titanium dioxide (1-TiO2) and conical titanium dioxide (2-TiO2), such as... Figure 10 As shown, the bottom peak of the spectrum corresponds to the rutile phase TiO2 standard card PDF#78-1508. The 2θ positions of all diffraction peaks in both sets of samples correspond one-to-one with the characteristic diffraction peaks of the rutile standard card, with no significant shift or extraneous peaks. No characteristic diffraction signals from other TiO2 crystal forms such as anatase or brookite were observed. The diffraction peaks of 1-TiO2 are sharper and have higher diffraction intensities; the diffraction peaks of 2-TiO2 have slightly lower intensities, but their positions perfectly match those of the standard rutile, indicating that both samples successfully synthesized high-purity rutile phase titanium dioxide, with only minor differences in grain size / crystallization integrity.

[0086] The absorptivity and reflectivity of the Janus thin film prepared in Example 1 were tested on both sides. The reflectivity of the solar spectrum was tested using 1-TiO2 / PDMS as the cooling section, and the absorptivity of the solar spectrum was tested using 2-TiO2@Ppy / PDMS as the de-icing section. The results are as follows: Figure 4As shown, the reflectance of the 1-TiO2 / PDMS end was tested against the solar spectrum. The film exhibited excellent reflectance (average reflectance >93%) in both the visible and near-infrared regions (0.5~2.5 μm). The absorptivity of the 2-TiO2@Ppy / PDMS end was tested against the solar spectrum. The film exhibited excellent absorptivity (average absorptivity >95%) across the entire solar spectrum.

[0087] 2. Performance testing of radiative cooling and photothermal de-icing

[0088] (1) Radiative cooling performance (simulated sunlight irradiation test) such as Figure 5 As shown

[0089] All samples were 50 mm × 50 mm in size. During testing, the sample films were placed face up (1-TiO2 / PDMS cooling side facing the light source, 2-TiO2@Ppy de-icing side facing down, attached to the insulation board) and laid flat on a polystyrene foam insulation board to avoid interference from heat conduction from the lower platform. The samples from Example 1, Comparative Example 1, and the sample without a film were first placed at room temperature for 20 min to equilibrate. Then, a solar simulator was turned on, and the irradiance at the sample surface was calibrated to 1000 ± 20 W·m using a solar radiometer. -2 Fix the K-type thermocouple at the center of each sample surface and connect it to a multi-channel temperature recorder. After turning on the light, record the surface temperature every 2 minutes, and continue testing for 60 minutes. Figure 5 As shown. Under simulated sunlight irradiation conditions, the surface temperature of Example 1 after 60 min was 35.90 °C, significantly lower than the 48.86 °C of the sample without a thin film and the 40.29 °C of Comparative Example 1. The average temperature drop of Example 1 relative to the sample without a thin film was 12.96 °C, and the average temperature drop relative to Comparative Example 1 was 4.39 °C, indicating that the Janus film structure can effectively reduce heat accumulation under light irradiation conditions. Notably, the cooling temperature of Example 1 was significantly lower than that of Comparative Example 1, which only contained cooling fillers, indicating that the Janus asymmetric structure produced an unexpected synergistic cooling effect. From a thermodynamic perspective, while the pure cooling film in Comparative Example 1 can efficiently reflect sunlight, it still absorbs mid-infrared thermal radiation from the environment and the bottom heat insulation plate, leading to an increase in surface temperature. In contrast, in Example 1, the bottom 2-TiO2@Ppy layer, due to its broad-spectrum strong absorption characteristics, forms an infrared shielding / blocking layer inside the film, effectively cutting off the infrared radiation channel from the bottom environment to the cooling surface. This further reduces the net heat input on the cooling side, thus achieving a cooling effect superior to that of a single-layer cooling film. This synergistic mechanism of "reflective cooling + bottom infrared shielding" overcomes the performance bottleneck of single-layer radiation cooling films.

[0090] (2) Radiative cooling performance (outdoor test) such as Figure 6As shown

[0091] Example 1, Comparative Example 1, and the sample without a film used the same size, substrate, and test stand. All samples were placed on an open, unobstructed outdoor platform with the film facing the sky. A minimum distance of 5 cm was maintained between each sample to avoid mutual obstruction. Before testing, the samples were fixed to a low thermal conductivity foam support, ensuring an air gap between the sample back and the platform. Thermocouples were fixed at the center of the sample surface, and a multi-channel temperature recorder was used to simultaneously collect the surface temperatures of Example 1, Comparative Example 1, and the sample without a film. Solar irradiance, ambient temperature, relative humidity, wind speed, and weather conditions were also recorded. Under continuous outdoor testing conditions, the average surface temperature of the sample in Example 1 was 27.88 °C, lower than the 36.88 °C of the sample without a film and the 31.48 °C of the film in Comparative Example 1. The average temperature drop of Example 1 relative to the sample without a film was 9.00 °C, and the average temperature drop relative to Comparative Example 1 was 3.60 °C. Under conditions of fluctuating solar irradiance and cloud cover, Example 1 maintained a low surface temperature, indicating that the film of Example 1 has superior outdoor radiative cooling performance, such as... Figure 6 As shown, consistent with the results of simulated light testing, Example 1 still exhibits superior cooling capabilities compared to a pure cooling film in complex outdoor environments, further verifying the effectiveness of the infrared shielding effect of the underlying 2-TiO2@Ppy in real-world conditions. This result demonstrates that the Janus structure is not a simple superposition of cooling and de-icing functions, but rather achieves intelligent control of the heat flow path through an asymmetric heterostructure.

[0092] (3) Photothermal de-icing performance: such as Figure 7 As shown

[0093] To evaluate the photothermal de-icing capability of the coating of Example 1 under low-temperature icing conditions, simulated sunlight irradiation de-icing tests were conducted on the samples of Example 1 and Comparative Example 2. During the test, for Example 1 (Janus film), the 2-TiO2@Ppy de-icing side was placed upwards (facing the light source and the iced side), and the 1-TiO2 / PDMS cooling side was placed downwards on the substrate. The coatings of Example 1 and Comparative Example 2 were coated onto substrates of the same size. The samples of Example 1 and Comparative Example 2 were placed in a low-temperature environment, with the temperature of the low-temperature chamber set to -10 °C. Subsequently, deionized water was uniformly sprayed onto the sample surface or a certain amount of artificial frost was spread to form a continuous ice layer on the sample surface. The iced samples were quickly transferred to the light irradiation test platform, keeping the sample surface facing the light source. A xenon lamp solar simulator was used as the light source, with the light intensity set to 1000 W·m. -2 ,like Figure 7As shown in the figure, before the light exposure began (0 min), both Example 1 and Comparative Example 2 samples were covered with a continuous layer of ice and snow, indicating that the two groups of samples had similar initial icing states. After 19.5 min of light exposure, the ice and snow on the surface of Example 1 sample began to loosen and melt significantly, and some substrate or coating surfaces were exposed; while after 60 min of light exposure, the surface of Comparative Example 2 sample was still covered with a large amount of ice and snow, and the overall structure of the ice and snow layer changed little. After 20.8 min of light exposure, most of the ice and snow on the surface of Example 1 sample had melted, slid off, or detached, and the coating surface was basically exposed, with only a small amount of water film or ice crystals remaining; while after 80 min of light exposure, the surface of Comparative Example 2 sample still had obvious ice and snow residue, especially at the sample edges and groove areas where thick ice and snow accumulation was still visible. The above test results show a significant anomaly: the de-icing efficiency of Example 1 (Janus membrane) far exceeds that of Comparative Example 2, which only contains photothermal filler. This may be attributed to the unexpected thermal insulation synergistic effect brought about by the 1-TiO2 / PDMS cooling layer in the Janus structure. In Comparative Example 2, the photothermal layer is directly attached to a cold substrate. The heat generated by the photothermal layer is easily conducted away by the -10°C cold substrate through thermal conduction (i.e., the "heat sink effect"), resulting in a lack of heat at the ice-film interface and slow melting. In contrast, the 1-TiO2 / PDMS composite layer at the bottom of Example 1 has extremely low thermal conductivity. Under de-icing conditions, it passively transforms into an excellent heat insulation layer, blocking the heat conduction from the photothermal layer to the cold substrate. This forces the heat generated by photothermal conversion to be highly concentrated at the ice-film interface, thereby significantly accelerating the melting and removal of ice and snow. This synergistic mechanism of "photothermal heat generation + bottom layer heat insulation" achieves targeted and efficient utilization of heat, giving the film extraordinary de-icing efficiency.

[0094] 3. Weather resistance and interface stability test

[0095] (1) Ultraviolet aging test: The test was conducted according to GB / T 16422.3-2022 "Laboratory Light Source Exposure Test Methods for Plastics - Part 3: Fluorescent Ultraviolet Lamps" and GB / T 14522-2008 "Artificial Climate Aging Test Methods for Plastics, Coatings and Rubber Materials for Mechanical Industry Products - Fluorescent Ultraviolet Lamps". The Janus film prepared in Example 1 was placed in an accelerated ultraviolet aging test chamber and continuously irradiated for 100 hours. The spectral reflectance / absorbance of the film was tested after irradiation for 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 hours, and the spectral reflectance / absorbance retention rate was calculated. Figure 8 As shown.

[0096] Formula for calculating reflection retention rate: Where R0 is the average reflectance of the thin film in the test wavelength range before ultraviolet irradiation (0h), R t The average reflectance of the film in the same wavelength band after t hours of ultraviolet irradiation is given.

[0097] Formula for calculating absorption retention rate: Where A0 is the average absorbance of the thin film in the test wavelength range before ultraviolet irradiation (0h), A t The average absorbance of the film in the same wavelength band after t hours of ultraviolet irradiation is given.

[0098] The results are as follows Figure 8 As shown, after aging, the reflectivity retention rate on the cooling side is >97.5%, and the absorptivity retention rate on the de-icing side is >97.9%. This demonstrates that the rutile phase TiO2 and polypyrrole coating structure used in this invention effectively inhibits photocatalytic degradation and exhibits excellent outdoor weather resistance.

[0099] (2) Interlayer bonding strength test:

[0100] The peel strength of the coating in Example 1 was tested according to GB / T 2790-1995, "Test Method for 180° Peel Strength of Adhesives - Flexible Materials vs. Rigid Materials". The coating was prepared on a rigid substrate with a sample width of 25.0 ± 0.5 mm and an effective peel length of not less than 100 mm. Before testing, a flexible release layer was applied to the coating surface, with one end retained as a clamping end. During testing, the rigid substrate was fixed in the testing machine fixture, and the free end of the flexible release layer was bent 180° and clamped in another fixture. Peeling was performed at a speed of 100 ± 10 mm / min. The peel force-displacement curve was recorded during the test. After removing the initial climbing segment, the average peel force during the stable peeling stage was used to calculate the peel strength. The peel strength was calculated using the formula P = F / b, where F is the average peel force during the stable peeling stage, and b is the sample width. When the sample width was 25 mm, the average peel force during the stable peeling stage of the coating in Example 1 was approximately 20 N, corresponding to a peel strength of approximately 800 N / m. This indicates that the coating has good interfacial adhesion and bonding stability with the substrate. Figure 9 As shown.

[0101] It is understood that the above specific description of the present invention is only for illustrating the present invention and is not limited to the technical solutions described in the embodiments of the present invention. Those skilled in the art should understand that modifications or equivalent substitutions can still be made to the present invention to achieve the same technical effect; as long as the use needs are met, they are all within the protection scope of the present invention.

Claims

1. A method for preparing a Janus-structured PDMS thin film, characterized in that: Conical and cracked spherical rutile phase titanium dioxide can be controlled by evaporation-driven hydrothermal method. Cracked spherical titanium dioxide is used as the cooling side base material, and polypyrrole-coated conical titanium dioxide is used as the de-icing side base material. The two base materials are dispersed in a mixture of PDMS prepolymer and tetrahydrofuran, respectively. Using a casting method, the PDMS mixture of cracked spherical titanium dioxide dispersion is first cast into a mold. After the film is formed and cured, the PDMS mixture of polypyrrole-coated conical titanium dioxide dispersion is cast on it. The tetrahydrofuran solvent is removed by drying and then cured to obtain a Janus structure PDMS film.

2. The method for preparing the Janus structure PDMS thin film according to claim 1, characterized in that, The specific steps include: (1) After mixing tetrahydrofuran, concentrated hydrochloric acid and glacial acetic acid, add poloxamer F-127 and stir to dissolve, then add tetrabutyl titanate; (2) Place the solution obtained in step 1 in an oven for evaporation. After evaporation, the titanium dioxide precursor solution is obtained. (3) The precursor solution obtained in step 2 is placed in a reactor and subjected to hydrothermal treatment at different hydrothermal temperatures; wherein, cracked spherical titanium dioxide is obtained at a hydrothermal temperature of 80°C and conical titanium dioxide is obtained at a hydrothermal temperature of 120°C. (4) Centrifuge the products obtained in step 3, then wash them twice with anhydrous ethanol and distilled water respectively and centrifuge them. After that, dry and grind the centrifuged products to obtain cracked spherical titanium dioxide and conical titanium dioxide. (5) Disperse the cone-shaped titanium dioxide obtained in step 4 in deionized water, perform ultrasonic dispersion, and add hydrochloric acid, ammonium persulfate and pyrrole monomer to the solution in sequence, and carry out in-situ polymerization in an ice-water bath; (6) The product obtained in step 5 is centrifuged, then washed twice with anhydrous ethanol and distilled water respectively and centrifuged again. After that, the centrifuged product is dried and ground to obtain polypyrrole-coated cone titanium dioxide. (7) Disperse the cracked sphere titanium dioxide and polypyrrole-coated cone titanium dioxide obtained in steps 4 and 6 into a mixed solution of PDMS prepolymer and tetrahydrofuran, and add a curing agent; (8) The mixed solution of cracked spherical titanium dioxide and PDMS from step 7 is poured into a mold, dried, and cured to obtain a cracked spherical titanium dioxide / PDMS film. (9) The mixed solution of polypyrrole-coated cone titanium dioxide and PDMS obtained in step 7 is poured onto the film cured in step 8, and then dried and cured to obtain the target product.

3. The method for preparing the Janus structure PDMS thin film according to claim 2, characterized in that: In step (1), 30 mL of tetrahydrofuran, 3 mL of concentrated hydrochloric acid and 2 mL of glacial acetic acid are mixed, and 1.6 g of poloxamer F-127 is added. The mixture is stirred at 700 r / min for 1 h until the solid dissolves. After dissolution, 3.4 mL of tetrabutyl titanate is added, and the mixture is stirred at 700 r / min for 1 h until the solution turns wine red. In step (2), the obtained mixed solution is placed in a 50 °C oven for 5 h until the solution becomes semi-gelatinous, thus obtaining a titanium dioxide precursor solution.

4. The method for preparing the Janus structure PDMS thin film according to claim 3, characterized in that: In step (3), the precursor solution is divided into two portions and placed in two 50 ml polytetrafluoroethylene liners. The two liners are then placed in different reaction vessels and hydrothermally heated at 80 °C and 120 °C for 24 h. In step (4), the product obtained in step (3) is centrifuged, then washed twice with anhydrous ethanol and deionized water respectively, and dried in an 80°C oven for 12 hours. After grinding the dried product, cracked spherical titanium dioxide and conical titanium dioxide are obtained.

5. The method for preparing the Janus structure PDMS thin film according to claim 4, characterized in that: In step (5), 2.5 g of conical titanium dioxide is dispersed in 100 mL of deionized water and sonicated for 30 min. Then, 2 mL of 1 mol / L hydrochloric acid solution, 20 mL of 0.01 mol / L ammonium persulfate solution, and 0.1 mL of pyrrole monomer are added to the solution in sequence, and the mixture is stirred at 700 r / min for 6 h in a water bath at a temperature maintained at 0-5 ℃.

6. The method for preparing the Janus structure PDMS thin film according to claim 5, characterized in that: In step (6), the product obtained in step (5) is centrifuged, then washed twice with anhydrous ethanol and deionized water respectively, and dried in an 80°C oven for 12 hours. After grinding the dried product, polypyrrole-coated cone titanium dioxide is obtained.

7. The method for preparing the Janus structure PDMS thin film according to claim 6, characterized in that: In step (7), tetrahydrofuran and PDMS prepolymer are mixed at a ratio of 3ml:10g, and the cracked sphere titanium dioxide and polypyrrole-coated cone titanium dioxide obtained in steps (4) and (6) are respectively dispersed in the mixed liquid at a mass ratio of 1:10 with the PDMS prepolymer. Curing agent is added at a mass ratio of 10:1 between the prepolymer and the curing agent.

8. The method for preparing the Janus structure PDMS thin film according to claim 7, characterized in that: In step (8), the mixed solution of cracked spherical titanium dioxide and PDMS from step (7) is poured into a mold and placed in an oven at 40 ℃ for 4 h to obtain a cracked spherical titanium dioxide / PDMS film with a thickness of 0.3~1.0 mm. In step (9), the mixed solution of polypyrrole-coated cone titanium dioxide and PDMS obtained in step (7) is poured onto the film cured in step (8), and then dried at 40°C for 6 h to obtain the target product with a top layer thickness of 0.3~1.0 mm.

9. A Janus-structured PDMS thin film prepared by the preparation method according to any one of claims 1-8.

10. An application of the Janus structure PDMS thin film as described in claim 9 in radiative cooling and photothermal de-icing.

Images