An anti-icing photothermal superhydrophobic composite film, its preparation method and uses

Abstract

The present invention provides a photothermal superhydrophobic composite film, which comprises a PVDF nanofiber-based membrane, a photothermal layer attached to the PVDF nanofiber-based membrane, and a hydrophobic layer attached to the photothermal layer. The photothermal superhydrophobic composite film of the present invention has ultra-high hydrophobicity, excellent photothermal conversion performance, excellent stability and good self-cleaning performance, and can be used as an anti-icing film for various substrates.

Description

Technical Field

[0001] The present invention relates to the technical field of anti-icing materials, and particularly to an anti-icing photothermal superhydrophobic material, a preparation method thereof, and uses thereof. Background Art

[0002] Ice formation is a common phenomenon in nature. The formation and accumulation of ice will cause great damage to transportation, wind power generation, housing, power transmission systems, etc., thus bringing many inconveniences and even significant economic losses to people's production and life. Developing a technology that can prevent and remove ice for a long time is crucial for the safety and efficiency of fields such as aviation, electricity, communication, and energy. Traditional ice removal methods, such as mechanical ice removal, thermal ice removal, and chemical ice removal, are usually inefficient, costly, and harmful to the environment. Therefore, it is crucial to develop a more efficient and environmentally friendly anti-icing and ice removal strategy.

[0003] Superhydrophobic materials can effectively prevent icing by forming micro-nano structures and low surface energy coatings on the surface, enabling water droplets to quickly bounce or roll off an inclined surface. The photothermal superhydrophobic coating technology prepared by combining superhydrophobic micro-nano structures and photothermal materials can increase the surface temperature by absorbing solar radiation. In addition, the superhydrophobic surface can quickly remove the melted water and maintain high solar thermal performance. It can also function even without sunlight, improving the stability and efficiency of material applications. Currently, researchers have achieved certain research results in this field. For example, combining laser etching with spin coating or deposition techniques not only takes a long time and effort but also increases the production difficulty and cost (Literature 1: Z. Lin, C. Ma, Z. Ma, L. Gao, W. Chen, G. Chen, Laser etching ultra-black coating with novel anti-icing performance, Chemical Engineering Journal, 466 (2023) 143067. https: / / doi.org / https: / / doi.org / 10.1016 / j.cej.2023.143067). In addition, the extensive use of expensive chemical reagents such as perfluorinated compounds also increases the economic burden, and most preparation processes also cause environmental pollution (Literature 2: G. Y. Liu, Y. Yuan, R. J. Liao, H. Y. Xiang, L. Wang, Q. Yu, C. Zhang, Robustand self-healing superhydrophobic aluminum surface with excellent anti-icingperformance, Surfaces and Interfaces, 28 (2022) 101588. https: / / doi.org / https: / / doi.org / 10.1016 / j.surfin.2021.101588). At the same time, considering the heating effect during the photothermal conversion process, directly coating the photothermal superhydrophobic coating on the equipment may cause overheating of the equipment. In addition, the anti-icing coating requires long-term maintenance, and there are problems such as poor long-term anti-icing effect and poor durability.

[0004] Current research mainly focuses on high-performance anti-icing / de-icing coatings on rigid and flat substrates such as metal plates, glass, and wood. There is relatively little research on flexible substrates such as textiles, sponges, and foams. Preparing a photothermal superhydrophobic anti-icing material that is suitable for both flexible and rigid substrates will greatly expand its application range. Summary of the Invention

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present invention is to provide a flexible photothermal superhydrophobic composite film and a preparation method thereof, which are used to solve the problems of poor durability, instability, high cost and environmental adaptability of the anti-icing materials in the prior art.

[0006] The first aspect of the present invention provides a photothermal superhydrophobic composite film, which comprises a PVDF nanofiber-based membrane, a photothermal layer attached to the PVDF nanofiber-based membrane, and a hydrophobic layer attached to the photothermal layer.

[0007] Preferably, the photothermal layer comprises photoabsorbing nanoparticles, a stabilizer and an oxidant; the photoabsorbing nanoparticles are polypyrrole nanoparticles, the stabilizer is polyvinyl alcohol, and the oxidant is one or more selected from FeCl3, FeCl3·6H2O.

[0008] In some specific embodiments, the oxidant is FeCl3·6H2O.

[0009] Preferably, the hydrophobic layer comprises functional particles, a hydrophobic modifier and a curing agent; the functional particles are one or two selected from titanium dioxide and silicon dioxide, the hydrophobic modifier is a polydimethylsiloxane prepolymer, and the curing agent is a polydimethylsiloxane curing agent.

[0010] In some specific embodiments, the functional particles are silicon dioxide.

[0011] Preferably, the mass ratio of the photoabsorbing nanoparticles, the stabilizer and the oxidant in the photothermal layer is 0.1-2:0.1-0.5:1-10.

[0012] More preferably, the mass ratio of the photoabsorbing nanoparticles, the stabilizer and the oxidant in the photothermal layer is 0.1-1:0.1-0.5:5-10.

[0013] Preferably, the mass ratio of the functional particles, the hydrophobic modifier and the curing agent in the hydrophobic layer is 0.1-10:0.1-10:0.01-1.

[0014] More preferably, the mass ratio of the functional particles, the hydrophobic modifier and the curing agent in the hydrophobic layer is 0.1-1:0.1-1:0.01-0.1.

[0015] Preferably, the photothermal superhydrophobic composite film further comprises a crosslinking agent for fixing the photothermal layer to the PVDF nanofiber-based membrane.

[0016] Preferably, the crosslinking agent is glutaraldehyde.

[0017] Preferably, the thickness of the photothermal superhydrophobic composite film is 60-100 μm.

[0018] More preferably, the thickness of the photothermal superhydrophobic composite film is 80-100 μm.

[0019] Preferably, the surface water contact angle of the photothermal superhydrophobic composite film is greater than 150°.

[0020] The second aspect of the present invention provides a method for preparing the above-mentioned photothermal superhydrophobic composite film, the method comprising coating a dispersion liquid of a photothermal layer on the surface of a PVDF nanofiber-based membrane to form a photothermal layer and coating a dispersion liquid of a hydrophobic layer on the surface of the photothermal layer to prepare the photothermal superhydrophobic composite film.

[0021] Preferably, the PVDF nanofiber-based membrane is prepared by electrospinning.

[0022] Preferably, the spinning solution for electrospinning uses DMF and / or acetone as solvents, and the concentration of PVDF in the spinning solution is 10-20 wt%.

[0023] Preferably, the electrospinning parameters are any one or more of the following: the pushing speed is 1-10 μL / min, the voltage is 25-40 kV, the collection distance is 10-20 cm, the spinning temperature is 20°C-30°C, and the spinning humidity is 20%-40%.

[0024] Preferably, the dispersion liquid of the photothermal layer is sprayed onto the surface of the PVDF nanofiber-based membrane to form a photothermal layer, and the coating amount of the dispersion liquid of the photothermal layer is 0.1-10 ml / cm 2 。

[0025] More preferably, the coating amount of the dispersion liquid of the photothermal layer is 0.1-1 ml / cm 2 。

[0026] Preferably, the method further includes soaking the PVDF nanofiber-based membrane coated with the photothermal layer in a crosslinking solution for crosslinking and fixing the photothermal layer, the crosslinking solution comprising a crosslinking agent and a solvent, the crosslinking agent being glutaraldehyde, and the solvent being one or more of acetone, water, ethanol, and ether.

[0027] Preferably, the dispersion liquid of the photothermal layer is formed by dispersing the materials in the photothermal layer using a solvent, the solvent being selected from deionized water, and based on the addition amount of 1 g of stabilizer, the addition amount of the solvent is 5-20 mL.

[0028] More preferably, based on the addition amount of 1 g of stabilizer, the addition amount of the solvent is 10-20 mL.

[0029] Preferably, the dispersion of the hydrophobic layer is formed by dispersing the materials in the hydrophobic layer with a solvent, and the solvent is one or more selected from ethyl acetate, ethanol, and deionized water. Based on the addition amount of 1 g of functional particles, the addition amount of the solvent is 100 - 500 mL.

[0030] More preferably, based on the addition amount of 1 g of functional particles, the addition amount of the solvent is 100 - 300 mL.

[0031] In some specific embodiments, the solvent in the crosslinking solution is acetone and water.

[0032] Preferably, the volume ratio of acetone to water is 1 - 5:1, and more preferably 1 - 3:1.

[0033] In some specific embodiments, the volume ratio of acetone to water is 3:2.

[0034] Preferably, the pH of the crosslinking solution is 1 - 3.

[0035] In some specific embodiments, the pH of the crosslinking solution is 2.

[0036] Preferably, the concentration of the crosslinking agent in the crosslinking solution is 0.5 wt%.

[0037] Preferably, the crosslinking time is 2 h.

[0038] Preferably, the method further includes spraying the dispersion of the hydrophobic layer onto the surface of the crosslinked photothermal layer, and the coating amount of the hydrophobic layer dispersion is 0.1 - 10 ml / cm 2 。

[0039] More preferably, the coating amount of the hydrophobic layer dispersion is 0.1 - 1 ml / cm 2 。

[0040] Preferably, the method further includes a solvent welding step, and the solvent welding is to place the coated photothermal superhydrophobic composite film at 60 - 100 °C for 3 - 10 h.

[0041] More preferably, the temperature of the solvent welding is 70 - 90 °C, and the time of the solvent welding is 4 - 8 h.

[0042] The third aspect of the present invention provides an application of the above-mentioned photothermal superhydrophobic composite film as an anti-icing film

[0043] As described above, the photothermal superhydrophobic composite film of the present invention has the following beneficial effects:

[0044] 1. The photothermal superhydrophobic composite film prepared in this application has extremely high hydrophobicity. With this superhydrophobic function, excellent passive anti-icing effects can be achieved, and the time for water droplets to freeze into ice can be significantly extended.

[0045] 2. The photothermal superhydrophobic composite film prepared in this application has excellent active anti-icing performance. Compared with the PVDF film without a photothermal layer, the water droplet freezing time can be extended by more than 2 times, and it has excellent photothermal conversion performance.

[0046] 3. The photothermal superhydrophobic composite film prepared in this application has good self-cleaning performance. When it is immersed in aqueous solutions of different colors and then taken out, there are no water stains and color depositions on the film surface.

[0047] 4. The photothermal superhydrophobic composite film prepared in this application has excellent stability and will not corrode or deform under various conditions of acids, alkalis, salts, heat, and cold. Description of the Drawings

[0048] Figure 1 It shows a schematic diagram of the preparation process of the photothermal superhydrophobic composite film of the present invention.

[0049] Figure 2 A shows the surface morphology diagram of the PPy-PVA / PVDF fiber film prepared with a spraying amount of 0.25 mL of PPy-PVA slurry in Example 3 of the present invention.

[0050] Figure 2 B shows the surface morphology diagram of the PPy-PVA / PVDF fiber film prepared with a spraying amount of 0.5 mL of PPy-PVA slurry in Example 3 of the present invention.

[0051] Figure 2 C shows the surface morphology diagram of the PPy-PVA / PVDF fiber film prepared with a spraying amount of 0.75 mL of PPy-PVA slurry in Example 3 of the present invention.

[0052] Figure 2 D shows the surface morphology diagram of the PPy-PVA / PVDF fiber film prepared with a spraying amount of 1 mL of PPy-PVA slurry in Example 3 of the present invention.

[0053] Figure 3 It shows the photothermal conversion temperature rise trend diagram of the PPy-PVA / PVDF fiber film under 1 sun condition in Example 3 of the present invention.

[0054] Figure 4 A shows the surface morphology diagram of the PPy-PVA-GA / PVDF composite film prepared with a volume ratio of acetone to water of 60:40 in the crosslinking solution used in Example 4 of the present invention.

[0055] Figure 4 Figure B shows the surface morphology of the PPy-PVA-GA / PVDF composite membrane prepared with a volume ratio of acetone to water of 70:30 in the crosslinking solution used in Example 4 of the present invention.

[0056] Figure 4 Figure C shows the surface morphology of the PPy-PVA-GA / PVDF composite membrane prepared with a volume ratio of acetone to water of 80:20 in the crosslinking solution used in Example 4 of the present invention.

[0057] Figure 5 Shows the water contact angle test results of different PPy-PVA-GA / PVDF composite membranes prepared with crosslinking solutions of different volume ratios of acetone to water in Example 4 of the present invention.

[0058] Figure 6 Figure A shows the surface morphology of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane prepared with a spraying amount of 1 mL of hydrophobic dispersion in Example 5 of the present invention.

[0059] Figure 6 Figure B shows the surface morphology of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane prepared with a spraying amount of 1.5 mL of hydrophobic dispersion in Example 5 of the present invention.

[0060] Figure 6 Figure C shows the surface morphology of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane prepared with a spraying amount of 2 mL of hydrophobic dispersion in Example 5 of the present invention.

[0061] Figure 7 Shows the test curve graph of the photothermal conversion performance of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane and the PPy-PVA / PVDF photothermal composite membrane in Example 5 of the present invention.

[0062] Figure 8 Shows the temperature change trend graph of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane under different irradiation conditions in Example 5 of the present invention.

[0063] Figure 9 Figure A shows the freezing process of droplets on the PPy-PVA / PVDF photothermal composite membrane in Example 6 of the present invention.

[0064] Figure 9 Figure B shows the freezing process of droplets on the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane in Example 6 of the present invention.

[0065] Figure 10 Shown is a comparison chart of the freezing times of droplets on the PPy-PVA / PVDF photothermal composite film and the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite film in Example 6 of the present invention.

[0066] Figure 11 A shows the freezing process of droplets on the PVDF nanofiber-based film in Example 6 of the present invention.

[0067] Figure 11 B shows the freezing process of droplets on the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite film in Example 6 of the present invention.

[0068] Figure 12 Shown is a comparison chart of the freezing times of droplets on the PVDF nanofiber-based film and the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite film in Example 6 of the present invention.

[0069] Figure 13 Shown is a comparison chart of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite film before and after being placed in and taken out of different solutions in Example 6 of the present invention. Detailed implementation manners

[0070] The following specific examples illustrate the implementation manners of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific implementation manners. Various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0071] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before and after the combined steps or the insertion of other method steps between these clearly mentioned steps, unless otherwise stated; it should also be understood that the combined connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before and after the combined devices / apparatuses or the insertion of other devices / apparatuses between these two clearly mentioned devices / apparatuses, unless otherwise stated. Moreover, unless otherwise stated, the numbers of the method steps are only convenient tools for identifying the method steps, rather than limiting the arrangement order of the method steps or the scope in which the present invention can be implemented. The change or adjustment of their relative relationship, without substantial change in the technical content, should also be regarded as the scope in which the present invention can be implemented.

[0072] When numerical ranges are given in the embodiments, it should be understood that unless otherwise specified in the present invention, both endpoints of each numerical range and any value between the two endpoints can be selected. Unless otherwise defined, all technical and scientific terms used in the present invention have the same meaning as commonly understood by those skilled in the art of this technology. In addition to the specific methods, devices, and materials used in the embodiments, according to the knowledge of those skilled in the art of this technology and the description of the present invention, any methods, devices, and materials of the prior art similar to or equivalent to those described in the embodiments of the present invention can also be used to implement the present invention.

[0073] Aiming at the problems of poor durability, instability, high cost, and environmental adaptability of anti-icing materials in the prior art, this application selects a hydrophobic PVDF nanofiber membrane with more excellent strength and lower thermal conductivity as the flexible substrate. Among them, the hydrophobic support layer can prevent the surface hydrophilic photothermal slurry from infiltrating into the fiber membrane and play a heat insulation effect. Aiming at the film-forming integrity of the photothermal functional layer and the complexity of the preparation process, PVA (polyvinyl alcohol) is used as a stabilizer in this patent. Through a simple one-step dispersion polymerization, PPy (polypyrrole) particles are formed. After FeCl3 is added as an oxidant for the PVA / Fe cation complex, the reaction sites of the pyrrole monomer and the complex are used to manufacture PPy nanoparticles, and the reaction forms PPy-PVA slurry. Then, the PPy-PVA functional layer is coated on the surface of the PVDF nanofiber membrane and crosslinked to achieve hydrolysis resistance. Aiming at the superhydrophobicity problem required for passive anti-icing, this patent selects a method of combining a low surface energy substance PDMS and nanoparticles SiO2 to construct a multi-scale micro-nano superhydrophobic structure. PDMS can reduce the surface energy of the composite membrane, further enhance the repellency, and effectively improve the performance of the membrane.

[0074] The anti-icing photothermal superhydrophobic composite membrane prepared in this application has ultra-high hydrophobicity, good self-cleaning performance, and excellent stability, and can play an anti-icing role through the active anti-icing of the photothermal layer and the passive anti-icing of the superhydrophobic layer. This kind of photothermal superhydrophobic composite membrane of this application can be coated or pasted on the surface of the rigid substrate or flexible substrate to be protected to play a role in protecting the substrate from icing.

[0075] Example 1

[0076] This example is the preparation process of the anti-icing photothermal superhydrophobic composite membrane.

[0077] Step 1: Preparation of the PVDF nanofiber base membrane.

[0078] Preparation of 15 wt% PVDF / DMF spinning solution: Weigh a certain amount of PVDF powder (Mw = 573000 g / mol, Solvay Shanghai Co., Ltd.) and dissolve it in DMF. Continuously stir in an oil bath at 70 °C for 3 days until the solution becomes transparent. Let it stand for 24 hours until all the bubbles are removed. Take 5 mL of the spinning solution and inject it into a syringe with a stainless-steel metal needle. Clamp the syringe on a micro-injection pump and adjust the injection speed to 5 μL / min. Apply a voltage of 28 kV to electrify the polymer solution. Then, under the action of electrostatic repulsion, the liquid droplets generate Taylor cones, overcome the surface tension to form jets, and the generated nanofibers are collected on a metal roller wrapped with aluminum foil. The rotation speed of the roller is 500 rpm / min, and the distance from the roller to the spinneret is 15 cm. During the electrospinning process, the environmental temperature and humidity are 27 ± 5 °C and 30 ± 5% respectively. Finally, place the prepared PVDF nanofiber-based membrane in a vacuum dryer at 60 °C for 12 h to remove the residual solvent, and hot press it at 155 °C for 10 min to improve the dimensional integrity of the membrane.

[0079] Step 2: Preparation of the photothermal functional layer of the composite membrane.

[0080] Dissolve 1.5 g of PVA (86 - 89% hydrolysis degree, low molecular weight, product number: 041238, Thermo Fisher Scientific (China) Co., Ltd.) in 20 ml of deionized water at 60 °C for 20 min, then cool it to room temperature and add FeCl3·6H2O (0.23 M) to it. After the system changes from clear to yellow and equilibrates for 1 h, add 0.1 M pyrrole monomer (analytical pure 9%, Shanghai Wendong Chemical Reagent Co., Ltd.) to the system and keep the system temperature at 5 °C and stir for 4 h to form PPy-PVA slurry. Then, load a certain amount of PPy-PVA slurry (0.25 mL, 0.5 mL, 0.75 mL, 1 mL, 1.25 mL, 1.5 mL) onto the 3×3 cm-sized PVDF nanofiber membrane prepared in Step 1 by spraying to obtain PPy-PVA / PVDF fiber membranes. Then, prepare a solution by mixing acetone and water in a certain ratio (60:40, 70:30, 80:20), and then add 1.5 M HCl solution to adjust its pH value to about 2. Add an appropriate amount of 25% glutaraldehyde aqueous solution (GA) to this solution to prepare a crosslinking solution with a crosslinking agent concentration of 0.5 wt%. Immerse the PPy-PVA / PVDF fiber membrane in 100 mL of the crosslinking solution for 2 h, and form a PPy-PVA-GA / PVDF composite membrane by crosslinking with GA.

[0081] Step 3: Preparation of the superhydrophobic layer of the composite membrane.

[0082] Add 0.2 g of fumed silica (7 - 40 nm, Shanghai Titan) to 0.2 g of polydimethylsiloxane prepolymer (PDMS prepolymer, 1 wt%), and ultrasonically treat it in 20 mL of ethyl acetate for 1 h. Subsequently, add 0.02 g of curing agent (PDMS prepolymer:curing agent) at a mass ratio of 10:1 and stir for 10 min to form a hydrophobic dispersion. Spray different volumes of the hydrophobic dispersion (1 mL, 1.5 mL, 2 mL) onto the PPy - PVA - GA / PVDF composite membrane prepared in the above step two to form a superhydrophobic layer, and dry it at 80 °C for 5 h to obtain the photothermal superhydrophobic composite membrane PDMS@SiO2 / PPy - PVA - GA / PVDF.

[0083] The preparation process of the photothermal superhydrophobic composite membrane of the present invention is as Figure 1 shown.

[0084] Example 2

[0085] Perform a membrane thickness test on the photothermal superhydrophobic composite membrane prepared in Example 1 of the present invention.

[0086] Specifically, in accordance with ASTM E252 - 2006, use a thousand - fraction digital thickness gauge to measure the thickness of the PVDF fiber composite membrane, measure 3 times at different parts of the PVDF fiber composite membrane and take the average value. The test shows that the thickness of the PVDF fiber composite membrane is between 80 - 100 μm.

[0087] Example 3

[0088] In this example, PPy - PVA / PVDF fiber membranes are prepared by spraying different amounts of PPy - PVA slurry on the PVDF nanofiber - based membrane, so as to evaluate the structural characteristics and photothermal conversion performance of the obtained photothermal composite membrane under the condition of different amounts of PPy - PVA slurry.

[0089] Respectively take 0.25 mL, 0.5 mL, 0.75 mL, 1 mL, 1.25 mL and 1.5 mL of PPy - PVA slurry, and spray it onto a 3×3 cm PVDF nanofiber membrane through a 0.5 - mm spray gun orifice in a small - amount - multiple - spraying manner to obtain PPy - PVA / PVDF fiber membranes, and then place them in an oven at 50 °C and dry for 10 min. Photothermal composite membranes with different loadings are obtained.

[0090] Figure 2A-2D are the surface morphology diagrams of the photothermal films under different PPy-PVA slurry loadings (0.25 mL, 0.5 mL, 0.75 mL, 1 mL) of the above four types observed by scanning electron microscopy. The results show that at a loading of 0.25 mL, the bare fiber morphology can be clearly seen. As the loading increases to 0.75 mL, only slight cracks exist in the surface photothermal layer. When 1 mL of PPy-PVA slurry is used as the spraying solution, the PPy-PVA slurry can completely cover the surface of the fiber membrane to form a complete photothermal layer. At the same time, it can be seen from the scanning electron microscopy images at a large magnification that the polymerized spherical PPy nanoparticles are densely aggregated on the surface.

[0091] To further verify the influence of the deposition amount of the PPy-PVA layer on the photothermal conversion of the PPy-PVA / PVDF fiber membrane, the photothermal conversion temperature increase trends of the fiber membranes with different loadings were tested under the irradiation condition of 1 sun by a xenon lamp solar simulator. The specific test results are as Figure 3 shown (the abscissa in the figure represents the spraying amount, and the ordinate represents the temperature). The results show that as the spraying amount of the PPy-PVA slurry gradually increases from 0.5 mL, the photothermal conversion temperature increase trend of the membrane gradually rises; while starting from 1 mL, as the spraying amount of the PPy-PVA slurry increases, the temperature increase trend line is not obvious.

[0092] Combined with Figure 2 A-2D and Figure 3 the results, it can be seen that a complete photothermal layer can be formed on the membrane surface when the spraying amount of the PPy-PVA slurry is 1 mL. At the same time, further observation shows that as the loading of the PPy-PVA slurry increases, the surface equilibrium temperature rapidly increases with the increase of the spraying amount. However, after spraying 1 mL of PPy-PVA slurry, the increase in the equilibrium temperature of the photothermal layer formed by continuing to increase the spraying amount of the PPy-PVA slurry is limited. Therefore, a spraying amount of 1 mL of PPy-PVA slurry can enable the composite membrane surface to have excellent photothermal conversion effect. Under the condition of 1 sun, the temperature rise of this photothermal composite membrane can reach 77 °C.

[0093] Example 4

[0094] In this example, when the spraying amount of the PPy-PVA slurry is 1 mL, only the volume ratio of acetone to water in the crosslinking solution is changed, so as to evaluate the structural characteristics of the crosslinked PPy-PVA-GA / PVDF composite membrane under different volume ratios of acetone to water.

[0095] The PPy-PVA / PVDF fiber membrane was immersed in crosslinking solutions with an acetone-to-water volume ratio of 60:40, 70:30, and 80:20 for 2 h, then taken out and washed with pure water, and crosslinked and dried at room temperature. PPy-PVA-GA / PVDF composite membranes with hydrolysis resistance under different crosslinking agent ratios were obtained.

[0096] Figure 4 A-4C is the surface morphology image of the PPy-PVA-GA / PVDF composite membrane observed by scanning electron microscopy after crosslinking with the above three different ratios of acetone and water crosslinking solutions. The results show that the crosslinked layer on the surface still retains the rough structure of microscopic spherical particles, and the basically pore-free PPy-PVA hydrogel layer completely covers the nanofiber support layer. It can be seen from this that when the ratio of acetone to water is 60:40, the rough structure on its surface is more obvious, and as the acetone content in the crosslinking solution increases, the surface morphology becomes more and more flat.

[0097] Furthermore, the water contact angle of the PPy-PVA-GA / PVDF composite membrane crosslinked with the above three different ratios of acetone and water crosslinking solutions was tested. Specifically, according to GB / T30447-2013, the water contact angle was measured using an OCA40 type dynamic contact angle measuring instrument (purchased from Dataphysics, Germany) to characterize the hydrophobicity of the membrane surface. Five different regions of each sample were measured and the average value was taken. The specific test results are as Figure 5 shown (the abscissa in the figure represents the ratio of water / acetone, and the ordinate represents the size of the water contact angle). The results show that when the ratio of acetone to water is 60:40, the water contact angle of the crosslinked composite membrane can reach 90°, and as the amount of acetone further increases, the water contact angle shows a downward trend.

[0098] Combined with Figure 4 A-4C and Figure 5 the results, it can be seen that when the ratio of acetone to water in the crosslinking solution is 60:40, the surface of the crosslinked PPy-PVA-GA / PVDF composite membrane is significantly rough and the water contact angle is large; selecting a crosslinking ratio (60:40) that can provide a higher rough surface is beneficial to increasing the interaction area when the two interfaces come into contact during the subsequent construction of a superhydrophobic layer on its surface, and further improving its interlocking performance.

[0099] Example 5

[0100] In this example, when the spraying amount of the PPy-PVA slurry is 1 mL and the ratio of acetone to water in the cross-linking solution is 60:40, only the spraying amount of the hydrophobic dispersion is changed, so as to evaluate the structural characteristics and photothermal conversion performance of the PDMS@SiO2 / PPy-PVA-GA / PVDF composite membrane under different spraying amounts of the hydrophobic dispersion.

[0101] Prepare the PPy-PVA-GA / PVDF composite membrane and the hydrophobic dispersion according to the steps in Example 1. Spray the hydrophobic dispersion onto the surface of the PPy-PVA-GA / PVDF composite membrane in different volumes (1 mL, 1.5 mL, 2 mL), and dry it at 80 °C for 5 h to obtain the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane.

[0102] Use a scanning electron microscope to observe the morphology of the above three fiber composite membranes prepared with different volumes of the hydrophobic dispersion. The results are as Figure 6 shown in A-6C. The results show that as the spraying amount of the hydrophobic dispersion increases, the number of particles on the membrane surface gradually increases, and finally completely spreads on the surface of the photothermal membrane when the spraying amount is 2 mL. At the same time, it can be observed that the hierarchical structure on the membrane surface is formed by stacking nanoparticles, thus constructing micron-scale protrusions. Test the water contact angle of the prepared photothermal superhydrophobic composite membrane according to the method in Example 4. When the spraying amount of the hydrophobic dispersion is 2 mL, the water contact angle of the membrane can reach 156°.

[0103] Furthermore, adopt the method in Example 3 to test the photothermal conversion performance of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane under 1 sun condition. The specific test results are as Figure 7 shown (the red dot trend line in the figure represents the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane, and the blue triangle trend line represents the PPy-PVA / PVDF photothermal composite membrane). According to Figure 7 the results, the temperatures of the PPy-PVA / PVDF photothermal composite membrane and the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane can reach 90.6 °C and 89.5 °C respectively, which indicates that the black PPy-PVA-GA cross-linked photothermal layer plays an important role, and the PDMS@SiO2 superhydrophobic layer has little effect on the photothermal performance of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane.

[0104] Furthermore, repeated heating-cooling tests were carried out under the conditions of 1 sun, 1.4 sun, and 1.6 sun to observe the temperature change of the film. Specifically, the film was irradiated for 2 min by turning on the light and then allowed to cool naturally for 2 min by turning off the light. Each condition was cycled 3 times. The specific results are as Figure 8 shown. Under different irradiation conditions, the temperature change on the surface of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite film was similar, indicating that the photothermal superhydrophobic composite film of this application has stable photothermal conversion ability.

[0105] Example 6

[0106] In this example, the optimal spraying amount of PPy-PVA slurry (1 mL), the ratio of acetone to water in the cross-linking solution (60:40), and the spraying amount of the hydrophobic dispersion liquid (2 mL) in Examples 3-5 above were selected. The PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite film was prepared by the same steps as in Example 1, and its anti-icing performance, stability, and self-cleaning performance were investigated.

[0107] In this example, a 60 μL methylene blue solution was used as the freezing liquid droplet, the cold source was controlled by a semiconductor cooling stage, and a xenon lamp was used as the test light source to measure the freezing time of the water droplet on the film surface to evaluate its anti-icing performance.

[0108] First, the freezing time of the liquid droplet under dark and cold conditions was tested. Specifically, the sample was placed on the semiconductor cooling stage, the temperature was set to -10 °C, and the relative humidity was 55 ± 5%. The cooling stage was placed in the dark to simulate a dark and cold environment. Then, a liquid droplet (60 μL) was dropped onto the sample surface using a pipette, and the freezing process of the liquid droplet was recorded. The time required for the liquid droplet to change from the liquid phase to the completely solid phase was defined as the freezing time.

[0109] Figure 9 A-9B shows the freezing process of the liquid droplet in the cold environment in the dark, Figure 10 and is the freezing time after the liquid droplet was dropped onto the PPy-PVA / PVDF photothermal composite film and the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite film. When the liquid droplet contacted the PPy-PVA / PVDF photothermal composite film ( Figure 9 A), the freezing time for the liquid droplet to freeze into a hemispherical shape was 762 s. However, when the liquid droplet contacted the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite film, the icing time was greatly delayed to 1113 s. More importantly, the ice droplet remained spherical after freezing.

[0110] When the liquid droplets are dropped onto the above two membranes, there are two reasons for the different freezing processes of the two: The first reason is that the water contact angle of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane is larger. When the water contact angle increases, the contact area between the water droplet and the substrate surface will decrease; Another reason is that different surfaces lead to different nucleation processes of ice crystallization of water. On the surface of the PPy-PVA / PVDF photothermal composite membrane, the ice nucleation process starts heterogeneously at the liquid-solid interface. However, on the surface of the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane, due to the many micron-sized protrusions on its hydrophobic layer, the ice nucleation process on this membrane occurs at the three-phase interface (gas-liquid-solid), which prolongs the time for the liquid droplet to completely freeze.

[0111] Furthermore, the freezing time of the liquid droplets under illuminated cold conditions was tested. Specifically, the sample was placed on a semiconductor cooling stage with the temperature set at -10°C and the relative humidity at 55±5%. The cooling stage was placed under a 1 sun light source condition to simulate an illuminated cold environment. Then, a liquid droplet (60 μL) was dropped onto the sample surface using a pipette, and the freezing process of the liquid droplet was recorded. The time required for the liquid droplet to change from the liquid phase to the completely solid phase was defined as the freezing time.

[0112] Figure 11 A-11B shows the freezing process of the liquid droplet in the illuminated cold environment. Figure 12 is the freezing time after the liquid droplet is dropped onto the PVDF nanofiber-based membrane and the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane. When the liquid droplet touches the PVDF nanofiber-based membrane ( Figure 11 A), the freezing time for the liquid droplet to freeze into a hemispherical shape is 714 s. However, when the liquid droplet touches the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane, the freezing time is greatly delayed to 1533 s, and the ice droplet remains spherical after freezing. This is because the PVDF nanofiber-based membrane without a photothermal layer cannot perform photothermal conversion, and the water droplet cannot absorb the heat from the surface and can only rely on the heat of the environment, so it will be frozen quickly. While the PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite membrane of the present application can not only absorb the heat from the environment but also absorb the heat brought by the photothermal conversion of the bottom photothermal layer, so its freezing time is significantly prolonged.

[0113] In addition, the stability and self-cleaning performance of the photothermal superhydrophobic composite film were further investigated. The prepared PDMS@SiO2 / PPy-PVA-GA / PVDF photothermal superhydrophobic composite film was respectively placed in cold water (0 °C), hot water (85 °C), HCl solution (pH = 2), 3.5 wt% NaCl solution and NaOH solution (pH = 12) for 6 min to test the self-cleaning property of the photothermal superhydrophobic coating. All the above test solutions were dyed different colors for easy observation of their self-cleaning performance. The specific test results are as Figure 13 shown. The results show that the shapes of all test samples did not change, and there were no water stains and color depositions of the staining solution on the surface of the film, proving that the photothermal superhydrophobic coating prepared in this application has excellent cold and heat and acid-base stability, and has good self-cleaning performance on the surface.

[0114] The above is only the preferred embodiment of the present invention, and it is not a limitation to any form and essence of the present invention. It should be pointed out that for those of ordinary skill in the art in this technical field, without departing from the premise of the method of the present invention, several improvements and supplements can still be made, and these improvements and supplements should also be regarded as the protection scope of the present invention. Any equivalent changes such as slight modifications, decorations and evolutions made by those who are familiar with the technology in this field without departing from the spirit and scope of the present invention by using the technical content disclosed above are all equivalent embodiments of the present invention; at the same time, any equivalent changes, modifications and evolutions made to the above embodiments according to the essence of the present invention still fall within the scope of the technical solution of the present invention.

Claims

1. A photothermal superhydrophobic composite film, characterized in that, The photothermal superhydrophobic composite film is composed of a PVDF nanofiber-based membrane, a photothermal layer attached to the PVDF nanofiber-based membrane, and a hydrophobic layer attached to the photothermal layer; the photothermal layer includes photoabsorbing nanoparticles, a stabilizer, and an oxidant; the photoabsorbing nanoparticles are polypyrrole nanoparticles, the stabilizer is polyvinyl alcohol, and the oxidant is one or more selected from FeCl3 and FeCl3·6H2O; the hydrophobic layer includes functional particles, a hydrophobic modifier, and a curing agent; the functional particles are one or two selected from titanium dioxide and silicon dioxide, the hydrophobic modifier is a polydimethylsiloxane prepolymer, and the curing agent is a polydimethylsiloxane curing agent; the method for attaching the photothermal layer to the PVDF nanofiber-based membrane is as follows: Spray the dispersion of the photothermal layer onto the surface of the PVDF nanofiber-based membrane to form the photothermal layer, and soak the PVDF nanofiber-based membrane coated with the photothermal layer in a crosslinking solution for crosslinking and fixing the photothermal layer. The crosslinking solution contains a crosslinking agent and a solvent. The crosslinking agent is glutaraldehyde, the solvent in the crosslinking solution is acetone and water, and the volume ratio of acetone to water is 1-3:1; the pH of the crosslinking solution is 1-3.

2. The photothermal superhydrophobic composite film according to claim 1, wherein The mass ratio of the photoabsorbing nanoparticles, the stabilizer, and the oxidant in the photothermal layer is 0.1-2:0.1-0.5:1-10; and / or, the mass ratio of the functional particles, the hydrophobic modifier, and the curing agent in the hydrophobic layer is 0.1-10:0.1-10:0.01-1.

3. The photothermal superhydrophobic composite film according to claim 1, wherein The thickness of the photothermal superhydrophobic composite film is 60-100 μm; and / or, the surface water contact angle of the photothermal superhydrophobic composite film is greater than 150°.

4. A method for preparing a photothermal superhydrophobic composite film according to any one of claims 1 to 3, characterized in that, The method includes coating the dispersion of the photothermal layer on the surface of the PVDF nanofiber-based membrane to form the photothermal layer and coating the dispersion of the hydrophobic layer on the surface of the photothermal layer to prepare the photothermal superhydrophobic composite film; soaking the PVDF nanofiber-based membrane coated with the photothermal layer in a crosslinking solution for crosslinking and fixing the photothermal layer. The crosslinking solution contains a crosslinking agent and a solvent. The crosslinking agent is glutaraldehyde, the solvent in the crosslinking solution is acetone and water, and the volume ratio of acetone to water is 1-3:1; the pH of the crosslinking solution is 1-3.

5. The preparation method according to claim 4, characterized in that, The PVDF nanofiber-based membrane is prepared by electrospinning, and the electrospinning parameters are any one or more of the following: the pushing speed is 1-10 μL / min, the voltage is 25-40 kV, the collection distance is 10-20 cm, the spinning temperature is 20°C-30°C, and the spinning humidity is 20%-40%.

6. The preparation method according to claim 5, characterized in that, The spinning solution for electrospinning uses DMF and / or acetone as the solvent, and the concentration of PVDF in the spinning solution is 10-20 wt%.

7. The preparation method according to claim 4, characterized in that, Spray the dispersion of the photothermal layer onto the surface of the PVDF nanofiber-based membrane to form the photothermal layer, and the coating amount of the photothermal layer dispersion is 0.1 to 10 ml / cm 2 .

8. The preparation method according to claim 4, characterized in that, The dispersion of the photothermal layer is formed by dispersing the materials in the photothermal layer with a solvent. The solvent is deionized water. Based on the addition amount of 1 g of stabilizer, the addition amount of the solvent is 5-20 mL; and / or, the dispersion of the hydrophobic layer is formed by dispersing the materials in the hydrophobic layer with a solvent. The solvent is one or more selected from ethyl acetate and n-hexane. Based on the addition amount of 1 g of functional particles, the addition amount of the solvent is 100-500 mL.

9. The preparation method according to claim 4, characterized in that, The concentration of the crosslinking agent in the crosslinking solution is 0.5 wt%; and / or, the crosslinking time is 2 h; and / or, the method further includes spraying a dispersion of the hydrophobic layer onto the surface of the crosslinked photothermal layer, and the coating amount of the hydrophobic layer dispersion is 0.1 to 10 ml / cm 2 .

10. The preparation method according to claim 4, wherein, The method further includes a solvent welding step. The solvent welding is to place the coated photothermal superhydrophobic composite film at 60-100 °C and keep it for 3-10 h.

11. Application of a photothermal superhydrophobic composite film as claimed in claims 1-3 as an anti-icing film.

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