Fluoride-free photo-thermal super-hydrophobic coating as well as preparation method and application thereof

Abstract

The invention provides a fluoride-free photo-thermal super-hydrophobic coating as well as a preparation method and application thereof, and belongs to the technical field of optical materials. The preparation method comprises the following steps: firstly, taking aminated silicon dioxide and carboxylated multi-walled carbon nanotubes as raw materials, and adding an activating agent for reaction to prepare an MCS composite material; then carrying out a modification reaction on the MCS composite material by using octyl triethoxy silane to obtain an OMCS composite material; finally, the OMCS composite material and silica sol are used as raw materials to prepare dispersion liquid, and the fluorine-free photo-thermal super-hydrophobic coating is prepared through spraying and curing. The fluoride-free photo-thermal super-hydrophobic coating can greatly prolong the icing time, the icing time is prolonged by 5 times compared with original glass, the coating can actively remove ice through the photo-thermal effect, ice drops on the surface can be completely melted when the coating is illuminated for 296 s under the 2sun intensity, and the fluoride-free photo-thermal super-hydrophobic coating has excellent ice preventing and removing capacity.

Description

Technical Field

[0001] The present invention relates to the technical field of optical materials, and in particular to a fluorine-free photothermal super-hydrophobic coating and a preparation method and application thereof. Background Art

[0002] Surface icing severely reduces the transparency of optical materials and devices, affecting their proper function. While transparent super-hydrophobic coatings can effectively prolong the freezing period, surfaces exposed to cold temperatures for extended periods inevitably freeze. Imparting a transparent super-hydrophobic coating with a certain light-to-heat conversion capability could effectively address this surface icing problem.

[0003] Multi-walled carbon nanotubes (MWCNTs) are photothermal nanomaterials with high strength, high thermal conductivity, high electrical conductivity, and high chemical stability. They are often added to various coatings to impart photothermal properties and enhance their stability and hydrophobicity. For example, Wenliang Zhang et al. used MWCNTs and epoxy resin as raw materials to prepare a superhydrophobic MWCNT / epoxy coating for anti-icing. This coating exhibits exceptional photothermal and electrothermal responses, completely melting ice droplets within 175 seconds under 1.5 sun irradiation intensity (see Super photothermal / electrothermal response and anti-icing / deicing capability of superhydrophobic multi-walled carbon nanotubes / epoxy coating [J]. Chemical Engineering Journal, 2024, 497: 154383.). Xiaohu Liu et al. hybridized modified MWCNTs and titanium dioxide nanoparticles and incorporated them into epoxy resin to prepare a super-hydrophobic surface with excellent wear resistance and deicing performance by a simple one-step spraying method (see Superhydrophobic surface of hybrid nanocomposites made of TiO2 and multi-walled carbon nanotubes:Photothermal ice removal performance and wear resistance[J].Applied Surface Science, 2023, 640:158318.). The addition of MWCNTs gives the coating excellent photothermal conversion performance, and compared with traditional super-hydrophobic coatings, the deicing efficiency is increased by 900%. However, for transparent super-hydrophobic coatings, while photothermal materials give the coating excellent photothermal conversion performance, they also reduce the transparency of the coating. Therefore, a fluorine-free photothermal super-hydrophobic coating and its preparation method are studied and used in optical devices. It is of great significance. Summary of the Invention

[0004] The purpose of the present invention is to provide a fluorine-free photothermal super-hydrophobic coating and its preparation method and application, so as to solve the problem in the prior art that photothermal materials reduce the transparency of transparent photo-hydrophobic coatings.

[0005] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0006] The present invention provides a method for preparing a fluorine-free photothermal super-hydrophobic coating, comprising the following steps:

[0007] (1) Aminated silica (SiO2-NH2) and carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were used as raw materials and an activator was added to react to prepare an MCS composite material;

[0008] (2) Modifying the MCS composite material with octyltriethoxysilane (OTEOS) to obtain the OMCS composite material;

[0009] (3) A dispersion liquid was prepared using OMCS composite material and silica sol as raw materials, and then sprayed and cured to produce a fluorine-free photothermal superhydrophobic coating.

[0010] Preferably, in step (1), the preparation method of the amino silica is: mixing a silica dispersion and an aminosilane coupling agent solution, reacting the mixture, and centrifuging to obtain the amino silica.

[0011] Preferably, in step (1), the activator comprises 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide.

[0012] Preferably, in step (1), the reaction temperature is 70-90° C., and the reaction time is 4-6 h.

[0013] Preferably, in step (2), the temperature of the modification reaction is 50-70° C., and the time of the modification reaction is 7-9 h.

[0014] Preferably, in step (3), the silica sol is prepared by mixing tetraethyl silicate (TEOS), octyltriethoxysilane, water and ethanol, adding hydrochloric acid solution and stirring to obtain silica sol.

[0015] Preferably, in step (3), the spraying pressure is 25 to 35 psi, the spraying time is 1 s, and the number of spraying times is 5 to 30 times.

[0016] Preferably, in step (3), the curing temperature is 70-90° C., and the curing time is 1-3 hours.

[0017] The present invention provides a fluorine-free photothermal super-hydrophobic coating prepared by the above-mentioned preparation method of the fluorine-free photothermal super-hydrophobic coating.

[0018] The present invention also provides an application of the above-mentioned fluorine-free photothermal super-hydrophobic coating in an optical device.

[0019] Beneficial effects of the present invention:

[0020] In the present invention, SiO2-NH2 and MWCNTs-COOH are reacted through amide to prepare a dot-line structured MCS composite material, which is then hydrophobically modified by OTEOS to ultimately obtain a hydrophobic OMCS composite material.

[0021] The present invention prepares a fluorine-free photothermal super-hydrophobic coating by spraying. When the number of spraying is 20 times, the coating has a uniform and dense rough structure, and the hydrophobicity and transparency of the coating are the best comprehensive performance, the contact angle reaches 157.5°, and the average visible light transmittance can reach 62.0%. The optimal coating has excellent self-cleaning ability, and surface pollutants can be effectively cleaned after a small amount of liquid is added to the surface. In the fluorine-free photothermal super-hydrophobic coating of the present invention, due to the presence of MWCNTs-COOH, the coating also has good photothermal conversion performance. After 5 minutes of illumination at 0.5, 1, 1.5 and 2 sun intensities, the coating surface temperature rises from 20°C ± 1°C to 26.1°C, 29.2°C, 32.2°C and 38.7°C, respectively.

[0022] The fluorine-free photothermal super-hydrophobic coating of the present invention can significantly prolong the freezing time. Compared with the original glass, the freezing time is extended by 5 times. In addition, the coating can also actively de-ice through the photothermal effect. Under 2s of illumination at an intensity of 2s, it can completely melt the ice droplets on the surface, and has excellent anti-icing and de-icing capabilities.

[0023] The introduction of the OMCS composite material in the present invention promotes the formation of a multi-level rough structure in the coating, while the silica sol as a matrix not only improves the adhesion of the coating but also fixes the OMCS composite material, giving the coating excellent mechanical durability. After experiencing 200 cm of sandpaper abrasion and 300 g of falling sand impact, the coating still maintains good superhydrophobicity. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Schematic diagram of the preparation process of the fluorine-free photothermal super-hydrophobic coating of the present invention;

[0025] Figure 2 IR spectra of silica, amino-treated silica, carboxylated multi-walled carbon nanotubes, MCS composite material, and OMCS composite material in Example 1, wherein a is an infrared spectra of silica and amino-treated silica, and b is an infrared spectra of carboxylated multi-walled carbon nanotubes, MCS composite material, and OMCS composite material;

[0026] Figure 3 1 are SEM images of the carboxylated multi-walled carbon nanotube and OMCS composite materials of Example 1, wherein a is a SEM image of the carboxylated multi-walled carbon nanotube, and b is a SEM image of the OMCS composite material;

[0027] Figure 4The dispersion of the carboxylated multi-walled carbon nanotubes and OMCS composite material in water of Example 1, wherein a is the dispersion of the carboxylated multi-walled carbon nanotubes in water, and b is the dispersion of the OMCS composite material in water;

[0028] Figure 5 The SEM images of the fluorine-free photothermal super-hydrophobic coatings of Examples 1 to 4, wherein a is a SEM image of the fluorine-free photothermal super-hydrophobic coating of Example 1, b is a SEM image of the fluorine-free photothermal super-hydrophobic coating of Example 2, c is a SEM image of the fluorine-free photothermal super-hydrophobic coating of Example 3, and d is a SEM image of the fluorine-free photothermal super-hydrophobic coating of Example 4;

[0029] Figure 6 are AFM 3D topography images of the fluorine-free photothermal super-hydrophobic coatings of Examples 1 to 4, wherein a is an AFM 3D topography image of the fluorine-free photothermal super-hydrophobic coating of Example 1, b is an AFM 3D topography image of the fluorine-free photothermal super-hydrophobic coating of Example 2, c is an AFM 3D topography image of the fluorine-free photothermal super-hydrophobic coating of Example 3, and d is an AFM 3D topography image of the fluorine-free photothermal super-hydrophobic coating of Example 4;

[0030] Figure 7 1 is a comparison diagram of the contact angle and sliding angle of the fluorine-free photothermal superhydrophobic coating of Examples 1 to 4;

[0031] Figure 8 1 is a comparison chart of the transmittance of the fluorine-free photothermal super-hydrophobic coatings of Examples 1 to 4;

[0032] Figure 9 The graphs of surface temperature variation over time of the fluorine-free photothermal super-hydrophobic coating of Example 3 under different light intensities and the infrared thermal imaging graphs of the fluorine-free photothermal super-hydrophobic coating of Example 3 under different light intensities are shown, wherein a is a graph of surface temperature variation over time, and b is an infrared thermal imaging graph;

[0033] Figure 10 The graphs of surface temperature variation over time and infrared thermal imaging images of the original glass and the coated glass of Example 3 under different light intensities in a low-temperature environment are shown, where a is the graph of surface temperature variation over time and b is the infrared thermal imaging image;

[0034] Figure 11 Graph showing the freezing process of water droplets on the original glass and the coated glass of Example 3;

[0035] Figure 12 1 is a diagram showing the frosting process of the original glass and the coated glass of Example 3 at low temperatures;

[0036] Figure 13 Schematic diagram of the photothermal deicing process of the original glass and the coated glass of Example 3;

[0037] Figure 14 Schematic diagram of the photothermal defrosting process of the original glass and the coated glass of Example 3;

[0038] Figure 15 Self-cleaning test diagrams of original glass and coated glass of Example 3;

[0039] Figure 16 Graphs showing wettability changes of the fluorine-free photothermal super-hydrophobic coating of Example 3 in the sandpaper abrasion test and the falling sand impact test, wherein a is a graph showing wettability changes in the sandpaper abrasion test, and b is a graph showing wettability changes in the falling sand impact test;

[0040] Figure 17 This is a comparison chart of the wettability of the fluorine-free photothermal super-hydrophobic coating of Example 3 after being immersed in solutions with different pH values;

[0041] Figure 18 The wettability change diagram of different types of substrates before and after spraying, where a and b are Chevron boards, c and d are aluminum sheets, e and f are wooden boards, g and h are sponges, and i and j are filter papers. DETAILED DESCRIPTION

[0042] The present invention provides a method for preparing a fluorine-free photothermal super-hydrophobic coating, comprising the following steps:

[0043] (1) Aminated silica (SiO2-NH2) and carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) were used as raw materials and an activator was added to react to prepare an MCS composite material;

[0044] (2) Modifying the MCS composite material with octyltriethoxysilane (OTEOS) to obtain the OMCS composite material;

[0045] (3) A dispersion liquid was prepared using OMCS composite material and silica sol as raw materials, and then sprayed and cured to produce a fluorine-free photothermal superhydrophobic coating.

[0046] In the present invention, in step (1), the preparation method of the amino silica is: mixing a silica dispersion and an aminosilane coupling agent solution, reacting the mixture, and centrifuging to obtain the amino silica.

[0047] In the present invention, the silica dispersion is prepared by dispersing silica in a mixed solution of ethanol and water; the aminosilane coupling agent solution is prepared by dissolving an aminosilane coupling agent in a mixed solution of ethanol and water; the mass volume ratio of the silica and the aminosilane coupling agent is 1g:200~300μL, preferably 1g:250μL; the aminosilane coupling agent is preferably γ-aminopropyltriethoxysilane (KH550); the reaction temperature is 50~70°C, preferably 60°C, and the reaction time is 3~5h, preferably 4h.

[0048] In the present invention, during the preparation of the MCS composite material, preferably, a dispersion of amino silica and a dispersion of carboxylated multi-walled carbon nanotubes are prepared separately, and then an activator is added to the dispersion of carboxylated multi-walled carbon nanotubes and stirred evenly, and then the dispersion of amino silica is added dropwise to react; the mass ratio of the amino silica to the carboxylated multi-walled carbon nanotubes is 1:0.2-0.3, preferably 1:0.25.

[0049] In the present invention, in step (1), the activator comprises 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide.

[0050] In the present invention, the activator is preferably added in the form of an aqueous solution, wherein the concentration of the aqueous solution of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide is 0.1 mol / L, and the concentration of the aqueous solution of N-hydroxysuccinimide is 0.1 mol / L; the mass volume ratio of the carboxylated multi-walled carbon nanotubes, the aqueous solution of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide, and the aqueous solution of N-hydroxysuccinimide is 0.2-0.3 g:0.5-1.5 mL:0.5-1.5 mL, preferably 0.25 g:1 mL:1 mL.

[0051] In the present invention, in step (1), the reaction temperature is 70-90°C, preferably 75-85°C, more preferably 80°C, and the reaction time is 4-6h, preferably 5h.

[0052] In the present invention, during the preparation of the OMCS composite material, it is preferred to prepare an MCS composite material dispersion and an octyltriethoxysilane solution separately, and then mix the MCS composite material dispersion and the octyltriethoxysilane solution before performing a modification reaction.

[0053] In the present invention, the mass volume ratio of the MCS composite material and octyltriethoxysilane is 1 g: 0.2-0.6 mL, preferably 1 g: 0.3-0.5 mL, and more preferably 1 g: 0.4 mL.

[0054] In the present invention, in step (2), the temperature of the modification reaction is 50-70°C, preferably 55-65°C, more preferably 60°C, and the time of the modification reaction is 7-9h, preferably 8h.

[0055] In the present invention, in step (3), the silica sol is prepared by mixing tetraethyl silicate (TEOS), octyltriethoxysilane (OTEOS), water and ethanol, adding hydrochloric acid solution and stirring to obtain silica sol.

[0056] In the present invention, the volume ratio of tetraethyl silicate (TEOS), octyltriethoxysilane (OTEOS), water and ethanol is 0.7-1.0:0.05-0.30:0.3-0.6:15-25, preferably 0.85-0.95:0.1-0.2:0.4-0.5:18-22, more preferably 0.85:0.15:0.5:20; the mixing temperature is 50-70°C, preferably 55-65°C, More preferably, the temperature is 60°C, the mixing time is 0.1 to 0.8 h, preferably 0.4 to 0.7 h, and more preferably 0.5 to 0.6 h; the volume ratio of the tetraethyl silicate and the hydrochloric acid solution is 0.7 to 1.0: 0.01 to 0.08, preferably 0.85 to 0.95: 0.03 to 0.06, and more preferably 0.85: 0.05, wherein the concentration of the hydrochloric acid solution is 7.5%; the stirring time is 5 to 7 h, preferably 6 h.

[0057] In the present invention, when preparing the fluorine-free photothermal superhydrophobic coating, it is preferred to prepare an OMCS dispersion and then mix it with the above-mentioned silica sol, and the obtained dispersion is sprayed on the substrate using a spray gun, wherein the distance between the spray gun and the substrate is preferably 10 cm.

[0058] In the present invention, the mass volume ratio of the OMCS composite material to tetraethyl silicate (TEOS) is 150-250 mg:0.7-1.0 mL, preferably 180-220 mg:0.85-0.95 mL, and more preferably 200 mg:0.85 mL.

[0059] In the present invention, in step (3), the spraying pressure is 25 to 35 psi, preferably 28 to 32 psi, more preferably 30 psi, the spraying time is 1 s, and the number of sprayings is 5 to 30 times, preferably 5 times, 10 times, 20 times, or 30 times.

[0060] In the present invention, in step (3), the curing temperature is 70-90°C, preferably 75-85°C, more preferably 80°C, and the curing time is 1-3 hours, preferably 2 hours.

[0061] The present invention provides a fluorine-free photothermal super-hydrophobic coating prepared by the above-mentioned preparation method of the fluorine-free photothermal super-hydrophobic coating.

[0062] The present invention also provides an application of the above-mentioned fluorine-free photothermal super-hydrophobic coating in an optical device.

[0063] The technical solutions provided by the present invention are described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0064] Example 1

[0065] Weigh 1g of SiO2 and add it to a mixture of 45mL of ethanol and 5mL of deionized water. After ultrasonic dispersion for 30 minutes, a SiO2 dispersion is obtained. Add 250μL of KH550 to a mixture of 45mL of ethanol and 5mL of deionized water to obtain a KH550 solution. The SiO2 dispersion and KH550 solution are mixed, and the resulting mixture is stirred at 60°C for 4 hours using a magnetic stirrer to react. The mixture is then centrifuged at 9000 rpm for 5 minutes. The resulting product is washed and dried to produce amino-silica (SiO2-NH2).

[0066] 1g of SiO2-NH2 was weighed and added to 100mL of deionized water and ultrasonically dispersed for 30 minutes to obtain a SiO2-NH2 dispersion. 0.25g of MWCNTs-COOH was weighed and added to 100mL of deionized water and ultrasonically dispersed for 30 minutes. 1mL of a 0.1mol / L aqueous solution of 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide (EDC) and 1mL of a 0.1mol / L aqueous solution of N-hydroxysuccinimide (NHS) were added to the dispersion. The resulting mixed solution was stirred at room temperature for 10 minutes using a magnetic stirrer. The SiO2-NH2 dispersion was then slowly added and the resulting mixed solution was stirred at 80° for 5 hours using a magnetic stirrer to react. The resulting product was washed and dried to obtain an MCS composite material.

[0067] 1g of the MCS composite was weighed and added to a beaker containing 40mL of ethanol and 10mL of distilled water. Ultrasonic dispersion was performed for 30 minutes to obtain an MCS dispersion. 0.4mL of OTEOS was added to a beaker containing 40mL of ethanol and 10mL of deionized water to obtain an OTEOS solution. The MCS dispersion and OTEOS solution were mixed, and the resulting mixture was stirred at 60°C for 8 hours using a magnetic stirrer to carry out the modification reaction. The mixture was then centrifuged at 9000 rpm for 5 minutes, washed, and dried to produce the OMCS composite.

[0068] 0.85 mL of TEOS, 0.15 mL of OTEOS, and 0.5 mL of deionized water were added to 20 mL of ethanol, and the resulting mixed solution was stirred at 60° C. for 0.5 h using a magnetic stirrer. Then, 0.05 mL of 7.5% hydrochloric acid solution was added and stirring was continued for 6 h to obtain a silica sol.

[0069] 200 mg of the OMCS composite material was weighed and added to 20 mL of ethanol. After ultrasonic dispersion for 0.5 h, an OMCS dispersion was obtained. The silica sol prepared above was mixed with the OMCS dispersion, ultrasonically dispersed for 30 min, and stirred with a magnetic stirrer at 60 ° C for 1 h. Finally, the solution was sprayed on the original glass using a spray gun. The spray gun was sprayed 5 times (the spray gun was 10 cm away from the glass plate, the spray pressure was fixed at 30 psi, and each spray was 1 second). After the sprayed sample was cured at 80 ° C for 2 h, a fluorine-free photothermal superhydrophobic coating was obtained.

[0070] Example 2

[0071] The difference from Example 1 is that the number of spraying is 10 times, and other conditions are the same to obtain a fluorine-free photothermal super-hydrophobic coating.

[0072] Example 3

[0073] The difference from Example 1 is that the number of spraying is 20 times, and other conditions are the same to obtain a fluorine-free photothermal super-hydrophobic coating.

[0074] During the test, the glass sprayed with the fluorine-free photothermal super-hydrophobic coating in Example 3 was referred to as coated glass.

[0075] Example 4

[0076] The difference from Example 1 is that the number of spraying is 30 times, and other conditions are the same to obtain a fluorine-free photothermal super-hydrophobic coating.

[0077] Testing and Characterization:

[0078] (1) The surface chemical composition of the SiO2, SiO2-NH2, MWCNTs-COOH, MCS composite material and OMCS composite material in Example 1 was analyzed using an infrared spectrometer (Spectrum 3) in the test range of 400-4000 cm -1 , the test results are as follows Figure 2 Shown: From Figure 2 As can be seen from a in the figure, the spectrum of SiO2 is at 3450cm -1 and 1630cm -1 There are two obvious absorption peaks at 963cm, which are the -OH stretching vibration peak and HOH bond bending vibration peak of SiO2 surface. -1There is a bending vibration absorption peak of Si-OH bond at 1095cm -1 There is an asymmetric stretching vibration peak of Si-O-Si bond at 812 cm -1 and 467cm -1 There are symmetrical stretching vibration peaks and bending vibration peaks of Si-O bonds. After modification, the hydroxyl groups on the SiO2 surface are replaced by aminopropyl groups in KH550. In the infrared spectrum of SiO2-NH2, it can be seen that the peak at 3450cm -1 The -OH absorption peak at 2937 cm -1 、692cm -1 There are -CH2 absorption peak and CC bond absorption peak at 1506cm -1 There is an absorption peak of -NH2 at the surface, but due to the short reaction time, only a small amount of aminopropyl is grafted on the surface, so the absorption peak is not obvious. Figure 2 As can be seen from b, compared with MWCNTs-COOH, MCS is at 1095cm -1 、812cm -1 、467cm -1 There is an obvious Si-O-Si bond absorption peak at 2912 cm -1 、2856cm -1 There are absorption peaks at , which are the stretching vibration peaks of -CH2 and -CH3 bonds, respectively, proving that the octyl group of the OTEOS hydrophobic modifier is successfully grafted onto the MCS surface, and finally a hydrophobic OMCS composite material is prepared.

[0079] (2) The micromorphology of the carboxylated multi-walled carbon nanotubes and OMCS composite material of Example 1 was tested using a scanning electron microscope. The results are as follows: Figure 3 As shown, from Figure 3 As can be seen from a in the figure, MWCNTs-COOH presents a standard tubular structure; Figure 3 As can be seen from b in the figure, the OMCS composite material is a dot-line structure. The carboxylated multi-walled carbon nanotubes and the OMCS composite material of Example 1 were placed in water respectively to observe the dispersion of the two materials in water. The results are shown in FIG. Figure 4 As shown. Figure 4 As can be seen from a in the figure, MWCNTs-COOH completely sinks to the bottom of the water, which is mainly due to the presence of hydrophilic carboxyl groups on the surface of MWCNTs-COOH. However, since the surface of the OMCS composite material is grafted with silica and hydrophobically modified by OTEOS, there are hydrophobic octyl groups on the surface. Therefore, the OMCS composite material has good hydrophobicity and can float on the water surface (see Figure 4 (b)

[0080] (3) The microscopic morphology of the fluorine-free photothermal super-hydrophobic coatings of Examples 1 to 4 was tested using a scanning electron microscope. The results are as follows: Figure 5 As shown; AFM 3D morphology of the fluorine-free photothermal super-hydrophobic coating of Examples 1 to 4 was tested using an atomic force microscope, and the results were as follows Figure 6 shown; from Figure 5 As can be seen from a in the figure, when the number of spraying is 5, due to the small number of spraying times, too little solution is deposited on the substrate, and the coating formed after the silica sol is cured does not completely cover the entire surface, and part of the surface is exposed. In addition, the average surface roughness of the coating is low, only 12.7nm (see Figure 6 As the number of spraying cycles increases, when the number of spraying cycles is 10, as shown in a). Figure 5 As shown in b, a relatively smooth coating is formed on the surface, and the coating almost completely covers the substrate surface. However, due to the low content of the OMCS composite material, a small amount of protrusions exist on the surface. At this time, the average roughness of the coating surface is 47.9 nm (see Figure 6 b) When the number of spraying is 20 times, Figure 5 As shown in Figure c, the surface is completely covered by the coating, the silica sol and the OMCS composite material are cross-linked, and a dense and uniform multi-level rough structure is formed on the surface. The average surface roughness is 86.2nm (see Figure 6 c). When the number of spraying cycles increases to 30 times, as shown in Figure 5 As shown in Figure d, due to excessive spraying times, a large amount of solution was deposited on the substrate surface, and the OMCS composite materials in the solution agglomerated to form large aggregates. A large amount of air existed in the structure, and the average surface roughness increased to 152.0 nm (see Figure 6 d) in the above.

[0081] (4) The wettability of the surface of the fluorine-free photothermal super-hydrophobic coating of Examples 1 to 4 was tested using a contact angle meter (DSA30). The results are as follows: Figure 7 As shown, from Figure 7It can be seen that when the coating spray cycle number is 5 times, the hydrophobicity of the coating is poor, the contact angle is only 101.2°, the rolling angle is greater than 120°, the surface has high adhesion to water, and the droplets hardly roll. As the number of spraying increases, the hydrophobicity of the coating surface is improved, the contact angle increases to 135.3°, and the rolling angle decreases to 32°. When the number of spraying increases to 20 times, the coating has super hydrophobicity, the contact angle is 157.5°, and the rolling angle is 3°. When the number of spraying continues to increase to 30 times, the coating contact angle continues to increase to 160.7°, and the rolling angle hardly changes. Overall, the hydrophobicity of the coating will increase with the increase in the number of coating spraying times. Combined with the surface morphology analysis of the coating, it can be seen that the change in the hydrophobicity of the coating is due to the change in the morphological structure. When the number of spraying is too few, the coating surface is not completely covered, and the exposed substrate has a strong hydrophilicity. When the number of spraying cycles was increased to 10, the surface was completely covered by the coating. Due to the hydrophobic octyl groups in the OTEOS silica sol, the coating became hydrophobic, but the surface roughness was too low to achieve superhydrophobicity. At 20 spraying cycles, a dense and uniform rough structure formed on the surface of the coating, indicating superhydrophobicity. Further increasing the number of spraying cycles further enhanced the surface roughness, further improving the superhydrophobicity.

[0082] (5) Transparency analysis

[0083] The transmittance of the fluorine-free photothermal super-hydrophobic coatings of Examples 1 to 4 was tested using an ultraviolet-visible spectrophotometer (UV-2550), and the visible light region ranged from 400 to 780 nm. The test results are shown in FIG. Figure 8 As shown, when the number of spraying cycles was 5, the visible light transmittance of the coating was 81.4%. The transmittance decreased with increasing spraying cycles, reaching an average visible light transmittance of 70.9%, 62.0%, and 46.6% for 10, 20, and 30 spraying cycles, respectively. According to Rayleigh scattering theory, transparency is closely related to surface roughness. The decrease in transmittance with increasing spraying cycles is primarily due to increased surface roughness, which increases the light scattering effect and thus causes a decrease in transmittance. Furthermore, increasing the number of spraying cycles also increases the amount of OMCS composite material in the coating. OMCS contains MWCNTs with high absorbance, which also contributes to a decrease in transmittance. Based on the wettability and transmittance of the coating, we determined the optimal number of spraying cycles to be 20. The optimal coating achieved a contact angle of 157.5°, a rolling angle of 4°, and an average visible light transmittance of 62.0%.

[0084] (6) Photothermal conversion performance test

[0085] A xenon lamp was used to simulate solar radiation, and a thermal infrared imager was used to record the sample surface temperature and image. The photothermal conversion performance of the coated glass of Example 3 was tested at room temperature (20°C ± 1°C) and low temperature (-10°C) environments.

[0086] Room temperature light-to-heat conversion performance test: The coated glass of Example 3 was placed on a platform at room temperature. The coating was exposed to light intensities of 0.5, 1, 1.5, and 2 sun by adjusting the power of the xenon lamp. The temperature change of the coating surface within 5 minutes was recorded. The results are shown in the figure. Figure 9 As shown, Figure 9 a is 0.5, 1.0, 1.5, 2.0 sun (1 sun = 96 mW / cm 2 ) The surface temperature curve under different light intensity changes with illumination time shows that the surface temperature gradually rises with increasing illumination time, especially in the first 2 minutes, when the temperature rises rapidly. After that, the temperature rise rate slows down and stabilizes. The final temperature of the coating surface also varies under different illumination conditions. When the illumination intensity is 0.5 sun, the coating surface temperature only rises to 26.1°C. When the illumination intensity is increased to 1 sun, 1.5 sun, and 2.0 sun, the final surface temperature of the coating is 29.2°C, 32.2°C, and 38.7°C, respectively. Figure 9 Figures b and c show infrared thermal images of the surface temperature at different light intensities versus exposure time. These images clearly show the temperature variations of the coating surface. As light intensity increases, the final surface temperature of the coating rises. This change is primarily due to the MWCNTs in the coating absorbing more light energy as light intensity increases, enhancing the photothermal effect and releasing more heat, which in turn increases the surface temperature. In practical applications, the coating surface temperature can be controlled by adjusting the illumination intensity to suit different environments.

[0087] Low-temperature photothermal conversion performance test: The original glass and the coated glass of Example 3 were placed on a -10°C cooling platform until the surface temperature of the sample dropped to -10°C. Then, the xenon lamp was turned on and the sample was exposed to 2 suns of light intensity. The temperature change of the sample surface within 5 minutes was observed. The results are shown in the figure. Figure 10 As shown, Figure 10 Figure a shows the surface temperature variation curve of the coating on the original glass and the coated glass of Example 3 under 2s of light intensity. It can be seen that since the original glass has almost no light-to-heat conversion ability, it heats up slowly under light. After 5 minutes of light exposure, the surface temperature rises from -10°C to -7.3°C, which is only 2.7°C higher. Figure 10(b) The MWCNTs-COOH present in the coating exhibits excellent photothermal conversion capabilities. After 5 minutes of illumination, the surface temperature of the coated glass dropped to 7.6°C, an increase of 17.6°C. These test results demonstrate that fluorine-free photothermal superhydrophobic coatings exhibit excellent photothermal performance even at low temperatures, making them suitable for use in low-temperature environments.

[0088] (7) Anti-icing and anti-frost test

[0089] In order to test the anti-icing and anti-frost performance of the samples, a cooling table was used to simulate a low temperature environment.

[0090] Anti-icing experiment: The original glass and the coated glass of Example 3 were placed on a -10°C cooling table. 10 μL of deionized water was placed on the coating surface using a pipette until the water droplet was completely frozen. The freezing process of the sample surface was recorded using a camera. The results are shown in the figure below. Figure 11 As shown in the figure, it can be seen that due to the hydrophilicity of the original glass surface, the water droplets spread almost completely on its surface. Initially, the water droplets appear transparent. Over time, ice nuclei form inside the water droplets, and the transparency begins to decrease. The water droplets become opaque at 18 seconds. After that, the water droplets gradually condense into ice from the bottom upwards. At 35 seconds, the water droplets are completely frozen. Because the coating is superhydrophobic, the high contact angle reduces the contact area between the droplet and the surface. In addition, the coating has a certain rough structure and there is air inside, resulting in low heat conduction efficiency. Therefore, the surface water droplets of the fluorine-free photothermal superhydrophobic coating are completely frozen at 186 seconds. The delayed freezing time of the fluorine-free photothermal superhydrophobic coating is 5 times that of the original glass.

[0091] In the anti-frost experiment, the original glass and the coated glass of Example 3 were placed on a cooling table at -10°C, and the frost on the sample surface was recorded using a camera within 20 minutes. Figure 12 As shown, from Figure 12 It can be seen that initially both the original glass and the coated glass have a high degree of transparency, and the font below is clearly visible, but the transparency of the original glass is higher than that of the coated glass. As time goes by, at the 5th minute, the transparency of the original glass decreases due to the condensation of moisture in the air, but the font below can still be clearly seen. At the 10th minute, a thin layer of frost formed on the surface of the original glass, and the font below began to become blurred. At the 15th minute, part of the area was covered by the frost layer, and the transparency further decreased, making it difficult to recognize the font below. Finally, at 20 minutes, due to the thicker frost layer on the surface, the transparency was severely reduced, and the font below could not be recognized. For the coated glass, the surface transparency only decreased slightly, and even at the 20th minute, the font below could be seen clearly. This is mainly due to the low surface energy of the fluorine-free photothermal superhydrophobic coating surface, which makes it difficult for moisture in the air to condense on the surface, reducing the accumulation of frost.

[0092] It can be seen that compared with the original glass, the coated glass can greatly delay the surface freezing time and reduce the accumulation of surface frost in low temperature environment. Therefore, the fluorine-free photothermal superhydrophobic coating has excellent anti-icing and anti-frost properties.

[0093] (7) Deicing and defrosting performance test

[0094] De-icing test: Place the original glass and the coated glass of Example 3 on a -10°C cooling table, add 10 μL of water droplets on the surface until the water droplets are completely frozen, then turn on the xenon lamp to irradiate the sample and record the changes in the ice droplets on the surface. Figure 13 As shown in the figure, we can see the change process of ice droplets on the original glass and coated glass under 2sun illumination intensity. Figure 13 It can be seen that after 296 seconds of irradiation, the ice drop on the original glass is still in a frozen state. However, due to the certain photothermal effect of the coating, as the irradiation time goes by, the coating generates heat and the surface temperature rises. At 162 seconds, the bottom of the ice drop begins to melt. At 296 seconds, the drop is completely melted and becomes transparent.

[0095] Defrosting test: The original glass and the coated glass of Example 3 were placed on a -10°C cooling table until the surface was completely covered with frost. Then, a xenon lamp was turned on to irradiate the sample and the change process of the surface frost was recorded. The results are shown in the figure. Figure 14 As shown. Figure 14 Initially, the surfaces of the original and coated glass were thick with frost, resulting in low transparency and the text underneath being indistinct. Over time, the frost on the original glass thinned slightly by the fifth minute, but the text underneath was still indistinct. On the coated glass, however, the frost partially melted by the third minute, allowing some of the text underneath to be seen. By the fifth minute, heat generated by the coating's photothermal effect had melted most of the frost, allowing almost complete visibility of the text underneath. These test results demonstrate the excellent photothermal deicing performance of the fluorine-free photothermal superhydrophobic coating.

[0096] (8) Self-cleaning performance

[0097] In order to test the self-cleaning performance of the fluorine-free photothermal super-hydrophobic coating, carbon black was selected as the pollutant and placed on the original glass and coated glass at a certain angle. Deionized water was added on top to observe the removal of pollutants on the sample surface. The test results are as follows Figure 15As shown in the figure, after adding water droplets, the original glass surface will be soaked by the water droplets, and the water droplets will be mixed with the pollutants, making it impossible to remove the surface pollutants. However, after adding water droplets to the coated glass surface, the water droplets will roll on the surface, taking away the pollutants on the surface and leaving clear traces. This is because the original glass is a hydrophilic surface, and water droplets can easily spread on its surface and it is difficult to roll, so it cannot effectively clean the surface pollutants. However, since the coated glass has excellent superhydrophobic properties on the surface, water droplets can easily roll on its surface and achieve a self-cleaning effect by adsorbing surface pollutants. The test results show that the fluorine-free photothermal superhydrophobic coating has excellent self-cleaning properties.

[0098] (9) Stability test

[0099] In order to test the stability of the fluorine-free photothermal superhydrophobic coating, the mechanical durability and chemical stability of the fluorine-free photothermal superhydrophobic coating were evaluated through sandpaper abrasion, falling sand impact and liquid immersion tests.

[0100] Sandpaper abrasion test: The fluorine-free photothermal superhydrophobic coating of Example 3 was placed face down on 1000-grit sandpaper. A 50g weight was placed on top of the sample. The sample was then moved 10cm in both the horizontal and vertical directions under the action of a horizontal force. The surface contact angle and rolling angle of the coating were tested every 10cm to evaluate the chemical resistance of the coating.

[0101] Falling sand impact test: The fluorine-free photothermal superhydrophobic coating of Example 3 was placed at an angle, and silica sand was released through a funnel 50 cm above the coating to impact the coating. After each 10 g of silica sand was released, the contact angle and rolling angle of the coating were measured.

[0102] The test results of sandpaper wear test and falling sand impact test are as follows Figure 16 Shown: From Figure 16 As can be seen from Figure a, with the increase of wear distance, the hydrophobicity of the coating slowly decreases. After 200 cm of wear, the contact angle of the coating is 151.9° and the rolling angle is less than 10°, which still maintains superhydrophobicity. Figure 16 As can be seen in Figure b, the wettability of the coating does not change much after being impacted by falling sand. After 300g falling sand impact, the contact angle of the coating is 153.4°, and the rolling angle is less than 10°, still maintaining super-hydrophobicity. The above results show that the fluorine-free photothermal super-hydrophobic coating has excellent mechanical stability. This mechanical stability is related to the chemical composition and morphology of the coating surface. The addition of silica sol can not only act as a binder to improve the adhesion between the coating and the glass surface, but also cross-link the OMCS composite material through the Si-O-Si structure to prevent the coating from falling off after being impacted or worn. In addition, the presence of OMCS material gives the coating a multi-level rough structure. Even if a part of the coating surface is worn away, the coating still has a certain rough structure to maintain super-hydrophobic properties.

[0103] Liquid immersion experiment: NaOH and concentrated hydrochloric acid were used to prepare solutions with pH values of 1, 3, 5, 7, 9, 11, and 13, and the fluorine-free photothermal super-hydrophobic coating of Example 3 was completely immersed in the above solutions for 24 hours. The surface contact angle and sliding angle were then measured. The test results are shown in Figure 2. Figure 17 As shown, after immersing the fluorine-free photothermal super-hydrophobic coating in an acidic solution with a pH value of less than 7 and a neutral solution with a pH value of 7 for 24 hours, the wettability does not change significantly and still has super-hydrophobicity. After immersing in an alkaline solution with a pH value of greater than 7, the hydrophobicity of the fluorine-free photothermal super-hydrophobic coating decreases, especially in a strongly alkaline solution with a pH value of 13. After immersing for 24 hours, the fluorine-free photothermal super-hydrophobic coating loses super-hydrophobicity, and the contact angle is reduced to 141.4 °, and the rolling angle is increased to 24 °. The decline in hydrophobicity is mainly due to the fact that the surface components of the fluorine-free photothermal super-hydrophobic coating are mainly silicon dioxide and silicon oligomers, which react with alkaline solutions, especially in strongly alkaline environments, and are likely to cause changes in the chemical composition and structure of the coating surface, so the alkali resistance of the fluorine-free photothermal super-hydrophobic coating is slightly poor. The experimental results show that the fluorine-free photothermal super-hydrophobic coating has good chemical stability, but should be avoided in a strongly alkaline environment for a long time in practical applications.

[0104] (10) Testing the applicability of fluorine-free photothermal superhydrophobic coatings to different substrate materials

[0105] According to the steps of Example 3, fluorine-free photothermal super-hydrophobic coatings were prepared on different substrates, wherein the substrates were respectively a chevron board, an aluminum sheet, a wood board, a sponge and a filter paper. The wettability of the original substrate was tested before spraying, and spraying was performed again after the test was completed. The results are shown in FIG. Figure 18 As shown in the figure, a, c, e, g, and i are the original substrates, and b, d, f, h, and j are the substrates coated with the fluorine-free photothermal superhydrophobic coating. It can be seen that before spraying, the surface hydrophobicity of these substrates was poor, and water droplets could not form spherical shapes on the surface. However, after spraying the fluorine-free photothermal superhydrophobic coating on the surface, the surface hydrophobicity was greatly improved, and water droplets on the surface could form spherical shapes. The results show that the coating prepared by this method has a wide range of applicability.

[0106] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present invention. These improvements and modifications should also be regarded as within the scope of protection of the present invention.

Claims

1. A method for preparing a fluorine-free photothermal super-hydrophobic coating, characterized in that: The steps include: (1) Aminated silica and carboxylated multi-walled carbon nanotubes are used as raw materials, an activator is added to react, and an MCS composite material is prepared; (2) Modifying the MCS composite material with octyltriethoxysilane to obtain the OMCS composite material; (3) A dispersion liquid was prepared using OMCS composite material and silica sol as raw materials, and then sprayed and cured to produce a fluorine-free photothermal superhydrophobic coating.

2. The method for preparing a fluorine-free photothermal super-hydrophobic coating according to claim 1, wherein In step (1), the preparation method of the amino silica is as follows: a silica dispersion and an aminosilane coupling agent solution are mixed, reacted, and centrifuged to obtain the amino silica.

3. The preparation method of the fluorine-free photothermal super-hydrophobic coating according to claim 1 or 2, wherein In step (1), the activator comprises 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide and N-hydroxysuccinimide.

4. The method for preparing a fluorine-free photothermal super-hydrophobic coating according to claim 3, wherein In step (1), the reaction temperature is 70-90° C., and the reaction time is 4-6 h.

5. The preparation method of the fluorine-free photothermal super-hydrophobic coating according to claim 1, 2 or 4, wherein In step (2), the temperature of the modification reaction is 50-70° C., and the time of the modification reaction is 7-9 hours.

6. The method for preparing a fluorine-free photothermal super-hydrophobic coating according to claim 5, wherein In step (3), the silica sol is prepared by mixing tetraethyl silicate, octyltriethoxysilane, water and ethanol, adding hydrochloric acid solution and stirring to obtain silica sol.

7. The method for preparing a fluorine-free photothermal super-hydrophobic coating according to claim 4 or 6, wherein In step (3), the spraying pressure is 25 to 35 psi, the spraying time is 1 s, and the number of spraying times is 5 to 30 times.

8. The method for preparing a fluorine-free photothermal super-hydrophobic coating according to claim 7, wherein In step (3), the curing temperature is 70 to 90° C., and the curing time is 1 to 3 hours.

9. A fluorine-free photothermal super-hydrophobic coating prepared by the method for preparing a fluorine-free photothermal super-hydrophobic coating according to any one of claims 1 to 8.

10. Use of the fluorine-free photothermal super-hydrophobic coating according to claim 9 in optical devices.

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