Fluorine-free transparent superhydrophobic coating and preparation method and application thereof

Abstract

The application provides a fluorine-free transparent super-hydrophobic coating and a preparation method and application thereof, and belongs to the technical field of coating materials. A three-dimensional network structure formed by self-assembly of a bisamidate derivative (1,4-di[(3,4-dioctyloxyphenyl)-bisamidyl]benzene, BPH-8) is used as a template, tetraethyl orthosilicate (TEOS) is used as a silica precursor to be adsorbed on the surface of the template to perform sol-gel polymerization to form silica with high transparency, then BPH-8 is removed by calcination to obtain a fibrous silica transparent surface, then octyltrichlorosilane is used for hydrophobic modification of the silica surface to obtain a transparent super-hydrophobic coating. The fluorine-free transparent super-hydrophobic coating prepared by the application has a water contact angle of 162.7°, a rolling angle less than 3°, an average visible light transmittance of 84.8%, and good self-cleaning capacity, and has potential application value in the fields of building glass, vehicle window glass, rearview mirror, optical lens, solar photovoltaic and the like.

Description

TECHNICAL FIELD

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

[0002] People can see many special wetting phenomena in nature, such as lotus leaves, butterfly wings, shark skin, etc., which have excellent water-repellent properties. People call the surface with a contact angle greater than 150° and a rolling angle less than 10° with water droplets as a super-hydrophobic surface. Super-hydrophobic surfaces have various functional properties, such as self-cleaning, anti-fouling, oil-water separation, corrosion resistance, etc., and can be widely used in daily life and industrial fields. However, for optical materials or electronic devices with high requirements for transparency, such as building glass, vehicle window glass, rearview mirror, optical lens, solar panel, etc., the environment is easily polluted due to frequent exposure to the outdoors, which will reduce the transparency and affect the working performance. For such applications, it is necessary to combine transparency with super-hydrophobicity, so that the self-cleaning and anti-fouling properties are maintained on the premise of maintaining transparency, so it has great application prospect to develop a transparent super-hydrophobic coating.

[0003] The construction of super-hydrophobic coating usually needs to meet two conditions, i.e. the surface has a certain rough structure and low surface free energy. From the perspective of surface roughness, the rough structure will affect the visible light transmittance, so the surface roughness needs to be prepared to balance between super-hydrophobicity and transparency. At present, people have prepared various transparent super-hydrophobic coatings through various methods such as vapor deposition, etching, electrochemical deposition, sol-gel method, template method, etc. For example, the Chinese patent with publication number CN115849295A first prepares a disordered nanopore structure on a silicon substrate by using phase separation technology, dry etching and vacuum evaporation, then copies the disordered nanopore structure on the silicon substrate to a quartz glass substrate by using ultraviolet nanoimprint technology, and finally obtains a transparent super-hydrophobic coating by combining vacuum evaporation, dry etching and using fluorinated alkyl chlorosilane for low surface energy treatment. The Chinese patent with publication number CN116535585A first prepares a fluorine-containing epoxy acrylate polymer by free radical polymerization using glycidyl acrylate and perfluoropolyether acrylate, then prepares a fluorinated silica dispersion liquid using nano-silicon dioxide, tridecafluoro-octyl triethoxysilane and gamma-glycidoxypropyl triethoxysilane, and finally compounding the fluorine-containing epoxy acrylate polymer, the fluorinated silica dispersion liquid and the epoxy resin for coating. The coating obtains a transparent super-hydrophobic coating after being cured by ultraviolet light.

[0004] However, most of these methods have problems such as complex process, need for professional equipment and use of fluorides, which greatly increases the production cost, and fluorides are not easy to degrade, which can easily cause health and environmental problems. SUMMARY

[0005] The present invention aims to provide a fluorine-free, transparent super-hydrophobic coating, a method for preparing the coating, and its application. The super-hydrophobic coating exhibits good transmittance in the visible light region and does not use fluorine-containing materials, thereby reducing health and environmental pollution. Furthermore, the present invention addresses the complex process requirements of existing super-hydrophobic coatings and reduces production costs.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a method for preparing a fluorine-free transparent super-hydrophobic coating, comprising the following steps:

[0008] Tetraethyl silicate, an organic solvent and an acid solution are mixed and subjected to hydrolysis-condensation to obtain a silica sol;

[0009] The silica sol is mixed with the BPH-8 gel factor under heating conditions, the resulting hot sol is coated on a substrate, and then dried to obtain a composite xerogel coating;

[0010] calcining the composite xerogel coating to obtain a calcined coating;

[0011] The calcined coating is immersed in a modifier solution to modify the coating to obtain a fluorine-free transparent super-hydrophobic coating;

[0012] The modifier in the modifier solution includes n-octyltrichlorosilane.

[0013] Preferably, the acid solution comprises hydrochloric acid; the mass concentration of the acid solution is 7.5-10%.

[0014] Preferably, the organic solvent includes ethanol; the usage ratio of tetraethyl silicate to the organic solvent is 3-30 mg:10 mL; the usage ratio of tetraethyl silicate to the acid solution is 3-30 mg:0.4 mL.

[0015] Preferably, the hydrolysis-condensation temperature is 10-30° C., and the time is 2-3 hours.

[0016] Preferably, the usage ratio of the silica sol to the BPH-8 gel factor is 10-11 mL:20 mg.

[0017] Preferably, the silica sol and the BPH-8 gel factor are mixed at a temperature of 160 to 170° C. and a time of 120 to 300 seconds.

[0018] Preferably, the calcination temperature is 500-600° C. and the calcination time is 2-3 hours.

[0019] Preferably, the concentration of the modifier solution is 2-5 wt %; the modification temperature is 10-30° C., and the modification time is 2-3 h.

[0020] The present invention provides a fluorine-free transparent super-hydrophobic coating prepared by the preparation method described in the above technical solution.

[0021] The present invention provides the application of the fluorine-free transparent super-hydrophobic coating described in the above technical solution in the field of architectural glass, vehicle window glass, rearview mirror, optical lens or solar photovoltaic.

[0022] The present invention provides a method for preparing a fluorine-free transparent super-hydrophobic coating. The present invention uses tetraethyl silicate (TEOS) as a silicon dioxide precursor, obtains a silica sol by hydrolysis-polycondensation, and then dissolves BPH-8 in a heated silica sol. The resulting hot sol is evenly coated on a substrate, and after cooling, BPH-8 self-assembles to form a three-dimensional network structure, and TEOS is adsorbed on the fiber surface and undergoes polymerization reaction, ultimately forming a composite gel coating; Subsequently, the solvent evaporates to obtain a dry gel coating, and BPH-8 is removed by calcining to obtain a fibrous silicon dioxide transparent surface. Then, octyltrichlorosilane is reacted with the silicon dioxide surface hydroxyl group to carry out hydrophobic modification, and a transparent super-hydrophobic coating is obtained. The super-hydrophobic coating prepared by the present invention has excellent hydrophobicity and light transmittance, and can reach 162.7 ° with water contact angle, and a rolling angle is less than 3 °, a visible light average transmittance of 84.8%, and has good self-cleaning ability.

[0023] The preparation process of the present invention is simple, and the prepared coating does not contain any fluoride, which solves the problems of complex process and use of fluoride in existing super-hydrophobic coatings. It is low-cost, does not require sophisticated equipment, and is environmentally friendly (fluoride is not easily degraded and can easily cause environmental problems). BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 This is the schematic diagram of the TEOS hydrolysis-condensation reaction;

[0025] Figure 2 This is the principle diagram of n-octyltrichlorosilane modification;

[0026] Figure 3 The transparency display effect photos of the coatings prepared in Examples 1 to 5;

[0027] Figure 4 is the contact angle of the coating prepared in Examples 1 to 5;

[0028] Figure 5 Transparency test results of the coatings prepared in Examples 1 to 5;

[0029] Figure 6Scanning electron micrographs of coatings prepared with different TEOS concentrations; (a) TEOS concentration is 0.3 mg / mL, (b) TEOS concentration is 1.0 mg / mL, (c) TEOS concentration is 1.5 mg / mL, (d) TEOS concentration is 2.0 mg / mL, and (e) TEOS concentration is 3.0 mg / mL;

[0030] Figure 7 Graph showing the self-cleaning ability test results of the coating prepared in Example 1 and an untreated glass substrate, wherein (a) is an untreated glass substrate and (b) is the coating prepared in Example 1;

[0031] Figure 8 The wetting conditions of different liquids on the coating surface prepared in Example 1. DETAILED DESCRIPTION

[0032] In the present invention, unless otherwise specified, the required raw materials or reagents are commercially available products well known to those skilled in the art.

[0033] The present invention provides a method for preparing a fluorine-free transparent super-hydrophobic coating, comprising the following steps:

[0034] Tetraethyl silicate, an organic solvent and an acid solution are mixed and subjected to hydrolysis-condensation to obtain a silica sol;

[0035] The silica sol is mixed with the BPH-8 gel factor under heating conditions, the resulting hot sol is coated on a substrate, and then dried to obtain a composite xerogel coating;

[0036] calcining the composite xerogel coating to obtain a calcined coating;

[0037] The calcined coating is immersed in a modifier solution to modify the coating to obtain a fluorine-free transparent super-hydrophobic coating;

[0038] The modifier in the modifier solution includes n-octyltrichlorosilane.

[0039] In the present invention, the acid solution preferably includes hydrochloric acid; the mass concentration of the acid solution is preferably 7.5-10%, more preferably 7.5-8.0%.

[0040] In the present invention, the organic solvent preferably includes ethanol; the usage ratio of tetraethyl silicate to the organic solvent is preferably 3-30 mg:10 mL, more preferably 15 mg:10 mL.

[0041] In the present invention, the ratio of tetraethyl silicate (TEOS) to the acid solution is preferably 3-30 mg:0.4 mL or 15 mg:0.4 mL. TEOS is a precursor for forming silica, and the surface structure of the silica coating after calcination is controlled by adjusting the amount of TEOS, thereby ensuring the hydrophobicity and transparency of the coating.

[0042] In the present invention, tetraethyl silicate is preferably added to an organic solvent and magnetically stirred for 10 minutes to obtain a tetraethyl silicate solution, and an acid solution is added and hydrolysis-condensation is performed under magnetic stirring to obtain a silica sol.

[0043] In the present invention, the hydrolysis-condensation temperature is preferably 10-30° C., more preferably 25° C., and the time is preferably 2-3 hours, more preferably 2 hours. The present invention has no particular limitation on the stirring, and stirring can be performed according to a process well known in the art.

[0044] The present invention carries out hydrolysis-condensation under acid catalysis conditions (principle see Figure 1 ) to obtain a silica sol containing TEOS hydrolysis condensation products.

[0045] After the hydrolysis-condensation is completed, the present invention preferably does not require post-treatment and directly mixes the obtained silica sol with the BPH-8 gel factor.

[0046] In the present invention, the BPH-8 gel factor is 1,4-bis[(3,4-dioctyloxyphenyl)-biphenylamide]benzene prepared according to the method described in patent CN 105858592A, and its structural formula is:

[0047]

[0048] In the present invention, the mass ratio of the silica sol to the BPH-8 gel factor is preferably 10-11 mL:20 mg, more preferably 10.4-10.6 mL:20 mg.

[0049] In the present invention, the temperature for mixing the silica sol and the BPH-8 gel factor is preferably 160-170° C., more preferably 160° C., and the time is preferably 120-300 s, more preferably 150-240 s.

[0050] The present invention preferably adds BPH-8 gel factor to silica sol, heats and dissolves it, and then coats it on a glass substrate. After drying in a ventilated place for 12 hours, a BPH-8 / SiO2 composite dry gel coating is obtained.

[0051] The present invention has no particular limitation on the glass substrate, and any corresponding substrate well known in the art may be used.

[0052] The present invention uses the three-dimensional network structure formed by BPH-8 as a template to induce the acid-catalyzed polymerization of TEOS hydrolysis-condensation products on the template surface to form fibrous silica. By adjusting the amount of TEOS used, the size of the nano-micron structure can be controlled, and the contradiction between the transparency of the coating and the structural requirements of hydrophobicity (super-hydrophobicity requires a high surface roughness, but high roughness will cause light scattering, thereby reducing transparency) is balanced to prepare a transparent super-hydrophobic coating.

[0053] In the present invention, the calcination temperature is preferably 500-600° C., and the calcination time is preferably 2-3 hours, more preferably 2 hours. During the calcination process, the organic BPH-8 component is removed, leaving only the silicon dioxide structure on the surface.

[0054] In the present invention, the modifier in the modifier solution includes n-octyltrichlorosilane; the concentration of the modifier solution is preferably 2-5 wt%, more preferably 3 wt%; and the solvent used in the modifier solution is preferably n-hexane. During the modification process described herein, the calcined coating can be completely immersed in the modifier solution; the amount of the modifier used is determined by the modification time and the concentration of the modifier solution.

[0055] In the present invention, the modification temperature is preferably 10 to 30° C., more preferably 25° C., and the modification time is preferably 2 to 3 hours, more preferably 2 hours.

[0056] like Figure 2 As shown, during the modification process, the chlorine groups in n-octyltrichlorosilane react with the hydroxyl groups on the surface of the coated silica, the hydrophilic hydroxyl groups on the coating surface are greatly reduced, while the hydrophobic octyl groups are increased, the silica is modified, and the hydrophobic properties of the coating surface are improved.

[0057] After the modification, the present invention preferably washes the obtained product with ethanol and then dries it to obtain a fluorine-free transparent super-hydrophobic coating.

[0058] The present invention provides a fluorine-free transparent super-hydrophobic coating prepared by the preparation method described in the above technical solution.

[0059] The present invention provides the use of the fluorine-free transparent super-hydrophobic coating described in the above technical solution in architectural glass, vehicle window glass, rearview mirror, optical lens or solar photovoltaic field. The present invention does not specifically limit the method of the application, and the application can be carried out according to methods well known in the art.

[0060] 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.

[0061] Example 1

[0062] (1) 15 mg of tetraethyl silicate (TEOS) was added to 10 mL of ethanol and magnetically stirred for 10 min to obtain an ethanol solution with a TEOS concentration of 1.5 mg / mL. 0.4 mL of a 7.5 wt% aqueous hydrochloric acid solution was then added and magnetically stirred at 25°C for 2 h to obtain a silica sol.

[0063] (2) 20 mg of 1,4-bis[(3,4-dioctyloxyphenyl)-bis(amino)benzene (BPH-8) gel factor was added to 10.416 mL of the silica sol prepared above, heated to 160°C for dissolution, mixed for 240 seconds, and the resulting hot sol was coated on a glass substrate to form an organic gel coating. After ventilation and drying for 12 hours, a BPH-8 / SiO2 composite xerogel coating was obtained;

[0064] (3) The obtained composite dry gel coating glass was calcined at 500°C for 2 h, and the obtained product was immersed in a n-hexane solution containing 3 wt% n-octyltrichlorosilane at 25°C for 2 h. The obtained product was washed with ethanol and dried to obtain a fluorine-free transparent superhydrophobic coating.

[0065] Example 2

[0066] The difference from Example 1 is that the amount of TEOS is adjusted to 3 mg, and the super-hydrophobic coating is prepared using an ethanol solution with a TEOS concentration of 0.3 mg / mL.

[0067] Example 3

[0068] The difference from Example 1 is that the amount of TEOS is adjusted to 10 mg, and the super-hydrophobic coating is prepared using an ethanol solution with a TEOS concentration of 1.0 mg / mL.

[0069] Example 4

[0070] The difference from Example 1 is that the amount of TEOS is adjusted to 20 mg, and the super-hydrophobic coating is prepared using an ethanol solution with a TEOS concentration of 2.0 mg / mL.

[0071] Example 5

[0072] The difference from Example 1 is that the amount of TEOS is adjusted to 30 mg, and the super-hydrophobic coating is prepared using an ethanol solution with a TEOS concentration of 3.0 mg / mL.

[0073] Test Example 1

[0074] Figure 3 The transparency display effect photos of the super hydrophobic coatings prepared in Examples 1 to 5; Figure 3 As shown in the figure, with the increase of TEOS concentration, the transparency of the coating gradually decreases and the word "superhydrophobic" under the coating becomes blurred.

[0075] The contact angles of the coatings prepared in Examples 1 to 5 were measured. The test results are shown in Figure 4 ,Depend on Figure 4 It can be seen that the wettability of the coating also changes with changes in TEOS concentration. When the TEOS concentration is 0.3 mg / mL, the water contact angle of the coating is 123.2°. As the TEOS concentration increases, the water contact angle of the coating gradually increases. When the TEOS concentration increases to 1.5 mg / mL, the water contact angle of the coating increases to 162.7°. Thereafter, as the TEOS concentration increases, the water contact angle gradually decreases. When the TEOS concentration is 3.0 mg / mL, the water contact angle is 156.3°. These results show that the coating has the best hydrophobicity when the TEOS concentration is 1.5 mg / mL. This is because as the TEOS concentration increases, the surface roughness of the coating also increases, thereby increasing the contact angle. However, when the TEOS concentration is too high, the surface structure of the coating changes, causing the contact angle to decrease.

[0076] Test Example 2

[0077] The transparency of the samples was tested using a UV-visible spectrophotometer with a wavelength range of 400 to 780 nm to measure the visible light transmittance of the coatings prepared in Examples 1 to 5. Figure 5 ,Depend on Figure 5 It can be seen that: with the increase of TEOS concentration, the visible light transmittance of the coating gradually decreases. The average transmittances of the samples prepared with TEOS concentrations of 0.3 mg / mL, 1.0 mg / mL, 1.5 mg / mL, 2.0 mg / mL, and 3.0 mg / mL are 87.9%, 86.0%, 84.8%, 77.7%, and 71.1%, respectively. This is because when the TEOS concentration is low, the surface roughness of the coating formed is small and the degree of light scattering is low, so the coating has higher transparency. However, with the increase of TEOS concentration, the surface roughness of the coating gradually increases, and the light scattering caused becomes more and more serious, and then the visible light transmittance of the coating decreases.

[0078] Test Example 3

[0079] The coatings prepared in Example 1 and Example 2 were tested by scanning electron microscopy. The test results are shown in Figure 6 .

[0080] Figure 6 , (a) TEOS concentration is 0.3 mg / mL, (b) TEOS concentration is 1.0 mg / mL, (c) TEOS concentration is 1.5 mg / mL, (d) TEOS concentration is 2.0 mg / mL, and (e) TEOS concentration is 3.0 mg / mL.

[0081] like Figure 6As shown in (a), when the TEOS concentration is 0.3 mg / mL, the coating surface morphology is relatively flat, with only a few protruding structures on the surface. When the concentration increases to 1.0 mg / mL, as shown in Figure 6 As shown in (b), a single layer of fibers appeared on the coating surface. When the concentration increased to 1.5 mg / mL, Figure 6 As shown in (c), the surface morphology of the coating changes into a multi-layer bundle fiber structure. When the concentration is 2.0 mg / mL, as shown in Figure 6 As shown in (d), it can be found that there are still many block structures on the fiber surface. When the concentration continues to increase to 3.0 mg / mL, as shown in Figure 6 As shown in (e), due to the excessive amount of TEOS, the bundled fibers on the coating surface mostly turned into a flaky structure, and there were also deep cracks.

[0082] Test Example 4

[0083] In practical applications, super-hydrophobic coatings are exposed to the air and often come into contact with dust or liquids. The self-cleaning properties of super-hydrophobic coatings make it difficult for pollutants to adhere to their surface, and surface pollutants can be easily removed by aqueous solutions. Therefore, the self-cleaning ability of ordinary glass (sailboat brand slide 7101) and the coating prepared in Example 1 were tested. Carbon black was placed on the sample surface as a pollutant, and then the sample was tilted and water droplets were dripped from above to observe the self-cleaning performance of the test sample. The test results are shown in Figure 2. Figure 7 , wherein (a) is an untreated glass substrate and (b) is the coating prepared in Example 1.

[0084] Test results for ordinary glass can be found in Figure 7 In (a), after adding water drops, due to the high adhesion of ordinary glass to water, the water drops adhere to its surface and cannot effectively remove surface pollutants; the test results of the coating prepared in Example 1 are shown in Figure 7 In (b), after adding water droplets, due to the ultra-low adhesion of the superhydrophobic surface to water, the water droplets roll rapidly on the coating surface and carry away the surface pollutants, leaving traces, indicating that the coating prepared in Example 1 has good self-cleaning ability.

[0085] Test Example 5

[0086] Take 20 μL of liquid and drop it on the surface of the coating prepared in Example 1. Observe the state of the droplet on the coating surface and test the wetting of different liquids (water (0.1 wt% methylene blue aqueous solution), acid (0.1 mol / L HCl solution), alkali (0.1 mol / L NaOH solution), juice (Huiyuan), cola (Coca-Cola), coffee, and Luckin Coffee) on the surface of the coating prepared in Example 1. The results are shown in FIG. Figure 8 .

[0087] Figure 8The wetting conditions of various liquids on the coating surface prepared in Example 1 are as follows: Figure 8 As shown in the figure, the various droplets tested showed regular spherical shapes on the coating surface, indicating that the coating has good repellency to these liquids and excellent hydrophobic effect.

[0088] 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 transparent super-hydrophobic coating, characterized in that: The following steps are involved: Tetraethyl silicate, an organic solvent and an acid solution are mixed and subjected to hydrolysis-condensation to obtain a silica sol; The silica sol is mixed with the BPH-8 gel factor under heating conditions, the resulting hot sol is coated on a substrate, and then dried to obtain a composite xerogel coating; calcining the composite xerogel coating to obtain a calcined coating; The calcined coating is immersed in a modifier solution to modify the coating to obtain a fluorine-free transparent super-hydrophobic coating; The modifier in the modifier solution includes n-octyltrichlorosilane; The calcination temperature is 500-600° C. and the calcination time is 2-3 hours.

2. The preparation method according to claim 1, characterized in that The acid solution includes hydrochloric acid; the mass concentration of the acid solution is 7.5-10%.

3. The preparation method according to claim 1 or 2, characterized in that The organic solvent includes ethanol; the usage ratio of tetraethyl silicate to the organic solvent is 3-30 mg:10 mL; the usage ratio of tetraethyl silicate to the acid solution is 3-30 mg:0.4 mL.

4. The preparation method according to claim 3, characterized in that The hydrolysis-condensation temperature is 10-30° C., and the time is 2-3 hours.

5. The preparation method according to claim 1, characterized in that The usage ratio of the silica sol to the BPH-8 gel factor is 10-11 mL: 20 mg.

6. The preparation method according to claim 1 or 5, characterized in that The silica sol and the BPH-8 gel factor are mixed at a temperature of 160-170° C. and a mixing time of 120-300 seconds.

7. The preparation method according to claim 1, characterized in that The concentration of the modifier solution is 2-5 wt %; the modification temperature is 10-30° C., and the modification time is 2-3 hours.

8. The fluorine-free transparent super hydrophobic coating prepared by the preparation method according to any one of claims 1 to 7.

9. Application of the fluorine-free transparent super-hydrophobic coating according to claim 8 in architectural glass, vehicle window glass, rearview mirror, optical lens or solar photovoltaic field.

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