Transparent Superhydrophobic Coating Prepared by One-step Method Based on Fluorinated Cage-like Sesimiloxane

The coating film-forming method has good application prospects in the preparation of transparent superhydrophobic coatings due to its simple process, good repeatability and low equipment requirements. However, the nanofillers in existing coating film-forming methods generally have defects such as easy aggregation and poor durability. POSS is an organicinorganic hybrid with a special cage-like structure. Compared with ordinary nanofillers, POSS has the characteristics of monodispersity and flexible functional modification. At present, most of the researches on POSS in the field of superhydrophobic coatings are based on rough substrate surfaces, but few researches have been done in the field of mirror-transparent optics. Therefore, the purpose of this study is to select POSS as a nanofiller and use a one-step coating film-forming method to construct a large-area transparent and durable superhydrophobic coating on a mirror substrate. In this study, an intermediate POSS-SH8 was synthesized from octavinyl POSS and ethanedithiol based on a two-step thiol-ene click chemistry reaction. Then, POSS-SH8 and dodecafluoroheptyl methacrylate monomer were used as reactants to obtain low surface energy modified product POSS-SH-DFMA7 through photoreaction. The effects of the doping mass fraction of F-POSS and the volume fraction of ethanol addition on the construction of superhydrophobic coatings were explored. The preparation of spraying prefabricated liquid was as follows: F-POSS with different mass fractions was blended in resin prepolymer. Resin prepolymer was composed of a mixture of hydrophobic photocurable resin (Changxing 6145-100) and diluent HDDA at 4∶1. After the prepolymer was evenly mixed, the dilution solvent THF was added to the system at a dilution ratio of 1∶20. It was dispersed uniformly in a stirrer and an ultrasonic shaker successively. In order to obtain the rough micro-nano composite structure on the smooth substrate surface, the method of spraying combined with non-solvent induced phase separation was adopted in this study. Different volume fractions of non-solvent ethanol were added to the above system to obtain a series of spraying prefabricated liquids. Next, the prefabricated solution was transferred to the surface of the smooth substrate by spraying and the coating was air-dried at room temperature. Finally, the air-dried coatings were cured in a UV curing apparatus under N2 atmosphere for 5 minutes. The chemical composition of the main substances in the obtained samples was analyzed by infrared spectrum curve. The static water contact angle and dynamic rolling angle of the coatings were recorded by contact angle analysis and self-made rolling angle measuring instrument to characterize the hydrophobicity of the coatings. The surface topography and roughness of the composite coatings with different rough structures were investigated by scanning electron microscopy and three-dimensional ultra-depth-of-field microscopy. The transmittance of the coatings was measured by a UV spectrophotometer to characterize the transmittance of the coating. A self-made device was used to set water droplets to be released at a uniform rate of 2 drops per second at a height of 30 cm. The hydrophobic property retention curve of the coatings at different times were obtained to characterize the mechanical stability of the coating. The three superhydrophobic coatings were placed in an outdoor open-air environment, and their contact angle changes were recorded every 3 days to evaluate their weatherability. In addition, the above three coatings were soaked in HCl and NaOH solutions with pH values of 1 to 14 for 24 hours. And the contact angle curves of each coating at different pH values were recorded to compare their resistance to reagents. The research results show that the coating exhibits excellent superhydrophobic properties when the doping mass fraction of POSS-SH-DFMA7 is 40% of the resin content and the addition volume fraction of ethanol is 25%. The static water contact angle and sliding angle can reach 156.92° and 3.24°, respectively. In addition, the superhydrophobic coating prepared under the optimal process conditions also has good optical transparency and its light transmittance is 85.63%. The coating still maintains superhydrophobic property after being impacted by water droplets for 6 hours, indicating its mechanical stability. Not only that, the original wetting property of the coating can still be maintained after experiencing various outdoor environments and the erosion of chemical agents with different pH values. Therefore, the introduction of a certain amount of fluorine-containing monomer to modify the POSS combined with the phase separation of ethanol into the photocurable resin system can prepare a large-area transparent and superhydrophobic coating with stable physical and chemical properties in one step. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.