Study On The Preparation And Application Of Superhydrophobic Silica Coatings

Superhydrophobicity is a special wetting phenomenon on solid surface.Superhydrophobic surface has the functions of self-cleaning,oil and water separation,water directional flowing and so on.Superhydrophobic surface has an important application prospect in the fields of self-cleaning material,fluid drag reduction,corrosion prevention,waterproof and antifouling.However,the widely reported superhydrophobic coatings have the disadvantages of low mechanical stability and low transparency,which restricts their practice application.In order to solve the practical application problems of superhydrophobic coating,this paper aims to prepare a transparent and durable superhydrophobic SiO2 coating via a simple approach with common apparatus and reagents.Our research work mainly includes the following three parts:In the first part,methyl modified hydrophobic SiO2 nanoparticles were obtained by hydrolysis and co-condensation reactions occurred in base-catalyzed system by carefully controlling the sol-gel process of Tetraethoxysilane(TEOS)and Methyltriethoxysilane(MTES).The hydrophobicity and surface structure of SiO2 coated glass were studied.The results show that the optimum reagent ratio for the synthesis of hydrophobic SiO2 nanoparticles is TEOS:EtOH:NH4OH:H2O:MTES = 1:30:3.6:1:0.5,and the SiO2 particle size ranges from 65 to 85 nm.The transmittance of superhydrophobic SiO2 coated glass at 550 nm wave length is 91.5%,only 0.3%less than that of glass matrix,and the coating still retain superhydrophobicity at a temperature up to 500 ℃,but its mechanical stability is very poor,and it can be destroyed by hand rubbing.In the second part,we developed transparent and durable superhydrophobic SiO2/EP bilayer coatings containing hydrophobic SiO2 particles on top and an epoxy resin(EP)bonding layer at the base.The influence of the setting time of epoxy resin adhesive,the modification of n-butyl glycidyl ether(BEP)and the concentration of SiO2 on the properties of the superhydrophobic coating were discussed.The results show that the coating can maintain superhydrophobicity within a wide range of SiO2 concentration of 6.5-1.3%w/v.The optimum setting time for EP and BEP adhesive is 15 min and 30 min respectively.The transmittances of SiO2/EP and SiO2/BEP bilayer coating prepared with SiO2 concentration of 6.5 w/v are 86.6%and 90.3%at 550 nm,respectively.Under the pressure of 2500 Pa,they can withstand 1460 cm and 960 cm friction without losing superhydrophobicity.These superhydrophobic coatings showed good stability in saline immersion test and heating experiment at 200 ℃.In the third part,we developed higher wear-resistant bilayer coatings with the mixture of epoxy resin,hydrophobic SiO2 particles and absolute ethanol as the base bonding layer,and hydrophobic SiO2 particles on top layer.The coating can withstand 1900 cm friction at 2500 Pa pressure without losing superhydrophobicity,and the heat resistance temperature can reach 200 ℃,but the transparency is lower than that of SiO2/EP coating.The structure of the composite EP-SiO2 layer cured at 80 ℃ is more compact than that cured at room temperature,and the corresponding SiO2/(SiO2-EP)coating has stronger wear resistance.