Design And Preparation Of High Transmittance Superhydrophobic SiO₂ Antireflective Coatings

The antireflection coating with hydrophobic properties on the outer glass of the solar vacuum collector tube can improve the solar utilization efficiency and at the same time prevent sand,rain,dust and other pollution to prolong the service life during operation.In this thesis,an antireflection coating with a transmittance of 95.37%and a maximum water contact angle of 122.750°was prepared by sol-gel method.The main research contents and results are as follows:In order to prepare antireflection coatings with hydrophobic properties,a kind of antireflection coatings were prepared by immersion pulling method in sol containing methyltriethoxysilane(MTES).And a kind of antireflection coatings without hydrophobic treatment were immersed into hexamethyldisilazane(HMDS)to introduce a hydrophobic group.The antireflection coatings with the best hydrophobic properties were obtained by studying the surface roughness variation,the amount of MTES and the immersion time of HMDS.The microstructure and morphology of the AR coating were investigated by means of high-resolution scanning electron microscopy(SEM)and atomic force microscopy(AFM).The results showed that the surface density of the AR coating at different aging time will change.The roughness increased first and then decreased with the aging time.The amount of MTES also affected the surface density of the AR coating,and the roughness increased first and then decreased with the increasing of MTES.The immersion time of the AR coating in the HMDS increased,the density of the antireflection coating also changed.The roughness first increased,and then the trend is basically unchanged.The microstructure of the antireflection coating was characterized by means of Fourier transform infrared spectrometer.It was found that the addition of MTES in the sol and the immersion of antireflection coating in the HMDS introduced the methyl group to replace the hydroxyl group on the surface.Thus the antireflection coating had hydrophobic properties.The UV-visible-near-infrared spectrophotometer was used to measure the transmittance of the antireflection coating at different aging time,different amounts of MTES and different immersion time of HMDS.It was found that the transmittance had a linear relationship with the surface roughness at different aging time.Besides,as the amount of MTES increased and the immersion time of HMDS increased,the transmittance will decrease.Combined with the microstructure and morphology analysis,this was due to the changes in surface density of the AR coating.It was found that only changing the surface roughness did not significantly change the hydrophobic properties of the AR coating.When the molar ratio of MTES to tetraethyl orthosilicate(TEOS)was 1:2,the contact angle reached a maximum of 118.00°.While the AR coating was immersed into the HMDS in 1 hour and dried at 160°C for 3 min reached a maximum contact angle of 122.75°.The hydrophobic properties of the antireflection coating improved was mainly because both MTES and HMDS introduced a hydrophobic group to replace the hydrophilic group to lower the surface energy and maximize the contact angle.