Effects of adding different proportions of ethanol or water/ethanol on performance of hydrophobic antireflection film

Abstract

Tetraethoxysilane (TEOS) was oscillated to accelerate hydrolysis. Hydrolysed TEOS reacted with hexamethydisizane to form hydrophobic sol–gels from which hydrophobic antireflection films were fabricated by spin coating. Enough solvent, such as ethanol, must be added to help the reaction proceed smoothly. Atomic force microscopy was employed to investigate the effect of the proportion of ethanol added on the nanostructure, water contact angle (WCA) and transmission of the spin coating film. A molar ratio of ethanol/TEOS of 12 is optimal for obtaining a uniformly nanoporous film. The average transmission, average and maximum WCA are 93·02%, 111·58 and 119·04° respectively. When silica sol was dispersed by both water and ethanol, trimethyl modified silica repelled water and aggregated to form submicrometre columnar structures after spin coating. Its performances on WCA and transmission are worse than silica sol dispersed by ethanol only. The hydrophobic functional group of silica sol influences WCA stronger than roughness does.

Keywords:

• Antireflection
• Hydrophobic
• Sol–gel
• Transmission
• Water contact angle

The authors would like to thank Dr Te-Ho Wu, Yen-Zen Wang and Yung-Kuan Tseng for the atomic force microscopy, contact angle tester and spin coater respectively.