Super-water-repellent coating on polymer substrates using fluorosilane-silica hybrid materials

The purpose of this study is to develop transparent super-water-repellent surfaces with a simple way and to apply this coating to polymer substrates. Super-water-repellent surfaces are generally made by controlling chemistry and roughness at the surface. In this study, surface roughness was controlled by the content of colloidal silica particles in a sol-gel thin film covered with fluoroalkyl silane coupling agent. When the fractional amount of colloidal silica was in the range of 10-30 wt%, root mean square roughness at the surface by AFM was around 30-70 nm. X-ray photoelectron spectroscopy revealed that these surfaces were covered with fluoroalkyl groups. Consequently, these surfaces exhibit excellent water repellencies such as contact angles of 150 deg. to water. This coating procedure can be applied to transparent polymer substrates such as poly(ethyleneterephtarate) (PET) films. In that case, transparency and durability of the sol-gel layer on the PET film are sufficient enough to be applied for practical use.