UV-resistant and transparent hydrophobic surfaces with different wetting states by a facile dip-coating method

Abstract

Hydrophobic surfaces with good resistance to UV radiation and high optical transparency are of great importance for various technological applications. In this work, we report a simple one-step approach to prepare such surfaces by the deposition of two different kinds of silanes, trimethylchlorosilane (TMCS), and perfluorooctyltrichlorosilane (PFOTCS). The surface coatings were obtained by dipping clean glass slides into the silane solutions of similar concentrations (˜ 0.1 M) in hexane. To obtain the surface with the best hydrophobic character, the immersion time of the substrate in both silanes was varied. Contact angle measurements with a goniometer showed the average static water angle values to be ˜ 110° and 120° for the TMCS- and PFOTCS-coated surfaces respectively. Sliding angle tests revealed an altogether different wetting state for the latter, Cassie impregnated state. The resulting surfaces were optically transparent having a visible light transmissivity similar to virgin glass. Atomic force microscopy (AFM) measurements showed both surfaces to be smooth with average roughness values ≤ 10 nm. X-ray photoelectron spectroscopy of the PFOTS modified surfaces confirmed fluorine enrichment at the top of the surface. Self-cleaning tests performed with dust particles showed the TMCS-coated surface to possess good cleaning characteristics. The synthesized surfaces retained their hydrophobic character after prolonged exposure (˜ 24 h) to concentrated UV light. The proposed preparation method is quite simple and can be applied to large-area substrates.