Evaluation of the Molecular Conformation of Surface Alkyl Chains of Alkylsilane-Derived Hybrid Films Using Sum-Frequency Generation Spectroscopy

Abstract

Alkylsilane-derived hybrid films exhibiting excellent dynamic dewetting behaviors toward various liquids are promising, since they are smooth, highly transparent, and a low environmental burden. However, the detailed mechanism of their unique dynamic dewetting behaviors and its relation to the surface segregation of alkylsilanes during the film formation have not yet been clearly identified. In this study, we prepared various hybrid films by varying the mixing ratios of tetraethoxysilane (TEOS) and n-dodecyltriethoxysilane (C12TES) and investigated the changes in the s-CH2/s-CH3 peak strength ratios of the resulting hybrid films under dry and wet conditions by sum-frequency generation (SFG) spectroscopy. When the static/dynamic water contact angles significantly changed, it was clearly observed that the s-CH2/s-CH3 ratio of each hybrid film under dry and wet condition also changed markedly. With increasing TEOS concentration, the static contact angles became smaller, while the contact angle hysteresis tended to increase because of the increase in gauche defects at the air interface and hydrogen bonds. This finding suggests that the concentration and conformation of the alkyl chains derived from surface-segregated C12TES molecules play an important role in determining the final dewetting behaviors of the hybrid films to water.