Kinetic studies of attachment and re-orientation of octyltriethoxysilane for formation of self-assembled monolayer on a silica substrate

The present study deals with kinetic studies of the chemical modification for synthesizing a hydrophobic silica surface. Surface silanization (modification) via formation of Self-Assembled Monolayer (SAM) using a short chain triethoxyoctylsilane (TEOS) was carried out under inert atmosphere at room temperature. Fourier transmission infrared (FTIR) spectroscopy, water contact angle (WCA) and atomic force microscopy (AFM) were employed to investigate surface modification. FTIR analysis in the range from 900-1200 cm(-1) and 28503000 cm(-1) confirmed surface modification and re-orientation of the attached molecules. Kinetic studies of TEOS SAM formation were fitted by Exponential Association function. Kinetic fitting of FTIR data in the range from 900-1200 cm(-1) revealed a very fast attachment of TEOS molecules resulting in total surface coverage within 16 min whereas re-orientation rate was slow and continued till 512 min. Further, change in orientation from lying-down to standing-up state was supported by contact angle analysis. AFM images initially showed small islands of-20 nm, which in-fill with time indicating formation of a smooth monolayer. Our findings indicate that formation of octyl SAM is fast process and completes within 8.5 h in contrary to reported 24 h in conventional SAM formation protocols. The kinetic fitting data can be explored to design a nanopatterned surface for a specific application. (C) 2016 Elsevier B.V. All rights reserved.