Vibrational spectroscopy of dimethylchlorooctadecylsilane covalently bonded to ultrathin silica films immobilized on Ag surfaces

FTIR and Raman spectroscopies have been used to characterize the structure and conformational order of dimethylchlorooctadecylsilane (DOS) covalently bonded to ultrathin silica films supported on Ag substrates. Ultrathin sili ca films of ca. 30 Angstrom thickness prepared from sol-gel methods are imm obilized on Ag surfaces modified with a self-assembled monolayer of (3-merc aptopropyl)trimethoxysilane (3MPT). This layered structure provides a uniqu e opportunity for acquiring complementary spectral data from both FTIR and Raman spectroscopies, which are useful in elucidating alkylsilane conformat ion pertaining to stationary phases for reversed-phase liquid chromatograph y (RPLC). Characterization of octadecyltrichlorosilane (OTS) layers on thin silica films of ca. 800 Angstrom thickness on 3MPT-modified Ag surfaces ha s been reported previously. Differences between the ultrathin silica films used in this study and the thin silica films used in this previous study ar e considered. The results from both FTIR and Raman spectroscopy presented h ere suggest that bonded DOS alkyl chains are in a disordered, liquid-like s tate with close to monolayer surface coverage.