Abstract
Raman spectroscopy was used to investigate the state of conformational and packing order for octadecyltrichlorosilane (OTS) attached to high surface area fumed silica as a function of the hydration state of the silica. The fumed silica had a surface area of 50 m2/g and a primary particle size of ∼40 nm. Room temperature and temperature-dependent spectra were obtained for OTS attached to the fumed silica and compared with those of polyoctadecyl siloxane (POS). Both the skeletal optical region, between 1000 and 1150 cm-1, and the high-frequency CH2 stretching region, between 2800 and 3000 cm-1, were monitored. The intensity ratios I(1060)/I(1080), which is indicative of the ratio of trans/gauche bonds, and I(2850)/I(2885), which is indicative of lateral packing order, were plotted as a function of temperature. For OTS attached to completely dehydrated and dehydroxylated surfaces, only disordered structures of alkyl chains, similar to those of molten alkane chains, were observed. With increasing hydration of...
Published Version
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