Surface modification of colloidal silica by sulfonation route for super-hydrophilicity

Colloidal silica was chemically modified by a two-step method including an olefin sulfonation route as a preliminary study for super-hydrophilic applications. The hydrophobic vinyl groups were initially bonded chemically to the hydroxylated silica surface using the trichlorosilane coupling agents. The vinyl-terminated silica was then sulfonated by addition reaction with chlorosulfonic acid. The modified silica was investigated using DRIFT, TGA, element analysis, solid-state Si-29- and C-13 CP-MAS NMR. The vinyl-terminated specimen showed a characteristic IR absorption band at 1600 cm(-1) and a weight loss of approximately 3% starting at 350degreesC while the Si-29 NMR peaks at 70.9 and 79.8 ppm and C-13 NMR at 136 ppm and 129.8 ppm were assigned to a vinyl group bonded to silica. Elemental analysis of the sulfonated silica indicated the presence of sulfur, carbon and hydrogen. Thermal decomposition in range 150-600degreesC was due to the presence of sulfonated organics and unreacted vinyl groups while the newsignals on C-13 NMR, which were in the range 70-15 ppm, were assigned to sulfonated carbons.