Abstract
The methyl-modified hybrid silica sols with methyltriethoxysilane and tetraethoxysilane were successfully prepared using alkaline (NH3 and tetra-methyl-ammonium hydroxide (TMAH)) and acid catalysts (HCl and CH3COOH) and characterized with thermogravimetric analysis, Fourier transform infra-red, and water contact angle. The methyl-modified silica film showed hydrophobic property with water contact angles over 90° under alkaline or acid catalyst. The methyl-modified silica membranes were fabricated and evaluated with He, H2, N2, C3H8, and SF6 at 200°C. He gas permeance for hybrid silica membranes was in the range of 0.61–1.91 × 10-6 mol m-2 s-1 Pa-1, while He/SF6 and N2/SF6 permeance ratios of acid-catalyzed membranes was quite higher than those of alkaline catalyzed. Pore size (dp) of membranes were evaluated with normalized Knudsen-based permeance method, and the order of pore size for methyl-modified silica membranes can be estimated as follows: HCl-catalyzed membrane < acetic acid-catalyzed membrane < TMAH-catalyzed membrane < ammonium-catalyzed membrane. Judging from the order of pore size for methyl-modified silica membranes, the pore size of methyl-modified silica membranes can be tuned by controlling of catalyst during the sol–gel processing.
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