Surface structural analysis of fine silica powder modified with butyl alcohol

The surface structure of modified silica powder has been studied by various experiments and simulations. In addition, the effect of surface structure on wettability has also been investigated. Nonporous silica powder was modi fied with n-and t-butyl alcohol. Two series of the modified silica surfaces were characterized by fractal dimension analysis from isotherms with some kinds of adsorptives. The fractal dimensions of the two series of modified surfaces were different from each other with an increase in modified ratio. The fractal dimension of the surface modified with t-butyl alcohol (t-modi fied surface) increased monotonously with butoxy group density. It is thoug ht that the structure of the t-butoxy group is rigid and that the t-butoxy group cannot change its conformation. On the other hand, the variation of t he surface fractal dimension value for the surface modified with n-butyl al cohol (n-modified surface), whose structure is flexible, was unique compare d with the t-modified surface. Such discrepancy was assumed to be caused by the difference in the structure of the modifier and the assembled state of modifiers between the t- and n-modified surfaces. In order to investigate the variation of surface structure of the surface modified by the butoxy gr oup with an increase in modified ratio, molecular dynamics simulations were performed. By comparing the results of these simulations with experimental results, it has been clarified that the variation in the mobility of the m ethyl group in the n-butoxy groups was closely related to the change in the surface fractal dimension value for the n-modified surface. It was then el ucidated that this mobility change was caused by steric hindrance among the groups. Furthermore, the variation of conformation in the n-butoxy groups, which was obtained from molecular dynamics simulations, was in good agreem ent with the change in the wettability of the n-modified surface. It is sug gested that the surface density of the modifier, the covering structure and the bulkiness significantly influence the wettability of the modified surf ace.