Effect of the additives in sols on the surface roughness of the coating films derived from mixtures of tetraethoxysilane- and methyltriethoxysilane-derived sols

We have examined the influence of additives to coating sols, such as water, aldehyde, acetal, ester, carboxylic acid and several kinds of diols on the surface roughness of coating films with a "concave-convex" surface, derived from the mixtures of tetraethoxysilane (TEOS) and methyltriethoxysilane (MTES). Among the additives tested, n-butyric acid and diols such as ethylene glycol, propanediol, butanediol or pentanediol increased the surface roughness of the resultant films. It was also found that the surface roughness (R-a) was controlled by changing the concentration of the additives and that the diols showed different effects among the isomers. Among normal butanediols, 1,4-butanediol of methylene-type diol was the most effective to increase Ra of the films, followed by 1,3-butanediol and then by 1,2-butanediol.