ABSTRACT
Silica and certain silsesquioxane dispersions obtained from alkoxysilanes are examples of sol-gel processing. They are obtained from the hydrolysis and condensation of metal alkoxides when the water-to-alkoxide molar ratio (R value) is greater than 2, or a base (alkaline) catalyst is used [1]. In these conditions, spherical or disk-shaped particles are obtained. One typical example is the Stöber process, reported in 1968, for preparing monodispersed, spherical silica particles from tetraethylorthosilicate (TEOS) with an R value between 7 and 25 and ammonia concentrations from ~1 to 7 molar [2]. Spherical particles of silsesquioxanes such as methylsilsesquioxane (CH3SiO3/2) can be prepared in a similar manner starting from organosilanes like CH3Si(OCH3)3 [3].
