(436a) Stratified Colloidal Silica Particles: Preparation and Characterization

Inorganic silica, also known as Stöber silica, is important in many applications. Among other colloidal particles, silica distinguishes itself as a low cost material with an easy-to-functionalize, nontoxic surface. A modified Stöber procedure was used to scale up the solid particle yield. Upon storage in the original basic conditions, the colloidal suspensions were found to separate into layers. Each layer contained paucidisperse particles capable of packing in 2D arrays resembling flower-like and zig-zag morphologies. A stability study showed that after several months silica evolved into cavitated structures due to slow, base-catalyzed etching. The mesoporous morphologies were found mostly in the top layer within a tall container chosen to encourage vertical stratification. Prolonged storage (~1 year) caused particle degradation. The size of the stratified colloid was monitored at each step by multi-angle dynamic light scattering and transmission electron microscopy. Asymmetric flow field flow fractionation, when equipped with light scattering detection, proved to be a reliable tool to fractionate the stratified colloid and also to resolve particles according to shape. The data gained by these techniques indicate that the stratified colloid formation is a density-driven process. This work was supported by grants DMR-1306262 from the National Science Foundation.