Preparation and characterization of colloidal silica particles under mild conditions

A microscale laboratory experiment for the preparation and characterization of silica particles at neutral pH and ambient temperature conditions is described. Students first employ experimental fabrication methods to make spherical submicrometer silica particles via the condensation of an alkoxysilane and polyethyleneimine, which act to catalyze the reaction in the presence of phosphate buffer. This is then followed by methods to characterize the particles by size and imaging and allows the students to describe particle growth and improve their skills in explaining results obtained while using different methods. This silica particle synthesis has the advantage over the Stöber method in that no extremes of pH or temperature are needed. In addition, the chemicals used in this experiment are less hazardous than those commonly used to make silica particles