Abstract
The diameter of monodispersed silica colloids is mainly affected by the relative contribution from nucleation and growth. Once the total number of nuclei is fixed, the resultant particle size is then determined via the growth process by the total quantity of TEOS. In this work, we will demonstrate the effect of cosolvent on particle size of silica colloids, in addition to the common parameters such as NH 3 and water concentrations. Experimental results indicate that the size of silica colloids decreases with increasing polarity index of the solvents. (The definition of polarity index of cosolevent: P AB = φ A P A + φ B P B ). Since the cosolvent is not directly involved in the preceding reactions of hydrolysis and condensation, we therefore suspect that the polarity of cosolvent would influence the solubility of intermediate [Si(OC 2 H 5 ) 4-x (OH) x ] and hence the supersaturation ( C* m ) for the nucleation process. With higher polarity of cosolvent, the number of nuclei is increased and therefore smaller silica colloids are obtained. Furthermore, the effects of ammonia and water will also be discussed by similar arguments based on relative contribution from nucleation and growth processes.