The critical conditions for secondary nucleation of silica colloids in a batch Stöber growth process

In this work, we determined experimentally the critical total surface area of silica seeds in the solution to avoid the formation of new particles (i.e. secondary nucleation) in a batch Stöber growth process. This critical surface area corresponded to the balance between the generation rate of reaction intermediate from the hydrolysis of TEOS and its consumption rate via the growth of existing seeds. Further calculation showed that the secondary nucleation was probably related to the average distance between seed particles. When the distance between seeds exceeded a critical value for each growth condition, i.e. for each generation rate, one would then observe secondary nucleation. Otherwise, simple growth was observed. Higher generation rate corresponded to shorter distance.