Electrostatic interactions in formation of particles from tetraethyl orthosilicate

The particle formation mechanism during hydrolysis and condensation of tetr aethyl orthosilicate (TEOS) was studied with in-situ measurements of partic le size distribution, electric surface potential and electric conductivity in the absence and in the presence of electrolytes, KCI and LiCl. Experimen ts were performed at a TEOS concentration of 0.4 mol/dm(3), a water concent ration of 11 mol/dm(3) and an ammonium concentration of 1 mol/dm(3). The ad dition of KCI has a greater effect on the particle sizes than that of LiCl, The average particle size attained 1 mu m at a KCI concentration of 1 mmol /dm(3) maintaining high monodispersity in particle sizes. Measurements of s urface potential and electric conductivity show that the increase in partic le size by the addition of the electrolytes is caused by both a reduction i n the surface potential and an increase in the ionic strength. The effect o f the electrolytes was also examined in seeded growth experiments. Addition of KCI to the system suppresses the generation of new particles and enable s the growth of seed particles by as much as fifty-fold in volume. Our expe rimental results show that electrostatic interaction between the particles is the dominant factor in controlling particle size distributions.