Quantitative aspects of the growth of (charged) silica spheres

It is shown that the growth of monodisperse, charged silica spheres in ethanolammonia upon addition of tetraethoxysilane can be adequately studied with static light scattering. The resulting growth curves (radius vs time) are analyzed in terms of a model for diffusion-controlled growth of (charged) spheres in a solution of reactive (charged) monomers, the bulk concentration of which decreases due to this growth. This decrease is sufficient to account for the essential shape of the curves. A coulombic sphere-monomer repulsion is theoretically shown to modify the growth rate only with a constant factor.