Journal of Chemical Engineering of Japan, Vol.34, No.2, 262-268, 2001
Effects of polyvinyl alcohol on the rheological behavior and phase stability of aqueous silica suspensions
In this world various silica suspensions mere synthesized by a single step Stober method and by a two-step grow th method using either fumed silica or colloidal silica as a seed. The synthesis proceeded through a controlled hydrolysis and condensation reactions of tetraethylorthosilicate (TEOS). After the reactions were completed, the solvent ethanol of the silica suspension was substituted by water through vacuum evaporation and ultra-centrifugation in order to obtain the aqueous silica suspension. Then, the silica suspension was stabilized by adjusting electrostatic repulsion, and by generating steric repulsion from the adsorbed polyvinyl alcohol (PVA). To elucidate the steric stabilization of colloidal silica by the polymeric surfactant of PVA, the adsorption isotherms of PVA in the aqueous silica suspension are determined. Moreover, the rheological behavior of the silica suspensions stabilized by PVA is investigated to characterize the dispersion stability of the colloidal silica suspensions. The results show that the phase stability of silica suspensions of relatively smaller particles is mainly induced by the electrostatic repulsion compared with steric stabilization contributed from the adsorbed layer of PVA. Meanwhile, for larger particle suspensions, the phase stability is governed predominantly by steric stabilization of the adsorbed PVA.
Keywords:silica suspension;wafer polishing slurry;steric stabilization;electrostatic stabilization;suspension rheology