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 h ydrolysis and condensation reactions of tetraethylorthosilicate (TEOS). Aft er the reactions were completed, the solvent ethanol of the silica suspensi on was substituted by water through vacuum evaporation and ultra-centrifuga tion in order to obtain the aqueous silica suspension. Then, the silica sus pension was stabilized by adjusting electrostatic repulsion, and by generat ing steric repulsion from the adsorbed polyvinyl alcohol (PVA). To elucidat e the steric stabilization of colloidal silica by the polymeric surfactant of PVA, the adsorption isotherms of PVA in the aqueous silica suspension ar e 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 stabil ity of silica suspensions of relatively smaller particles is mainly induced by the electrostatic repulsion compared with steric stabilization contribu ted from the adsorbed layer of PVA. Meanwhile, for larger particle suspensi ons, the phase stability is governed predominantly by steric stabilization of the adsorbed PVA.