Silica particles were prepared using Stober's method. Their obtained in a suspension had a range of 0.05 μ to 2 μ in diameter.
The adsorption of poly(viny alcohol) (PVA) on silica particles and its effect on the diffusivity and viscosity of the suspensions were studied with photon correlation spectroscopy and Cannon-Fenske capillary type viscometer. The viscosity of silica suspensions in PVA solutions were measured for various ranges of particle concentrations, particle diameters, pH, and molecular weight of PVA.
The adsorption of PVA on silica particles were very sensitive to surface functional groups. In addition, it was shown that the degree of flocculation was also dependent on functional groups on the particle surface. Most of groups were essentially silanol. Maximum adsorption of PVA was shown at the point of zero charge(pzc) of the oxide, above which there was a gradual decrease in adsorption with an increase in pH.
Adsorption caused depletion of the polymers in the liquid phase and volume augmentation of the dispersed phase. Therefore, the viscosity of suspensions did not increase monotonically with particle concentrations. The following two unique observations were reported: ⑴ For sterically stabilized suspension, the viscosity of suspension became lower than that of the medium, because polymers were depleted from the liquid phase by the adsorption. ⑵ The viscosity of suspension increased by the aggregation of particles. The aggregation of particle was interpretated in term of polymer bridging.
