Effect of polyvinylpyrrolidone on the physical properties of titanium dioxide suspensions

Abstract

The effect of polyvinylpyrrolidone (PVP) on the physical properties of aqueous and non-aqueous (methanol-based) TiO 2 suspensions was studied by measuring PVP adsorption and the rheological properties and dispersion stability of the suspensions. The amount of PVP adsorbed onto TiO 2 from the methanol solution is much larger than that from the aqueous solution and the effect on the dispersion stability of the suspension is much greater in the methanol-based suspension than in the aqueous suspension. The amount of adsorption of PVP is independent of the molecular weight, while the thickness of the adsorbed layer increases as the molecular weight increases. As the PVP concentration increases, the viscosity of the PVP solution increases, while the relative viscosity and the dynamic rheological parameters (G′, G″) of the suspension decrease, indicating that the network structure formed by dispersed TiO 2 particles in the absence of PVP diminishes with the increase in the PVP concentration. The dispersion stability of the methanol-based suspension increases with the increase in the concentration of PVP of high molecular weight, while the dispersion stability of the aqueous suspension is not significantly improved by PVP. It appears from the conformation of the adsorbed PVP molecules, determined by the measurement of the amount adsorbed and the thickness of the adsorbed layer, that the stabilization of the methanol-based suspension by PVP is due to entropic repulsion caused by the interaction of protruded tails of the adsorbed PVP molecules. It also appears from the measurement of the adsorption isotherm and the rheological properties that the increase in the dispersion stability with PVP at high PVP concentration is due to the increase in the concentration of non-adsorbing free PVP molecules.