A study on the stability and rheological behavior of concentrated TiO2 dispersions

The stability and rheological behavior of dilute and concentrated dispersions of TiO2 powders in aqueous solution have been investigated. It was found that the repulsive interaction between the electrical double layers around the TiO2 particles is the dominant factor influencing the stability of the dispersions. The stability of the TiO2 dispersions shows a minimum at their isoelectric point, and, correspondingly, the viscosity at infinite shear rate and the yield value of the concentrated TiO2 dispersion reach their maximum at about the same pH. Either increasing or decreasing the pH will result in the enhancement of the stability of the TiO2 dispersion, and, concomitantly, a decrease in the viscosity and yield value of the concentrated TiO2 dispersion. The addition of ionic surfactants, sodium dodecyl sulfate and tetradecylpyridine bromide, which can be adsorbed strongly at the TiO2/solution interface, increases the stability of the TiO2 dispersion and decreases the viscosity and yield value of the concentrated dispersion effectively by increasing the absolute value of the zeta potential of the TiO2 particles. In contrast, the non-ionic surfactant, Triton X-100, whose adsorption on the surface of TiO2 particle is much less than that of the ionic surfactants, shows a negligible effect on the stability and rheological properties of the TiO2 dispersion. (C) 1998 Elsevier Science S.A. All rights reserved.