The Determination of the Isoelectric Point from Measurements of Dispersion Viscosity as a Function of pH

Abstract

The isoelectric point of a zirconia‐ and alumina‐coated TiO₂ was established from the acoustic response of 2% aqueous dispersions. The viscosities of 5.0% aqueous dispersions of the TiO₂ were measured as a function of pH using a stress‐controlled rheometer. The viscosity was found to have a maximum at the isoelectric point and to be directly related to the square of pH difference near the isoelectric point in a manner analogous to that reported for yield stress. This work showed that a reasonable estimate of the isoelectric point could be made by conducting straightforward experiments on an instrument as simple as a Brookfield viscometer.

Keywords:

• Isoelectric point
• zeta potential
• viscosity
• TiO₂
• pH
• dispersion

Acknowledgments

This project is supported financially by the Australian Research Council via its SPIRT scheme and Selleys Pty Ltd. Special thanks is also due to Mr. Koogan Moodliar for his support. Extensive discussions with Prof. Robert Hunter and Prof. Gregory Warr were very helpful. We also thank Dr. Alexander Djerdjev for performing the measurements on the AcoustoSizer.