Visco-coulombic characterization of aqueous and alcoholic titania suspensions

The influence of oxalic acid and phosphoric acid on the charging of titania particles suspended in water, methanol and ethanol reported previously is related to the concentration dependent viscosity. The viscosity enhancement due to charge neutralization at the isoelectric concentration (concentration of charge reversal) is of particular interest. In order to evaluate their applicability to alcoholic suspensions, six models based on the classical DLVO-model for colloidal stability has been evaluated: two Schulze-Hardy models for determination of critical (coagulation) concentration, Morris model for critical stability ratio in low-dielectric media, as well as three models for determination of yield shear stress. The results are discussed in terms of charge controlled aggregation and aggregate structure. The acid solubility and dissociation as well as surface-induced reactions due to specific adsorption of solvated acid molecules are found to influence the charging and viscosity of anatase particles.