ESTIMATION OF THE EQUIVALENT HARD-SPHERE RADIUS OF CHARGED COLLOIDS IN CONCENTRATED SUSPENSIONS

CLAUDIO L. A. BERLI, JULIO A. DEIBER, D. QUEMADA

Foz do Iguazu, Brasil

Congreso; 11th International Conference on Surface and Colloid Science; 2003

International Association of Colloid and Surface Scientists

The idea that electrostatically charged particles behave as equivalent hard-spheres (HS), the radius of which involves the exclusion distance due to the repulsive forces, is widely used to interpret experimental data obtained from different techniques like dynamic rheometry and light scattering. This work is concerned with the theoretical estimation of the HS radius of concentrated colloids. In particular, we consider zero-shear viscosity data of charge stabilized latex suspensions. Numerical prediction of the HS radius through Barker-Henderson equation requires the knowledge of the pair potential. The usual treatment of the double-layer interaction was firstly considered, namely DLVO potential with effective or renormalized parameters. Since this prescription was unable to describe viscosity data as a function of particle concentration, a nobel expression of the interaction potential was investigated. Calculations were carried out by using linear Poisson-Boltzmann theory with particles confined into Wigner-Seitz cells. Therefore this potential predicts appropriately the dependence of the HS radius on particle volume fraction and salt concentration. Also the problem concerning the effective surface charge displayed by latex particles in experiments is widely discussed.