CHARACTERIZATION OF COLLOIDAL SILICA PARTICLES WITH RESPECT TO SIZE AND SHAPE BY MEANS OF VISCOSITY AND DYNAMIC LIGHT-SCATTERING MEASUREMENTS

A simple method has been developed to determine the axial ratios and s olvation volume of small colloidal silica particles characterised as e quivalent ellipsoids of revolution with the same hydrodynamic properti es as the actual particles. The method is based on a combination of vi scometry and dynamic light scattering and uses the relations of Simha and Perrin for the specific viscosity and frictional factors respectiv ely of ellipsoids of revolution. The axes of the unsolvated equivalent ellipsoid and the solvation volume can be determined by knowing or as suming the thickness of the solvation shell. Silica particles form elo ngated aggregates and the method is applied to particles having three different degrees of aggregation.