Effect of hydrodynamic interaction on the coagulation rate of hydrophobic colloids

Abstract

The hydrodynamic interaction which occurs when particles are close to each other diminishes the coagulation rate of colloidal particles. We have evaluated this effect, improving a previous treatment by Derjaguin and Muller (7). The absolute rate of rapid coagulation has been computed numerically, with the help of the complete Hamaker equation for the van der Waals force. We have found that hydrodynamic interaction diminishes this rate by a factor of about 0.4 to 0.6, depending on the Hamaker constant. This result agrees completely with that of Spielman (8). The ratio W of the rates of rapid and slow coagulation has been calculated analytically with a simplified Hamaker equation and an approximate expression for the double-layer interaction, following, with modifications, the procedure of Reerink and Overbeek (21). The factor W has also been computed by numerical integration with the complete Hamaker equation. In either calculation the effect of hydrodynamic interaction on d(ln W) /d (ln ce) (where ce is the concentration of indifferent electrolyte) is found to be small. We conclude, in agreement with Derjaguin and Muller, that the existing discrepancy between theory and experiment with regard to d(ln W)/d (ln ce) cannot be explained by this hydrodynamic effect. © 1971.