EFFECT OF ELECTROVISCOUS DRAG ON THE COAGULATION AND DEPOSITION OF ELECTRICALLY CHARGED COLLOIDAL PARTICLES

The relative friction or diffusion coefficient for two electrically charged colloidal particles differs from that of two neutral ones. The increase in friction for charged particles is called the electroviscous drag, which is responsible for the dependence of coagulation rates on the sizes of ions in the electric double layer. We developed an approximate theory for calculating the electroviscous drag between two discs using the squeezing flow approximation. For the electric double layer interaction, both the constant charge and the constant potential model was discussed. Using the Derjaguin approximation the electroviscous drag between a disc and a sphere and between two spheres was calculated. The theory was compared to experimental coagulation and deposition data. Good agreement was found for coagulation, whereas a significant discrepancy found for deposition indicated that besides electroviscous drag additional effects should be considered as well.