On the Theory of the Soret Effect in Colloids

Abstract

Movement of colloidal particles can be driven by the inhomogeneous temperature field. In this paper the relation between the phenomenon of the migration of colloidal particles and the characteristics of the protective layer around the grain is established. Two cases of surfacted and ionic colloids are considered. The temperature gradient in the fluid induces the redistribution of surfactant molecules or ions near the particle. The redistribution leads to a loss in the balance of the stress on the particle surface, and that results in the grain movement along the temperature gradient. The values of the Soret coefficient of thermodiffusion motion in colloids turn out to be extremely high—two-four orders larger than the values of the Soret coefficient for molecular systems. The analytical solution of the problem of thermodiffusion motion in surfacted colloids is obtained using an assumption for the solute-particle interaction. The particles of these colloids always migrate towards colder temperature regions of the fluid. In the case of ionic colloids the direction of the particle movement depends on the magnitude of the double layer thickness and the value of the electric potential of the particle surface. The slowing-down of the thermodiffusion motion and the changing of its direction as a result of an increase in the ionic force of the solution are predicted.