The dynamic double layer - Part 1 - Theory of a mobile Stern layer

The theory developed (C. S. Mangelsdorf and L.R. White, J. Chem. Sec., Faraday Trans., 1992, 88, 3567) to calculate the electrophoretic mobility of a solid, spherical colloidal particle subjected to an oscillating electric field is reviewed and extended. The equations governing the ion distribution, electrostatic potential and hydrodynamic flow held around the particle are modified to allow for the lateral movement of ions within the Stern layer and a time-dependent particle surface charge density. Two classes of Stern-layer adsorption isotherms are considered: (1) Adsorption of ions onto available surface area and (2) Adsorption of ions onto underlying surface charge. An equilibrium model is used for the changes in particle surface charge density arising from the flux of ions into and out of the particle surface.