A study of polymer depletion layers by electrophoresis: The influence of viscosity profiles and the nonlinearity of the Poisson-Boltzmann equation

Electrophoretic measurements of lipid liposomes in aqueous solutions of high molecular weight dextrans yielded a hydrodynamic depletion layer thickness of approximately 1 nm, assuming an exponential. viscosity profile. This is significantly less than the corresponding radius of gyration of the dextran molecules in solution. The theory of electrokinetics in the presence of depletion layers has been extended to the case of nonlinear effects and arbitrary viscosity profiles. It is shown that the underlying functional character of the viscosity profile has only a small effect on the mobility. On the other hand, the depletion effect is very sensitive to the thickness of the depletion layer and to a shift, of the plane of shear. The nonlocal character of the viscosity is also discussed.