The interpretation of dielectric response measurements on colloidal dispersions using the dynamic Stern layer model

The standard description of electrokinetic phenomena deals with a particle whose charge is uniformly smeared over its surface and considers ion transport only within a Gouy-Chapman diffuse layer. Experimental studies with colloidal dispersions have shown that this model is not applicable to many systems. To encompass a wider class of behavior, the standard model was extended to include ion migration within the Stern layer, the region between the shear envelope and the rigid particle. Computations show that Stern layer transport increases the conductivity and dielectric response of suspensions as well as the magnitude of the ζ potential inferred from mobility measurements. Model predictions are compared with experimental measurements on two well-defined systems - colloidal silica and a polymer latex. The inclusion of surface transport processes markedly improves agreement between theory and the experimental data. For example, in situations where the standard theory underpredicts the measured dielectric increments by factors of 2 or 3, the dynamic Stern layer model yields results within 5% to 20% of the experimental data at frequencies in the kHz range.