Evidence for the Validity of Electrokinetic Theory in the Thin Double Layer Region

Mobility vs potassium chloride concentration data in the thin double layer region has been determined for three untreated commercial polystyrene latices. Using classical thin double layer electrokinetic theory, it has been possible to fit these plots theoretically if it is assumed that there is a constant electrokinetic charge and no anomalous surface conduction. Calculating the ζ potential using the same theory gave data that when plotted against log10[electrolyte concentration] gave linear plots with slopes approximately equal to the Nernst constant. The calculated electrokinetic charge was almost constant across the electrolyte concentration range, and for the lowest charged latex it was close to the titration charge. As a result, it was concluded that these latices, at least in the electrolyte concentration range studied, do not exhibit anomalous surface conduction inside the shear plane and that their behavior may be described as almost ideal. The data therefore provide further evidence for the validity of classical electrokinetic theory.