Part Of Double Layer Research Articles

Low-Frequency Electrical Conductivity of Aqueous Kaolinite Suspensions II: Counterion Effects and Estimating Stern Layer Mobilities of Counterions

AbstractThe electrical state of the interface between a kaolinite-dominated clay sample and aqueous electrolyte solutions was characterized using low-frequency conductance measurements. From these measurements, the ζ-potential and surface conductivity contributions from the diffuse and non-diffuse parts of the electrical double layer were obtained. The suspensions were studied as a function of volume fraction, electrolyte concentration, and electrolyte type (LiCl, NaCl, KCl, CsCl, CaCl2, SrCl2, and BaCl2). Interpretation in terms of the surface conductance revealed that a substantial part of the surface conductivity originates in the inner part of the double layer. Electrokinetic potentials and related diffuse double layer properties are highly dependent on the nature of monovalent counterions, whereas divalent counterions do not show such clear dependencies. Further presented was a simple way to estimate the order of magnitude of counterion mobilities in the inner part of the electrical double layer. All counterions were shown to have a substantial mobility in the inner part of the double layer. Finally, we suggest that the apparent ion-specific effects observed in the diffuse part of the double layer are at least in part related to the finite size of the counterions. Our findings are relevant to scenarios where fluid flow in porous media is accompanied by charged species transport, e.g., in electro-osmotic remediation, spectral-induced polarization, or permeability measurements.

Charge and Potential of the Diffuse Part of the Double Layer for Sodium Dodecyl Sulfate Micelles in NaCl Solutions

A method is proposed for calculating the ψd potential of the diffuse part of the electrical double layer in micelles on the basis of data concerning the binding of counterions by these micelles, the composition of the intermicellar medium, and the association of surface-active ions. The charges of sodium dodecyl sulfate micelles in aqueous solutions at various concentrations of the surfactant and background electrolyte are determined by the potentiometric method. The calculated ψd values turned out to be much lower than the values of the electrokinetic potentials, thus allowing the conclusion that the slipping plane corresponding to the electrophoretic motion of micelles with respect to the intermicellar medium is localized in the dense part of the double layer.

Model of inner part of electrical double layer on a recharged electrode surface

The specific adsorption of various anions has been studied on the bismuth electrode in the aqueous and ethanolic solutions of mixed electrolytes with constant ionic strength by measuring the potential dependence of differential capacity of bismuth. The charge due to specifically adsorbed anions was calculated by the Hurwitz-Dutkiewicz-Parsons method. Assuming the entrance of cations into the inner part of the double layer on the bismuth electrode, recharged by the specifically adsorbed anions, the charge due to the cations in the inner layer, the corrected values of the outer Helmholtz plane potential and of the potential drop across the inner layer have been calculated. A simple model of the inner layer in presence of ionic associates is developed. The main parameters characterizing the specific adsorption of ions and the structure of the inner layer have been calculated. A procedure has been developed for the calculation of the charge due to the cations in the inner layer by the dependence on the electrode potential on the charge of specifically adsorbed anions.

Model of inner part of electrical double layer on a recharged electrode surface

The specific adsorption of various anions has been studied on the bismuth electrode in the aqueous and ethanolic solutions of mixed electrolytes with constant ionic strength by measuring the potential dependence of differential capacity of bismuth. The charge due to specifically adsorbed anions was calculated by the Hurwitz-Dutkiewicz-Parsons method. Assuming the entrance of cations into the inner part of the double layer on the bismuth electrode, recharged by the specifically adsorbed anions, the charge due to the cations in the inner layer, the corrected values of the outer Helmholtz plane potential and of the potential drop across the inner layer have been calculated. A simple model of the inner layer in presence of ionic associates is developed. The main parameters characterizing the specific adsorption of ions and the structure of the inner layer have been calculated. A procedure has been developed for the calculation of the charge due to the cations in the inner layer by the dependence on the electrode potential on the charge of specifically adsorbed anions.

Boundary layer near the surface of a solid body and low-frequency dielectric dispersion

The paper deals with the possibility of studying the stagnant part of the boundary layer on the basis of effects due to polarization of the electrochemical double layer (DL). A theory is developed for polarization of the diffuse part of a thin DL of a spherical particle in a direct and alternating field, allowing for the effect of ion flow through the stagnant part of the DL. Formulae are obtained on the basis of this theory for electrophoresis complicated by polarization and for the large low-frequency dielectric dispersion (ω). Calculation of the stagnant layer thickness and the ionic mobilities of this layer is shown to be possible on the basis of electrophoretic measurement on three fractions of spherical particles with identical values of ψd and ζ. Using only one fraction, we can obtain similar information from the low-frequency section of (ω).