A grahame triple-layer model unifies mica monovalent ion exchange, zeta potential, and surface forces

A triple-layer model of the mica/water electrical double layer (EDL) unifies prediction of zeta potential, ion-exchange, and surface-force isotherms. The theory treats cations as partially dehydrated and complexed specifically to the anionic exchange sites of mica. A diffuse layer commencing at the outer Helmholtz plane (OHP) balances the surface charge not neutralized by adsorbed cations in the inner Helmholtz plane (IHP). Ion-binding equilibrium constants are assessed from zeta-potential measurements and used thereafter to predict ion-exchange isotherms and surface forces. Basal-plane mica surface charge is almost completely neutralized by specific binding of cations, including hydronium ions. The charge in the diffuse layer is only a few percent of the mica crystallographic charge density but leads to long-range electrostatic interactions between charged surfaces. The Grahame triple-layer model of the aqueous EDL provides a robust, quantitative, and unified description of the mica/water interface. (C) 2020 Elsevier B.V. All rights reserved.

Automated summary

The triple-layer model of the mica/water electrical double layer unifies prediction of zeta potential, ion-exchange, and surface-force isotherms by treating cations as partially dehydrated and specifically complexed to the anionic exchange sites of mica. This model provides a robust, quantitative, and unified description of the mica/water interface, with ion-binding equilibrium constants assessed from zeta-potential measurements used to predict ion-exchange isotherms and surface forces. The diffuse layer in the model balances the surface charge, not neutralized by adsorbed cations, by starting at the outer Helmholtz plane.