Models for electrokinetic phenomena in montmorillonite

Clays present remarkable electrokinetic features since they exist from very dilute colloidal state to nanoporous materials, depending on the water/clay ratio. The case of low volume fraction V-water/V-tot which corresponds to compact systems is examined. The ionic distributions have been evaluated by Poisson-Boltzmann like models and compared to discrete solvent simulations. Several electrokinetic properties (electroosmosis and conductance) have been calculated, in the framework of the mean spherical approximation introduced in the Fuoss-Onsager transport theory. It is found that Onsager's limiting laws in terms of external concentration are not valid on the grounds of the Donnan effect. (C) 2001 Elsevier Science B.V. All rights reserved.