OSMOTIC EQUILIBRIUM AND DEPLETION INDUCED BY POLYELECTROLYTES IN CLAYDISPERSIONS

Pseudoternary systems of negatively charged clay (montmorillonite), an ionic polyelectrolyte (sodium polyacrylate), counterions, and water ex hibit a local segregation of two distinct phases on a colloidal scale. The microscopic osmotic equilibrium condition in the diphasic dispers ion sets the spacing observed between the sodium montmorillonite plate lets: the effect of polyelectrolyte is equivalence to an external depl etion force equilibrating electrostatic repulsion. In the case of calc ium montmorillonite clay, the osmotic stress effect is only observed w hen sufficient polyelectrolyte is added to saturate the ion condensati on of all calcium clay counterions on the polyelectrolyte chain.