THE STABILITY OF CHARGED COLLOIDS - ATTRACTIVE DOUBLE-LAYER FORCES DUE TO ASYMMETRIC CHARGE-DISTRIBUTION

The interaction between one charged surface with terminally grafted po lyelectrolyte chains and one similarly charged surface neutralized by mobile counterions is investigated by Monte Carlo simulations. It is f ound that the force between the surfaces differs significantly from th e forces obtained in symmetric systems. Due to entropic contributions the counterions penetrate into the half-cell containing polyelectrolyt e, giving rise to an attractive force component of considerable streng th between the subsystems. This force is affected by the chain structu re of the polyelectrolyte and becomes more attractive with increasing flexibility. Asymptotic behavior, as well as salt dependence, of the s urface force is estimated by mean field calculations on a related mode l system. Long-range attraction in asymmetric systems has recently bee n observed experimentally by surface force-distance measurements. (C) 1996 Academic Press, Inc.