The electrostatic interaction in colloidal systems with low added electrolyte

In a colloidal system in which the amount of added electrolyte is sufficiently low (e.g., nonaqueous dispersions or aqueous dispersions that have been treated by ion-exchange r sins or micellar systems with no added electrolyte) conventional double-layer theory cannot be used to describe the electrostatic interaction between the particles. A theoretical treatment of such systems which takes into account the contribution of the counterions derived from the colloidal particles in screening the coulombic repulsion, is proposed. This leads to an effective colloid-colloid pair potential which varies with the volume fraction of the colloidal particles present in the system. A striking consequence of the theory is that under certain conditions, correlations in the spatial distribution of particles can persist over four orders of magnitude of the volume fraction. Moreover, these correlations, as measured by the height of the first peak of the structure factor, may not be a monotonically increasing function of the particle charge. These theoretical predictions are compared with neutron and light-scattering studies on the structure of colloidal systems. © 1985 Academic Press, Inc. 1