A theory of void formation in charge-stabilised colloidal suspensions at low ionic strength

Using a carefully justified development of Debye-Huckel theory for highly asymmetric electrolytes, one finds that a region of expanded phase instability, or miscibility gap, can appear for charge-stabilised colloidal suspensions at high charges and low ionic strengths. It is argued that this is offers a straightforward explanation for the observations of void structures and other anomalies in such suspensions in this region. The nature of the interface between coexisting phases, and general arguments that many-body attractions form a key part of the underlying physical picture, are also examined. The present analysis may also generate new insights into old problems such as coacervation in oppositely charged colloid or protein / polyelectrolyte mixtures, and suggests interesting new possibilities such as the appearance of charge density wave phases in colloidal systems in the vicinity of the critical solution points.