  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.
