Liquid-like behavior in colloidal crystals

The van der Waals approach to predict liquid-vapor coexistence becomes exact in the limit of weak, long-ranged attractive forces. However, for shorter-ranged attractions, the liquid range shrinks and eventually disappears altogether. When the width of the attractive well becomes very small (less than 7% of the diameter of particles), an iso-structural solid-solid transition, reminiscent of the liquid vapor transition, appears in the crystalline phase. This transition, that should be experimentally observable in certain colloidal suspensions, ends in a critical point. In quasi-two-dimensional systems (e.g. confined colloids), this critical point induces the formation of a stable hexatic phase.