The van der Waals approach to predict liquid-vapor coexistence, become
s exact in the limit of weak, long-ranged attractive forces. However,
for shorter-ranged am-actions, 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-structu
ral solid-solid transition, reminiscent of the liquid-vapor transition
, appears in the crystalline phase. This transition, that should be ex
perimentally observable in certain colloidal suspensions, ends in a cr
itical point. In quasi-two-dimensional systems (e.g. confined colloids
), this critical point induces the formation of a stable hexatic phase
.