Freezing in confined suspensions

The freezing transition of hard sphere colloids confined between two parallel hard plates is studied for different plate distances ranging from one to two particle diameters. Using Monte Carlo simulations and free volume theory, the full phase diagram is obtained exhibiting solid-to-solid transitions between buckled, rhombic and layered crystals involving several triangular or square layers. While the fluid freezing transition is always strongly first order, both strong and extremely weak transitions occur between different crystalline structures. These predictions should be experimentally observable in confined suspensions of sterically stabilized or highly salted charge-stabilized colloidal particles.