Phase behaviour of hard spheres confined between parallel hard plates: manipulation of colloidal crystal structures by confinement

Abstract

We study the phase behaviour of hard spheres confined between two parallelhard plates using extensive computer simulations. We determine the fullequilibrium phase diagram for arbitrary densities and plate separations fromone to five hard-sphere diameters using free energy calculations. We find afirst-order fluid–solid transition, which corresponds to either capillary freezingor melting depending on the plate separation. The coexisting solid phaseconsists of crystalline layers with either triangular () or square () symmetry.Increasing the plate separation, we find a sequence of crystal structures from· · · n→(n + 1) → (n + 1) · · ·, where n is the number of crystal layers,in agreement with experiments on colloids. At high densities, the transitionbetween square to triangular phases is interrupted by intermediate structures,e.g., prism, buckled, and rhombic phases.