Novel phase transitions as bridges for broken ergodicity in confined colloidal prisms

We used Monte Carlo simulations to study the assembly behavior of square and hexagonal prisms under quasi-2D confinement separations, within a hard-wall slit. Our results for hexagonal prisms revealed two types of first order phase transitions at increasing concentration: 1) solid-solid transition (6-fold→4-fold symmetry solid) occurring through lattice symmetry breaking, and 2) solid to dense-liquid (disorder) to solid. The predicted dense-liquid has a density intermediate to those of the two solid phases and high translational/orientational mobility. We showed that similar phase behavior can be expected for other n-gonal prisms (n > 6). For square prisms, we observed a solid-solid phase transition where a square lattice spacing rearrangement gives rise to a polycrystalline phase with multiple locally ordered domains. These unusual phase transitions are attributed to the broken ergodicity associated with a dynamically disconnected rotational phase space accessible to the particles. As an experimentally viable strategy to dynamically bridge those rotational states observed for hard-slit phase behavior, we also investigated and validated a soft-repulsive wall model.