Phase behavior and structure of colloidal bowl-shaped particles: simulations.

We study the phase behavior of bowl-shaped particles using computer simulations. These particles were found experimentally to form a metastable wormlike fluid phase in which the bowl-shaped particles have a strong tendency to stack on top of each other [M. Marechal, Nano Lett. 10, 1907 (2010)]. In this work, we show that the transition from the low-density fluid to the wormlike phase has an interesting effect on the equation of state. The simulation results also show that the wormlike fluid phase transforms spontaneously into a columnar phase for bowls that are sufficiently deep. Furthermore, we describe the phase behavior as obtained from free energy calculations employing Monte Carlo simulations. The columnar phase is stable for bowl shapes ranging from infinitely thin bowls to surprisingly shallow bowls. Aside from a large region of stability for the columnar phase, the phase diagram features four novel crystal phases and a region where the stable fluid contains wormlike stacks.