(477b) Entropically Engineered Formation of Fivefold and Icosahedral Twin Clusters of Colloidal Shapes

Fivefold and icosahedral symmetries induced by multiply twinned crystal structures have been extensively studied to control the growth and final shape of synthetic nanomaterials with those symmetries. Numerous methods have been proposed to control the formation of such structures, and certain surrounding conditions or geometric confinement are widely considered to be essential. Here, we report the purely entropy-driven formation of the fivefold and icosahedral twin clusters in Monte Carlo simulation. Hard truncated tetrahedra self-assemble into either cubic or hexagonal diamond crystals depending on the amount of edge and vertex truncation. By engineering particle shape to achieve a negligible free-energy difference between the cubic and the hexagonal diamond phases, we show the formation of twin boundaries or stacking faults is easily induced. This strategy can be used to induce the formation of fivefold and icosahedral twin clusters in colloidal fluids through seed-assisted growth. Interestingly, the formation of the fivefold twin cluster in equilibrium with a dense fluid phase follows an error-and-repair process, increasing structural quality. The fivefold and icosahedral twin crystals of the hard truncated tetrahedra are entropically stabilized within a dense fluid due to a strong fluid-crystal interfacial tension, unlike hard spheres where interfacial tension is weak. Our findings show that twinning behavior and fluid-crystal interfacial properties in hard particle systems can be entropically engineered to obtain fivefold and icosahedral twin clusters.