Role of local assembly in the hierarchical crystallization of associating colloidal hard hemispheres

Hierarchical self-assembly consisting of local associations of simple building-blocks for the formation of complex structures widely exists in nature, while the essential role of local assembly remains unknown. In this work, by using computer simulations, we study a simple model system consisting of associating colloidal hemispheres crystallizing into face-centered-cubic crystals comprised of spherical dimers of hemispheres, focusing on the effect of dimer formation on the hierarchical crystallization. We found that besides assisting the crystal nucleation because of increasing the symmetry of building-blocks, the association between hemispheres can also induce both re-entrant melting and re-entrant crystallization depending on the range of interaction. Especially when the interaction is highly sticky, we observe a novel re-entrant crystallization of identical crystals, which melt only in certain temperature range. This offers a new axis in fabricating responsive crystalline materials by tuning the fluctuation of local association.