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

## TL;DR

This study uses computer simulations to explore how local associations of colloidal hemispheres influence hierarchical crystallization, revealing novel re-entrant behaviors and potential for designing responsive materials.

## Contribution

It demonstrates the dual role of local assembly in promoting nucleation and inducing re-entrant melting and crystallization in colloidal systems.

## Key findings

- Local association increases symmetry and aids nucleation.
- Re-entrant melting and crystallization depend on interaction range.
- Highly sticky interactions lead to re-entrant crystallization in specific temperature ranges.

## Abstract

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.