Colloidal crystals formed by size-asymmetric binary particles co-assemble into a wide variety of colloidal compounds with lattices akin to ionic crystals. Here, we describe a transition from a compound phase to a metal-like phase in which the small particles are delocalized. In this colloidal metallic phase, the small particles roam the crystal maintaining the integrity of the lattice of large particles, as electrons do in metals. We analyze mixtures as a function of the small and large particles ratio (n<sub>s</sub>/n<sub>l</sub>), which is found to be the primary determinant of crystal type due to energetic interactions and interstitial site filling. We find that the number of grafted chains per small particle determines the stability of these crystals. Analogous sublattice transitions driven primarily by lattice vibrations have been seen in some atomic materials exhibiting an insulator-metal transition also referred to as metallization.

Metallization of colloidal crystals

ACS Spring 2022

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