A design strategy for open structures via host–guest–mediated self-assembly

Entropically driven self-assembly of hard anisotropic particles, where particle shape gives risetoemergent valency, provides a useful perspective for the design of nanoparticle and colloidal systems. Hard particles self-assemble into a rich variety of crystal structures, ranging in complexity from simple close-packed structures to structures with 432 particles in the unit cell. Entropic crystallization of open structures, however, is missing from this landscape. Here, we report on the self-assembly of a binary mixture of hard particles into an open host–guest structure, where host particles form a honeycomb lattice that encapsulates smaller guest particles [1]. Notably, this open structure forms in the absence of enthalpic interactions and is the first such structure to be observed in a two-dimensional athermal system. We discuss the various entropic stabilization effects present in this system and show that certain guest particle sizes can produce reentrant phase behavior. This reentrance suggests the possibility for a reconfigurable colloidal material, and we provide a proof-of-concept by showing the assembly behavior while changing the size of the guest particles on the fly. Our findings provide a strategy for designing open colloidal crystals, as well as binary systems that exhibit co-crystallization, which have been elusive thus far.

[1] Moore, T.C., Anderson, J.A. and Glotzer, S.C., 2021. Shape-driven entropic self-assembly of an open, reconfigurable, binary host–guest colloidal crystal. Soft Matter, 17(10), pp.2840-2848.