Langmuir Award: A Theory of Entropic Bonding in Colloidal Crystals

A central paradigm of science, chemical bonding permits atoms to form everything from molecules and compounds to crystals. Remarkably, nanoparticles can self-assemble into the same crystal structures as atoms – even quasicrystals and crystals with large unit cells, and even when only entropic forces are present. In crowded colloidal systems of hard particles, emergent, directional, and effectively attractive entropic forces create valency that leads, counterintuitively, to long-range order. Entropic ordering leads to a host of surprises, from purely entropic fluid-fluid phase transitions in one component systems to five-fold and icosahedral twins to host-guest colloidal clathrates stabilized by the rotational motion of the guest particles. Can we describe the entropic assembly of nanoparticle shapes and the assembly of atoms using an analogous framework? In this talk, we discuss parallels between “shape valency” and electronic valency, and present a classical density functional theory of entropic bonding that predicts thermodynamically stable colloidal crystal structures from nanoparticle shape.