Hard Particle Colloidal Clathrates with Rotating Guest

Clathrate crystal consisting of polyhedral cages is usually found in gas hydrate or intermetallic systems where the size of particles forming the structures is mostly atomic or molecular length scale. In this work, we report a design strategy of hard colloidal particles that self-assemble into various colloidal clathrate crystals with single or multiple rotating guests. Monte Carlo simulations show that a single component system of hard truncated triangular bipyramids (TBPs) self-assembles into five different clathrates with rotating guests depending on the truncation of the TBP. Truncation of the TBP creates a cavity at the center of the clathrate cage-like motifs, and the cavity is occupied by guest particles when the size of the cavity reaches a comparable size of the guest. Thermodynamic stability of the clathrates is confirmed by Frenkel-Ladd free energy calculations. The dynamics of the guests can be categorized as free rotation, rotation around a fixed axis, or quantized rotation and rattling, with the mode determined by guest/cavity size ratio, prolateness of the cavity and shape of the guest. In addition, when the TBPs are mixed with other hard shapes, clathrates encapsulate these different guest particles.