(53h) Entropy Compartmentalization of Host-Guest Colloidal Clathrates

Clathrates are open crystal structures in which atoms and molecules are arranged in a hierarchy of polyhedral cages that encapsulate guest molecules and ions. Colloidal clathrate crystals self-assembled from nanoparticles were recently reported, but with closed cages unable to accommodate guests, limiting their potential applications. Here we report the first entropy-driven self-assembly of seven host-guest colloidal clathrate crystals in simulation with unit cells as large as 364 particles. Hard truncated triangular bipyramids self-assemble into five clathrates where guests and hosts are the same species and two clathrates comprised of different species. In all cases, crystallization occurs via entropy compartmentalization, where the entropy of the system partitions into low (host particle) and high (guest particle) entropy subsystems. As in molecular clathrates, such as clathrate hydrates, the guests rotate freely or with preferred orientations depending on the clathrate, providing thermodynamic stability to the structure. The type of clathrate depends on the amount of bipyramid truncation, which determines the guest/cavity size ratio, while the dynamical behavior of the guests depends on the shape and symmetry of the guest and cavity. We use entropic bonding theory to design host-guest colloidal clathrates assembled in silico from truncated triangular bipyramids with explicit interparticle attraction, providing an immediate route to realize host-guest colloidal clathrates in the lab.