(527c) Crystal Structures Of Dipolar Colloids And Binary Hard- And Charged Spheres

Using computer simulations, we look at the possible crystal structures in three systems: (i) colloids with dipole-dipole interactions, (ii) oppositely charged colloids with screened-Coulomb interactions, and (iii) binary mixture of large and small hard-spheres. For dipolar colloids, we study how the stability of the crystal structures changes when the relative strengths of spherically symmetric and dipolar interactions is adjusted. For a system where dipoles are electric-field induced, we make a comparison between the theoretical predictions and experiments on micrometer-size PMMA spheres. In the case of oppositely charged spheres with screened-Coulomb interactions, we show that the system exhibits a great variety of crystal structures, some of which display analogs of known binary atomic structures, doped fullerene C₆₀ structures, but also novel structures that do not have an atomic of molecular analog. Three of the structures are also found in experiments. Finally, we show that binary hard-spheres can crystallize into a colloidal analog of the MgCu₂ structure. A very interesting feature of the MgCu₂ structure is that the large (Mg) and small (Cu) sphere component structures correspond, respectively, to the diamond and pyrocholore lattices, which have applications as photonic crystals with a bandgap in the visible region.