Superlattice formation in mixtures of hard-sphere colloids

Abstract

We report a detailed experimental study of the superlattice structures formed in dense binary mixtures of hard-sphere colloids. The phase diagrams observed depend sensitively on the ratio alpha=R(S)/R(L) of the radii of the small (S) and large (L) components. Mixtures of size ratio alpha=0.72, 0.52, 0.42, and 0.39 are studied. The structures of the colloidal phases formed were identified using a combination of light-scattering techniques and confocal fluorescent microscopy. At alpha=0.39, ordered binary crystals are formed in suspensions containing an equal number of large and small spheres which microscopy shows have a three-dimensional structure similar to either NaCl or NiAs. At the larger size ratio, alpha=0.52, we observe LS2 and LS13 superlattices, isostructural to the molecular compounds AlB2 and NaZn13, while at alpha=0.72 the two components are immiscible in the solid state and no superlattice structures are found. These experimental observations are compared with the predictions of Monte Carlo simulations and cell model theories.

Microstructure and macroscopic properties of polydisperse systems of hard spheres

“…This is consistent with results from Ref. [189], where the structure of binary hard sphere mixtures is studied in more detail. This kind of partial crystallization happens since the small particles fit into interstices of a crystal made of the large particles [24].…”

The Effect of Centrifugal Force on the Assembly and Crystallization of Binary Colloidal Systems: Towards Structural Gradients

“…It is obvious that the N PF of the AlB 2 structure deviates from the initial N PF value (= 1). The AlB 2 structure is an important structure for colloidal crystallization and has already been observed experimentally by others [34,67,68]. A further change of the latex concentrations to 5 wt.-% 154 nm latex +12 wt.-% 300 nm latex (centrifugal time = 28 min) leads to the situation shown in Fig.…”

Packing of Soft Asymmetric Dumbbells

“…Next is the NiAs-type, where the large spheres pack in an HCP lattice and the small ones again fill the octahedral holes, this time in form of an interpenetrating simple hexagonal lattice. Coexistence of NaCl/NiAs-type crystalline phases in the AB-type mixtures has been observed experimentally and theoretically also in [32,38]. The third crystal type is the FCC lattice of the large spheres, but no order for the small ones.…”