Assembly of shape-tunable colloidal dimers in a dielectrophoretic field

The shape of colloid particles plays an important role in directing the structure of their assemblies. Anisotropic colloids can adopt more complex structures than can their spherical counterparts, illustrated here by organosilica dimers fabricated with precise control of particle shape. Dielectrophoretic fields were used to coerce the assembly of 19 uniquely shaped dimers, which allowed direct visualization of the assembly process as well as the structure, symmetry, and long-range order (or lack thereof) of the final state. The various particle shapes resulted in crystalline phases with p6m, cmm, or p2 plane group symmetries, two plastic phases, and a disordered phase. The observations establish a relationship between particle shape and the resulting 2D structures, providing guidance for the design of 2D colloidal crystals.