(358d) The Impact of Geometric Anisotropy On Colloids Under Electric Fields

Colloids possessing anisotropic interactions could potentially assemble into a much wider range of crystalline arrays and meso-structures than spherical particles with isotropic interactions. Here, we specifically investigate the impact of geometric anisotropy on the assembly of colloidal dimers on conducting substrates under applied electric fields. By systematically tuning the size ratio between two lobes on dimers, we have found that interactions between dimers are strongly dependent on the their relative orientations. For example, the interaction between lying and standing dimers on the substrate is attractive. When all dimers stand on the substrate, the interaction between neighboring dimers with alternating orientations is also attractive. Otherwise, it is repulsive. Such kind of orientation-dependent interactions generate a good variety of new structures, such as chiral clusters and dimer crystals with alternating orientations. We will discuss the physical origin of those orientation-dependent interactions and the impacts of experimental conditions such as the ionic concentrations and surface charges. Our numerical model based on electrostatics agrees well with experimental observations and provide further insights on electric-field assisted assembly of anisotropic particles.