We design a nematic collider for controlled out-of-equilibrium anisotropic aggregation of spherical colloidal particles. The nematic surrounding imparts dipolar interactions among the spheres. A bidirectional backflow of the nematic liquid crystal in a periodic electric field forces the spheres to collide with each other. The inelastic collisions are of two types, head to tail and head to head. Head-to-tail collisions of dipoles result in longitudinal aggregation while head-to-head collisions promote aggregation in the transversal direction. The frequency of head-to-head collisions is set by the impact parameter that controls the resulting shape of aggregates, their anisotropy, and fractal dimension.

• Received 7 August 2010

DOI:https://doi.org/10.1103/PhysRevLett.106.047801