  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 (NLC) 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 allows one to control the resulting shape of aggregates,
their anisotropy and fractal dimension.
