Temperature dependence of equilibrium separation and lattice parameters of nematic boojum-colloids

We report experimental studies on the temperature dependence of equilibrium separation of a pair of nematic boojum colloids. The interparticle separation is linearly proportional to the elastic anisotropy and the orientation angle with respect to the rubbing direction. The latter result is in agreement with the recent prediction of computer simulations. We prepared two-dimensional colloidal crystals assisted by a laser tweezer and measured the temperature dependence of the lattice parameters. We observe a structural transition in boojum colloidal crystal across the N-SmA transition. The structural transition is mediated by the transformation of boojum defects into focal conic lines across the phase transition. The hexagonal close pack structure of the colloidal crystal in the SmA phase could be useful for designing photonic crystal.