Colloidal inclusions in liquid crystals: Phase separation mechanisms and some dynamical aspects 

This article reviews recent findings on the formation of ordered colloidal structures from bulk demixing in liquid crystalline materials. In contrast to classical phase separations, which lead to randomly distributed macrodomains of various sizes, demixing in liquid crystals leads to remarkably uniform droplets that form ordered arrays of either infinitely long straight chains (nematic phase) or highly curved chains (cholesteric phase). This distinctive behaviour arises from the presence of topological defects and elastic distortions around the inclusions formed during the separation. These distortions induce long-range attractions and short-range repulsions. These forces direct the ordering of microdomains and stabilize them against coalescence, thereby limiting the coarsening mechanism of the separation. We show that the ordering can be controlled on a large scale by simply controlling the macroscopic alignment of the liquid crystal. We also discuss the influence of an electric field and demonstrate marked differences with classical emulsions and colloids in isotropic fluids. Finally, we analyse the Brownian fluctuations of an isolated droplet immersed in a nematic phase and derive a quantitative determination of the Stokes drag coefficients and their anisotropy.