Optical manipulation and self-assembly of nematic colloids: colloidal crystals and superstructures 

Optical manipulation of colloidal particles in nematic liquid crystals is far more complex than manipulation in water-based colloids. Owing to the long-range nature of the orientational ordering, their elasticity and topological conservation laws, almost any kind of object can be trapped and manipulated in liquid crystals. Furthermore, local heating due to the absorption of light can be used to create microdroplets of the isotropic phase, which interact strongly with colloidal particles. This leads to a broad variety of colloidal assemblies in liquid crystals, which cannot be observed in isotropic solvents: colloidal wires, assembled by entangled topological defects, superstructures in mixtures of large and small colloidal particles and a broad variety of two-dimensional nematic colloidal crystals. In all cases, the colloidal binding energy is several orders of magnitude stronger compared with water-based colloids. The large variety of colloidal superstructures, which can be assembled in nematic colloids, makes them highly interesting for application in photonic materials.