We have studied the interparticle force between two colloidal particles in a nematic liquid crystal experimentally and theoretically. The force F was directly measured using dual-beam optical tweezers and was numerically calculated from the equilibrium tensor field around the particles. The dependence of F on the center-to-center distance R between the particles was studied not only for equal-sized particles but also for different-sized ones in various kinds of configurations and arrangements. The magnitude of F between different-sized particles in the dipole configuration depends on their relative arrangement. Both experimental and theoretical force curves are found to be in good agreement with each other. At large R, they also make agreement with those predicted by an electrostatic analogy of nematic field.

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We have experimentally studied the interparticle force between two particles accompanied by hyperbolic hedgehog defects in a nematic liquid crystal. The force F was measured with dual-beam optical tweezers at various temperatures and in cells with various thicknesses. In a thick cell, the dependence of F on the interparticle distance R obtained at different temperatures can be scaled to a universal curve of F∝R^(-4) for R>3a , where a is the radius of a particle. The effective elastic constant evaluated from F is found to be in good agreement with splay constant of the nematic liquid crystal. In a thin cell, the magnitude of F decreases and the dependence of F on R becomes short-ranged as the thickness of a cell, L , decreases. The reduced force curves, FL(4) against R/L , at different L are found to be scaled to a single theoretical curve which has been proposed recently.

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We discuss novel interparticle force between colloids in nematic liquid crystal. The dependence of the interparticle force on the interparticle distance was experimentally measured by optical tweezers for the same and different sized particles. The obtained force curves quantitatively make agreement with the theory based on electrostatic analogy and the numerical calculation. We also present the self-assembling and artificial ways for building colloidal assemblies in nematic liquid crystal.