Dependence of interparticle force on temperature and cell thickness in nematic colloids

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 alpha 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, FL4 against R/L, at different L are found to be scaled to a single theoretical curve which has been proposed recently.