ANNIHILATION OF POINT-DEFECTS IN NEMATIC LIQUID-CRYSTALS

Point defects are likely to be generated in the process of filling a c apillary tube subject to homeotropic conditions on the boundary. There is plenty of experimental evidence to hold that, when two defects wit h opposite topological charge happen to be closer than a critical dist ance, they attract each other. At first, they move very slowly; then, as the distance between them becomes less than a diameter, their relat ive speed increases dramatically, until they annihilate one other. In this paper we describe, by means of a simple dynamical model, the attr action and annihilation of two defects in an infinite tube. We write t he balance between the rate of change in the elastic free energy and t he energy dissipated in the director motion. Hence, we derive and solv e the differential equation that describes the evolution in time of th e distance between the defects. The outcomes of our analysis confirm m any qualitative aspects of the experimental evidence.