Istituto di Matematica Applicata e Tecnologie Informatiche     
Bajc J., Guidone Peroli G., Virga E. G., Zumer S. Dynamics of nematic point defects in a capillary with tilted boundary conditions. Preprint ercim.cnr.ian//2002-1318, 2002.
The motion of a single point defect in a cylindrical cavity filled with a nematic liquid crystal is studied theoretically. Perfect homeotropic anchoring on the lateral boundary would result in the creation of domains escaped alternatively upwards and downwards along the cavity axis, separated by point defects alternating in sign. Both configurations adjacent to each defect have the same elastic energy, and so the defects do not move, as long as they are sufficiently far apart. However, small deviations from the homeotropic anchoring remove this degeneracy and the energetically favourable domains start to expand at the expenses of the others, thus setting the defects in motion along the tube. For a single defect, this problem is first approached through an analytical model in the one-constant approximation: it allows for an explicit expression of the velocity of the defect in terms of the {it pretilt} angle. A numerical model is then set forth, which studies the influence of the elastic anisotropy ($K_{33}ne K_{11}$) on the motion of the defect. We confirm a good qualitative agreement between the two approaches and show how even very small pretilt angles ($sim 1^circ$) result in considerable speeds. In this preliminary report we neglect the coupling between the director reorientation and mass flow, often called the {it backflow}.
Subject Nematic liquid crystals
Defect dynamics

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