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Soft Matter and Biological Physics
Eur. Phys. J. E 10, 281-288 (2003)
DOI: 10.1140/epje/i2002-10116-y

Controlled nucleation of point defects on a disclination line near a free surface during smectic-A-to-nematic directional melting

J. Ignés-Mullol, L. Scurtu and P. Oswald

Laboratoire de Physique, Ecole Normale Supérieure de Lyon, 46 allée d'Italie, 69364 Lyon, Cedex 07, France

jignes@qf.ub.es

(Received 1 October 2002 / Published online: 15 April 2003)

Abstract
A disclination line populated with point defects that break the translational symmetry forms near a free nematic (N) interface in a confined geometry. The disclination line is, however, absent in the smectic-A phase (SmA). We use this fact to control the formation of point defect distributions on a disclination line by directional melting of the SmA phase in a temperature gradient. A threshold velocity ( $v_{\rm th}$) exists below which a defect-free disclination line is formed. The frequency of nucleation of point defects increases steadily for $v>v_{\rm th}$ and exhibits a remarkable regularity. We derive an empirical scaling for $v_{\rm th}$ in terms of the experimental tuning parameters. We propose a simple model that allows to understand the formation of the point defects.

PACS
61.30.Jf - Defects in liquid crystals.
61.30.Pq - Microconfined liquid crystals: droplets, cylinders, randomly confined liquid crystals, polymer dispersed liquid crystals, and porous systems.
64.70.Md - Transitions in liquid crystals.
61.30.Hn - Surface phenomena: alignment, anchoring, anchoring transitions, surface-induced layering, surface-induced ordering, wetting, prewetting transitions, and wetting transitions.

© EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2003