SMECTIC MENISCUS AND DISLOCATIONS
Résumé
In ordinary liquids the size of a meniscus and its shape is set by a competition between surface tension and gravity. The thermodynamical process of its creation can be reversible. On the contrary, in smectic liquid crystals the formation of the meniscus is always an irreversible thermo-dynamic process since it involves the creation of dislocations (therefore it involves friction). Also the meniscus is usually small in experiments with smectics in comparison to the capillary length and, therefore, the gravity does not play any role in determining the meniscus shape. Here we discuss the relation between dislocations and meniscus in smectics. The theoretical predictions are supported by a recent experiment performed on freely suspended films of smectic liquid crystals. In this experiment the measurement of the meniscus radius of curvature gives the pressure difference , ∆p, according to the Laplace law. From the measurements of the growth dynamics of a dislocation loop (governed by ∆p) we find the line tension (∼ 8×10 −8 dyn) and the mobility of an elementary edge dislocation (∼ 4 × 10 −7 cm 2 s/g).
Domaines
Physique Générale [physics.gen-ph]
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