Defects in a TGBA phase: A theoretical approach |
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Authors: | M Kleman YuA Nastishin J Malthête |
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Institution: | (1) Laboratoire de Minéralogie-Cristallographie de Paris (UMR7590), T16 case 115, 4 place Jussieu, F-75252 Paris cédex 05, France, FR;(2) Institute for Physical Optics, 23 Dragomanov str., Lviv 79005 Ukraine, UA;(3) Institut Curie, Section de recherche, CNRS UMR 168, 11 rue Pierre et Marie Curie, Paris cédex, 05 France, FR |
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Abstract: | Following our experimental observations of disclination lines in freely suspended droplets and free-standing films (Yu.A.
Nastishin et al., Eur. Phys. J. E 5 353 (2001)), topological defects of the twist grain boundary (TGBA) phase are considered according to two aspects: topological
and energetical. There are two classes of line defects, disclinations (as in the cholesteric (N*) phase and the liquid vortices phase (NL*), relating to the directors tripod symmetries) and dispirations (relating to the translation-rotation symmetries); there are no topological point defects. Differences between N*, NL* and
TGBA disclinations are physical, not topological. The absence of focal conic domains in the TGBA phase is an immediate consequence of the materialization of the helical axis
(along the χ-director); the same feature, coupled to the trend to parallelism of the smectic layers, accounts for the predominance
of λ-lines. Finally, the presence of defects akin to developable domains is explained in the frame of the leastcurvaturemodel, that requires the introduction of a third type of defects: the densitiesofedgedislocations of the smectic layers.
Received 20 February 2002 |
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Keywords: | PACS 61 30 Jf Defects in liquid crystals – 64 70 Md Transitions in liquid crystals |
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