Chiral Smectic C Liquid Crystal, Thick Sample Textures
Résumé
The texture of ferroelectric chiral smectic liquid crystal confined between two aligning plates is studied in the case of thick samples i.e. samples whose thickness is higher than the helical pitch. The helical texture with periodic unwinding disclination lines appears in these samples. A theoretical elastic calculation is made assuming in the defect lines the melting of the smectic C phase into the smectic A phase. It allows the calculation of the line positions and the local helical pitch versus the sample thickness. In the case of the bookshelf geometry and in that of the chevron our observations are well explained by the model. The pitch measurement allows an estimation of the defect core energy and confirms the A melting. We show the existence of the chevron plane in thick samples, plane which plays the role of an unwinding surface, for the helical structure.
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