Visual observation of dispirations in liquid crystals

ArticleinPhysical review. B, Condensed matter 45(14):7684-7689 · May 1992with4 Reads
DOI: 10.1103/PhysRevB.45.7684 · Source: PubMed
Abstract
In this work, wedge-screw and twist-edge dispirations in liquid crystals were visually observed. In smectic phases, such as the antiferroelectric SmCA and the dimeric SmC2, where the molecules or the mesogenic groups in the adjacent smectic layers tilt in opposite senses, we found the schlieren texture with the strength of m=+/-1/2 which should not be seen in the normal SmC phase. The observation indicates the existence of a wedge-screw dispiration; i.e., a pi-wedge disclination (m=1/2) accompanied by a screw dislocation that is characterized by the Burgers vector b whose magnitude is equal to the layer thickness d. A threadlike defect line with +/-pi-wedge disclinations at the ends observed in freely suspended films manifests a twist-edge dispiration; i.e., a linked structure of a pi-twist disclination and a ||b||=d edge dislocation.
    • "Thus, in a regular SmC phase without any inclusions, we can normally expect no more than two defects per shell interface. However, in the SmC a phase, the sign invariance is re-established through the possibility of dispirations [28], a special type of defect allowed by the anticlinic tilting arrangement that is the hallmark of this smectic-C type phase. In a shell made from this phase, we can thus again expect four defects per shell interface, although the alignment is quasi-homeotropic as induced by standard ionic surfactants. "
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    Article · Mar 1993
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