Visual observation of dispirations in liquid crystals.

Physical review. B, Condensed matter (Impact Factor: 3.77). 05/1992; 45(14):7684-7689. 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.

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