Topological Point Defects in SmC* Liquid Crystals Under Mechanical Disturbance

ABSTRACT Smectic C (SmC) liquid crystals are tilted layered phases, while their chiral counterpart, chiral smectic C (SmC*), exhibits an additional helical superstructure arising from molecular chirality. In SmC*, the average molecular long axes (directors) are tilted with respect to the layer normal, giving rise to a helical arrangement. In freely suspended SmC and SmC* films, the in‐plane projection of the director defines a quasi‐2D vector field that supports a wide variety of topological point defects. In this review, we summarize current understanding of the formation, dynamics, and interactions of such defects, with particular emphasis on mechanical disturbances induced by air‐jet shear. We outline the fundamental properties of nematic and smectic liquid‐crystal phases, highlighting features of SmC and SmC* films that make them ideal model systems for studying defect coarsening and annihilation. We discuss experimental and theoretical work on defect pairs, dislocation loops around islands and holes, and textural transformations in freely suspended films. Special attention is given to air‐jet experiments generating islands, disclination pairs, and subsequent defect annihilation, compared with continuum theories of defect motion. Finally, we survey recent developments and identify open questions on modeling defect dynamics, elastic anisotropy, saddle‐splay, and controlled defect engineering.