Surface-tension-gradient-induced flow in freely suspended liquid crystalline films.

Abstract

Flow was created in freely suspended liquid crystal films (FSLCFs) in the smectic-C phase using gradients in the surface tension to drive the motion. The director field was distorted into a pattern of vortices which wind upon themselves while a temperature gradient was applied. A dependence of the pattern in the director field on the topological defects of index s=+1,0, or -1 that are isolated in the vortex of the flow was observed. The flow pattern for the s=-1 defect has not been observed in FSLCFs with other flow fields. The diffusion constant for the c\ensuremath{\rightarrow}^-director orientation is extracted from the orientation field patterns under flow and is com- pared to other independent measurements. The Schlieren pattern of the c\ensuremath{\rightarrow}^-director field will be shown to arise from the coupling between the fluid velocity and director orientation and will also be shown to be mediated by the topological index of the defect through the use of a model of the dynamical equations of a two-dimensional nematic. \textcopyright{} 1996 The American Physical Society.