Structure and Lehmann rotation of drops in a surfactant-doped bent-core liquid crystal

Abstract

The structure of the nematic (cholesteric) drops that form at the clearing temperature of a mixture of the bent-core molecule CB7CB and the rod-like molecule 8CB doped with a surfactant is optically determined. Using experimental observations and numerical simulations, it is demonstrated that the director field inside these drops is not escaped-concentric as previously proposed, but twisted-bipolar. The Lehmann rotation of these drops in the presence of a temperature gradient is described. Their rotation velocity is shown to be proportional to the temperature gradient and to the surface twist angle of the director field and inversely proportional to the drop radius, thus revealing a fundamental scaling law for the Lehmann effect of nematic/cholesteric twisted bipolar droplets.

Chemical Leslie effect in a chiral smectic-C★ film: Nonsingular target patterns

“…But the final blow to Leslie's theory was given by Ignés-Mullol et al [11] when they discovered that it was also possible to induce rotation in drops of the nematic -and so achiral-phase of a chromonic lyotropic liquid crystal (provided that the director field inside the drops is twisted, as required by symmetries). We mention that the same phenomenon was also observed recently in the nematic phase of a thermotropic LC made of bent-shaped molecules [12,13].…”