On chirality induction in lyotropic nematic liquid crystals

The induction of lyotropic chiral phases by different, structurally related alpha-hydroxy carboxylic acids as well as the corresponding potassium salts has revealed a distinct dependence of their helical twisting power upon their molecular structure. Obviously there is an effect of the mean electronic polarizability of the moiety neighbouring the chiral centre of the dopant, similar to that in the case of thermotropic induced chiral phases. A significantly non-linear dependence of the inverse pitch on the concentration has been found and is explained as a micelle size effect. The absolute value of the helical twisting power decreases if instead of a chiral acid, the corresponding potassium salt is used to induce the phase chirality; moreover, the handedness of the twist is inverted. A microscopic model for the evolution of chirality in a micellar phase is proposed.