The Chiral Twist-Bend Nematic Phase (N*TB )

Abstract

The twist-bend nematic, N_TB , phase has been observed for chiral materials in which chirality is introduced through a branched 2-methylbutyl terminal tail. The chiral twist-bend nematic phase, N*_TB , is completely miscible with the N_TB phase of the standard achiral material, CB6OCB. The N*_TB phase exhibits optical textures with lower birefringence than those observed for the achiral N_TB phase, suggesting an additional mechanism of averaging molecular orientations. The N*-N*_TB transition temperatures for the chiral materials are higher than the N_TB -N transition temperatures seen for the corresponding racemic materials. This suggests the double degeneracy of helical twist sense in the $N_{TB}^{{}^{*}}$ phase is removed by the intrinsic molecular chirality. A square lattice pattern is observed in the N* phase over a temperature range of several degrees above the N*_TB -N phase transition, which may be attributed to a non-monotonic dependence of the bend elastic constant.

Keywords: chirality; liquid crystals; spontaneous symmetry breaking; twist-bend nematic phase.