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

摘要

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.