Rational Design of Rod-Like Liquid Crystals Exhibiting two Nematic Phases.

Recently a polar, rod-like liquid-crystalline material was reported to exhibit two distinct nematic mesophases (termed N and NX¬) separated by a weakly first order transition. In this work we present our initial studies into the structure-property relationships that underpin the occurrence of the lower temperature nematic phase, and in doing so report several new materials that exhibit this same transformation. In doing so we have prepared material with significantly enhanced temperature ranges, allowing us to perform a detailed study of both the upper- and lower- temperature nematic phases using small angle X-ray scattering. We observe a continuous change in d-spacing rather than a sharp change at the phase transition, a result consistent with a transition between two nematic phases whose structures are presumably degenerate.