The observation of a novel twist inversion in a chiral nematic phase and an induced TGBA∗ phase in a binary liquid-crystalline mixture of a chiral propanonitrile and a chiral 1-alkoxypropane

Abstract

Binary mixture studies involving the chiral nematogens (R)-2-[4-(2′-fluoro-4′-pentylbiphenyl-4-carbonyloxy)phenoxy]propanoitrile and (R)-2-{4-[4-(trans-4-pentylcyclohexyl)benzoyloxy]phenoxy}-1-methoxypropane revealed that these compounds show opposite helical twist senses, reinforcing existing selection rules relating twist sense to chemical structure. Certain mixture compositions displayed a N∗_RH-N∗∞-N∗_LH twist inversion sequence, while other compositions showed an induced TGBA∗ phase mediating the N∗_LH-S∗_A phase transition. This paper presents a complete phase diagram for the binary mixture as determined by polarizing light microscopy and differential scanning calorimetry and gives pitch measurements and determinations of helical twist senses above and below the inversion point.