MESOGEN EXHIBITING A CH-A-STAR-A PHASE SEQUENCE, A LIQUID-CRYSTALLINE ANALOG OF THE ABRIKOSOV PHASE

A number of optically active liquid-crystalline compounds have been prepared that have a chlorine atom attached to their asymmetric centres. Many of these materials exhibit unusual properties at their transitions to the liquid state. In this article we report the properties of one of these compounds: S-2-chloro-4-methylpentyl 4'-(4"-n-nonyloxybenzoyloxy)biphenyl-4-carboxylate. From thermal and optical studies it appears that this material undergoes a transition from a cholesteric phase to a smectic A phase via an intermediary twisted phase. The intermediary A* phase is believed to have a structure where there is helical ordering of the molecules occurring in the planes of the molecular layers. Theoretical models suggest that this twist is effected by the inclusion of screw dislocations in the structure of the phase in the form of a lattice of defects. This lattice is thought to be similar in nature to the Abrikosov flux lattice found in superconductors.