Abstract
NMR measurements on a selectively deuterated liquid crystal dimer CB-C9-CB, exhibiting two nematic phases, show that the molecules in the lower temperature nematic phase, N(X), experience a chiral environment and are ordered about a uniformly oriented director throughout the macroscopic sample. The results are contrasted with previous interpretations that suggested a twist-bend spatial variation of the director. A structural picture is proposed wherein the molecules are packed into highly correlated chiral assemblies.
Highlights
The twist-bend model has been proposed[8,9,11,12,16,20] for the consistent interpretation of various experimental observations on the dimer NX phase, there is, to our knowledge, no direct identification of the heliconical structure and, there are indications[21,22] that the dominant molecular arrangement in the NX phase could differ from that of the twist-bend model. In this communication we show, based on NMR studies of a selectively deuterated material of the structure CB-C9-CB presented in Figure 1a, that the helicoidal conical structure is not identified as the organisation of the NX phase in the bulk
The sequence is determined by DSC at 10oC min-1
The onset, through a first order phase transition, of the low temperature NX phase is accompanied by a significant increase of the viscosity
Summary
In this communication we show, based on NMR studies of a selectively deuterated material of the structure CB-C9-CB presented in Figure 1a, that the helicoidal conical structure is not identified as the organisation of the NX phase in the bulk. The measured splitting in the quadrupolar spectrum of the α-CD2 group in the nematic phase is related to the respective orientational order paramete= r Sα(H−C)D P2 (eα −CD ⋅ H )
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