Reduced odd–even effects in liquid crystalline carbonate dimers: molecular field analysis

Abstract

Four liquid crystalline carbonate dimers DCn containing the dimethylbenzalazine mesogen, bis(oxycarbonyloxy)alkane flexible spacers with three to six methylene units and acetate terminal groups were synthesised and their mesogenic behaviour investigated. As compared with the corresponding ester dimers a strong reduction of odd–even fluctuations of nematic–isotropic (N–I) transition entropy is observed. A theoretical analysis of the dimers within the rotational isomeric states (RIS) mean-field approach is also reported. A satisfying agreement between calculated and observed thermodynamic properties is obtained. In fact, the theoretical analysis correctly predicts a significant reduction of the odd–even fluctuations for the core order parameter S as well as for the nematic to isotropic transition entropy △S_NI . The calculated distributions of conformers also show reduced differences between even and odd members. In particular, for even dimers the calculated fraction of linear extended conformers in the nematic phase at the N–I transition is around 27%, which is far below that of the corresponding ester dimers (46%).

Keywords:

• dimers
• molecular-field analysis
• liquid crystals
• carbonate

Acknowledgement

I thank Professor A. Abe for sending me a preprint version of his and Professor Furuya's most recent paper entitled ‘Spatial configuration and thermodynamic characteristics of main chain liquid crystals’.