On the twist-bend nematic phase formed directly from the isotropic phase

Dawood, Alya A., Grossel, Martin C., Luckhurst, Geoffrey R., Richardson, Robert M., Timimi, Bakir A., Wells, Neil and Yousif, Yousif Z. (2016) On the twist-bend nematic phase formed directly from the isotropic phase. Liquid Crystals, 43 (1), 2-12. (doi:10.1080/02678292.2015.1114158).

Abstract

The intriguing twist-bend nematic (NTB) phase is formed, primarily, by liquid crystal dimers having odd spacers. Typically, the phase is preceded by a nematic (N) phase via a weak first-order transition. Our aim is to obtain dimers where the NTB phase is formed directly from the isotropic (I) phase via a strong first-order phase transition. The analogy between such behaviour and that of the smectic A (SmA)–N–I sequence suggests that this new dimer will require a short spacer. This expectation is consistent with the prediction of a molecular field theory, since the decrease in the spacer length results in an increase in the molecular curvature. A vector of odd dimers based on benzoyloxybenzylidene mesogenic groups with terminal ethoxy groups has been synthesised with spacers composed of odd numbers of methylene groups. Spacers having 5, 7, 9 and 11 methylene groups are found to possess the conventional phase sequence NTB–N–I; surprisingly, for the propane spacer, the NTB phase is formed directly from the I phase. The properties of these dimers have been studied with care to ensure that the identification of the NTB phase is reliable.

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Contributors

Author: Martin C. Grossel

Author: Neil Wells

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