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

Alya A. Dawood, Martin C. Grossel, Geoffrey R. Luckhurst*, Robert M. Richardson, Bakir A. Timimi, Neil J. Wells, Yousif Z. Yousif

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)peer-review

75 Citations (Scopus)
232 Downloads (Pure)

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.

Original languageEnglish
Pages (from-to)2-12
Number of pages11
JournalLiquid Crystals
Volume43
Issue number1
Early online date8 Jan 2016
DOIs
Publication statusPublished - Jan 2016

Keywords

  • H NMR spectroscopy
  • first-order phase transitions
  • helicoidal structure
  • liquid crystal dimers
  • molecular field theory
  • prochiral splitting
  • rope-like texture
  • Twist-bend nematic

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