Issue 32, 2016

Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl)hexane (CB6OCB) and comparison with CB7CB

Abstract

The synthesis and characterisation of the nonsymmetric liquid crystal dimer, 1-(4-cyanobiphenyl-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl)hexane (CB6OCB) is reported. An enantiotropic nematic (N)–twist-bend nematic (NTB) phase transition is observed at 109 °C and a nematic–isotropic phase transition at 153 °C. The NTB phase assignment has been confirmed using polarised light microscopy, freeze fracture transmission electron microscopy (FFTEM), 2H-NMR spectroscopy, and X-ray diffraction. The effective molecular length in both the NTB and N phases indicates a locally intercalated arrangement of the molecules, and the helicoidal pitch length in the NTB phase is estimated to be 8.9 nm. The surface anchoring properties of CB6OCB on a number of aligning layers is reported. A Landau model is applied to describe high-resolution heat capacity measurements in the vicinity of the NTB–N phase transition. Both the theory and heat capacity measurements agree with a very weak first-order phase transition. A complementary extended molecular field theory was found to be in suggestive accord with the 2H-NMR studies of CB6OCB-d2, and those already known for CB7CB-d4. These include the reduced transition temperature, TNTBN/TNI, the order parameter of the mesogenic arms in the N phase close to the NTB–N transition, and the order parameter with respect to the helix axis which is related to the conical angle for the NTB phase.

Graphical abstract: Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl)hexane (CB6OCB) and comparison with CB7CB

Supplementary files

Article information

Article type
Paper
Submitted
01 Mar 2016
Accepted
11 Jul 2016
First published
11 Jul 2016
This article is Open Access
Creative Commons BY license

Soft Matter, 2016,12, 6827-6840

Understanding the twist-bend nematic phase: the characterisation of 1-(4-cyanobiphenyl-4′-yloxy)-6-(4-cyanobiphenyl-4′-yl)hexane (CB6OCB) and comparison with CB7CB

D. A. Paterson, M. Gao, Y. Kim, A. Jamali, K. L. Finley, B. Robles-Hernández, S. Diez-Berart, J. Salud, M. R. de la Fuente, B. A. Timimi, H. Zimmermann, C. Greco, A. Ferrarini, J. M. D. Storey, D. O. López, O. D. Lavrentovich, G. R. Luckhurst and C. T. Imrie, Soft Matter, 2016, 12, 6827 DOI: 10.1039/C6SM00537C

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements