Molecular organization in the twist–bend nematic phase by resonant X-ray scattering at the Se K-edge and by SAXS, WAXS and GIXRD

Stevenson, W. D.; Ahmed, Z.; Zeng, X. B.; Welch, C.; Ungar, G.; Mehl, G. H.

Abstract

© the Owner Societies 2017. Using a magnetically aligned liquid crystal mixture containing a novel Se-labelled dimer and the difluoroterphenyl dimer DTC5C7, the twist-bend nematic phase (N tb ) was studied by the resonant scattering of hard X-rays and by conventional small and wide-angle X-ray scattering (SAXS, WAXS). Resonant diffraction spots indicated a helix with a 9-12 nm pitch in the N tb phase and an unprecedentedly high helix orientation. This enabled deconvolution of global and local order parameters. These findings, combined with the simultaneously recorded resonant and non-resonant SAXS and WAXS data, allowed us to construct a locally layered molecular model of the N tb phase, where the average twisted conformation of each molecule was idealised as a helical segment, matching the local heliconical director field. The dimers were found to be less bent in the N tb phase than in their minimum energy conformation, and straightening further with increasing temperature. It is proposed that on further heating their low bend angle allows the transition to the normal nematic phase, where the molecules can freely move longitudinally, without the need to perform screw-like motion as in the N tb phase. At the low-temperature end, the increasing molecular twist becomes unsustainable, leading to a transition to a smectic phase, where no twist is required.

Citation

Stevenson, W. D., Ahmed, Z., Zeng, X. B., Welch, C., Ungar, G., & Mehl, G. H. (2017). Molecular organization in the twist–bend nematic phase by resonant X-ray scattering at the Se K-edge and by SAXS, WAXS and GIXRD. Physical chemistry chemical physics : PCCP, 19(21), 13449-13454. https://doi.org/10.1039/c7cp01404j

• Journal Article Type: Article
• Acceptance Date: Apr 26, 2017
• Publication Date: May 3, 2017
• Deposit Date: May 10, 2017
• Publicly Available Date: May 11, 2018
• Journal: Physical chemistry chemical physics
• Print ISSN: 1463-9076
• Publisher: Royal Society of Chemistry
• Peer Reviewed: Peer Reviewed
• Volume: 19
• Issue: 21
• Pages: 13449-13454
• DOI: https://doi.org/10.1039/c7cp01404j
• Keywords: Physical and Theoretical Chemistry; General Physics and Astronomy
• Public URL: https://hull-repository.worktribe.com/output/451258
• Publisher URL: http://pubs.rsc.org/en/Content/ArticleLanding/2017/CP/C7CP01404J#!divAbstract
• Additional Information: : This document is Similarity Check deposited; : Supplementary Information; : Z. Ahmed (ResearcherID); : X. B. Zeng (ORCID); : The PCCP Owner Societies have an exclusive publication licence for this journal; OPEN ACCESS: This article is freely available. This article is licensed under a Creative Commons Attribution 3.0 Unported Licence (CC BY 3.0); : Single-blind; : Received 3 March 2017; Accepted 26 April 2017; Accepted Manuscript published 3 May 2017; Advance Article published 17 May 2017; Version of Record published 31 May 2017
• Contract Date: May 11, 2018