The twist-bend nematic phase: translational self-diffusion and biaxiality studied by H-1 nuclear magnetic resonance diffusometry
2017 (English)In: Liquid crystals (Print), ISSN 0267-8292, E-ISSN 1366-5855, Vol. 44, no 1, 204-218 p.Article in journal (Refereed) Published
Recently, there has been a surge of interest in mesogens exhibiting the twist-bend nematic (N-TB) phase that is shown to be chiral even though formed by effectively achiral molecules. Although it now seems to be clear that the N-TB phase in the bulk is formed by degenerate domains having opposite handedness, the presence of a supramolecular heliconical structure proposed in the Dozov model has been contradicted by the Hoffmann et al. model in which the heliconical arrangement is replaced by a polar nematic phase. The evidence in support of this is that the quadrupolar splitting tensor measured in various experiments is uniaxial and not biaxial as expected for the twist-bend nematic structure. In this debate, among other evidence, the molecular translational diffusion, and its magnitude with respect to that in the nematic phase above the N-TB phase, has also been invoked to eliminate or to confirm one model or the other. We attempt to resolve this issue by reporting the first measurements of the translational self-diffusion coefficients in the nematic and twist-bend nematic phases formed 1 '',7 ''-bis-4-(4'-cyanobiphenyl-4'-yl) heptane (CB7CB). Such measurements certainly appear to resolve the differences between the two models in favour of that for the classic twist-bend nematic phase. [GRAPHICS] .
Place, publisher, year, edition, pages
TAYLOR & FRANCIS LTD , 2017. Vol. 44, no 1, 204-218 p.
Twist-bend nematic, local phase biaxiality, molecular translational diffusion coefficients, macroscopic rotational diffusion, motional averaging, residual quadrupolar tensors
IdentifiersURN: urn:nbn:se:kth:diva-205171DOI: 10.1080/02678292.2016.1254292ISI: 000397105800017OAI: oai:DiVA.org:kth-205171DiVA: diva2:1088224
QC 201704112017-04-112017-04-112017-04-11Bibliographically approved