Probing molecular ordering in the nematic phases of para-linked bimesogen dimers through NMR studies of flexible prochiral solutes

Heist, Leah M.; Samulski, Edward T.; Welch, Chris; Ahmed, Ziauddin; Mehl, Georg H.; Vanakaras, Alexandros G.; Photinos, Demetri J.

Abstract

The quadrupolar splittings of perdeuteriated n-decane dissolved in nematic phases formed by mesogenic dimers of the CBnCB series, for n = 7,9,10,11, are measured throughout the entire temperature range of these phases. These results are reported together with related measurements using the common nematic phase of 5CB as a solvent for n-decane. The data obtained from the 13C spectra of the cyanobiphenyl mesogenic units of the monomeric and dimeric solvent molecules yield the order parameter of those units. The information obtained from this set of experiments is used to elucidate the structure of the low temperature (NX) and the high temperature (N) nematic phases of CBnCB dimers with n = 7,9,11. The polar twisted nematic (NPT) model is found to provide a consistent description not only of our experimental results but also of NMR measurements previously reported in the literature for these phases. These findings suggest that the high temperature nematic (N) is not a common, locally uniaxial and apolar nematic, but rather a nematic phase consisting of NPT clusters. The twist-bend (NTB) model, often identified with the NX phase, is shown to be inadequate to account even qualitatively for crucial features of the experimental findings.

Citation

Heist, L. M., Samulski, E. T., Welch, C., Ahmed, Z., Mehl, G. H., Vanakaras, A. G., & Photinos, D. J. (2020). Probing molecular ordering in the nematic phases of para-linked bimesogen dimers through NMR studies of flexible prochiral solutes. Liquid crystals, 1-16. https://doi.org/10.1080/02678292.2019.1711214

• Journal Article Type: Article
• Acceptance Date: Jan 30, 2019
• Online Publication Date: Jan 28, 2020
• Publication Date: Jan 1, 2020
• Deposit Date: Jan 29, 2020
• Publicly Available Date: Jan 2, 2021
• Journal: Liquid Crystals
• Print ISSN: 0267-8292
• Electronic ISSN: 1366-5855
• Publisher: Taylor and Francis
• Peer Reviewed: Peer Reviewed
• Pages: 1-16
• DOI: https://doi.org/10.1080/02678292.2019.1711214
• Keywords: General Materials Science; General Chemistry; Condensed Matter Physics; Nenatic-nematic phase transitions; NMR; potential of mean torque; symmetric dimers; prochiral solutes
• Public URL: https://hull-repository.worktribe.com/output/3395378
• Additional Information: Peer Review Statement: The publishing and review policy for this title is described in its Aims & Scope.; Aim & Scope: http://www.tandfonline.com/action/journalInformation?show=aimsScope&journalCode=tlct20; Published: 2020-01-28