Issue 8, 2016

Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal

Abstract

We report the structural characterization of the nematic phase of 2,6-biphenyl naphthalene (PPNPP). This lath-like all-aromatic mesogen provides a valuable benchmark for classical theories of nematic order. PPNPP exhibits a very high temperature nematic phase (417–489 °C) above an enantiotropic smectic A phase. X-ray diffraction reveals a surprisingly strong tendency towards molecular layering in the nematic phase, indicative of “normal cybotaxis” (i.e. SmA-like stratification within clusters of mesogens). Although stronger at low temperatures, the layering is evident well above the smectic A-nematic transition. The nematic order parameter is evaluated as a function of temperature from the broadening of the wide-angle diffuse diffraction feature. Measured values of the orientational order parameter are slightly larger than those predicted by the Maier–Saupe theory over the entire nematic range except for a narrow region just below the clearing point where they significantly drop below the theoretical prediction.

Graphical abstract: Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal

Supplementary files

Article information

Article type
Paper
Submitted
06 Nov 2015
Accepted
11 Jan 2016
First published
19 Jan 2016
This article is Open Access
Creative Commons BY license

Soft Matter, 2016,12, 2309-2314

Author version available

Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal

F. Vita, M. Hegde, G. Portale, W. Bras, C. Ferrero, E. T. Samulski, O. Francescangeli and T. Dingemans, Soft Matter, 2016, 12, 2309 DOI: 10.1039/C5SM02738A

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