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

Soft Matter
Francesco VitaTheo Dingemans

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.

References

Sep 16, 2006·Philosophical Transactions. Series A, Mathematical, Physical, and Engineering Sciences·T J DingemansE T Samulski
Jan 22, 2011·The Journal of Physical Chemistry. B·Stefan KuiperStephen J Picken
Dec 21, 2011·Physical Review Letters·Oriano FrancescangeliEdward T Samulski
Apr 17, 2014·Chemphyschem : a European Journal of Chemical Physics and Physical Chemistry·Yoann OlivierClaudio Zannoni
Aug 19, 2014·Soft Matter·Oriano FrancescangeliEdward T Samulski

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Citations

Aug 30, 2020·Nanomaterials·Francesco VitaOriano Francescangeli

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