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Issue 8, 2016
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Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal

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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

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The article was received on 06 Nov 2015, accepted on 11 Jan 2016 and first published on 19 Jan 2016


Article type: Paper
DOI: 10.1039/C5SM02738A
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Citation: Soft Matter, 2016,12, 2309-2314
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    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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