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.

Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal / Vita, Francesco; Hegde, Maruti; Portale, Giuseppe; Bras, Wim; Ferrero, Claudio; Samulski, Edward T.; Francescangeli, Oriano; Dingemans, Theo. - In: SOFT MATTER. - ISSN 1744-683X. - STAMPA. - 12:8(2016), pp. 2309-2314. [10.1039/c5sm02738a]

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

VITA, Francesco;FRANCESCANGELI, ORIANO
;
2016-01-01

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.
2016
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/11566/235989
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