Molecular ordering in the high-temperature nematic phase of an all-aromatic liquid crystal. Issue 8 (19th January 2016)

• Record Type: Journal Article
• Authors: Vita, Francesco; Hegde, Maruti; Portale, Giuseppe; Bras, Wim; Ferrero, Claudio; Samulski, Edward T.; Francescangeli, Oriano; Dingemans, Theo
• Is Part Of: Soft matter. Volume 12:Issue 8(2016)
• Page Start: 2309
• Page End: 2314
• Publication Date: 2016-01-19
• Subjects: Soft condensed matter -- Periodicals; 530.413
• DOI: 10.1039/c5sm02738a
• Languages: English
• ISSNs: 1744-683X

Abstract

Abstract : The high-temperature nematic phase of all-aromatic lath-like 2, 6-biphenyl naphthalene (PPNPP) exhibits a surprisingly strong tendency towards molecular layering ( i.e. SmA-like cybotaxis) and an orientational order parameter slightly deviating from Maier–Saupe theoretical prediction. 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.