FisMat2017 - Submission - View

Abstract's title: Insights into the nematic phase of all-aromatic liquid crystals
Submitting author: Fabrizio C. Adamo
Affiliation: Dipartimento di Scienze e Ingegneria della Materia, dell’Ambiente ed Urbanistica - Università Politecnica delle Marche
Affiliation Address: Via brecce Bianche, 60131 Ancona (AN)
Country: Italy
Oral presentation/Poster (Author's request): Poster
Other authors and affiliations: Francesco Vita (Dipartimento di Scienze e Ingegneria della Materia, dell’Ambiente ed Urbanistica and CNISM, Università Politecnica delle Marche, Ancona, Italy), Oriano Francescangeli (Dipartimento di Scienze e Ingegneria della Materia, dell’Ambiente ed Urbanistica and CNISM, Università Politecnica delle Marche, Ancona, Italy)
Abstract

Rod-like all-aromatic nematogens represent an ideal benchmark to compare theories of nematic order to experiments. The scientific literature provides very few structural studies on these compounds, such as p-quinquephenyl (PPPPP), 2,6-biphenyl naphthalene (PPNPP) and α-sexithiophene (6T), mostly due to the challenge of performing measurements at temperatures exceeding 400°C where the mesogens exhibit the nematic (N) phase.  Here we provide an overview of our most recent research on this class of nematogens.  In particular, we report strong experimental evidence of the presence of cybotactic clusters in the N phase as well as a significant deviation of the orientational order parameter from the classic Maier-Saupe theoretical predictions. Moreover, the diffraction patterns observed in the aligned N phase differ substantially from those of conventional calamitics, displaying relatively narrow meridional arcs together with an unusually large number of high-order reflections. The longitudinal correlation length largely exceeds the typical values found in conventional calamitics. Our results unveil the fundamental role of cibotaxis in the thermodynamics of nematogens and raise fundamental questions about the true nature of the short-range order in the N phase of liquid crystals, an issue that has come to the focus of the soft matter scientists only very recently.