Complex molecular dynamics of a symmetric model discotic liquid crystal revealed by broadband dielectric, thermal and neutron spectroscopy

  • The molecular dynamics of the triphenylene-based discotic liquid crystal HAT6 is investigated by broadband dielectric spectroscopy, advanced dynamical calorimetry and neutron scattering. Differential scanning calorimetry in combination with X-ray scattering reveals that HAT6 has a plastic crystalline phase at low temperatures, a hexagonally ordered liquid crystalline phase at higher temperatures and undergoes a clearing transition at even higher temperatures. The dielectric spectra show several relaxation processes: a localized gamma-relaxation a lower temperature and a so called alpha-2-relaxation at higher temperatures. The relaxation rates of the alpha-2-relaxation have a complex temperature dependence and bear similarities to a dynamic glass transition. The relaxation rates estimated by hyper DSC, Fast Scanning calorimetry and AC Chip calorimetry have a different temperature dependence than the dielectric alpha-2-relaxation and follows the VFT-behavior characteristic for glassyThe molecular dynamics of the triphenylene-based discotic liquid crystal HAT6 is investigated by broadband dielectric spectroscopy, advanced dynamical calorimetry and neutron scattering. Differential scanning calorimetry in combination with X-ray scattering reveals that HAT6 has a plastic crystalline phase at low temperatures, a hexagonally ordered liquid crystalline phase at higher temperatures and undergoes a clearing transition at even higher temperatures. The dielectric spectra show several relaxation processes: a localized gamma-relaxation a lower temperature and a so called alpha-2-relaxation at higher temperatures. The relaxation rates of the alpha-2-relaxation have a complex temperature dependence and bear similarities to a dynamic glass transition. The relaxation rates estimated by hyper DSC, Fast Scanning calorimetry and AC Chip calorimetry have a different temperature dependence than the dielectric alpha-2-relaxation and follows the VFT-behavior characteristic for glassy dynamics. Therefore, this process is called alpha-1-relaxation. Its relaxation rates show a similarity with that of polyethylene. For this reason, the alpha-1-relaxation is assigned to the dynamic glass transition of the alkyl chains in the intercolumnar space. Moreover, this process is not observed by dielectric spectroscopy which supports its assignment. The alpha-2-relaxation was assigned to small scale translatorial and/or small angle fluctuations of the cores. The neutron scattering data reveal two relaxation processes. The process observed at shorter relaxation times is assigned to the methyl group rotation. The second relaxation process at longer time scales agree in the temperature dependence of its relaxation rates with that of the dielectric gamma-relaxation.zeige mehrzeige weniger

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Autor*innen:Arda Yildirim, Christina Krause, R. Zorn, W. Lohstroh, G. J. Schneider, M. Zamponi, O. Holerer, B. Frick, Andreas SchönhalsORCiD
Dokumenttyp:Zeitschriftenartikel
Veröffentlichungsform:Verlagsliteratur
Sprache:Englisch
Titel des übergeordneten Werkes (Englisch):Soft Matter
Jahr der Erstveröffentlichung:2020
Organisationseinheit der BAM:6 Materialchemie
6 Materialchemie / 6.6 Physik und chemische Analytik der Polymere
Verlag:Royal Chemical Society
Jahrgang/Band:16
Ausgabe/Heft:8
Erste Seite:2005
Letzte Seite:2016
DDC-Klassifikation:Naturwissenschaften und Mathematik / Chemie / Analytische Chemie
Technik, Medizin, angewandte Wissenschaften / Ingenieurwissenschaften / Ingenieurwissenschaften und zugeordnete Tätigkeiten
Freie Schlagwörter:Discotic Liquid Crystals
Themenfelder/Aktivitätsfelder der BAM:Chemie und Prozesstechnik
Material
DOI:10.1039/c9sm02487e
Verfügbarkeit des Dokuments:Datei im Netzwerk der BAM verfügbar ("Closed Access")
Datum der Freischaltung:27.02.2020
Referierte Publikation:Ja
Datum der Eintragung als referierte Publikation:27.02.2020
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