Journal Article

FZJ-2020-01120

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Complex molecular dynamics of a symmetric model discotic liquid crystal revealed by broadband dielectric, thermal and neutron spectroscopy

Yildirim, A. ; Krause, C. ; Zorn, R.FZJ* ; Lohstroh, W. ; Schneider, G. J.FZJ* ; Zamponi, M.FZJ* ; Holderer, O.FZJ* ; Frick, B. ; Schönhals, A. (Corresponding author)

2020
Royal Soc. of Chemistry London

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Please use a persistent id in citations: http://hdl.handle.net/2128/24659  doi:10.1039/C9SM02487E

Abstract: 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 γ-relaxation at lower temperatures and a so called α2-relaxation at higher temperatures. The relaxation rates of the α2-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 α2-relaxation and follow the VFT-behavior characteristic for glassy dynamics. Therefore, this process is called α1-relaxation. Its relaxation rates show a similarity with that of polyethylene. For this reason, the α1-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 α2-relaxation is 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 γ-relaxation.

Keyword(s): Basic research (1st) ; Soft Condensed Matter (2nd)

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Contributing Institute(s):

1. Neutronenstreuung (JCNS-1)
2. JCNS-FRM-II (JCNS-FRM-II)
3. Neutronenstreuung (ICS-1)
4. Heinz Maier-Leibnitz Zentrum (MLZ)

Research Program(s):

1. 551 - Functional Macromolecules and Complexes (POF3-551) (POF3-551)
2. 6G4 - Jülich Centre for Neutron Research (JCNS) (POF3-623) (POF3-623)
3. 6215 - Soft Matter, Health and Life Sciences (POF3-621) (POF3-621)
4. 6G15 - FRM II / MLZ (POF3-6G15) (POF3-6G15)

Experiment(s):

1. SPHERES: Backscattering spectrometer (NL6S)
2. TOFTOF: Cold neutron time-of-flight spectrometer (NL2au)

Appears in the scientific report 2020

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Database coverage:
; ; Allianz-Lizenz / DFG ; Clarivate Analytics Master Journal List ; Current Contents - Physical, Chemical and Earth Sciences ; IF < 5 ; JCR ; National-Konsortium ; Nationallizenz ; SCOPUS ; Science Citation Index ; Science Citation Index Expanded ; Web of Science Core Collection

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