Multiple glass transitions in the plastic crystal phase of triphenylene derivates

Z. Yildirim, M. Wubbenhorst, E. Mendes, S.J. Picken, I. Paraschiv, A.T.M. Marcelis, H. Zuilhof, E.J.R. Sudhölter

Research output: Contribution to journalArticleAcademicpeer-review

30 Citations (Scopus)

Abstract

The dynamics and phase behavior of the discotic liquid crystalline compound hexahexyloxytriphenylene (HAT6) and a derivative were studied by broad-band dielectric spectroscopy, differential scanning calorimetry, X-ray diffraction and optical microscopy. While the pristine compound HAT6 forms both a columnar mesophase (Colh) and a plastic crystal phase, no liquid crystallinity was observed for the highly asymmetric compound HAT6-C10Br. This paper focuses on the dielectric relaxations in the plastic crystal phase. For HAT6-C10Br, a `high temperature¿ glass transition, manifested by a Vogel¿Fulcher¿Tammann (VFT) type ¿2-process, was found at ¿31 °C that was assigned to the columnar glass transition in accordance with previous literature. The main result of our study is the observation of a second, low-temperature VFT process (¿1) for both compounds, which indicates co-operative liquid dynamics within the framework of the plastic crystal order at temperatures as low as ¿100 °C. Comparison of these fast dynamics with relaxation data from polyethylene and polymer series with long alkyl groups identifies this process as a `hindered¿ polyethylene-like dynamic glass transition that originates from the nanophase-separated, spatially confined fraction of aliphatic tails.
Original languageEnglish
Pages (from-to)2622-2628
JournalJournal of Non-Crystalline Solids
Volume351
Issue number33-36
DOIs
Publication statusPublished - 2005

Keywords

  • dielectric-relaxation spectroscopy
  • molecular-dynamics
  • liquid-crystal
  • nematic-columnar
  • separation
  • viscosity
  • polymers
  • mesogens
  • spectra
  • probes

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