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Issue 16, 2014
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Vibrational density of states of triphenylene based discotic liquid crystals: dependence on the length of the alkyl chain

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Abstract

The vibrational density of states of a series of homologous triphenylene-based discotic liquid crystals HATn (n = 5, 6, 8, 10, 12) depending on the length of the aliphatic side chain is investigated by means of inelastic neutron scattering. All studied materials have a plastic crystalline phase at low temperatures, followed by a hexagonally ordered liquid crystalline phase at higher temperatures and a quasi isotropic phase at the highest temperatures. The X-ray scattering pattern for the plastic crystalline phase of all materials shows a sharp Bragg reflection corresponding to the intercolumnar distance in the lower q-range and a peak at circa 17 nm−1 related to intracolumnar distances between the cores perpendicular to the columns as well as a broad amorphous halo related to the disordered structure of the methylene groups in the side chains in the higher q-range. The intercolumnar distance increases linearly with increasing chain length for the hexagonal columnar ordered liquid crystalline phase. A similar behaviour is assumed for the plastic crystalline phase. Besides n = 8 all materials under study exhibit a Boson peak. With increasing chain length, the frequency of the Boson peak decreases and its intensity increases. This can be explained by a self-organized confinement model. The peaks for n = 10, 12 are much narrower than for n = 5, 6 which might imply the transformation from a rigid system to a softer one with increasing chain length. Moreover the results can also be discussed in the framework of a transition from an uncorrelated to a correlated disorder with increasing n where n = 8 might be speculatively considered as a transitional state.

Graphical abstract: Vibrational density of states of triphenylene based discotic liquid crystals: dependence on the length of the alkyl chain

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Publication details

The article was received on 17 Dec 2013, accepted on 26 Feb 2014 and first published on 27 Feb 2014


Article type: Paper
DOI: 10.1039/C3CP55303E
Citation: Phys. Chem. Chem. Phys., 2014,16, 7324-7333
  • Open access: Creative Commons BY-NC license
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    Vibrational density of states of triphenylene based discotic liquid crystals: dependence on the length of the alkyl chain

    C. Krause, R. Zorn, F. Emmerling, J. Falkenhagen, B. Frick, P. Huber and A. Schönhals, Phys. Chem. Chem. Phys., 2014, 16, 7324
    DOI: 10.1039/C3CP55303E

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