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Vibrational density of states of triphenylene based discotic liquid crystals: dependence on the length of the alkyl chain
Citation Link: https://doi.org/10.15480/882.2187
Publikationstyp
Journal Article
Date Issued
2014
Sprache
English
TORE-DOI
TORE-URI
Volume
16.2014
Start Page
7324
End Page
7333
Citation
Phys. Chem. Chem. Phys. 16 (16): 7324-7333 (2014)
Publisher DOI
Scopus ID
Publisher
Royal Society of Chemistry (RSC)
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.
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.
DDC Class
620: Ingenieurwissenschaften
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