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Orientational order parameters of a de Vries–type ferroelectric liquid crystal obtained by polarized Raman spectroscopy and x-ray diffraction

Sanchez-Castillo, A. and Osipov, Mikhail A. and Jagiella, S. and Nguyen, Z.H. and Kaspar, M. and Hamplova, V. and Maclennan, J. and Giesselmann, F. (2012) Orientational order parameters of a de Vries–type ferroelectric liquid crystal obtained by polarized Raman spectroscopy and x-ray diffraction. Physical Review E, 85 (6). ISSN 1539-3755

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    Abstract

    The orientational order parameters 〈P2〉 and 〈P4〉 of the ferroelectric, de Vries–type liquid crystal 9HL have been determined in the SmA* and SmC* phases by means of polarized Raman spectroscopy, and in the SmA* phase using x-ray diffraction. Quantum density functional theory predicts Raman spectra for 9HL that are in good agreement with the observations and indicates that the strong Raman band probed in the experiment corresponds to the uniaxial, coupled vibration of the three phenyl rings along the molecular long axis. The magnitudes of the orientational order parameters obtained in the Raman and x-ray experiments differ dramatically from each other, a discrepancy that is resolved by considering that the two techniques probe the orientational distributions of different molecular axes. We have developed a systematic procedure in which we calculate the angle between these axes and rescale the orientational order parameters obtained from x-ray scattering with results that are then in good agreement with the Raman data. At least in the case of 9HL, the results obtained by both techniques support a “sugar loaf” orientational distribution in the SmA* phase with no qualitative difference to conventional smectics A. The role of individual molecular fragments in promoting de Vries–type behavior is considered.

    Item type: Article
    ID code: 41273
    Keywords: Ferroelectric liquid crystal, raman spectra, orientational order parameters, x-ray scattering, Physical and theoretical chemistry, Statistical and Nonlinear Physics, Statistics and Probability, Condensed Matter Physics
    Subjects: Science > Chemistry > Physical and theoretical chemistry
    Department: Faculty of Science > Mathematics and Statistics
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    Depositing user: Pure Administrator
    Date Deposited: 28 Sep 2012 14:38
    Last modified: 27 Mar 2014 22:19
    URI: http://strathprints.strath.ac.uk/id/eprint/41273

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