On the measurement of the orientational order parameters in biaxial liquid crystals using the polarised infrared technique

M.V. Gorkunov, Mikhail Osipov

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

The limits of the applicability of the Polarised Infrared (Fourier transform infrared) spectroscopy technique, which is used to measure the order parameters of biaxial liquid crystals, is investigated in detail for different experimental geometries and cell thicknesses. General expressions for the transmittance of the polarised infrared radiation by a biaxial liquid crystal material in planar and homeotropic cells are obtained in the general case of oblique incidence. These expressions are then simplified in the limiting cases of thin and thick cells, and in both cases the relationship is established between the cell transmittance and the components of the imaginary part of the infrared molecular permittivity. It is shown that simple expressions, used in the literature to extract the values of the biaxial order parameters, are valid only for thin cells and in specific geometries when light propagates along one of the optical axes of the material. For thicker cells typical for experimental conditions, approximate expressions are obtained which are to be used to reveal the order parameters of biaxial liquid crystals. Various types of experimental geometries are discussed including those suitable for measurements of the order parameters, and those to be avoided
LanguageEnglish
Pages1569 - 1576
Number of pages8
JournalLiquid Crystals
Volume37
Issue number12
DOIs
Publication statusPublished - 12 Dec 2010

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Liquid Crystals
Liquid crystals
liquid crystals
Infrared radiation
Geometry
cells
transmittance
geometry
Fourier transform infrared spectroscopy
Permittivity
Cells
infrared radiation
incidence
infrared spectroscopy
permittivity

Keywords

  • biaxial order parameters
  • infrared spectroscopy
  • biaxial nematics
  • theory

Cite this

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abstract = "The limits of the applicability of the Polarised Infrared (Fourier transform infrared) spectroscopy technique, which is used to measure the order parameters of biaxial liquid crystals, is investigated in detail for different experimental geometries and cell thicknesses. General expressions for the transmittance of the polarised infrared radiation by a biaxial liquid crystal material in planar and homeotropic cells are obtained in the general case of oblique incidence. These expressions are then simplified in the limiting cases of thin and thick cells, and in both cases the relationship is established between the cell transmittance and the components of the imaginary part of the infrared molecular permittivity. It is shown that simple expressions, used in the literature to extract the values of the biaxial order parameters, are valid only for thin cells and in specific geometries when light propagates along one of the optical axes of the material. For thicker cells typical for experimental conditions, approximate expressions are obtained which are to be used to reveal the order parameters of biaxial liquid crystals. Various types of experimental geometries are discussed including those suitable for measurements of the order parameters, and those to be avoided",
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On the measurement of the orientational order parameters in biaxial liquid crystals using the polarised infrared technique. / Gorkunov, M.V.; Osipov, Mikhail.

In: Liquid Crystals, Vol. 37, No. 12, 12.12.2010, p. 1569 - 1576 .

Research output: Contribution to journalArticle

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AU - Osipov, Mikhail

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