1 February 1998 Dielectric spectroscopy of nematic liquid crystals confined to anapore membranes
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Dielectric studies of nematic liquid crystals (NLC) have proved to be a valuable source of information on the mesomorphic, liquid crystalline phase. Oriented samples of liquid crystal are dielectrically anisotropic, and both the real and imaginary parts of the permittivity tensor yield two independent main components. The frequency dependent dielectric anisotropy is governed by permanent and induced dipole moments at low frequencies, and at the short wave side of the dispersion steps only by the induced dipole moment. From the observed dispersion curves of (epsilon) (parallel) and (epsilon) (perpendicular) we could show experimentally that the dielectric anisotropy (Delta) (epsilon) equals ((epsilon) (perpendicular) - (epsilon) (perpendicular)) of 4-n-pentyl-4'-cyanobiphenyl changes its sign twice over the frequency range covered by our experiments. The static dielectric anisotropy, as well as the optical anisotropy are positive, therefore this behavior should be expected. The change of sign in (Delta) (epsilon) would imply that the nematic director will align parallel to the external electric field in the low and high frequency limits, whereas it orients perpendicularly to the field at some intermediate frequency range.
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Stanislaw A. Rozanski, Stanislaw A. Rozanski, Ralf Stannarius, Ralf Stannarius, Herbert Groothues, Herbert Groothues, Friedrich Kremer, Friedrich Kremer, } "Dielectric spectroscopy of nematic liquid crystals confined to anapore membranes", Proc. SPIE 3318, Liquid Crystals: Physics, Technology, and Applications, (1 February 1998); doi: 10.1117/12.299977; https://doi.org/10.1117/12.299977

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