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| Volume 2, Issue 03 - 2006 |
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| 3 |
ON THE MEASUREMENT OF THE DIRECTOR RELAXATION TIME
OF PERIODICALLY REORIENTED NEMATIC LIQUID CRYSTAL LAYER
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| Pages 96-105 |
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| P.L. PAPADOPOULOS, H.M. ZENGINOGLOU, J.A. KOSMOPOULOS AND N.T. TSIBERIS |
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| University of Patras, Dept. of Physics, Patras 26500, Greece |
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| Received 1 November 2006 ; accepted 8 December 2006 |
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| The director of a periodically reoriented monomolecular or polymeric nematic liquid crystal layer decays towards its initial orientation direction when the external means, by which the reorientation was induced, vanish. The relaxation time characterizing the decay process depends, on the measurable quantities such as the layer thickness and the spatial period of the reorientation, as well as on the elastic constants and the viscosity coefficients of the nematic material. Thus, its measurement may be proved to be a useful tool for the characterization of the nematic material. The measurement is effected by optical means i.e. by measuring the time dependence of the intensity of the first order fringe resulting from the illumination of the nematic layer by a monochromatic light-beam. The experiment was carried out using a nematic material (MBBA) with known material parameters. The quality of fit of the experimental data to a theoretical formula, which gives the intensity of the mentioned fringes as a function of the reorientation parameters is examined and is found quite satisfactory. The accuracy of the value of the relaxation time determined by the fitting process was about 1.5%, whereas, for the used nematic material, the difference of this value from the expected one was about 3%, a percentage that can be attributed to the uncertainties of the used material parameters. |
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