ANISOTROPY OF THE TURBIDITY OF AN ORIENTED NEMATIC LIQUID CRYSTAL

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Abstract
In a nematic liquid crystal, thermal fluctuations of the orientation of molecules give rise to an intense scattering of light which confers to the system a characteristic turbidity. The resulting absorption coefficient is equal to the total scattering cross-section. We compute the cross section for an oriented liquid crystal, taking into account the role of the optical anisotropy of the medium for the propagation of the scattered waves. We show that the measurement of the absorption coefficients in three simple geometries allows the determination of the three Frank elastic constants on the same sample, provided that the refractive indices are known. We give the results obtained for MBBA at room temperature. The measured values of the elastic constants are in good agreement with determinations by other methods. We also discuss the influence on this experiment coming from the scattering by static defects inside the sample

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