J. Phys. II France
Volume 4, Numéro 9, September 1994
Page(s) 1451 - 1456
DOI: 10.1051/jp2:1994102
J. Phys. II France 4 (1994) 1451-1456

Pretransitional behaviour of a nematic liquid crystal in the isotropic phase

J. Fuchs and W. Burchard

Institute of Macromolecular Chemistry, University of Freiburg, Stefan-Meier-Str. 31, 79104 Reiburg, Germany

(Received 23 March 1994, revised 14 June 1994, accepted 20 July 1994)

Polarized and depolarized light scattering measurements have been performed from a nematic liquid crystalline material in the isotropic region, approaching the nematic phase transition. A critical static scattering intensity and a critical slowing-down of the orientational fluctuations were observed in a temperature range of about 10 $^{\circ}$C above the phase transition which followed a $(T - T_{\rm c}^{*})^{-\gamma}$ dependence, but with an exponent slightly smaller than unity. The angular dependence of the polarized static scattering intensity differed in behaviour from other liquid crystals by the occurrence of a strong excess scattering at small scattering angles. These observations give evidence for spatial structural heterogeneities, spherical in shape and optically isotropic, in a bath of a nematic liquid crystalline system. This conclusion is confirmed by dynamic light scattering where in addition a slow mode appeared in the time correlation function which results from random migration of these heterogeneities.

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