Complex Shear Viscosity of Liquid Crystals in the Isotropic Phase of Nematics

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Abstract
By use of the torsional quartz crystal method, the real and imaginary parts of the complex shear mechanical impedance of several nematogenic materials were measured as functions of the temperature at frequencies ranging from 50 to 150 kHz. From the impedance, we have determined the real and imaginary parts of the complex shear viscosity, in which a remarkable pretransitional anomaly is observed in the isotropic phase near the isotropic-nematic phase transition temperature, T c. In the nematic phase and the isotropic phase except for the vicinity of T c, the Newtonian behaviour is observed. The behaviour of the complex shear viscosity in the isotropic phase has been analyzed by the theory of de Gennes, and it is shown that the observed behaviour can be well described by the theory.

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