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1 Polish Journal of Chemistry

1 2002

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Linear and Nonlinear Dielectric Properties of 4-Heptyl-4'cyano-biphenyl Solutions in Benzene

Małecki J., Nowak J.

Polish Journal of Chemistry

2002

Vol. 76 / nr 2-3

435-441

Linear electric susceptibility and nonlinear dielectric effect (NDE) of the isotropic phase of the benzene solutions of 4-heptyl-4_-cyano-biphenyl (7CB4) are described in the whole concentration and temperature ranges. At the molar fraction above 0.85 strong, critical pre-transitional effects are observed, associated with the imminent nematic phase. The effects of the molecular reorientation and dipolar association, the latter manifesting itself by positive NDE and near the transition to the solid phase with a strong negative NDE, are taken into account. Otherwise, critical fluctuations occurring near the nematic phase transition lead to a strong, critical increase of the electric susceptibility change in electric field. The observed effects, with supplementary optical and microscopic studies, allow an accurate determination of the temperatures of phase transitions and setting up the phase diagram of these solutions.