MOLECULAR-OPTICAL AND STRUCTURAL ANISOTROPY OF THE NEMATIC MIXTURE E7
The relation of the refractive indices n<sub>j</sub> of the nematic mixture E7 consisting of cyanobiphenyl derivatives for the light-wave polarization along (j = || ) and across (j = ^ ) the optical axis with the polarizability parameters (components g<sub>j</sub><sup>a</sup>, mean value g<sub>m</sub><sup>a</sup> = (g <sub>||</sub><sup>a</sup>+ 2g <sub>^</sub><sup>a</sup>)/3, anisotropy dg<sub>a</sub> = g <sub>||</sub><sup>a</sup>- g <sub>^</sub><sup>a</sup>) and orientational order of a-type molecules comprising the mixture was investigated. The local-field tensor with components f<sub>j</sub> =1+L<sub>j</sub>(n<sub>j</sub><sup>2 </sup>- 1) was introduced for the mixture and the relationship between the Lorentz-tensor components L<sub>j</sub> and the components L<sub>j</sub><sup>a</sup> was established. The temperature dependences L<sub>j</sub>(T) for the E7 mixture were obtained using experimental dependences n<sub>j</sub>(l, T). The relationship L<sub>j</sub>(L<sub>j</sub><sup>a</sup>) was confirmed. The temperature dependence of the material order parameter S(T) was obtained. The change of the mean value g<sub>m</sub>(Т) = (g <sub>|| </sub> + 2g <sub>^</sub> )/3 for the studied mixture due to changing of S(Т) was observed. The dependence g<sub>m</sub>(S) was shown to be caused by two opposite-sign contributions due to changing conformation of molecular biphenyl cores and intermolecular interactions. The obtained results were compared with the consequences of using model tensors f<sub>j</sub>, which literature data are known for mixtures.