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100%
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vol. 96
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issue 3-4
341-352
EN
A new method of investigation of electro-optical properties of conducting media is proposed based on a contactless scheme for capacitance measurements. Using alternating electric current, the method is applied to study Kerr effect in a series of single and multi-component conducting liquid systems.
EN
The electro-optical Kerr effect of n-alkanes from C_5 to C_{16} was investigated in gas phase, liquid phase, and solution. The values of the Kerr constants in gas phase are noticeably distinguishable from those in liquids, where the molecules interact by the London dispersion forces. Both the energy of the dispersion interaction and the difference in the Kerr constants in liquid and gas phase grow with molecular size, indicating the key influence of the interaction on the magnitude of the Kerr effect. Several orientation and molecular-statistical theories of electro-optical Kerr effect were applied to model the change in electro-optical Kerr effect due to the dispersion force. Most theories show significant divergence compared to the experimental data. It is argued that the decisive contribution to electro-optical Kerr effect in liquids and the deviations between the experiment and theory arise due to local liquid structures that collectively orient in the external electric field.
EN
Applications of the electro-optical Kerr effect in physical-chemical analysis of binary mixtures are reviewed. Improvements in the experimental techniques, in particular, development of the pulsed and alternating electric field based approaches, have led to significant advances in this area. However, problems associated with the description of the internal field of liquids remain and hamper broader applications of the techniques. It is shown that a further progress in the electro-optical Kerr effect characterization of chemical systems relies on the development of a more general theory of optical properties of condensed phase chemical mixtures that can account for nonlinear effects, such as hyperpolarizability, dispersion and specific conditions of the Kerr constant measurements.
EN
The Kerr constants of pure liquid organic compounds, which exhibit weak intermolecular interactions and possess widely varying electric, optical and polarizational molecular parameters, were computed from the data on dielectrometry and electric birefringence. Good agreement of the calculated and observed values was reached as the result of the introduction of the local field model, which develops the concepts of reactive field and local electric induction of a polarized fluid, into the orientational theory of the Kerr effect.
EN
An attempt was made to modify the model Onsager theory. A polarizable molecular dipole enclosed in a spherical cavity is substituted for a rigid one submerged in the polarizable medium which fills the cavity. The local dielectric permittivity of the Heaviside type is replaced for the oscillating, rapidly damping function of the Fresnel integral. The analytical expressions deduced allow to estimate dipoles of free molecules, starting from the results of dielectrometry of polar fluids. The obtained values are as close as possible to the experimental data on a great variety of pure organic liquids.
EN
A comparative analysis of several methods of interpretation of solvent influence on molar Kerr constants of solutes was done. The analysis was based on experimentally determined electro-optical and dielectric properties of binary solutions of organic substances with various polarities, polarizabilities and optical anisotropies. It was found that the role of universal van-der-Waals interactions treated via London-Debye-Keesom potentials was best accounted for by a modified orientational theory of Kerr effect that developed the ansatz of reactive field and local dielectric permittivity. An extrapolation method of determination of gas phase molar Kerr constants of solutes was deduced from the theory.
EN
Set forth in the previous report [1], the continual theory of dipole polarization of molecular fluids, which suggests substitution of the rigid Onsager sphere for the polarizable body and takes into consideration electric induction of this body and its nearest surroundings, is extended in this paper to binary solutions with diverse polarities. Dipole moments of free molecules of dissolved substances were calculated from experimental data of dielectrometry of a large number of extremely diluted organic substances and are close to the corresponding gaseous phase values. On the ground of solution polarization measurements the criterion of physical consistency of various models of the condensed medium internal field is proposed.
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