engleski

Light scattering in binary liquid mixtures. II. Anisotropic scattering

Anisotropic light scattering in liquid mixtures of small nonelectrolyte molecules was measured at the wavelengths 546 and 436 nm. The mixtures of cyclohexane, n-heptane and carbon tetrachloride (component 1) with benzene and carbon disulfide (component 2) were examined. The optical anisotropy terms were determined from experimental data and their concentration dependence was analysed. So was validity of the additivity principle of optical anisotropy. It has been concluded that deviation from linearity of the eUective molecular anisotropy plots indicates changes in the orientational correlations of molecules in mixtures. By analysing the excess thermodynamic functions of the same mixtures it has been concluded that such plots describe molecular interactions and their changes in dependence of concentration. Existing theoretical formulae in which orientational correlations effects have been considered, are discussed. It is emphasized that the parameters needed are concentration dependent and that explanation of their physical meaning is not possible at present. In testing methods for determining molecular anisotropies of isolated molecules based on the determination at infinite dilution it has been found that the intermolecular interactions between solute and solvent molecules, if the molecules are of comparable size, are always so strong that the anisotropy of isolated molecules cannot be determined by such methods.

light scattering ; anisotropic scattering ; binary liquid mixtures

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