Relative permittivity of dipolar liquids and their mixtures. Comparison of theory and experiment

An empirical extension, based on the Kirkwood–Fröhlich equation, of a molecular based second-order perturbation theory is proposed to calculate the relative permittivity of dipolar liquids and mixtures in terms of the molecular dipole moment, the refractive index, density and temperature. Using the resulting equation, and giving an estimation for the dipole moments of the pure components, good agreement is obtained between the theoretical and experimental results for the relative permittivity of mixtures of carbonyl compounds with aprotic liquids. We show that our extension of the Kirkwood–Fröhlich equation describes the dielectric properties of mixtures more accurately than the original equation.