Examination of the role of long range dipole-dipole forces on the dynamic dielectric response in liquids

摘要

To isolate the influence of long range dipole-dipole forces on dielectric relaxation (internal field effect), one seeks a system for which the microscopic response (γ, molecular dipolar auto-correlation function) is well characterized and then observes the effect on the complex dielectric permittivity (ε?) ascribable to long range dipolar interactions. Generally speaking, the theory of the internal field furnishes a relation of the form Liω(?γ) = f(εo ε?, ε∞) where the values of the parameters of γ are usually unknown in advance.1,2,3 In principle, for ellipsoidal molecules with nonvanishing dipole moment components along two or more symmetry axes or for mixtures of rigid molecules, the functional form of the microscopic response is known a priori or may be determined via measurements using nonpolar solvents. In practice, the models are over-parameterized with respect to the accuracy of permittivity and loss measurements in the appropriate frequency region (microwave) and no definitive separation of the internal field influence and the long range dipolar interaction free molecular reorientation [i. e., testing of the relation f = L(?γ)] has been described in the literature.