Complex permittivity spectra of binary pyridine-amide mixtures using time-domain reflectometry

Frequency spectra of the complex permittivity for pyridine--amide binary mi xtures have been determined over the frequency range 10 MHz to 10 GHz, at 5 , 15, 25, and 40 degrees C, using the time-domain reflectometry method, for 11 compositions of each pyridine-amide system, e.g., formamide, N-methylfo rmamide, and N,N-dimethylformamide. The relaxation in these systems can be described by a single relaxation time using the Debye model. The static die lectric constant, relaxation time, the corresponding excess dielectric prop erties, Kirkwood correlation factor, and molar activation energy of the mix tures have been determined. The excess permittivity is found to be positive in the amide-rich region and negative in the pyridine-rich region. The exc ess inverse relaxation time is negative, except in the pyridine-rich region . The static dielectric constants for the mixtures have been fitted with th e modified Bruggeman model. The temperature-dependent relaxation times show the expected Arrhenius behavior.