Dielectric behaviour of propylene glycol-water mixtures studied by time domain reflectometry

Dielectric relaxation measurements on water mixtures of propylene glycol ac ross the entire concentration range were carried out using time domain refl ectometry at 25 degreesC over the frequency range from 10 MHz to 4 GHz. For all the mixtures, only one dielectric loss peak was observed in this frequ ency range. The relaxation in these mixtures can be described by a single r elaxation time using the Debye model. A plot of the calculated relaxation t ime of the mixtures gives a straight line against the mole fraction of wate r, X-W. It is reasoned that the diameter of the water cluster is nearly the same as the length of propylene glycol. Further, a plot of the dielectric relaxation strength Delta epsilon against X-W suggests that there is a chan ging pattern of dielectric behaviour from below X-W = 0.5 to higher values of X-W. The excess permittivity, the excess inverse relaxation time and the activation free energy have been determined, to confirm the formation of h ydrogen bonded homogeneous and heterogeneous cooperative domains, the dynam ics of solute-solvent interaction and the hindrance to molecular rotation i n the hydrogen bonded glass forming propylene glycol-water system.