Studies on the effect of temperature on dielectric relaxation, activation energy (ΔG*), enthalpy (ΔH*), entropy (ΔS*) and molecular interactions of some anilines, phenol and their binary mixtures using X-band microwave bench

Abstract In the present study, the variation of dielectric relaxation time (τ) with temperature is carried out on four polar molecules viz., 2-Nitroaniline, 4-Bromoaniline, 4-Chloroaniline and 4-Chlorophenol and also on the binary mixtures (1:1) viz., (2-Nitroaniline + 4-Bromoaniline) and (4-Chloroaniline + 4-Chlorophenol) in benzene and results are analysed using Whiffen and Thompson model in order to understand the nature of the relaxation process involved. Microwave bench operating at a frequency of 9.59 GHz is used for this purpose. It is observed that, relaxation time (τ) decreases with increase in temperature for all the systems studied and the results are in agreement with Debye’s theory. The linearity in the log (τT) versus 1/T plots for all the cases indicates that, relaxation process can be treated as rate process according to Eyring’s theory. Further, thermodynamic parameters like change in activation energy (ΔG*), enthalpy of activation (ΔH*) and entropy of activation (ΔS*) have been determined for all the cases. It is observed that, values of ΔH* are higher than the values of ΔG*, thus leading to the positive values of ΔS*. The positive values of ΔS* indicates that, the environment of the system is non-cooperative for the activated process and the activated state is less stable and disordered than the normal state for all the cases studied. The molecular radii estimated from SED theory, Edward’s atomic increment method and from DFT computations using Gaussian 09W are found to be in good agreement with each other and suggest that, the molecular dynamics follows SED theory.