Dielectric relaxation and molecular dynamics in poly(vinyl pyrrolidone)–ethyl alcohol mixtures in pure liquid state and in non-polar solvent

Abstract

Dielectric relaxation and molecular dynamics in poly(vinyl pyrrolidone)–ethyl alcohol (PVP–E) mixtures with varying concentration in pure state and also in very dilute solutions of benzene were studied for their molecular conformation at 35 °C. Dielectric permittivity ε′ and dielectric loss ε″ of PVP–E mixtures were measured by a time domain reflectometry technique in the frequency range 10 MHz to 10 GHz. The value of static dielectric constant ε 0, dielectric relaxation time τ, and dielectric free energy of activation Δ F τ has been evaluated by fitting the complex dielectric data into Debye equation. The variation in ε 0 was discussed by considering the volume effect and the structuring effects of the PVP on ethyl alcohol molecules. The formation of cooperative domains between PVP and ethyl alcohol molecules, CD PVP–E and between the ethyl alcohol–ethyl alcohol molecules CD E and their dynamics in the PVP–E mixtures were explored by using the evaluated values of τ and Δ F τ . The PVP–E mixtures of low PVP concentration were also studied in very dilute solutions of benzene at 10.1 GHz. The value of average relaxation time τ 0, distribution parameter α, and relaxation time corresponding to the motion of small multimer species of alcohol molecules τ 1 and group rotation τ 2 has been determined. It has been observed that in dilute solution of benzene the value of τ 0 and τ 1 increases with the increase in concentration of PVP in PVP–E mixture but the τ 2 value is found independent of the mixture constituent concentration. The entanglement of the CD PVP–E and the increase in the length of CD E in dilute solution of benzene due to dissociation of the complexes between carbonyl and hydroxyl groups has been explored. The value of τ 2 is assigned to the rotation of –OH group about C–O bond in the ethyl alcohol species in dynamic equilibrium with larger steric hindrance due to hydrogen bonding.