RELATIVE PERMITTIVITY AND DIELECTRIC-RELAXATION IN AQUEOUS ALCOHOL-SOLUTIONS

In this work, our objective was to study the hydrogen bonding of alcoh ols in aqueous solutions and alcohol dipole relaxation by measuring th e complex permittivity. Alcohols chosen for study were methanol, ethan ol and propanol over the full composition range and from 297-363 K. Me asurements were made with a frequency domain technique from 100 MHZ to 20 GHz. All of the alcohol-water mixtures studied had a negative exce ss permittivity that was skewed towards higher water mole fractions. T he composition dependence of the dielectric relaxation showed remarkab le behavior. At water concentrations of x(water) < 0.2 there was littl e change in the alcohol relaxation time constant, whereas at x(water) > 0.85 or so, the relaxation time had a sharp slope. Our data show tha t there is a distinct curvature between the pure component time consta nts, which indicates a gradual, nonlinear change of the relaxation tim e with composition. From the dielectric data, it would seem that there are three subtle but distinct regions of hydrogen-bonding environment s. (C) 1998 Elsevier Science B.V.