Dielectric Relaxation and Molecular Interactions in Acetic Acid

This article presents the results of measurements of the dielectric coefficients of acetic acid and its solutions. Measurements were carried out at wavelength λ = 40.0; 30.0; 20.0; 10.0; 6.4; 4.4; 2.1; 1.2; and in the temperature range 20 ÷ 50°C. Models of molecular clustering in liquid acetic acid were studied based on analysis of the dielectric absorption spectrum. The results of a study of the radio frequency absorption spectrum of acetic acid indicate the presence of two polymorphic forms of this compound. The characteristic temperature dependences of the dielectric constant ε' of acetic acid have been determined, from which two isothermal rotational transitions are clearly visible. The first - at the melting point - is accompanied by a sharp decrease in the number of dielectrically active units. The second, at a temperature below the melting point, leads to dielectric constant ε' values close to the high frequency (HF) limit of the total orientation contribution for microwave absorption in liquid acid. At temperatures above the first and below the second transitions, the values of the dielectric constant ε' do not depend on the frequency of the electromagnetic wave; on the contrary, pronounced dispersion is observed in the interval between two transitions.