Dielectric Relaxation of H-Bonded Liquids. Mixtures of Ethanol and n-Hexanol at Different Compositions and Temperatures

Abstract

At different temperatures T (0 °C ≤ T ≤ 60 °C) and mole fractions x of ethanol (0 ≤ x ≤ 1) the complex (electric) permittivity of ethanol/n-hexanol mixtures has been measured as a function of frequency ν between 1 MHz and 18 GHz. Within this frequency range of measurement the dielectric spectra reveal two relaxation regions. The relaxation time of the dominating relaxation process varies between τ1 = 63 ps (x = 1; 60 °C) and τ1 = 2.8 ns (x = 0; 0 °C). The relaxation time τ2 of the second process is smaller (5 ps ≤ τ2 ≤ 109 ps). The extrapolated static permittivity ε(0) of the alcohol systems is evaluated to show that there is a noticeable effect of permanent electric dipole orientation correlation. The relaxation terms are discussed in the light of hydrogen bond fluctuations and modes of reorientational motions of alcohol molecules. A remarkable result is the finding that the activation enthalpy associated with the dominating relaxation process can be represented by a sum of contributions from interactions between the hydrogen bonding OH-groups and between the methylene as well as methyl groups of the alcohol molecules. This finding suggests intermolecular interactions between the aliphatic groups to play a siginificant role in the dynamics of the molecular reorientations.