Dielectric relaxation of H-bonded liquids.: Mixtures of ethanol and n-hexanol at different compositions and temperatures

At different temperatures T (0 degrees C less than or equal to T less than or equal to 60 degrees C) and mole fractions x of ethanol (0 less than or equal to x less than or equal to 1) the complex (electric) permittivity of ethanol/n-hexanol mixtures has been measured as a function of frequency nu 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 tau(1) = 63 ps (x = 1; 60 degrees C) and tau(1) = 2.8 ns (x = 0; 0 degrees C). The relaxation time tau(2) of the second process is smaller (5 ps less than or equal to tau(2) less than or equal to 109 ps). The extrapolated static permittivity is an element of(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.