Relaxation processes of the structural rearrangement of clusters in liquids: 1,2-ethanediol, 1,2-propanediol, and 1,2,6-hexanetriol

Abstract

The dielectric relaxation spectra (DRS) of 1,2-ethanediol, 1,2-propanediol, and 1,2,6-gexanetriol are analyzed in terms of the Dissado-Hill (DH) model in a wide range of temperatures, with all parameters required for calculating the cluster dipole moments being determined within the DH molecular model itself. The dependence of the equilibrium and relaxation properties of DRS on the hydrocarbon radical length and the number of OH groups is studied. The dipole moments of the clusters are calculated. It is shown how the roles of the processes of intracluster rearrangement are redistributed due to the break of hydrogen bonds and fluctuation processes of synchronous exchange of molecules between the clusters.Dielectric spectroscopy studies both the equilibrium and kinetic (relaxation) properties of substances [1,2]. In liquid diols and triols above their glass transition temperatures T g , three-dimensional network structures (clusters) are present, which are formed by intra-and intermolecular hydrogen Н bonds. At each temperature, there is a size and shape distribution of clusters, to which the mean statistical square of the cluster dipole moment 2 c 〈μ 〉 corresponds.An analysis of static dielectric permittivities ε s within Onsager-Kirkwood-Frölich (OKF) theory allows us to estimate the mean statistical dipole moments of molecules μ m [1, 2]. A comparison of μ m values with the dipole moments of molecules in the gas phase μ v provides qualitative information on the preferred orientation of molecules in diol and triol clusters [3-9]. Molecular modeling makes it possible to construct the spatial models of clusters and their concentration distribution, but there is no theory linking the calculations with the dielectric properties, as in the case of monohydric alcohols (alkanols) (see, for example, [10]).Dissado-Hill (DH) theory [11][12][13][14][15][16] enables the calculation of cluster dipole moments μ c for diols and triols, however without detailing the cluster structure. This requires the experimental data on the relaxation dielectric properties of liquids, such as dispersion amplitudes and relaxation times. The DH model for the description of macroscopic experimental dielectric spectra ε(ω) = ε′(ω) + ε″(ω), where ε′(ω) and ε″(ω) are the dielectric permittivities and losses, has two correlation parameters of the processes of structural rearrangement of the clusters, as opposed to the Havriliak-Negami (HN) equation [17]. In [16,18], the formulas relating the parameters of the HN and DH equations are presented. Moreover, the DH model contains two equations relating the relaxation time and the dispersion amplitude with the energy characteristics of the processes of microstructural rearrangement and the average cluster dipole moment μ c .

Dielectric properties of benzylamine in 1,2,6-hexanetriol mixture using time domain reflectometry technique

“…0m and " 1m are the static dielectric constant and dielectric constant at high frequency of the mixtures. To calculate the values of g eff , we have taken ¼ 1:38 and 2.73 D 29 for benzylamine and 1,2,6-hexanetriol, respectively. 30 The Kirkwood correlation factor g eff for benzylamine-1,2,6-hexanetriol mixtures at different volume fractions of 1,2,6-hexanetriols are shown in Table 2.…”