Phase Behavior of the Supercooled Aqueous Solutions of Dimethyl Sulfoxide, Ethylene Glycol, and Methanol As Seen by Dielectric Spectroscopy

Abstract

The dielectric behavior of the supercooled aqueous solutions of dimethyl sulfoxide (DMSO), ethylene glycol (EG), and methanol (MeOH) has been examined in the frequency range 106−10-3 Hz and in the xm range of 0.19−0.40, 0.25−0.85, and 0.50−0.85, respectively, where xm is the mole fraction of the second component. Differential scanning calorimetric measurements have also been carried out on the samples. At temperatures above the glass transition temperature (Tg), it was found that the Hevriliak−Negami relaxation function is appropriate to describe the data. The “apparent” distribution in relaxation times increases with increasing water content and also on lowering the temperature. But at temperatures just above Tg, an Arrhenius branch of considerable polarization and with an activation energy of ∼21.5 kJ/mol separates out to continue to the sub-Tg region, which more or less disappears around xm = 0.33 in DMSO solutions and around xm = 0.50 in EG solutions. It is suggested that the complexes of 2:1 (in DMSO solutions) and 1:1 (in EG solutions) are present in the liquid that are thermolabile and exist in an undissociated state only near Tg, and the sub-Tg process is due to the relaxation of water molecules. No evidence of complex formation is found in MeOH solutions.