The dielectric properties of alcohols–water solutions. I. The alcohol rich region

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Abstract
We present here the first results of a systematic study of the dielectric properties of alcohols–water solutions. The complex dielectric constant ε̃=ε′−iε′′ and the dielectric relaxation time τ of MeOH, EtOH, 2-PrOH alcohols, and their aqueous solutions are reported for some values of the water mole fraction xw in the range 0≤xw≤0.5, at various temperatures (from 30 °C down to −43 °C for MeOH and its solutions). τ has been measured by a two coaxial resonators spectrometer in a significant frequency range for the principal relaxation region of these liquids (0.47–4 GHz). Measurements of ε′ at 13 MHz with a different experimental apparatus have also been made. Our data do not confirm previous determinations of τ vs xw at 30 °C. In all the investigated temperature range, τ is a decreasing monotone function of xw for the aqueous solutions of EtOH and 2-PrOH. On the contrary, the dielectric relaxation time of MeOH aqueous solution is practically constant up to xw=0.1 at 30 °C; at 0° and −25 °C, τ increases at the beginning and a maximum is present; at lower temperature, τ increases with xw. The observed behavior of τ is discussed and a model for the dielectric relaxation in H-bond associated liquids is suggested.