Microwave dielectric properties of binary solvent wateralcohol, alcohol-alcohol mixtures at temperatures between -35°C and +35°C and dielectric relaxation studies

Abstract

In this work, our objective was to study the complex permittivity of binary mixtures of water-ethanol, water-methanol and methanol-ethanol with various mole fractions at temperature between -35 and 35 °C.
Measurements were made in the frequency domain from 300 kHz to 1.3 GHz by means of an open ended coaxial line technique coupled to a network analyzer. Water-ethanol and water-methanol mixtures display a Kraszewski Law while methanol-ethanol mixture shows a Shivola-Kong Law. The static dielectric constant, εs were obtained from the plateau of ε'(ω) curve, in water rich mixture or alcohol rich mixture has similar real permittivity ε' of pure liquids. The values of εs mixtures increase by decreasing the temperature assigned to the cooperative dynamics H-bond system in mediums. The validity of permittivity measurements according to the temperature are verified by the Queen-King Law and the j (0ï‚£ jï‚£2) A constants are compared with literature data. The dielectric relaxation behaviour of water-ethanol mixture can be better described with a Cole-Davidson function while for methanol-ethanol one, a Debye function gives a good fit. At 25 °C, the relaxation time ï´ in the aqueous mixtures of ethanol and methanol sharply increased with increasing alcohol concentration.