DIELECTRIC PROPERTY AND MICROSTRUCTURE OF WATER-ALCOHOL SOLUTIONS

A simple method for measuring dielectric properties of water-alcohol s olutions for structural studies was proposed. The apparatus consists o f three components: RF-generator, resonator with parallel planar elect rodes, and detector. The resonators composed of a coaxial line and a c ouple of electrodes, generates characteristic resonance frequencies (f (R)) related to the relative dielectricity of the sample. Shifts of f( R) with change of temperature, alcohol concentration and the kind of a lcohol have been measured for water-alcohol binary solutions. The valu e of f(R) was found to be proportional to the ethanol molar fraction ( x(E)) at x(E)'s more than 0.15, but remained constant at lower concent rations. This suggests that the structure of a binary solution changes at this concentration and the relative dielectric permittivity of the system is no longer affected by more alcohol added. This characterist ic concentration agrees well with that obtained by the TDR method, as well as that by mass spectrometric measurements. From the measurements for alcohol-alcohol mixtures, a discontinuity of f(R) was found at a certain temperature for 1:1 methanol-2-propanol mixture.