DIELECTRIC-PROPERTIES OF ALKANEDIOL WATER MIXTURES/

At 25 degrees C the complex dielectric permittivity has been measured as a function of frequency v (1 MHz less than or equal to v less than or equal to 56 GHz) and mole fraction x (0 less than or equal to x les s than or equal to 1) for mixtures of water with 1,3-propanediol, 1,4- butanediol, 1,5-pentanediol, and 1,7-heptanediol. Some parameters like the (extrapolated) static permittivity and the characteristic relaxat ion time can be directly taken from the spectra. But the spectra can b e also analytically represented by semiempirical relaxation spectral f unctions. A function containing two relaxation terms, a high-frequency Cole-Cole term and a Debye term with smaller relaxation frequency, ap pears to be appropriate. The relaxation parameters of the water/diol m ixtures have been evaluated and compared to other water/organic solven t systems to show that (i) a high degree of permanent electric dipole orientation correlation exists in the diols that is significantly redu ced on addition of water, (ii) the characteristic relaxation time refl ects a substantial effect of entropy in the mechanism of dielectric re laxation but exhibits also a significant difference from monohydric al cohol/water systems, and (iii) the subdivision of the spectra into two relaxation terms seems to be due to regions of different concentratio n of hydrogen-bending sites within the mixtures.