Far infrared and dielectric relaxation spectra in supercooled water and water + propylene glycol solutions

We report the first measurements of far IR absorption in supercooled water, and extend the temperature range of study of the most interesting feature, an H-bond stretching mode at ∼200cm^-1, to -85°C by incorporation of propylene glycol, PG, as solute. Low frequency dielectric relaxation measurements on a series of glass-forming PG + water solutions spanning the range 30 - 100% PG when fitted to the Vogel-Tammann-Fulcher equation suggest this resonance absorption mode may be the attempt frequency for the relaxation process. Comparison of the strengths of the two dissipation regions in the same (absorptivity α) units shows dielectric relaxation as a weak shoulder sliding, with changing temperature, on the α =kf^γ edge of the quasi-resonant absorption band. For most compositions, the dielectric loss spectrum is only weakly dependent on temperature, but as the composition approaches the edge of the glass-forming region, the spectral widths become strongly temperature-dependent due, evidently, to a clustering phenomenon which results finally in an (unexpected) liquid-liquid phase separation.