Freezing of glycerol-water mixtures under pressure.

We investigated freezing of pure glycerol as well as glycerol-water (GW) mixtures with 3:1 and 3:2 volume fractions as a function of pressure in the 0-10 GPa range by ruby fluorescence spectroscopy and neutron scattering. We find that the glass transition pressure increases from 5.5 GPa for pure glycerol to 6.5 GPa for the 3:1 GW mixture, with unusually small pressure gradients above. For higher water concentrations close to 3:2, phase separation occurs above 2 GPa where most of the water is expelled in the form of ice VII. The results suggest that glycerol is able to effectively hydrogen bond not more than ≈2.5 H(2)O molecules per glycerol, which seems to support conclusions from molecular dynamics simulations. The data indicate that these fluids could become important as pressure transmitting media for neutron scattering in the 0-7 GPa range, including at low temperatures.