Phase separation during freezing upon warming of aqueous solutions.

Using differential scanning calorimetry, we show that the addition of solute(s) to emulsified water lowers the freezing temperature to <231 K, the homogeneous nucleation temperature of pure bulk water, or even completely suppresses freezing. In the latter case, freezing upon warming occurs above T(X) ≈ 150 K and leads to a phase separation into pure ice and a freeze-concentrated solution (FCS) which crystallizes upon further warming. We also show that emulsified 20-21.5 wt. % HCl solutions and the FCS of HCl/H2O solutions transform to glass at T(g) ≈ 127-128 K, i.e., lower than T(g) ≈ 136 K of water. We suggest that water nanodrops adsorbed on fumed silica resemble bulk water more than water confined in nanoscaled confinement and also more than nanoscaled water domains in aqueous solution.