Liquid-liquid phase transition and dynamic properties of low-temperature water under pressure, and chemical-pressurization effects on water

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Heat capacities of the dilute aqueous solutions, with different second components, confined within silica nanopores were measured by calorimetry. The heat capacity maximum, which appeared around 233 K in pure water, developed to a clear peak with doping hydroxylamine(HA) while it disappeared with doping methanol and so on. The peak revealed characters of first-order transitions, and the transition temperature increased with increase in the HA composition x and decreased with pressurization. Simultaneously the transition peak area in the thermal analysis of a 5 wt% HA solution decreased with pressurization. Based on these results, we proposed a new model of p-T-x phase diagram in which HA doping provides an effect of negative pressurization on water and a liquid-liquid phase transition line and a critical point as the line terminal exist in a negative pressure range.