Abstract
The anomalies of supercooled water may be explained by an underlying liquid-liquid phase transition (LLPT) between high- and low-density states. Recently, its observation at 185 K was inferred using solutions containing aqueous ionic liquids at a solute mole fraction of x=0.156 [Woutersen et al., Science 359, 1127 (2018)10.1126/science.aao7049]. We employ x-ray diffraction, calorimetry, and dilatometry on these hydrazinium trifluoroacetate solutions at x=0.00-0.40 to show that the transition at 185 K is not related to a genuine LLPT of water. Continuous densification upon compression, continuous changes of halo position, and absence of thermal signatures for a high- to low-density transition rule out the possibility of an LLPT for x≥0.13. The data show that employing sophisticated solutions adds a layer of complexity that hampers extrapolation of the LLPT concept from one- to two-component systems. The possibility of an LLPT can only be probed for pure water or sufficiently dilute aqueous solutions.
Highlights
The anomalies of supercooled water may be explained by an underlying liquid-liquid phase transition (LLPT) between high- and low-density states
The scenario involves a second critical point around 220 K below which water separates into two liquids: low-density liquid (LDL) and high-density liquid (HDL)
These liquids are encountered in their glassy states, low-density amorphous (LDA) and high-density amorphous (HDA) ice [4]
Summary
The anomalies of supercooled water may be explained by an underlying liquid-liquid phase transition (LLPT) between high- and low-density states. These liquids are encountered in their glassy states, low-density amorphous (LDA) and high-density amorphous (HDA) ice [4].
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