Direct observation of the reversible liquid-liquid transition in an aqueous solution of trehalose
Recent studies on liquid water suggest that both liquid waters exist in the supercooled temperature region and their existence is related to the abnormal behavior of liquid water at low temperature such as maximum density at 4°C. However, the experimental study of two liquid waters is difficult due to rapid crystallization. In this study, a reversible liquid-liquid transition in an aqueous solution of trehalose by the pressure change was observed directly. This result strongly suggests that two liquid waters exist in the aqueous solution. This study has implications for broad fields related to liquid water, such as solution chemistry, cryobiology, meteorology and food engineering.
The water forms two glassy, amorphous waters of low density and high density, which undergo a reversible polyamorphic transition with the change in pressure. The two glassy waters change into different liquids, low-density liquid (LDL) and high-density liquid (HDL), at high temperatures. Both liquid waters are predicted to also undergo a liquid-liquid transition (LLT). However, reversible LLT, especially the LDL-HDL transition, has not been observed directly due to rapid crystallization. Here, I prepared an aqueous solution of vitreous dilute trehalose (mole fraction 0.020) without segregation and measured the isothermal volume change at 0.01 to 1.00 GPa below 160 K. The polyamorphic transition and the glass transition -liquid for high density and low -density solutions were examined and the liquid region where both LDL and HDL existed was determined. The results show that the reversible polyamorphic transition induced by the pressure change above 140 K is the LLT. That is, the transition from LDL to HDL is observed. Moreover, the pressure hysteresis of LLT strongly suggests that LLT has a first-order nature. Direct observation of reversible LLT in aqueous trehalose solution has implications for understanding not only the liquid-liquid critical point hypothesis of pure water, but also the relationship between aqueous solution and water polyamorphism. .
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