Non-segregated crystalline state of dilute glycerol aqueous solution

Interplay of vitrification and ice formation in a cryoprotectant aqueous solution at low temperature

The proneness of water to crystallize is a major obstacle to understanding its putative exotic behavior in the supercooled state. It also represents a strong practical limitation to cryopreservation of biological systems. Adding some concentration of glycerol, which has a cryoprotective effect preventing, to some degree, water crystallization, has been proposed as a possible way out, provided the concentration is small enough for water to retain some of its bulk character and/or for limiting the damage caused by glycerol on living organisms. Contrary to previous expectations, we show that, in the “marginal” glycerol molar concentration ≈ 18%, at which vitrification is possible with no crystallization on rapid cooling, water crystallizes upon isothermal annealing even below the calorimetric glass transition of the solution. Through a time-resolved polarized neutron scattering investigation, we extract key parameters, size and shape of the ice crystallites, fraction of water that crystallizes, and crystallization time, which are important for cryoprotection, as a function of the annealing temperature. We also characterize the nature of the out-of-equilibrium liquid phases that are present at low temperature, providing more arguments against the presence of an isocompositional liquid–liquid transition. Finally, we propose a rule of thumb to estimate the lower temperature limit below which water crystallization does not occur in aqueous solutions.

Direct observation of reversible liquid-liquid transition in a trehalose aqueous solution

Recent studies on liquid water suggest that the two liquid waters exist in the supercooled temperature region and that their existence relates to the anomalous behavior of low-temperature liquid water such as the maximum density at 4 °C. However, the experimental investigation of two liquid waters is difficult because of the rapid crystallization. In this study, a reversible liquid–liquid transition in a trehalose aqueous solution by the change in pressure was observed directly. This result suggests strongly that two liquid waters exist in the aqueous solution. This study has implications for wide fields related to liquid water, such as solution chemistry, cryobiology, meteorology, and food engineering.

Water forms two glassy waters, low-density and high-density amorphs, which undergo a reversible polyamorphic transition with the change in pressure. The two glassy waters transform into the different liquids, low-density liquid (LDL) and high-density liquid (HDL), at high temperatures. It is predicted that the two liquid waters also undergo a liquid–liquid transition (LLT). However, the reversible LLT, particularly the LDL-to-HDL transition, has not been observed directly due to rapid crystallization. Here, I prepared a glassy dilute trehalose aqueous solution (0.020 molar fraction) without segregation and measured the isothermal volume change at 0.01 to 1.00 GPa below 160 K. The polyamorphic transition and the glass-to-liquid transition for the 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 suggests strongly that the LLT has a first-order nature. The direct observation of the reversible LLT in the trehalose aqueous solution has implications for understanding not only the liquid–liquid critical point hypothesis of pure water but also the relation between aqueous solution and water polyamorphism.

Transformation process of ice crystallized from a glassy dilute trehalose aqueous solution

Crystal growth of ice Isd occurring after crystallization of a glassy dilute trehalose aqueous solution is slower than that of ice Isd in a dilute glycerol solution and pure ice Isd, and ice Isd in trehalose aqueous solution survives to ∼230 K.

Slow Crystal Growth of Cubic Ice with Stacking Faults in a Glassy Dilute Glycerol Aqueous Solution

Control of ice formation is an important issue as catastrophic ice growth influences our life activities and many industrial systems. We prepared a homogeneous glass of a dilute glycerol aqueous solution by a pressure liquid cooling vitrification method and examined the effect of solute on the ice formation of solvent water using a powder X-ray diffraction method. The solvent water immediately after the crystallization is composed of nanosized pure cubic ice (ice Ic). The crystal growth of ice Ic with stacking faults is much slower than that of pure water. The presence of glycerol molecules dispersing homogeneously may hinder crystal growth. The macroscopic segregation occurs rapidly during the transformation from stacking disordered ice to hexagonal ice. The results suggest that ice formation can be controlled by changing the solute type and concentration. This study has implications for thawing technology in cryobiology and frozen food engineering.