Vitrification and increase of basicity in between ice Ih crystals in rapidly frozen dilute NaCl aqueous solutions

Abstract

The freezing of ionic aqueous solutions is common in both nature and human-conducted cryopreservation. The cooling rate and the dimensions constraining the solution are known to fundamentally influence the physicochemical characteristics of the sample, including the extent of vitrification, morphology, and distribution of ions. The presence of some salts in an aqueous solution often suppresses the ice crystallization, allowing bulk vitrification during relatively slow cooling. Such a process, however, does not occur in NaCl solutions, previously observed to vitrify only under hyperquenching and/or in sub-micrometric confinements. This work demonstrates that, at freezing rates of ≥100 K min −1 , crystallized ice I h expels the freeze-concentrated solution onto the surfaces of the crystals, forming lamellae and veins to produce glass, besides eutectic crystallization. The vitrification covers (6.8% ± 0.6%) and (17.9% ± 1.5%) of the total eutectic content in 0.06M and 3.4 mM solutions, respectively. The vitrified solution shows a glass-to-liquid transition succeeded by cold crystallization of NaCl ⋅ 2H 2 O during heating via differential scanning calorimetry. We establish that ice crystallization is accompanied by increased basicity in freeze-concentrated solutions, reflecting preferential incorporation of chloride anions over sodium cations into the ice. After the sample is heated above the glass transition temperature, the acidity gradually returns towards the original value. The morphology of the samples is visualized with an environmental scanning electron microscope. Generally, the method of vitrifying the freeze-concentrated solution in between the ice I h crystals via fast cooling can be considered a facile route towards information on vitrified solutions.

Partitioning of Crystalline and Amorphous Phases During Freezing of Simulated Enceladus Ocean Fluids

“…%) can rapidly become prohibitive for further crystallization, as solutes are both highly concentrated and confined into ice grain boundaries. Similar partial vitrification behavior has been observed following brine vein supercooling in dilute Na-Cl solutions at cooling rates far below those required to vitrify the bulk solution (Imrichová et al, 2019).…”

“…These latter textures reflect the rapidity at which the system solidified, with crystal growth of different phases occurring simultaneously and/or in fixed positions, rather than in a sequence that allows for partitioning and aggregation of crystal suspensions. Crystal growth upon warming of a supercooled or vitrified fluid can progress directly from glass (similar to the formation of spherulites from glass in silicate igneous systems; Watkins et al., 2009) or from a metastable supercooled brine (Imrichová et al., 2019). Either process requires nucleation cores for crystal growth, hence we consider the rapid formation and incorporation of micro‐crystals and/or silica nanoparticles into brine veins during flash‐freezing as likely, where they can template later crystal growth when increased temperatures permit.…”

“…Rapid cooling however is not the only pathway to vitrification; confinement of fluid in microporous spaces can also inhibit crystallization (Gallo et al., 2016). Other studies have noted that with certain solute compositions and/or supersaturation during confinement, vitrification can occur without the need for excessively rapid cooling rates (Imrichová et al., 2019; Toner et al., 2014). Correspondingly, our results show that when fluid is confined into restrictive brine veins, crystallization is avoided, even at gradual cooling rates of 0.01 K s –1 , down to 172.98 K (Figure 2b), which is below the temperature of the surface of the tiger stripes (∼197 K; Goguen et al., 2013).…”

“…This may allow partial vitrification to occur at slower cooling rates than those required to vitrify FOX-POWELL AND COUSINS 10.1029/2020JE006628 bulk solutions, leading to products comprising both crystalline and amorphous phases. For example, vitrification of freeze-concentrated solutions between ice crystals has been demonstrated experimentally in dilute Na + /Cl − brines at cooling rates of 10 1 -10 2 K s −1 (Imrichová et al, 2019).…”

ESEM Methodology for the Study of Ice Samples at Environmentally Relevant Subzero Temperatures: “Subzero ESEM”

“…Since the dissolved ions and molecules are expelled from hexagonal ice (I h ) by freezing under environmentally relevant conditions and are concentrated between the I h grains into the freeze-concentrated solution (FCS) trapped in the thin grain boundaries (veins) (Petrenko & Whitworth, 1999;Imrichova et al, 2019), we consider the sample as pure I h for setting the parameters for thermodynamic equilibrium in the specimen chamber.…”