Nucleation and growth of crystalline ices from amorphous ices

Abstract

We here review mostly experimental and some computational work devoted to nucleation in amorphous ices. In fact, there are only a handful of studies in which nucleation and growth in amorphous ices are investigated as two separate processes. In most studies, crystallization temperatures T x or crystallization rates R JG are accessed for the combined process. Our Review deals with different amorphous ices, namely, vapor-deposited amorphous solid water (ASW) encountered in many astrophysical environments; hyperquenched glassy water (HGW) produced from μm-droplets of liquid water; and low density amorphous (LDA), high density amorphous (HDA), and very high density amorphous (VHDA) ices produced via pressure-induced amorphization of ice I or from high-pressure polymorphs. We cover the pressure range of up to about 6 GPa and the temperature range of up to 270 K, where only the presence of salts allows for the observation of amorphous ices at such high temperatures. In the case of ASW, its microporosity and very high internal surface to volume ratio are the key factors determining its crystallization kinetics. For HGW, the role of interfaces between individual glassy droplets is crucial but mostly neglected in nucleation or crystallization studies. In the case of LDA, HDA, and VHDA, parallel crystallization kinetics to different ice phases is observed, where the fraction of crystallized ices is controlled by the heating rate. A key aspect here is that in different experiments, amorphous ices of different “purities” are obtained, where “purity” here means the “absence of crystalline nuclei.” For this reason, “preseeded amorphous ice” and “nuclei-free amorphous ice” should be distinguished carefully, which has not been done properly in most studies. This makes a direct comparison of results obtained in different laboratories very hard, and even results obtained in the same laboratory are affected by very small changes in the preparation protocol. In terms of mechanism, the results are consistent with amorphous ices turning into an ultraviscous, deeply supercooled liquid prior to nucleation. However, especially in preseeded amorphous ices, crystallization from the preexisting nuclei takes place simultaneously. To separate the time scales of crystallization from the time scale of structure relaxation cleanly, the goal needs to be to produce amorphous ices free from crystalline ice nuclei. Such ices have only been produced in very few studies.

Special Topic Preface: Nucleation—Current understanding approaching 150 years after Gibbs

“…Eickhoff et al 12 study the impact of poly(vinyl alcohol) (PVA) molecular size on ice nucleation using a microfluidic setup. They show that shorter PVA chains, especially oligomers, exhibit reduced ice nucleation activity, supporting the 13 surveys experimental and some computational studies on the formation of crystalline ice from amorphous ices, including amorphous solid water, hyperquenched glassy water, and low-, high-, and very-high-density amorphous water. Complexity is shown to arise from the different degrees by which crystalline nuclei are absent from samples, affecting crystallization kinetics and making direct comparison to the results reported by different laboratories challenging.…”

Photochemistry of CH3I···(H2O)n Complexes: From CH3I···H2O to CH3I in Interaction with Water Ices and Atmospheric Implications

“…34,35 Earth's atmosphere also contains water ice, which is able to trap at its surface (ASW, I c and I h ) but also in pores (ASW), 28 a significant quantity of iodomethane. Indeed, in the case of adsorption of small molecules on amorphous ice, including methane, Roubin and co-workers 29 gave a specific area of ≈100 m 2 g −1 while Loerting and co-workers, 36 gave a specific area comprised between <0.1 to 280 m 2 g −1 . There is no comparison between a complex water/iodomethane and a solid able to offer ≈100 m 2 g −1 to adsorption, as ASW.…”

“…In our previous work on CH 3 I···(H 2 O) n complexes and aggregates trapped in argon cryogenic matrices, we observed some mixed aggregates and complexes, but the main phenomenon was the homoaggregation of CH 3 I making the association with water less favorable. , Earth’s atmosphere also contains water ice, which is able to trap at its surface (ASW, I c and I h ) but also in pores (ASW), a significant quantity of iodomethane. Indeed, in the case of adsorption of small molecules on amorphous ice, including methane, Roubin and co-workers gave a specific area of ≈100 m 2 g – 1 while Loerting and co-workers, gave a specific area comprised between <0.1 to 280 m 2 g – 1 . There is no comparison between a complex water/iodomethane and a solid able to offer ≈100 m 2 g – 1 to adsorption, as ASW.…”

Glass Polymorphism in Hyperquenched Aqueous LiCl Solutions

“…That is, we assign this exotherm to the cold-crystallization of LDA to ice I, which is well-known to occur in this temperature range. 47 …”