High-density amorphous ice: nucleation of nanosized low-density amorphous ice

Abstract

The pressure dependence of the crystallization temperature of different forms of expanded high-density amorphous ice (eHDA) was scrutinized. Crystallization at pressures 0.05-0.30 GPa was followed using volumetry and powder x-ray diffraction. eHDA samples were prepared via isothermal decompression of very high-density amorphous ice at 140 K to different end pressures between 0.07-0.30 GPa (eHDA). At 0.05-0.17 GPa the crystallization line T (p) of all eHDA variants is the same. At pressures>0.17 GPa, all eHDA samples decompressed to pressures <0.20 GPa exhibit significantly lower T values than eHDA and eHDA. We rationalize our findings with the presence of nanoscaled low-density amorphous ice (LDA) seeds that nucleate in eHDA when it is decompressed to pressures <0.20 GPa at 140 K. Below ~0.17 GPa, these nanosized LDA domains are latent within the HDA matrix, exhibiting no effect on T of eHDA. Upon heating at pressures ⩾0.17 GPa, these nanosized LDA nuclei transform to ice IX nuclei. They are favored sites for crystallization and, hence, lower T . By comparing crystallization experiments of bulk LDA with the ones involving nanosized LDA we are able to estimate the Laplace pressure and radius of ~0.3-0.8 nm for the nanodomains of LDA. The nucleation of LDA in eHDA revealed here is evidence for the first-order-like nature of the HDA → LDA transition, supporting water's liquid-liquid transition scenarios.

Evidence for high-density liquid water between 0.1 and 0.3 GPa near 150 K

“…The difference in terms of the maximum pressure, at which HDL can be observed, also reflects the different timescales inherent to the different methods in the different studies. At the low-pressure end, below 0.1 GPa equilibration of the high-density liquid is likely jeopardized by the formation of low-density amorphous nanodomains, as was shown by Tonauer et al (28) and Handle et al (30)…”

“…We rationalize this bump in terms of transformations in the nanocrystalline seeds embedded in the matrix. Seidl et al (20) as well as Tonauer et al (28) have presented evidence for the formation of ice IX nuclei rather than distorted ice I h nuclei near 0.4 GPa. Depending on the ice phases crystallizing these nuclei are more or less effective in enhancing crystal growth rates, so that the bump shape appears close to pressures where the embedded nanodomains experience a transformation and the composition of the crystallizing ice polymorphs changes.…”

Glass transition of LiCl aqueous solutions confined in mesoporous silica

“…20 This route is necessary to remove seeds still present in uHDA that reduce the thermal stability. [21][22][23] Specifically, the preparation route involves high-pressure annealing (1.1 GPa) and high-temperature (140 K) decompression to relax the sample to form expanded HDA (eHDA). The higher thermal stability of eHDA allows us to reveal the existence of two glass transitions: first, the eHDA to HDL (high-density liquid) transition that takes place at around 116 K in pure water at a heating rate of 10 K/min.…”

Calorimetric study of water's two glass transitions in the presence of LiCl

“…Fig. 1 , derived from phase diagrams presented in ref. 19 and 20 , includes the metastable amorphous phases LDA, HDA and VHDA, the critical point (LLCP) and the proposed LDL and HDL regions as well as the T g lines connecting them to LDA and HDA, respectively.…”