Spectroscopy approach challenges views that water droplets are static in cryogenic conditions

Amorphous, noncrystalline ice is crucial to the cryopreservation of biological samples such as sperm cells, tissue, small organs, and proteins. It is also crucial for imaging: Cryo-electron microscopy relies on vitrification, in which aqueous samples are cooled without causing damage from ice crystals. However, relatively little is known about the ultrastructure of such vitrified, glassy water samples and how this structure develops.

Giebelmann et al. characterized the ultrastructural dynamics of glassy water droplets coalescing at the micro- and mesoscale. Using X-ray photon correlation spectroscopy, they observed the changes as droplets were subjected to a series of heating and cooling and reheating, studying how they coalesced, underwent glass transition, and eventually crystallized into ice.

Many researchers assumed that water droplets are static in cryogenic conditions, but the group found this not to be the case.

“There are many controversial studies evolving around the glass transition and the possible existence of deeply supercooled liquid water below the cold-crystallization temperature of 156 K,” said author Thomas Loerting. “Often, indirect probes of the structural dynamics, such as calorimetry or spectroscopy, were employed in literature and interpreted ambiguously. Here we use a method that directly probes translational motion, leaving little room for interpretation.”

When the researchers examined the interfaces between thousands of micron-sized vitrified droplets, they found that coalescence itself does not need bulk diffusion to progress at 125 K, but significant diffusive dynamics are present after coalescence at 145 K, consistent with the formation of a deeply supercooled liquid. Between 130 and 145 K, they observed ballistic motion in addition to significant diffusive dynamics.

The group next looks to examine the impact of solutes on such phenomena.

Source: “Dynamics of coalescence in hyperquenched glassy water probed by x-rays,” by Johannes Giebelmann, Tobias Eklund, Christina M. Tonauer, Lilli-Ruth Fidler, Louisa E. Kraft, Isabell Zick, Niels C. Giesselmann, Fiona Berner, Leah Schwerdtfeger, Randeer Gautam, Robert P. C. Bauer, Alexander Gierke, Fabian Westermeier, Felix Lehmkühler, Katrin Amann-Winkel, and Thomas Loerting, Journal of Chemical Physics (2026). The article can be accessed at https://doi.org/10.1063/5.0325404 .