PNNL

The Science

Ice is everywhere, but its full structure at the atomic level has remained challenging to determine. Researchers obtained the first images of ice crystallized from liquid water with atomic resolution. This required developing a new electron microscopy approach, called cryogenic liquid-cell transmission electron microscopy (CRYOLIC-TEM), to stabilize the ice crystals under the electron beam. Combining their microscopy data with simulations, the team found that ice formation is highly tolerant to nanoscale defects, including trapped gas bubbles. These gas bubbles are stabilized by the ice crystal and can form, grow, and change inside still-crystalline ice.

The Impact

Ice plays a key role in applications as varied as airplane safety and food preservation. The edges of ice can have defects, even while the crystal looks complete. By imaging ice crystals, researchers identified that ice can tolerate a range of defects and gas bubbles while remaining crystalline at a higher level. These atomic-level insights can help researchers better understand the role of ice in the air, biological systems, and materials. Additionally, the atomic precision of the measurements allows for comparison with molecular simulations and opens the door to understanding how the unusual nature of intermolecular bonding in ice controls the crystallization pathway.

Summary

When water freezes into ice crystals, the crystal edges can be highly defective despite appearing like a single crystal. Researchers discovered that ice has a high tolerance for defects both at the edges and internally due to flexible hydrogen bond networks. These networks lead to a diminishment of the typical energy penalties for forming various structural configurations. Trapped gas bubbles are particularly common defects, they form as dissolved air precipitates in water. For the first time, researchers directly observed how the internal bubble surfaces are structured using CRYOLIC-TEM, which they developed. These bubble surfaces are faceted on the atomic level with specific nanoscale plateaus and steps, a thermodynamically favored structure. Unlike hard materials, the nanobubbles/holes in the ice induce minimal strain fields to the crystal, increasing their stability. Using the electron beam to image and energetically excite the crystals, the researchers controllably generated new gas bubbles in the ice by splitting water into hydrogen and oxygen gases. They observed the nucleation, growth, migration, dissolution, and merging of these nanobubbles in real time while the ice remained solid.

Contact

Jim De Yoreo, Pacific Northwest National Laboratory, James.DeYoreo@pnnl.gov 

Jingshan Du, Pacific Northwest National Laboratory, jingshan.du@pnnl.gov 

Funding

Microscopy and analysis were supported by the Department of Energy (DOE) Office of Science (SC) Basic Energy Sciences (BES) Division of Materials Science and Engineering, Synthesis and Processing Sciences program (FWP 67554) at PNNL (J.J.D.Y.). Molecular dynamics simulations were supported by the Data, Artificial Intelligence, and Machine Learning at Scientific User Facilities program under the Digital Twin Project at Argonne National Laboratory (S.K.R.S.S.). Development of ice encapsulation and imaging methodology was supported by a DOE SC Distinguished Scientist Fellows award (FWP 77246) at PNNL (J.J.D.Y.). A portion of this research was performed on project awards (60286, 60620, and 60789) from the Environmental Molecular Sciences Laboratory at PNNL (J.S.D. and J.J.D.Y.). Work at the Molecular Foundry and the National Energy Research Scientific Computing Center was supported by the DOE SC BES under Contract No. DE-AC02-05CH11231. Work at the Center for Nanoscale Materials was supported by the DOE SC BES under Contract No. DE-AC02-06CH11357. J.S.D. acknowledges a Washington Research Foundation Postdoctoral Fellowship. PNNL is a multiprogram national laboratory operated for the DOE by Battelle under Contract DE-AC05-76RL01830.