Within the enigmatic realm of physics, one need not look further than an ordinary ice cube to encounter mysteries that captivate scientific curiosity. The familiar phenomenon of ice melting at room temperature is just the tip of the iceberg. Even in frigid temperatures far below freezing, ice undergoes imperceptible shifts that continue to baffle scientists. Researchers, armed with cutting-edge imaging tools at the U.S. Department of Energy’s Argonne National Laboratory, have unraveled a phenomenon called premelting, occurring at temperatures significantly lower than previously recorded.
Published in the journal Proceedings of the National Academy of Sciences, their findings shed light on the intriguing world of premelting—a phenomenon responsible for the slipperiness of an icy patch on an otherwise clear and cold day. Michael Faraday first proposed the notion of a premelted, liquid-like layer on ice in the mid-1800s. The revelation of a liquid layer atop frozen ice introduces a cascade of questions about the fundamental transformations of water, oscillating between liquid, solid, and vapor states. Under certain conditions, water can even exhibit characteristics of all three states simultaneously, prompting further exploration into the complex interplay of physical states at the molecular level.
In the recent investigation, researchers delved into the behavior of ice crystals formed at temperatures plummeting below minus 200 degrees Fahrenheit. Utilizing the capabilities of Argonne’s Center for Nanoscale Materials (CNM), a Department of Energy (DOE) Office of Science user facility, the team cultivated and scrutinized minuscule ice nanocrystals, measuring a mere 10 millionths of a meter across.
This study not only offers insights into the intricate nature of water at subfreezing temperatures but also showcases a groundbreaking method for examining delicate samples at the molecular level. The researchers employed low-dose, high-resolution transmission electron microscopy (TEM), a technique that directs a stream of subatomic particles known as electrons toward an object. The resulting image is formed by capturing how the electrons scatter off the object, providing a detailed molecular perspective. This innovative approach not only advances our comprehension of subfreezing water dynamics but also paves the way for enhanced molecular investigations across diverse scientific domains.
Jianguo Wen, a materials scientist at Argonne and a lead author of the study, highlighted the challenges posed by beam-sensitive materials, emphasizing that electron beams used for imaging can alter or even destroy them. An illustrative example is electrolytes, crucial components in batteries that exchange charged particles. The ability to study such materials in intricate detail without compromising their structure holds significant potential for advancing battery development.
Initially, the researchers are applying the low-dose TEM technique to investigate frozen water. Beyond its affordability and abundance, water serves as an ideal starting point for honing the methodology. Wen noted the inherent difficulty in imaging ice due to its instability under high-energy electron beams. Success in employing this technique on ice sets the stage for effortlessly imaging other beam-sensitive materials.
The low-dose technique involves the integration of Argonne’s aberration-corrected TEM with a specialized direct electron detection camera. This system excels at efficiently capturing information from each electron interacting with a sample, enabling high-resolution imaging with minimal electron exposure. This innovative approach not only minimizes damage to the target, particularly beneficial for sensitive materials like electrolytes, but also opens avenues for broader applications in materials science research and development.
The minimal electron exposure facilitated by the low-dose technique enables the capture of delicate structures like ice crystals in situ, providing a window into their natural environment. In this study, the research team utilized liquid nitrogen to cultivate ice crystals on carbon nanotubes at an ultra-low temperature of 130 degrees Kelvin, equivalent to minus 226 degrees Fahrenheit.
Previous research had primarily focused on observing premelting near water’s triple point, where ice, liquid, and water vapor coexist. This point occurs at a temperature just above freezing and under low pressure conditions. At temperatures and pressures below the triple point, ice sublimates directly into water vapor.
While the conventional understanding of water’s behavior is often encapsulated in a simple phase diagram depicting its states under varying temperature and pressure combinations, Tao Zhou, an Argonne materials scientist and corresponding author of the paper, emphasized the complexity of the real-world scenario. The team demonstrated that premelting can occur at points far along the curve, challenging the simplicity of the traditional phase diagram. However, the underlying reasons for this occurrence remain elusive, adding a layer of complexity to our comprehension of water’s behavior in diverse environmental conditions.
The experiment, captured in a video, unfolds as two distinct nanocrystals dissolve into each other when the ice is gradually warmed under constant pressure, reaching 150 degrees Kelvin, or minus 190 degrees Fahrenheit. Remarkably, even at this temperature significantly below freezing, the ice transforms into an ultraviscous water, exhibiting a quasi-liquid-like layer. This intriguing phenomenon, not accounted for in the conventional phase diagram where water transitions directly from ice to vapor, adds a layer of complexity to our understanding of water’s behavior.
The study prompts compelling questions for future exploration. What precisely constitutes the liquid-like layer observed by the researchers? How would alterations in pressure, combined with changes in temperature, influence this behavior? Moreover, does this innovative technique offer a pathway to explore the elusive “no-man’s land,” a state where super-cooled water undergoes a sudden transition from liquid to ice? The centuries-long scientific inquiry into the multifaceted states of water continues, with this study opening new avenues for unraveling the mysteries of water’s behavior in extreme conditions.
Resources
- ONLINE NEWS Argonne National Laboratory. (2024, January 4). Even far below freezing, ice’s surface begins melting as temperatures rise. Phys.org. [Phys.org]
- JOURNAL Lin, Y., Zhou, T., Rosenmann, N. D., Yu, L., Gage, T., Banik, S., Neogi, A., Chan, H., Lei, A., Lin, X., Holt, M. V., Arslan, I., & Wen, J. (2023). Surface premelting of ice far below the triple point. Proceedings of the National Academy of Sciences of the United States of America, 120(44). [PNAS]
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APA 7: TWs Editor. (2024, January 5). Surface of Ice Begins to Melt When It Warms Up Even at Far Below Freezing Temperatures. PerEXP Teamworks. [News Link]
