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The smallest piece of ice reveals its true nature
June 21, 2007Collaborative research between scientists in the UK and Germany (published in this week's Nature Materials) has led to a breakthrough in the understanding of the formation of ice. Dr Angelos Michaelides of the London Centre for Nanotechnology (formerly of the Fritz-Haber Institut der Max-Planck Gesellschaft in Berlin) and Professor Karina Morgenstern of the Leibniz University Hannover have combined experimental observations with theoretical modelling to reveal with unprecedented resolution the structures of the smallest pieces of ice that form on hydrophobic metal surfaces.
The results provide information about the process of ice nucleation at a molecular level and take science a significant step closer to understanding the mysterious process through which ice forms around microscopic dust particles in the upper atmosphere. Because this is the basis of cloud formation, knowing how different particles promote ice formation is crucial for climate change models.
The authors began by cooling down a metallic surface to 5 degrees above absolute zero (around -268 Celsius) at which temperature it was possible to "trap" and obtain images of the smallest possible pieces (hexamers) of ice using a scanning tunnelling microscope (STM). The hexamer - the simplest and most basic "snow flake" - is composed of just six water molecules. Other ice nanoclusters containing seven, eight and nine molecules were also imaged.
On the difficulties of imaging these ice clusters, Prof Morgenstern said: "Scientists have long struggled to resolve single water molecules within ice clusters, because they are so vulnerable to damage induced by electrons - the very thing that creates the image. The high resolution could only be achieved by reducing the current to the smallest value technically possible."
As well as performing experiments, the team used highly-accurate ('first principles') theoretical models to analyse how such a structure could form. Here the theory provided some surprising insights. In ice, water molecules usually bond to each other with equal strength but with the ice nanoclusters the team identified a pattern of alternating shorter and longer bonds between the water molecules. This pattern provided new information about the ability of water molecules to share their hydrogen bonds, revealing a hitherto unknown competition between the ability of water molecules to bind to a metal surface and simultaneously accept hydrogen bonds.
Dr Michaelides said, "We are all familiar with the freezing of water. It features prominently in our daily lives, from fridge freezers to winter snow. Despite all this, the question of how individual water molecules come together and give birth to ice crystals remains mysterious. Our research provides an insight into the most important and ubiquitous type of ice nucleation event, namely heterogeneous nucleation. State-of-the-art experimental and theoretical techniques allowed us to "watch" and accurately model what happens at very low temperatures."
The research makes it possible to explain the ways in which water structures form on different substrates, such as transition metals and salt surfaces. It may also provide a new way of thinking about the structure of ice clusters that form on solid surfaces in general, opening the door for applications in a variety of fields as diverse as astronomy, electrochemistry, and energy research. It also takes us a step closer to understanding how water interacts with different aerosols and dust particles in the atmosphere, processes which drive cloud formation and have a large impact on the planet's climate.
University College London
On the difficulties of imaging these ice clusters, Prof Morgenstern said: "Scientists have long struggled to resolve single water molecules within ice clusters, because they are so vulnerable to damage induced by electrons - the very thing that creates the image. The high resolution could only be achieved by reducing the current to the smallest value technically possible."
As well as performing experiments, the team used highly-accurate ('first principles') theoretical models to analyse how such a structure could form. Here the theory provided some surprising insights. In ice, water molecules usually bond to each other with equal strength but with the ice nanoclusters the team identified a pattern of alternating shorter and longer bonds between the water molecules. This pattern provided new information about the ability of water molecules to share their hydrogen bonds, revealing a hitherto unknown competition between the ability of water molecules to bind to a metal surface and simultaneously accept hydrogen bonds.
Dr Michaelides said, "We are all familiar with the freezing of water. It features prominently in our daily lives, from fridge freezers to winter snow. Despite all this, the question of how individual water molecules come together and give birth to ice crystals remains mysterious. Our research provides an insight into the most important and ubiquitous type of ice nucleation event, namely heterogeneous nucleation. State-of-the-art experimental and theoretical techniques allowed us to "watch" and accurately model what happens at very low temperatures."
The research makes it possible to explain the ways in which water structures form on different substrates, such as transition metals and salt surfaces. It may also provide a new way of thinking about the structure of ice clusters that form on solid surfaces in general, opening the door for applications in a variety of fields as diverse as astronomy, electrochemistry, and energy research. It also takes us a step closer to understanding how water interacts with different aerosols and dust particles in the atmosphere, processes which drive cloud formation and have a large impact on the planet's climate.
University College London
Ice Current Events and Ice News RSSResearch challenges for understanding landscape changes identified
Nine research challenges and four research initiatives that are poised to advance the study of how Earth's landscapes change were unveiled today in a new report by the National Research Council.
Warmer means windier on world's biggest lake
Rising water temperatures are kicking up more powerful winds on Lake Superior, with consequences for currents, biological cycles, pollution and more on the world's largest lake and its smaller brethren.
How much water does the ocean have?
The calculation of variations in the sea level is relatively simple. It is by far more complicated to then determine the change in the water mass.
Iowa State scientist develops lab machine to study glacial sliding related to rising sea levels
Neal Iverson opened his laboratory's walk-in freezer and said the one-of-a-kind machine inside could help scientists understand how glaciers slide across their beds. And that could help researchers predict how glaciers will react to climate change and contribute to rising sea levels.
Controversial new climate change results
New data show that the balance between the airborne and the absorbed fraction of carbon dioxide has stayed approximately constant since 1850, despite emissions of carbon dioxide having risen from about 2 billion tons a year in 1850 to 35 billion tons a year now.
Cave Study Links Climate Change to California Droughts
California experienced centuries-long droughts in the past 20,000 years that coincided with the thawing of ice caps in the Arctic.
Antarctica glacier retreat creates new carbon dioxide store
Large blooms of tiny marine plants called phytoplankton are flourishing in areas of open water left exposed by the recent and rapid melting of ice shelves and glaciers around the Antarctic Peninsula.
Ice cream researchers making sweet strides with 'functional foods'
A comfort food, a tasty treat, an indulgence - ice cream conjures feelings of happiness and satisfaction for millions. Ice cream researchers at the University of Missouri have discovered ways to make ice cream tastier and healthier and have contributed to ice cream development and manufacturing for more than a century.
Past climate of the northern Antarctic Peninsular informs global warming debate
The seriousness of current global warming is underlined by a reconstruction of climate at Maxwell Bay in the South Shetland Islands of the Antarctic Peninsula over approximately the last 14,000 years, which appears to show that the current warming and widespread loss of glacial ice are unprecedented.
Texas A&M prof to predict weather on Mars
Is there such a thing as "weather" on Mars? There are some doubts, considering the planet's atmosphere is only 1 percent as dense as that of the Earth.
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