When ice interacts with liquid, such as when sliding on ice, forming snowflakes, or licking ice cream, the surface of the ice is coated with liquid water. Understanding this interaction is crucial, yet direct observation has been elusive due to the rapid transformation between ice and water.
To delve into this interaction, researchers led by Kobe University's ONISHI Hiroshi explored a novel approach. He explained, "We came up with the idea of measuring ice immersed in antifreeze colder than 0 C. This way, the ice doesn't melt and the interface doesn't move, and it should be possible to make precise observations." However, achieving accurate measurements was challenging. "Through various trial and error processes, we found that we had to cool the entire microscope system in a cooling box, and it took some ingenuity to ensure that the atomic force microscope, a precision measuring instrument, could operate stably at sub-zero temperatures," added the Kobe University researcher.
The results, published in The Journal of Chemical Physics, revealed that ice surrounded by antifreeze exhibits a perfectly flat surface with occasional steps one molecular layer high, contrasting with the "frost pillars" observed in ice without surrounding liquid. "We think that the flat surface is formed through ... partial dissolution and recrystallization of the ice surface in the 1-octanol liquid (the antifreeze)," the researchers noted in their paper.
The team also experimented with various alcohols similar to 1-octanol, finding that each liquid produced different ice surface structures, emphasizing the necessity of direct measurements. Additionally, they discovered that ice under 1-octanol is significantly harder than previously estimated by indirect methods.
The researchers aim to inspire further studies of the ice-liquid interface. They also have ambitious plans for their own future research, stating, "We expect to increase the resolution of the microscope to single water molecules and use measurement methods other than atomic force microscopy. In this way, we hope to expand the range of possible applications of molecular-level measurements of the ice-antifreeze interface."
This research was funded by the Ministry of Education, Culture, Sports, Science and Technology Japan (grants JPMXP1222MS0008 and JPMXP1223MS0001) and the Japan Society for the Promotion of Science (grants 21K18935 and 23H05448). It was conducted in collaboration with researchers from the Institute for Molecular Science, National Institutes of Natural Sciences.
Research Report:The interface between ice and alcohols analyzed by atomic force microscopy
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