Ice quickly shields itself from intense heat
Put a drop of water into a very hot pan and it can skitter across the surface on a cushion of vapor. This is known as the Leidenfrost effect. Now, scientists have observed a related phenomenon involving ice and an extremely hot surface – on a length scale of nanometers and within nanoseconds. The effect was discovered and investigated by an international team of researchers at the FXE instrument at European XFEL and could influence, for instance, laser processing, data storage technologies, and catalysis. The results have been published in the Nature portfolio journal Communications Chemistry.
In the experiment, the scientists heated a platinum film beneath an ultra-thin layer of amorphous ice, i.e., a non-crystalline glassy form of ice. They found, unexpectedly, that the ice barely warmed or changed structure on nanosecond timescales.
"This result is an example of how scientific research can take you in unexpected directions. What started as an experiment to study the phase transitions of amorphous ice revealed an anomalous interfacial energy transport that can be explained by the formation of an insulating vapor layer," said Tobias Eklund, Ph.D. student at European XFEL and Johannes Gutenberg University Mainz (JGU).
"An odd measurement result, some careful analysis and modeling, and some new science," added Christopher Milne, group leader at the FXE instrument, where the experiment was conducted.
X-ray measurements, together with computer simulations, indicate that the rapid heating creates a vapor gap around six nanometers thick between the platinum and the ice. This tiny gap acts as a thermal barrier, strongly reducing the flow of heat. The findings show that under extremely rapid heating, the boundary where the metal and the ice meet can reorganize itself. Rather than passing directly from the metal into the ice, heat is blocked by the newly formed vapor layer in a way that conventional heat-transfer models do not predict.
"It's amazing to see how water can still surprise us. The results are important for our understanding of water and ice in the atmosphere but also in outer space, where amorphous ice attaches to tiny dust grains," added Professor Katrin Amann-Winkel, Principal Investigator from JGU and group leader at the Max Planck Institute for Polymer Research.
The researchers now hope to investigate whether similar insulating layers can form at other material interfaces exposed to rapid heating.
Reference Formation of nanoscale vapour films governing thermal resistance in amorphous ice
Liu, Y., Eklund, T., Karina, A. et al.
