Once in a while physics throws us a curveball, allowing something familiar to have unconventional properties under certain conditions. One of these curveballs is supercooled water, which remains liquid below its freezing point.
A good understanding of how molecules behave in such an unusual liquid has eluded scientists so far, but a new study, published in the Journal of Chemical Physics, is helping to clarify how to study it in lab conditions.
Researchers from Roma Tre University in Italy have developed a simulation of supercooled water and discovered that the way water molecules are distributed can be used to work out important thermodynamic properties.
Water can be supercooled if it has no impurities and if there are no forces suddenly acting on it. These conditions make supercooled water great for visual experiments, as you can pour out liquid water that begins freezing in mid-air, but they are not so great in the lab. It’s difficult to study something you can’t interact with without messing with it.
So far supercooled water has been studied in nanopores. Being confined in such a space makes it easier for researchers to look at the curious liquid, but it also got scientists wondering if the confined water was interacting with the pores or if it retained the same properties as a larger sample, where molecules can interact freely in a larger volume.
“This question has been a point of ongoing interest in our work. In previous studies, we have shown that interactions with other chemicals affect only those water molecules that are very physically close to the molecules of another chemical, such as the molecules that make up the wall of the pore,” said Professor Paola Gallo, the senior author of the study, in a statement. “The water molecules at the center of the pore, the free water, retain many of the properties of bulk water.”
The simulation highlighted how the properties of the free water in the pores are consistent with what’s expected in a much larger sample. In particular, the scientists noticed that it is possible to measure and verify experimentally the properties of the structure of the network of water molecules and that one can work out the entropy of the system.
Entropy is the measure of disorder in a system and is a crucial thermodynamics quantity. By measuring this, researchers hope to learn a lot more about supercooled water.
The study provides a roadmap to measuring these properties in the lab and hopefully unlocking the secrets of supercooled water.