Exploring the mysteries of supercooled water

February 28, 2017
Top left panel: Snapshot of a slice of water confined in the silica pore. The blue circle contains the 'free water,' the water molecules that are not in contact with the substrate.Bottom left panel: Density profile of the water molecules along the pore radius. The regions occupied respectively by the free water and the "bound water," water attached to the substrate, are indicated.Top right panel: The curves represent how the oxygen atoms of the molecules are arranged in shells around a given oxygen atom in the origin at different temperatures. The peaks represent the positions where the different shells are located. The structure is shown for some of the supercooled temperatures investigated.Bottom right panel: The main result of our computer simulation is given by the behavior of the excess entropy, a fraction of the total entropy, obtained from the oxygen structure of free water. The deviation of the calculated black points from the theoretical (red) curve indicates that water undergoes a change of behavior before and upon approaching the glass transition. Credit: Margherita De Marzio, Gaia Camisasca, Maria Martin Conde, Mauro Rovere and Paola Gallo

There are few things more central to life on earth than water. It dominates the physical landscape, covering much of the planet as oceans. It's also a major component of the human body, comprising, for example, more than 70% of the mass of a newborn baby.

Yet despite its omnipresence, water has many physical properties that are still not completely understood by the scientific community. One of the most puzzling relates to the activity of after they undergo a process called "supercooling."

Now, new findings from Roma Tre University, in Rome, Italy, on the interactions of water molecules under these exotic conditions appear this week in the Journal of Chemical Physics.

"Normally, when is cooled below its freezing point, the water molecules arrange themselves in the ordered, crystal structure that is ice," said Paola Gallo, an associate professor of physics at Roma Tre University. "With supercooling, special techniques are employed to cool water very quickly in such a way that it remains a liquid even though its temperature has been lowered well below its . There are a number of anomalies in water molecules' activity in these supercooled conditions that have not yet been fully explained."

Using a computer-based simulation, Gallo and her colleagues shed light on a thermodynamic property of water that helps explain how water molecules in a supercooled state interact with each other and with the molecules of other materials.

"While supercooling is an important phenomenon to study, the challenge is that it's very difficult to supercool water in a lab," said Gallo.

In the past, scientists have attempted to address this issue by supercooling water "in confinement," focusing efforts on studying water confined in manufactured pores having a radius of a few namometers (i.e. one or two orders of magnitude larger than the diameter of the molecule of water). This, however, has raised a question of whether the properties of this confined water differ from that of bulk water, where water molecules interact freely in larger volumes.

"This question has been a point of ongoing interest in our work," said Gallo. "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. The water molecules at the center of the pore, the free water, retain many of the properties of bulk water."

"With this study, we discovered that there are further parallels," Gallo also said. "Specifically, our simulation shows that a property of the structure of the network of water molecules, which can be measured and verified experimentally, can be used to determine the changes in water's entropy, the thermodynamic quantity that measures disorder in a system [...] that may offer insights on some of the more unusual thermodynamic facets of water's activity in this supercooled state."

These findings create a framework for other experimental physicists to recreate the simulation with physical samples in a lab. For Gallo and her colleagues, their work offers a foundation for further investigation of the relationships between the thermodynamic characteristics of confined and bulk water.

"Water is the most important liquid that we have on earth," explained Gallo. "Any insights that researchers can uncover about its properties can advance not only our collective understanding of physics, but also of biology and chemistry, and open up new possibilities for integrating this knowledge into different technological applications."

Explore further: How water can split into two liquids below zero

More information: "Structural properties and fragile to strong transition in confined water," The Journal of Chemical Physics Feb. 28, 2017. DOI: 10.1063/1.4975624

Related Stories

How water can split into two liquids below zero

January 25, 2017

Did you know that water can still remain liquid below zero degrees Celsius? It is called supercooled water and is present in refrigerators. At even smaller temperatures, supercooled water could exist as a cocktail of two ...

An interesting twist on supercooled liquid water

February 24, 2016

Water is known to have various anomalous properties, and they are especially prominent below room temperature. For example, liquid water exhibits expansion when it is cooled below 4°C, and it keeps expanding when it is supercooled ...

Competing coexisting phases in two-dimensional water

June 17, 2016

On Earth, water is abundant substance, the cycle of evaporation - condensation - solidification (steam transitions - liquid - solid) falls within everyday experience. The physical properties of water and its phase diagram ...

Scientists discover a new state of matter for water

December 22, 2016

One of the most basic things we are taught in school science classes is that water can exist in three different states, either as solid ice, liquid water, or vapour gas. But an international team of scientists have recently ...

Recommended for you

New type of electron lens for next-generation colliders

October 18, 2017

Sending bunches of protons speeding around a circular particle collider to meet at one specific point is no easy feat. Many different collider components work keep proton beams on course—and to keep them from becoming unruly.

Spider-web 'labyrinths' may help reduce noise pollution

October 17, 2017

(Phys.org)—Researchers have demonstrated that the geometry of a natural spider web can be used to design new structures that address one of the biggest challenges in sound control: reducing low-frequency noise, which is ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.