By supercooling liquids, scientists can determine the physics happening in glasses

June 21, 2012
As liquids cool, they can take on different states depending on various conditions. A liquid can cool to become a supercooled liquid and then a glass, given the right conditions. The more common route is for the liquid to cool into a crystalline solid.

( -- The whereabouts of exceedingly slow-moving molecules in glasses can be quickly and efficiently measured, thanks to a new technique that uses vapor and extreme cold to drop the molecules' speed a trillion times. Designed by Dr. Scott Smith and Dr. Bruce Kay at Pacific Northwest National Laboratory, the method supercools vapor molecules turning them into a glassy film. Then, they heat the film just enough to get the molecules moving at the desired speed to study. An overview of this new method appears in an invited Perspective article in Journal of Physical Chemistry Letters.

While glass is ubiquitous in the world today, from to fuel cells to pharmaceuticals, and even nuclear waste storage, fundamental glass properties are not clearly understood. exist, in part, because supercooling alcohols, water and other small molecular liquids was not easy. This difficulty meant that fundamental questions were the purview of and models. With this new technique, scientists can get precise data. The data will answer basic questions, and one day may guide transformations into key industries.

"This work is not immediately relevant to nuclear waste or pharmaceuticals. What we are trying to do is understand the elementary that occur around the glass transition," said Kay.

To understand a supercooled liquid, it is helpful to look at how liquids change when chilled. As liquids are cooled, the molecules slow down and take up set positions. As more molecules take up set positions, the liquid solidifies or crystallizes. This is the change that happens when water freezes into ice. But, if the circumstances are just right, the liquid takes a different path. It becomes a viscous, syrupy concoction, known as a supercooled liquid. This happens because the molecules slow down, but stay disorganized. If the temperature drops a bit more, to the , the supercooled liquid turns into a glass.

The challenge for years has been supercooling a liquid to low temperatures without getting the crystal form.

From fiber optic cables to fuel cells, and even nuclear waste storage, glass is pervasive in today’s world; however, the fundamental properties of glass are not clearly understood.

The new PNNL technique turns that problem around by starting with the gaseous form of the sample. The scientists deposit the vapor onto a super cold surface, creating a nanometer-deep glass. The glass film is then heated slightly to create a supercooled liquid. Before the liquid molecules can rearrange themselves into crystals, the scientists can apply different analytical techniques.

"The trouble with cooling from the liquid phase is that the samples crystallize too early in the process for studying," said Smith. "This new method may be a way to learn something about liquids and test theoretical ideas and models."

Smith and Kay have been working with supercooled liquids for more than a decade. In 2009, they devised a method that placed a layer of krypton atoms under the sample liquid at low temperatures. Then, they applied heat that caused the sample to start moving and allowed the krypton atoms to bubble through. Using a mass spectrometer, they measured when the krypton atoms reached the material's surface. These data are used to calculate diffusion rates for different supercooled liquid materials.

Smith and Kay are focusing on using the vapor deposition approach to determine the properties of super cold mixes. "We want to study mixtures of alcohol and water; nobody has been able to measure this before," said Kay.

Explore further: Measuring the Speed of Noble 'Bubbles'

More information: RS Smith and BD Kay. 2012. "Breaking Through the Glass Ceiling: Recent Experimental Approaches to Probe the Properties of Supercooled Liquids near the Glass Transition." The Journal of Physical Chemistry Letters 3(6):725-730. DOI: 10.1021/jz201710z

Related Stories

Measuring the Speed of Noble 'Bubbles'

February 12, 2010

( -- Using a layer of noble gas "bubbles," scientists at Pacific Northwest National Laboratory devised a straightforward way to measure how fast molecules diffuse in supercooled liquids. Working at temperatures ...

Supercooled: Water doesn't have to freeze until -55 F

November 23, 2011

( -- We drink water, bathe in it and we are made mostly of water, yet the common substance poses major mysteries. Now, University of Utah chemists may have solved one enigma by showing how cold water can get before ...

Scientists Observe Liquid Water Below Freezing

June 24, 2009

( -- Below 0 °C, water turns to ice. But beyond that, or below about -75 °C, the ice may turn back into liquid water. While scientists have previously predicted this phase transition with computer simulations, ...

Cracking a controversial solid state mystery

February 6, 2009

( -- Scientists can easily explain the structural order that makes steel and aluminium out of molten metal. And they have discovered the molecular changes that take place as water turns to ice. But, despite the ...

Recommended for you

Single-photon detector can count to four

December 15, 2017

Engineers have shown that a widely used method of detecting single photons can also count the presence of at least four photons at a time. The researchers say this discovery will unlock new capabilities in physics labs working ...

Complete design of a silicon quantum computer chip unveiled

December 15, 2017

Research teams all over the world are exploring different ways to design a working computing chip that can integrate quantum interactions. Now, UNSW engineers believe they have cracked the problem, reimagining the silicon ...

A shoe-box-sized chemical detector

December 15, 2017

A chemical sensor prototype developed at the University of Michigan will be able to detect "single-fingerprint quantities" of substances from a distance of more than 100 feet away, and its developers are working to shrink ...

Real-time observation of collective quantum modes

December 15, 2017

A cylindrical rod is rotationally symmetric - after any arbitrary rotation around its axis it always looks the same. If an increasingly large force is applied to it in the longitudinal direction, however, it will eventually ...


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.