Glass is truly a peculiar material. Despite being solid, its components are not organized in a nice crystalline structure like other solids. Its molecules get frozen in place before they can organize themselves into a crystal. The quest to understand glass has led researchers to discover a new state of matter: liquid glass.
Liquid glass was created with particles that were able to flow, but couldn’t rotate. As reported in the Proceedings of the National Academy of Sciences, this new state gives insight into how regular glass might form.
The starting point of this investigation was the use of colloids, mixtures of “large” particles dispersed through a second substance. Gels and emulsions are examples of colloids. These substances can experience many phenomena that occur in glass-forming material, so they are a good proxy to study these glass transition.
The team involved in this research decided to attempt something different than previous studies. Instead of using spherical particles in their colloid, they manufactured special elliptical (egg-shaped) particles. By changing the concentration of these in the mixtures, they discovered the unusual liquid glass behavior.
"Due to their distinct shapes our particles have orientation – as opposed to spherical particles – which gives rise to entirely new and previously unstudied kinds of complex behaviors," senior author Professor Andreas Zumbusch, from the University of Konstanz, said in a statement. "At certain particle densities orientational motion froze whereas translational motion persisted, resulting in glassy states where the particles clustered to form local structures with similar orientation."
What the researchers saw in this particular substance were two competing glass transitions. One was a regular phase transformation, which is reversible. The other was a non-equilibrium one, which is irreversible. This combination might be what produces the peculiar properties of glass.
"This is incredibly interesting from a theoretical vantage point," says Dr Matthias Fuchs, professor of soft condensed matter theory at the University of Konstanz and the other senior author on the paper. "Our experiments provide the kind of evidence for the interplay between critical fluctuations and glassy arrest that the scientific community has been after for quite some time."
Understanding glass is not just about the material that makes our windows. A wide range of materials behave like glass, including plastics and metals, as well as organic substances such as proteins and even biological cells.
Theoretical investigations of liquid glass have been going on for two decades. This first result will have a long-reaching effect in the field of material science.