KONSTANZ, Germany — When we look at the world around us, nearly every object fits into the basic states of matter — solid, liquid, or gas. A study of glass has uncovered a new state of matter which researchers at the University of Konstanz call liquid glass. The discovery is giving scientists new insights into how objects like glass, which change under heat, form.
The glass transition is a process where matter in a brittle and solid state becomes rubbery and semi-fluid using heat. This process can also be reversed and the matter returned to a solid, glassy form.
Although we see glass everywhere in our daily lives, scientists say many of its properties still remain a mystery. In fact, in chemistry and physics, glass refers to several materials which have similar properties including window glass, metals, plastics, and even biological cells.
Not your average solid
Although you can’t put your hand through it without breaking it, study authors say glass is far from a typical solid object. Usually when matter turns from liquid to solid, the molecules which make up that item shift around to form a solid, crystal-like pattern. The study finds this doesn’t happen with glass. Instead, molecules simply freeze in place without forming a crystalline pattern.
Researchers experimented on ellipsoidal colloids to see why glass structures stay in this semi-stable form. Colloids are mixtures consisting of large particles which scientists can see using a typical optical microscope. This makes them very popular with scientists studying how particles react under various conditions, such as the glass transition.
The study reveals liquid glass forms when individual particles are still able to move but can no longer rotate. These clusters of particles obstruct each other and therefore keep the object from forming the normal crystalline patterns of solids. Researchers say this type of behavior has never been observed before in bulk glasses.
The perfect shape for discovery
Study authors say most experiments using colloids feature spherical particles. In nature however, most objects are made of non-spherical particles. Using polymer chemistry, the German team created their own plastic particles by stretching and cooling the colloids until they formed more elliptical shapes.
“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,” explains senior study author Andreas Zumbusch in a university release.
“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.”
The fight between solids and liquids
Researchers say this clustering effect that prevents the glass particles from moving into a perfectly solid form is apparently two separate glass transitions competing with each other.
“This is incredibly interesting from a theoretical vantage point,” says Matthias Fuchs, professor of soft condensed matter theory. “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.”
The team adds, until now, theories about the existence of liquid glass have only been conjecture for 20 years.
The study appears in the Proceedings of the National Academy of Sciences.