Liquid glass, new state of matter

WEDNESDAY, JANUARY13TH, 2021.-

A study from the University of Konstanz revealed this astonishing discovery

🖊 EUROPA PRESS 📸 Universidad de Constanza


Researchers from the University of Konstanz in Germany have discovered a new state of matter, liquid glass, with new knowledge of the nature of glass and its transitions.

While glass is a truly ubiquitous material that we use on a daily basis, it also represents an important scientific conundrum. Contrary to what would be expected, the true nature of glass remains a mystery, and scientific research into its chemical and physical properties is still ongoing.

In chemistry and physics, the term glass itself is a mutable concept: it includes the substance we know as window glass, but it can also refer to a variety of other materials with properties that can be explained by reference to glass-like behavior, including, for example, metals, plastics, proteins and even biological cells.

While it can give the impression, glass is anything but conventionally solid. Typically, when a material moves from a liquid state to a solid state, molecules align to form a crystal pattern. In glass, this doesn't happen. Instead, molecules effectively freeze in place before crystallization occurs. This strange and messy state is characteristic of glass in different systems and scientists are still trying to understand how exactly this metaestable state is formed.

Research led by Professors Andreas Zumbusch (Department of Chemistry) and Matthias Fuchs (Department of Physics), both based at the University of Konstanz, has just added another layer of complexity to the glass conundrum. Using a model system involving custom-made ellipsoidal colloid suspensions, the researchers discovered a new state of matter, liquid glass, where individual particles can move but cannot rotate, a complex behavior that had not previously been observed in bulk glass. The results are published on PNAS.

Colloidal suspensions are mixtures or fluids that contain solid particles that, in micrometer sizes (one millionth of a meter) or more, are larger than atoms or molecules and are therefore suitable for research with optical microscopy. They are popular among scientists who study glass transitions because they present many of the phenomena that also occur in other glass-forming materials.

To date, most experiments involving colloidal suspensions have been based on spherical colloids. However, most natural and technical systems are composed of non-spherical particles. Using polymer chemistry, the andreas Zumbusch-led team manufactured small plastic particles, stretching and cooling them until they achieved their ellipsoid shapes and then placed them in a suitable solvent.

"Because of their different shapes, our particles are oriented, unlike spherical particles, resulting in completely new and previously un studied types of complex behaviors," Zumbusch, a professor of physical chemistry and lead author of the study, explains in a statement.

The researchers then changed particle concentrations in the suspensions and tracked the translation and rotational movement of the particles using confocal microscopy. Zumbusch says:

"At certain particle densities, the orientation movement froze while the translation motion persisted, resulting in glassy states where particles were grouped together to form local structures with similar orientation."

What researchers have called liquid glass is the result of these groups obstructing each other and mediating long-range characteristic spatial correlations. These prevent the formation of a liquid crystal that would be the globally ordered state of matter expected from thermodynamics.

What the researchers observed were, in fact, two vitreous transitions in competition, a regular phase transformation and a non-balancing phase transformation, interacting with each other.

"This is incredibly theoretically interesting," says Matthias Fuchs, professor of condensed soft matter theory at the University of Konstanz and the other lead author of the paper. "Our experiments provide the kind of evidence of the interaction between critical fluctuations and the crystalline detention that the scientific community has been looking for for quite some time."

A prediction of liquid glass had been a theoretical conjecture for twenty years.

The results further suggest that a similar dynamic may be working in other glass formation systems and can therefore help shed light on the behavior of complex systems and molecules ranging from the very small (biological) to the very large (cosmological). It also has a potential impact on the development of liquid glass devices.

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