While glass is an ever-present material in our world that we use daily, it represents a major scientific puzzle. Researchers are still trying to understand its chemical and physical properties, meaning its true nature remains something of a mystery.
To this day, scientists are discovering new things about the material. Now, a team of physicists and chemists from the University of Konstanz has found a new state of matter, hidden amid the mysterious transformations between liquid and solid states of glass. They’re calling it liquid glass. It’s considered a new state of matter because it possesses previously unknown structural elements and behavior at the microscopic level never before seen.
The team used the confocal microscopy technique to observe how the suspensions of ellipsoidal colloids behave in liquid glass. In this phenomenon, individual particles can move yet unable to rotate. This new state appears to exist between a solid and a colloid (like a gel).
Co-senior author Professor Andreas Zumbusch from the University of Konstanz’s Department of Chemistry and colleagues said:
Suspensions of colloidal particles are widely spread in nature and technology and have been studied intensely over more than a century. When the density of such suspensions is increased to high volume fractions, often their structural dynamics are arrested in a disordered, glassy state before they can form an ordered structure.
To date, most experiments have been done using spherical colloids. However, the recent interest in synthetic colloids as material building blocks has led to the development of a multitude of novel techniques for the synthesis of colloidal particles with specific geometries and interactions.
The team used tiny custom-made plastic ellipsoidal polymethylmethacrylate colloids mixed in a solvent in the experiments, rather than spherical particles. Professor Zumbusch explained:
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.
The researchers captured the temporal development of the 3D positions and orientations for over 6,000 ellipsoidal particles using confocal laser scanning microscopy. Professor Zumbusch said:
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. We’ve termed liquid glass is a result of these clusters mutually obstructing each other and mediating characteristic long-range spatial correlations. These prevent the formation of a liquid crystal which would be the globally ordered state of matter expected from thermodynamics.
Glass is not your average solid. During a typical material transition from a liquid to a solid-state, the molecules line up in a crystal pattern. That doesn’t happen in the glass. Instead, the molecules become frozen in place in a strange disordered state before crystallization occurs.
Liquid glass is even stranger; it’s two competing liquid-to-solid transitions interacting, creating a mixture of different properties. The researchers found that the concentration and shape of the particles are crucial in creating liquid glass. In the experiments, the ellipsoidal colloids enabled liquid glass to happen because the particles can move but can’t rotate. The situation resulted in local particle clusters that obstruct each other and prevent the formation of an ordered state of matter.
Co-senior author Matthias Fuchs, a professor at the University of Konstanz in Germany, said:
This is incredibly interesting from a theoretical vantage point. Our experiments provide evidence for the interplay between critical fluctuations and glassy arrest that the scientific community has been after for quite some time. A prediction of liquid glass had remained a theoretical conjecture for twenty years.
The results further suggest that similar dynamics may be at work in other glass-forming systems and may thus help to shed light on the behavior of complex systems and molecules ranging from the very small (biological) to the very big (cosmological). It also potentially impacts the development of liquid crystalline devices.
The findings could go way beyond the glass, shedding light on any scenario where there is an unexplained disorder. The researchers wrote in their paper:
Our results give insight into the interplay between local structures and phase transformations. This helps to guide applications such as self-assembly of colloidal superstructures and also gives evidence of the importance of shape on the glass transition in general.
There remain a lot of unanswered questions, as always with glass transition. Nevertheless, the team is hopeful that its discovery can improve our understanding of how glass transitions work at the smallest of scales.
