The discovery of liquid glass sheds light on the old scientific problem of glass formation. An interdisciplinary team of researchers from the University of Konstanz (Germany) discovered a new state of matter – liquid glass with previously unknown structural elements.
Although glass has long been a truly ubiquitous material that we use on a daily basis, it also presents a serious scientific puzzle. Contrary to what might 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” is itself a fluid concept: it includes the substance we know as window glass, but it can also refer to a number of other materials with properties that can be explained by referring to the behavior of glass, including, for example, metals, plastics, proteins, and even biological cells.
While this may give the impression, glass is anything but always solid. Usually, when a material goes from liquid to solid, the molecules line up to form a crystalline pattern. This doesn’t happen in glass. Instead, the molecules are actually frozen in place before crystallization occurs. This strange and disordered state is still a subject of study for scientists.
Research conducted by Professors Andreas Zumbusch and Matthias Fuchs of the University of Konstanz has added another level of complexity to the glass puzzle. Using a model system involving suspensions of specially made ellipsoidal colloids, the researchers discovered a new state of matter, liquid glass, in which individual particles can move but cannot rotate, a complex behavior not previously observed in bulk glasses. Their results are published in Proceedings of the National Academy of Sciences.
Colloidal suspensions are mixtures or liquids that contain solid particles one micrometer (one-millionth of a meter) or larger than atoms or molecules, and are therefore well suited for study using optical microscopy. They are popular among scientists studying glass transition because they possess many of the phenomena that also occur in other glass-forming materials.
To date, most experiments with colloidal suspensions use spherical colloids. However, most natural and technical systems consist of non-spherical shaped particles. Using polymer chemistry, the scientists produced small plastic particles by stretching and cooling them until they became ellipsoidal and then placing them in a suitable solvent.
The researchers then changed the concentration of the particles in the suspensions and monitored the progressive and rotational motion of the particles using confocal microscopy. They noted that at certain particle densities, the orientational motion is frozen, while the translational motion is preserved, resulting in glassy states in which the particles cluster to form local structures with similar orientations. What the researchers called liquid glass is the result of these clusters interfering with each other and mediating characteristic long-range spatial correlations. They prevent the formation of a liquid crystal, which would be the globally ordered state of matter expected from thermodynamics.
In fact, the researchers observed two competing glass transition – a regular phase transformation and a nonequilibrium phase transformation – interacting with each other. “This is incredibly interesting from a theoretical point of view. Our experiments provide a kind of evidence for the interaction between critical fluctuations and frozen light, which the scientific community has been reaching for quite some time,” explained Matthias Fuchs. The prediction of liquid glass has remained a theoretical hypothesis for twenty years.
The results also suggest that similar dynamics may work in other systems that form glass, and thus may help shed light on the behavior of complex systems and molecules, from very small (biological) to very large (cosmological). This also has potential implications for the design of liquid crystal devices.