Using a technique called confocal microscopy, a team of scientists from Germany and the Netherlands found that suspensions of ellipsoidal colloids form an unexpected state of matter, a liquid glass in which individual particles can move but are unable to do not turn.
Scanning electron microscope image of the ellipsoidal colloids. Insert shows a confocal microscopy image highlighting the core shell structure. Scale bar – 5 μm. Image Credit: Roller et al., doi: 10.1073 / pnas.2018072118.
“Suspensions of colloidal particles have been widespread in nature and technology and have been studied intensively for over a century,” said fellow senior professor Professor Andreas Zumbusch of the Department of Chemistry at the University of Konstanz and his colleagues.
“If the density of such suspensions is increased after large-volume fractures, their structural dynamics are often arrested in a disordered, glassy state before they can form an ordered structure.”
‘To date, most experiments have been done with spherical colloids. However, the recent interest in synthetic colloids as material building blocks has led to the development of a multitude of new techniques for the synthesis of colloidal particles with specific geometry and interactions. ”
In their experiments, Professor Zumbusch and co-authors focused on ellipsoid polymethyl methacrylate colloids.
“Because of their different shapes, our particles have orientation, as opposed to spherical particles, which give rise to completely new and previously unexplored types of complex behaviors,” Professor Zumbusch explained.
Using confocal laser scanning microscopy, the researchers recorded the temporal evolution of the 3D positions and orientations for more than 6,000 ellipsoid particles.
“At certain particle densities, orientation motion freezes while translational motion continues, resulting in glassy conditions where the particles are joined together to form local structures with similar orientations,” Professor Zumbusch said.
“What we call liquid glass is the result of these groups interfering with each other and mediating characteristic spatial correlations over long distances.”
“This prevents the formation of a liquid crystal that would be the globally ordered state of matter expected from thermodynamics.”
Computer rendered 3D reconstruction of a subset of a sample volume with the red-green-blue value of the color indicating the particle orientations. Scale bar – 20 μm. Image Credit: Roller et al., doi: 10.1073 / pnas.2018072118.
The team observed two glass transitions – a regular phase transformation and a non-equilibrium phase transformation – that interacted with each other.
“It’s incredibly interesting from a theoretical point of view,” said fellow senior author Professor Matthias Fuchs, a researcher in the Department of Physics at the University of Konstanz.
“Our experiments provide the kind of evidence for the interaction between critical fluctuations and glassy arrest that has plagued the scientific community for some time.”
A prediction of liquid glass has remained a theoretical conjecture for twenty years. ‘
The results further indicate that similar dynamics may be at work in other glass-forming systems and thus may help to shed the behavior of complex systems and molecules, ranging from the small (biological) to the large (cosmological).
“It can also affect the development of liquid crystal devices.”
The discovery is reported in an article published in the Proceedings of the National Academy of Sciences.
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Jörg Roller et al. 2021. Observation of liquid glass in suspensions of ellipsoidal colloids. PNAS 118 (3): e2018072118; doi: 10.1073 / pnas.2018072118