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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 are able to move. without being able to turn.
Scanning electron microscope image of ellipsoidal colloids. The inset shows a confocal microscopy image, highlighting the core-shell structure. Scale bar – 5 μm. Image Credit: Roller et al., doi: 10.1073 / pnas.2018072118.
“Colloidal particle suspensions are widely used in nature and technology and have been intensely studied for over a century,” said co-lead author Professor Andreas Zumbusch from the Department of Chemistry at the University of Constance and his colleagues.
“When the density of these suspensions is increased to high volume fractions, their structural dynamics are often arrested in a messy and glassy state before they can form an ordered structure.
“To date, most of the experiments have been carried out with spherical colloids. The recent interest in synthetic colloids as building blocks of materials has however led to the development of a multitude of new techniques for the synthesis of colloidal particles with specific geometries and interactions.
In their experiments, Professor Zumbusch and his coauthors focused on the ellipsoidal polymethylmethacrylate colloids.
“Due to their distinct shapes, our particles have orientation, as opposed to spherical particles, which gives rise to entirely new and never-studied types of complex behaviors,” explained Professor Zumbusch.
Using confocal laser scanning microscopy, the researchers recorded the temporal development of 3D positions and orientations for more than 6,000 ellipsoidal particles.
“At certain particle densities, the orienting motion froze as the translational motion persisted, resulting in glassy states where the particles clustered together to form local structures with similar orientation,” Prof. Zumbusch said.
“What we have called liquid glass is the result of the mutual obstruction of these clusters and the mediation of characteristic long-range spatial correlations.”
“These prevent the formation of a liquid crystal which would be the generally ordered state of matter expected from thermodynamics.”
3D computer-rendered reconstruction of a subset of a sample volume with the red-green-blue value of the color indicating the orientations of the particles. 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 an unbalanced phase transformation – interacting with each other.
“It’s incredibly interesting from a theoretical point of view,” said co-lead author Prof Matthias Fuchs, researcher at the Department of Physics at the University of Constance.
“Our experiments provide the kind of evidence for the interplay between critical fluctuations and glass stops that the scientific community has been looking for for 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 thus may help shed light on the behavior of complex systems and molecules ranging from very small (biological) to very large ( cosmological). “
“It also has a potential impact on 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 Rollerblading et al. 2021. Observation of liquid glass in suspensions of ellipsoidal colloids. PNAS 118 (3): e2018072118; doi: 10.1073 / pnas.2018072118
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