By Michael
Irving
January 05, 2021
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Researchers have discovered a new state of matter called liquid glass Photo
credit:
aetb/Depositphotos
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It’s a persistent fallacy that
glass already is a liquid, spread by misinformed high school teachers and tour
guides. But that’s not technically true – glass is an amorphous solid. Normally
when a substance transitions from a liquid to a solid, the formerly free-flowing
atoms line up into a rigid crystal formation. That’s not the case with glass
though: its atoms “freeze” in their disordered state.
Or at least, that’s how it
usually goes. In the new study, the researchers discovered a form of glass where
the atoms exhibit a complex behavior that’s never been seen in bulk glass
before. Essentially, the atoms can move but aren’t able to rotate.
The team made this discovery in a
model system of colloidal suspensions. These mixtures are made up of large solid
particles suspended in a fluid, making it easier for scientists to observe the
physical behavior of atoms or molecules. Normally these particles are spheres,
but for this experiment the team used elliptical ones so they could tell which
direction they were pointing.
A diagram showing the positions
and orientation of the team's elliptical particles in the liquid glass state
Photo: Research groups of Professor Andreas Zumbusch and Professor Matthias
Fuchs
The researchers tested different
concentrations of particles in the fluid, tracking how well they could move and
rotate. Eventually they found that at higher concentrations, the particles
blocked each other from rotating, but they could still move, forming a liquid
glass state.
“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,” says Andreas Zumbusch, lead author of the study.
The team says that the observed
behavior comes from two competing glass transitions interacting with each other.
Liquid glass has been predicted for decades, and the new observation suggests
that similar processes could be at work in other glass-forming systems.
“This is incredibly interesting
from a theoretical vantage point,” says Matthias Fuchs, senior author of the
study. “Our experiments provide the kind of evidence for the interplay between
critical fluctuations and glassy arrest that the scientific community has been
after for quite some time.”
The research was published in the
journal Proceedings
of the National Academy of Sciences.
Source: University
of Konstanz