In cooperation with the Max Planck Institute for Polymer Research (MPI-P) in Mainz, physicists from the University of Vienna have discovered a new type of glass that is formed from long circular molecules.
By making parts of the rings more mobile, the rings become more entangled and the molecular liquid forms a glass. The novel “active topological glass”Was featured in the latest issue of Nature Communications.
Classic glass
Glass materials are omnipresent in everyday life and range from window panes to PET bottles to porcelain espresso cups. Glass is created by the rapid cooling of molten particles, such as silicon dioxide in windows or polymers in plastic bottles. The properties of such substances as transparency or tensile strength result from their microscopically disordered and dense structure. When hot, all particles can move freely past one another and thus be rearranged, for example when blowing glass. When the melt cools down, however, each particle is concentrated by its neighbors, which makes the glass firm and dimensionally stable.
Topological glass
About 25 years ago, scientists suggested that there could be another, new type of glass. The components of this new type of glass are no longer linear molecular chains, but very long ring polymers.
Such “rings” can thread each other, i.e. a ring is threaded through the eye of another ring. The rings restrict each other in their movement. If many rings are threaded, several rings must gradually separate from each other so that even a single macromolecule is released. As long as such a process is only controlled by thermal fluctuations, the ring takes a long time to free itself and the predicted disordered structure actually behaves like a solid glass.
Such a glassy state has never been observed in any experiment. This may be due to the ring polymers that are currently too short to synthesize.
For currently available ring lengths, the previous computer simulations showed that such glass could only be produced by conditions that are difficult to achieve, such as artificial freezing of the rings. It seemed as if a real “topological glass”, a glass made of intricate ring-shaped molecules, would remain unreachable.
“We have taken the opposite path to previous attempts to find a topological glass. Instead of freezing the rings physically, we made some ring segments more flexible in our simulations. We do this by forcing parts of the rings to fluctuate more“Explain Iurii Chubak and Jan Smrek, colleagues at the University of Vienna and joint main authors of the study. “These stronger fluctuations can be achieved by embedding molecular motors – molecules with forces locally exerted at the expense of energy. Another possibility is the synthesis of rings that contain segments with increased light absorption. Such actively driven rings then thread and become so tangled that they practically cannot move past each other. It is remarkable that we observe the topological glass with experimentally accessible ring lengths and driving forces”Says Jan Smrek, who carried out his work in cooperation with the Max Planck Institute for Polymer Research in Mainz and with support from the Lise Meitner program of the Science Fund FWF.
“This glass differs microscopically from the material of the bottle from which you normally drink your favorite drink. More detailed material properties of active topological glass will be investigated further in the future. But it is already exciting, not only from the perspective of basic research, but also because of the possible applications, for example liquid material with reversible glazing when exposed to light“, Adds senior author Christos Likos from the Faculty of Physics at the University of Vienna.
Interestingly, the same basic physical ingredients are found in the nuclei of living eukaryotic cells as in the newly discovered active topological glass. In fact, the DNA fibers are long, impenetrable, high-density polymers that are actively driven by various molecular motors. “We are aware of the similarities between our simulated system and the nuclei of living cells. However, whether the DNA could be in the state of the active topological glass under real living conditions remains an open question“Concludes Jan Smrek.
Original Publication:
Active topological glass
Jan Smrek, Iurii Chubak, Christos N. Likos & Kurt Kremer
Nature Communications volume 11, Article number: 26 (2020)
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