Harvard materials scientists have come up with what they believe is a new way to model the formation of glasses, a type of amorphous solid that includes common window glass.
Glasses form through the process of vitrification, in which a glass-forming liquid cools and slowly becomes a solid whose molecules, though they've stopped moving, are not permanently locked into a crystal structure. Instead, they're more like a liquid that has merely stopped flowing, though they can continue to move over long stretches of time.
"A glass is permanent, but only over a certain time scale. It's a liquid that just stopped moving, stopped flowing," said David Weitz, Mallinckrodt Professor of Physics and Applied Physics at Harvard's School of Engineering and Applied Sciences (SEAS) and the Department of Physics. "A crystal has a very unique structure, a very ordered structure that repeats itself over and over. A glass never repeats itself. It wants to be a crystal but something is preventing it from being a crystal."
Other than window glass, made from silica or silicon dioxide, Weitz said many sugars are glasses. Honey, for example, is not a glass at room temperature, but as it cools down and solidifies, it becomes a glass.
Scientists like Weitz use models to understand the properties of glasses. Weitz and members of his research group, together with colleagues at Columbia University and the University of North Texas, report in this week's Nature a new wrinkle on an old model that seems to improve how well it mimics the behavior of glass.
The model is a colloidial fluid, a liquid with tiny particles, or colloids, suspended evenly in it. Milk, for example, is a familiar colloidial fluid. Scientists model solidifying glasses using colloids by adding more particles to the fluid. This increases the particles' concentration, making the fluid thicker, and making it flow more slowly. The advantage of this approach to studying glasses directly is size, Weitz said. The colloid particles are 1,000 times bigger than a molecule of a glass and can be observed with a microscope.
"They're big; they're slow. They get slower and slower and slower and slower," Weitz said. "They don't behave like a fluid. They don't behave like a crystal. They behave in many ways like a glass."
The problem with traditional colloids used in these models, however, is that they often rapidly solidify past a certain point, unlike most glasses, which continue to flow ever more slowly as they gradually solidify. Weitz and colleagues created a colloid that behaves more like a glass in that way by using soft, compressible particles in the colloid instead of hard ones. This makes the particles squeeze together as more particles are added, making them flow more slowly, but delaying the point at which it solidifies, giving it a more glasslike behavior.
By varying the colloidal particles' stiffness, researchers can vary the colloidal behavior and improve the model's faithfulness to various glasses.
"There's this wealth of behavior in molecular glass and we never saw this wealth of behavior in colloid particles," Weitz said. "The fact you can visualize things gives you tremendous insight you can't get with molecular glass."
Weitz's co-authors are Johan Mattsson, Hans M. Wyss, and Alberto Fernandez-Nieves of Harvard's Department of Physics and School of Engineering and Applied Sciences; Kunimasa Miyazaki and David R. Reichman of Columbia University; and Zhibing Hu of the University of North Texas. Their work was funded by the National Science Foundation, Harvard's Materials Research Science and Engineering Center, the Hans Werthén Foundation, the Wenner-Gren Foundation, the Knut and Alice Wallenberg Foundation and the Royal Society of Arts and Sciences in Göteborg, the Ministerio de Ciencia e Innovación and the University of Almeria, and KAKENHI.
Steve Bradt | EurekAlert!
Nagoya physicists resolve long-standing mystery of structure-less transition
21.08.2017 | Nagoya University
Scientists from the MSU studied new liquid-crystalline photochrom
21.08.2017 | Lomonosov Moscow State University
Whether you call it effervescent, fizzy, or sparkling, carbonated water is making a comeback as a beverage. Aside from quenching thirst, researchers at the University of Illinois at Urbana-Champaign have discovered a new use for these "bubbly" concoctions that will have major impact on the manufacturer of the world's thinnest, flattest, and one most useful materials -- graphene.
As graphene's popularity grows as an advanced "wonder" material, the speed and quality at which it can be manufactured will be paramount. With that in mind,...
Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.
Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...
For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.
While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...
An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.
The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...
A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.
Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...
16.08.2017 | Event News
04.08.2017 | Event News
26.07.2017 | Event News
21.08.2017 | Materials Sciences
21.08.2017 | Health and Medicine
21.08.2017 | Materials Sciences