Glass may appear to be a perfectly ordered solid, but the chaotic structure of its particles resembles the turbulent chaos of a free-falling liquid that solidifies over time.
Materials in this state, known as amorphous solids, defy simple description. New research involving computation and simulation provides clues. In particular, it suggests that we don’t know that there is some sort of recombination somewhere between the liquid and solid states.
According to According to scientists Dimitrios Vragakis, Mohamed Hashem and Granti Mantadabo of the University of California, Berkeley, there is a temperature boundary behavior for supercooled liquids and solids in which stable particles are excited and “contract”.
We are widely aware of the three basic states of matter in everyday life: solid, liquid, and gas or vapor. Each is defined by the relationships between its molecules and the environment.
When one of these elements changes into another—melting a solid into a liquid or evaporating a liquid into a gas, for example—it’s called a transformation.
But the matter is more complicated than these three basic stages. Atoms become so hot that their charges separate to form plasma. Upon cooling, certain types of particles lose their identity entirely and merge into quantum blur.
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Amorphous solids They are strange mixtures of well-ordered solids and liquids that do not bind together. Particles within solids tend to form predictable connections with their neighbors.
It is not clear how these seemingly random connections transition from viscous streams of liquid molecules to a stable landscape.
A very common example uses glass, the building blocks of oxygen and silicon flux when heated. On slow cooling, these particles have time to form an organized crystalline structure called quartz. If cooled rapidly, the particles somehow retain a disordered structure; It is the point at which it becomes an amorphous solid, and the temperature at which this occurs is the onset temperature.
Vragidakis, Hasim, and Mandadapo used calculations and simulations, along with results from previous experiments, to determine that this transition is not so sharp that it is characterized by the peculiar behavior of particles between their normal liquid states and their supercooled states.
“Our theory predicts the initial temperatures measured in model systems and explains why supercooled liquids behave like solids at these temperatures, even though their structure is similar to that of a liquid.” Mantabo explains.
“The onset temperature of glass dynamics is the same as the melting temperature at which a supercooled liquid ‘melts’ into a liquid. This should be relevant for all supercooled liquids or glass systems.
Although the total flux of atoms in a supercooled liquid is almost zero, the particles constantly change their composition as they become stuck in place, leading to motions known as impulses. Researchers manipulate these excitations in a supercooled 2D liquid, such as defects in a crystalline solid, and calculate what happens when the temperature changes.
They discovered that at an initial temperature the corresponding exciton pairs relax, causing the material to lose its solidity and behave as a normal liquid.
The team hopes that their model can be extended to understand how change works in three dimensions and provide a theoretical basis for future experimental work.
“The whole effort is to separate a supercooled liquid from a liquid at a higher temperature under a microscope.” Mantabo says.
“It is fascinating from a basic science perspective to study why these supercooled liquids exhibit different dynamics than the ordinary liquids we know.”
Published in Research Proceedings of the National Academy of Sciences.
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