A new model of the energy landscape of glass shows that the landscape contains fractal basins (far right) that are rougher than previously thought. Credit: Duke U.
Glass is a mystery.
That’s because because glasses are amorphous and lack the degree of order achieved in crystalline structures. In a glass, molecules are held in place by their neighbor molecules in less predictable and disordered configurations.
Because of these interesting features, the thermodynamics of glass states are not described by a simple model. But research from Duke University offers insights that may be help to unlock these mysteries by providing a new energy landscape of glasses. The work shows that the landscape, which maps all possible energy positions of the glass molecules, is much rougher than previously believed.
According to a Duke press release, lead author Patrick Charbonneau says, “There have been beautiful mathematical models, but with sometimes tenuous connection to real, structural glasses. Now we have a model that’s much closer to real glasses.” Charbonneau, a professor of chemistry and physics at Duke, and a team of scientists used mathematical models and theory to analyze how glass molecules behave, complete with a new energy landscape and phase diagram.
The article, published in Nature Communications, establishes a new model in which the molecules within a glass settle into fractal states within basins in the energy landscape (see image above). In the paper, the authors liken movement between the energy positions to boating on a system of lakes:
“In the liquid, all of the space can be explored. At lower water levels, each basin is a different glass. The free energy barriers hinder passing from one glass to another; the basin width allows for vibrational relaxation. The water level further determines what features of the landscape are experienced. Deep into the glass, the landscape roughness results in intra-state barriers that are associated with secondary relaxations. In [the proposed model, far right above] at very low water levels—deep into the fractal glass—lakes transform into a complex wetland with a hierarchy of small ponds. The very bottom of each of these ponds corresponds to a given realization of the force network, but the identification of the force contacts remains undetermined before the fractal regime is reached.”
According to the press release, “The new description makes sense of several behaviors seen in glasses, like the property known as avalanching, which describes a random rearrangement of molecules that leads to crystallization.”
The authors say their work could lead to better control of aging of glasses and help manipulate the properties of manufactured glasses.
The paper is “Fractal free energy landscapes in structural glasses” (DOI: 10.1038/ncomms4725).
Feature image credit: Jdrewitt, Wikimedia Creative Commons License.