Glass's perplexing strength
Posted by David Nield on 4th Oct 2020
We're Finally Getting Closer to Solving The Mystery of Glass's Perplexing Strength
4 OCTOBER 2020
A windowpane or a tumbler might shatter quite easily, but solid glass is actually a lot more rigid and strong than it technically should be, if we consider its molecular make-up.
Now, scientists have come closer to revealing the source of this secret strength.
Using a newly devised computer model to figure out how the atomic particles in glass might keep it together, despite lacking a conventionally ordered structure, a new study observes that these particles can put a force-carrying backbone in place before the glass fully cools from an unstable, viscous state.
The calculations showed that the skeleton of particles taking the strain inside viscous glass successfully met the percolation threshold – the point at which this particle network is dense enough to support the material and keep it strong.
When a granular material is compressed so much it forms a solid - think of compacting grains of sand, for example - researchers describe the resulting solid as a 'jammed system'. These systems bear some similarities to what happens in cooling glass, and the team used their computer model to compare the two.
"At zero temperature, a jammed system will show long-range correlations in stress due to its internal percolating network," says physicist Hua Tong, from Shanghai Jiao Tong University in China.
"This simulation showed that the same is true for glass even before it has completely cooled."
Glass is part of a group of amorphous solids that lack the normal long-range order and lattice pattern in their atoms and molecules that is found in crystals, despite being as strong in cooled form.
Instead, a small proportion of the overall particles take the strain, in the midst of general chaos and disorder, from a microscopic perspective. However, those force-bearing particles need to spread or percolate far enough through the material first, and this study highlights how that percolation takes place as the material undergoes glass transition.
Particles in this critical network must be connected by at least two strong bonds, the scientists explain, at which point a network can form that links the entire system together – even if most of the molecular arrangement is disordered.
Glass is one of the most fascinating materials for scientists, not least because it changes so much depending on whether it's heated or cooled. It might even represent a new state of matter at very low temperatures.
Studies have even shown glass apparently defying the laws of thermodynamics, confounding scientific predictions about how it should behave under certain conditions. All these findings make the study of glass about not just glass itself, but about everything we understand to be true in physics.
Developing tougher, more rigid and longer-lasting glass is useful in all kinds of products, from cookware to smartphones, and the researchers are hoping that their findings lead to new, practical innovations for this material, as well as more detailed lab tests.
"Our findings may open up a way towards a better understanding of amorphous solids from a mechanical perspective," says physicist Hajime Tanaka, from the University of Tokyo.
The research has been published in Nature Communications.