Researchers from the University of Tokyo used computer simulations to study the rigidity of amorphous materials like glass. Image: Institute of Industrial Science, the University of Tokyo.
Researchers from the University of Tokyo used computer simulations to study the rigidity of amorphous materials like glass. Image: Institute of Industrial Science, the University of Tokyo.

Researchers from the University of Tokyo in Japan employed a new computer model to simulate the networks of force-carrying particles that give amorphous materials their strength even though they lack long-range order. Their work, which they report in a paper in Nature Communications, may lead to new advances in high-strength glass for use in cooking, industrial and smartphone applications.

Amorphous materials such as glass can possess surprising strength and rigidity, despite being brittle and having constituent particles that do not form ordered lattices. This is even more unexpected because amorphous systems also suffer from large anharmonic fluctuations. Their secret is an internal network of force-bearing particles that span the entire solid, which lends strength to the system.

This branching, dynamic network acts like a skeleton that prevents amorphous materials from yielding to stress even though it comprises only a small fraction of the total particles. But this network only forms after a 'percolation transition', when the number of force-bearing particles exceeds a critical threshold. As the density of these particles increases, the probability that a percolating network extending from one end of the material to the other will form increases from zero to almost certain.

Now, scientists from the Institute of Industrial Science at the University of Tokyo have used computer simulations to carefully show the formation of these percolating networks as an amorphous material is cooled below its glass transition temperature. In these calculations, binary particle mixtures were modelled with finite-range repulsive potentials. The team found that the strength of amorphous materials is an emergent property caused by the self-organization of the disordered mechanical architecture.

"At zero temperature, a jammed system will show long-range correlations in stress due to its internal percolating network," explains first author Hua Tong. "This simulation showed that the same is true for glass even before it has completely cooled."

The force-bearing backbone can be identified by recognizing that particles in this network must be connected by at least two strong force bonds. Upon cooling, the number of force-bearing particles increases, until a system-spanning network links together.

"Our findings may open up a way towards a better understanding of amorphous solids from a mechanical perspective," says senior author Hajime Tanaka. Since rigid, durable glass is highly prized for smartphones, tablets and cookware, this work could find many practical uses.

This story is adapted from material from the University of Tokyo, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.