New theory predicts a way to double the strength of glass

As long as there are no surface cracks, glasses can withstand tremendous stress.  However, a new investigation by researchers at Rice University proposes that glass could be made even stronger. The study suggests that by adopting a technique similar to…

As long as there are no surface cracks, glasses can withstand tremendous stress.  However, a new investigation by researchers at Rice University proposes that glass could be made even stronger. The study suggests that by adopting a technique similar to the vapor deposition used to make films, the strength of glass could be doubled.  To do so, the researchers, who reported their results in the Proceedings of the National Academy of Sciences, investigated where glass had the biggest room for improvement.“The theory is as much about the weakness of glass as it is of the strength [of glass],” says Peter Wolynes, a senior scientist with the Center for Theoretical Biological Physics at Rice’s BioScience Research Collaborative. Wolynes’s new theory states that current glasses are made at about a quarter of ideal strength. When glass cools from a liquid to solid, its atoms arrange themselves randomly. This event, called random first order transition, is partially why glass is resistant to breaking; the randomly deposited atoms form tight bonds that are not easily disrupted. Though this intrinsic property makes glass stronger than crystalline formations, there may be ways to make it stronger, says Wolynes. The property he examined was yield stress, the amount a material can bend before it breaks. Current glasses have a lower yield stress than they could have. This is because the disordered nature of the atoms creates a higher configurational entropy, reflecting the amount of energy that remains after the cooling process. The higher the configurational entropy, the less stable the material.But going all the way to a completely ordered configuration also has its problems. Materials that are completely crystalline also have a low yield stress because fractures can occur along grain boundaries.  So forming stronger glass is about creating a balancing act between amorphous and crystalline states, says Wolynes. “Most glasses…have a configurational entropy of 0.8 kB [Boltzmann constant] per molecular unit,” he says. “If you were able to cool things much, much more slowly, you’d be able to get that number down.” If the number could be brought close to zero, the glass would be as strong as ideally possible while remaining amorphous.One alternative to slow cooling is using vapor deposition similar to that used to make films. Creating a glass one microscopically thin layer at a time may help atoms line up in a slightly more orderly manner. This effect could help increase elastic modulus and prevent shear banding, a force that creates weak points along the glass.Still, the theory predicts that the technique would not be perfect. The investigation into yield stress doubles the strength of glass, but that only brings it about halfway to ideal strength, says Wolynes. Further investigations into the properties of glass, how it cools, and how its atoms interact will be needed to push the strength of glass even farther.The abstract for this paper can be found here.