This image shows the effect of strain on graphene oxide sheets, which take on a corrugated form when pulled apart. Image: Ajayan Research Group/Rice University.The same slip-and-stick mechanism that leads to earthquakes is also at work on the molecular level in nanoscale materials, where it determines the shear plasticity of the materials, according to scientists at Rice University and the State University of Campinas, Brazil. The Rice lab of materials scientist Pulickel Ajayan found that random oxygen molecules scattered within layers of otherwise pristine graphene affect how the layers interact with each other under strain.
Plasticity is the ability of a material to permanently deform when strained. The Rice researchers wanted to see how graphene oxide ‘paper’ would handle shear strain, in which the sheets are pulled by their ends. Such knowledge is important when making novel advanced materials, said Chandra Sekhar Tiwary, a Rice postdoctoral research associate and lead author of a paper describing the research in Nano Letters.
"We want to build three-dimensional structures from two-dimensional materials, so this kind of study is useful," he said. "These structures could be a thermal substrate for electronic devices, they could be filters, they could be sensors or they could be biomedical devices. But if we're going to use a material, we need to understand how it behaves."
The graphene oxide paper they tested was a stack of sheets that lay atop each other like pancakes. Oxygen molecules ‘functionalized’ the surfaces, adding roughness to the otherwise atom-thick sheets of graphene.
In experiments and computer models, the team found that with gentle, slow stress, the oxides would indeed catch, causing the paper to take on a corrugated form when the layers were pulled apart. But a higher strain rate made the material brittle. "The simulation performed by our collaborators in Brazil provides insight and confirms that if you pull it very fast, the layers don't interact, and only one layer comes out," Tiwary said.
"After this study, we now know there are some functional groups that are useful and some that are not," he added. "With this understanding we can choose the functional groups to make better structures at the molecular level."
This story is adapted from material from Rice University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.