Research Team Discovers New Behavior of Friction
A group of physics students and their faculty advisor recently tested a theory that was thought untestable and observed an atomic behavior that had never been seen before. Their findings could mean big things for the future of friction and wear-reduction technologies.
The team, advised by Masahiro Ishigami, Ph.D., associate professor of physics and nanoscience technology, had its paper published in Scientific Reports, a Nature publication, on August 24. The team was composed of two UCF physics graduate students, Michael Lodge and Brandon Blue, as well as a former UCF postdoctoral fellow, Ben Dawson. Additional contributors include William Hubbard from UCLA and Dr. Chun Tang and Prof. Ashlie Martini from U.C. Merced.
The team tested the friction of gold nanocrystals on graphite at high surface speeds and compared the results to the predictions of Guerra, Tartaglino, Vanossi, and Tosatti made in their 2007 study. That 2007 study theorized that these nanocrystals can slide with extremely low friction when “kicked” rapidly across a graphite surface.
“It [friction] sounds so easy to understand, but it turns out that the reason there’s friction of a certain magnitude at certain surfaces is not understood in terms of fundamental science,” Ishigami, who holds a doctorate in physics, said.
The UCF researchers conducted the experiments. Ishigami describes the actual testing of the theory as a considerable challenge for the group. At the beginning of the research period, no system existed to “kick” the gold nanocrystals at the necessary velocity.
“Theorists do their best to make their parameters reasonable,” Blue said. “But in the end, they aren’t in a lab, and rely on experiments to fine-tune some of the parameters.”
Undeterred, the team used a quartz crystal microbalance, a sensor that can detect a few layers of atoms on its surface.
They grew their own graphene in their lab at UCF, which is a single atomic layer of graphite. They then performed experiments in an absolutely clean vacuum chamber, which was used to conduct the experiment without any risk of outside contamination.
They found that the gold nanocrystal’s lubricity actually exceeded the prior calculations – meaning that the friction was even lower than expected. The nanocrystals in their experiment behaved in a way that had never been observed before.
“[The 2007 study] predicted this incredible effect that was thought to be impossible to measure,” Ishigami said. “We measured it, and it’s actually even better than predicted.”
Ishigami said that there has been an active push for further research on the mechanism of friction at a nanoscale. A lack of understanding of this level of friction accounts for what the team estimates to be $250 billion worth of “wear and tear” annually. Even a small reduction of friction can have a large economic impact.
The find is revolutionary in that it illustrates completely new behavior by these nanocrystals.
“It’s very surprising that we observed this,” Lodge, the lead researcher of the team, said. “It means that the interactions of these systems are not what people thought they were.”
Applications involving graphene-based technology are slowly on the rise, Ishigami said. He credits the lofty material price of graphene as a factor in why it has only begun to rise to prominence in the last two years with improvements in production techniques. The UCF team’s work was funded by a Career grant from the National Science Foundation.
The team is actively looking for collaborators and one day hopes to put graphene-based friction reduction technologies in applications ranging from micro-machines to gears and bearings used in cars. But for now, these UCF scientists are busy building a solid technological foundation for these systems of the future.