New graphene printing technology can produce electronic circuits that are low-cost, flexible, highly conductive and water repellent. The nanotechnology "would lend enormous value to self-cleaning wearable/washable electronics that are resistant to stains, or ice and biofilm formation," according to a recent paper describing the discovery. "We're taking low-cost, inkjet-printed graphene and tuning it with a laser to make functional materials," said Jonathan Claussen, an Iowa State University assistant professor of mechanical engineering, an associate of the U.S. Department of Energy's Ames Laboratory and the corresponding author of the paper recently featured on the cover of the journal Nanoscale.
The paper describes how Claussen and the nanoengineers in his research group use inkjet printing technology to create electric circuits on flexible materials. In this case, the ink is flakes of graphene -- the wonder material can be a great conductor of electricity and heat, plus it's strong, stable and biocompatible. The printed flakes, however, aren't highly conductive and have to be processed to remove non-conductive binders and weld the flakes together, boosting conductivity and making them useful for electronics or sensors. That post-print process typically involves heat or chemicals. But Claussen and his research group developed a rapid-pulse laser process that treats the graphene without damaging the printing surface -- even if it's paper. And now they've found another application of their laser processing technology: taking graphene-printed circuits that can hold water droplets (they're hydrophilic) and turning them into circuits that repel water (they're superhydrophobic). "We're micro-patterning the surface of the inkjet-printed graphene," Claussen said. "The laser aligns the graphene flakes vertically -- like little pyramids stacking up. And that's what induces the hydrophobicity." Claussen said the energy density of the laser processing can be adjusted to tune the degree of hydrophobicity and conductivity of the printed graphene circuits. And that opens up all kinds of possibilities for new electronics and sensors, according to the paper.