Highly Conductive, Water-Repellent Graphene Circuits Created for Washable Electronics
New graphene printing technology can create electronic circuits that are economical, highly conductive, flexible and water repellent.
According to a recent paper illustrating the discovery, the nanotechnology “would lend enormous value to self-cleaning wearable/washable electronics that are resistant to stains, or ice and biofilm formation.”
“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 included on the cover of the Nanoscale journal.
The paper describes how Claussen along with some nanoengineers in his research group used inkjet printing technology to develop electric circuits on flexible materials. Here, the ink is flakes of graphene – the wonder material that is a superb conductor of heat and electricity, as well as being stable, strong and biocompatible.
The printed flakes, however, are not extremely conductive and have to be processed to eliminate non-conductive binders and weld the flakes together, increasing conductivity and making them beneficial for sensors or electronics.
That post-print process usually involves chemicals or heat. But Claussen and his team formed a rapid-pulse laser process that treats the graphene without deforming the printing surface – even if it’s paper.
Now they have found another application of their laser processing technology: taking graphene-printed circuits that can contain water droplets (hydrophilic) and converting them into circuits that repel water (super-hydrophobic).
We’re micro-patterning the surface of the inkjet-printed graphene. The laser aligns the graphene flakes vertically – like little pyramids stacking up. And that’s what induces the hydrophobicity.
Jonathan Claussen, Author
Claussen said the energy density of the laser processing can be modified to tweak the degree of conductivity and hydrophobicity of the printed graphene circuits.
That further paves way for all kinds of possibilities for new electronics and sensors, according to the paper.
“One of the things we’d be interested in developing is anti-biofouling materials,” said Loreen Stromberg, co-author of the paper and an Iowa State postdoctoral research associate in mechanical engineering and for the Virtual Reality Applications Center. “This could eliminate the buildup of biological materials on the surface that would inhibit the optimal performance of devices such as chemical or biological sensors.”
The technology could also be used in flexible electronics, electrochemical sensors, microfluidic technologies, drag reduction, de-icing, washable sensors in textiles and technology that uses graphene structures and electrical simulation to create stem cells for nerve regeneration.
The researchers wrote that additional studies should be performed to better understand how the nano- and microsurfaces of the printed graphene develops the water-repelling capabilities.
The latest studies have been supported by grants from the National Science Foundation, the U.S. Department of Agriculture’s National Institute of Food and Agriculture, the Roy J. Carver Charitable Trust plus Iowa State’s College of Engineering and department of mechanical engineering.
The Iowa State University Research Foundation aims to patent the technology and has optioned it to an Ames-based startup, NanoSpy Inc., for possible commercialization. NanoSpy, located at the Iowa State University Research Park, is creating sensors to detect salmonella and other pathogens in food processing units. Stromberg and Claussen are part of the company.
The graphene printing, processing and tweaking technology is turning out to be very beneficial, Stromberg said. After all, “electronics are being incorporated into everything.”