Water-repellent circuits for washable electronics

US researchers have developed graphene printing technology that can produce flexible, low-cost, conductive and water-repellent electronic circuits. Described in the journal Nanoscale, the technology would lend itself to self-cleaning wearable/washable electronics that are resistant to stains, ice and biofilm formation.

Nanoengineers at Iowa State University, led by Assistant Professor Jonathan Claussen, used inkjet printing technology to create electric circuits on flexible materials. The ink in question was in fact flakes of graphene — a great conductor of electricity and heat that is additionally strong, stable and biocompatible. The printed flakes, however, aren’t highly conductive and have to be processed to remove non-conductive binders and welded together, boosting conductivity and making them useful for electronics or sensors.

This post-print process typically involves heat or chemicals, but Claussen and his research group previously developed a rapid-pulse laser process that treats the graphene without damaging the printing surface — even if it’s paper. 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. This opens up all kinds of possibilities for new electronics and sensors.

“One of the things we’d be interested in developing is anti-biofouling materials,” said study co-author Loreen Stromberg. “This could eliminate the build-up of biological materials on the surface that would inhibit the optimal performance of devices such as chemical or biological sensors.”

The technology could also have applications in flexible electronics, washable sensors in textiles, microfluidic technologies, drag reduction, de-icing, electrochemical sensors and technology that uses graphene structures and electrical simulation to produce stem cells for nerve regeneration.

The Iowa State University Research Foundation is working to patent the technology and has optioned it to Iowa-based start-up company NanoSpy, which is developing sensors to detect pathogens in food processing plants for possible commercialisation. The researchers also believe that further studies should be done to better understand how the nano- and microsurfaces of the printed graphene create the water-repelling capabilities.

Image caption: Jonathan Claussen and his research group are printing and processing graphene ink to make functional materials. Image credit: Christopher Gannon.