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John O | February 2018

Flexible, water-repellent graphene circuits developed for washable electronics

by josh perry, editor


scientists at iowa state university (ames, iowa) used inkjet printing technology to build circuits on flexible materials using flakes of graphene that are then welded together with a rapid-pulse laser process that removes non-conductive binders and can be used on any surface, even paper.


jonathan claussen and his research group are printing and processing graphene ink to make functional materials. (christopher gannon/iowa state university)


according to a report from the university, this process has been adapted to turn hydrophilic graphene-printed circuits into super-hydrophobic circuits.


the laser process is used to align the graphene flakes vertically to induce hydrophobic properties and it can be tuned to alter the amount of hydrophobicity and conductivity is present in the graphene circuits.


“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 article explained.


researchers also want to create circuits that avoid the buildup of biological materials on the surface, an issue that has hindered the manufacture of chemical or biological sensors.


further study will go into the nanostructures of the graphene to better understand what is causing the change in properties. the technology is currently being optioned to ames-based startup nanospy, inc., which is building sensors to detect salmonella and other pathogens in food processing plants.


the research was recently published in nanoscale. the abstract read:


“solution-phase printing of exfoliated graphene flakes is emerging as a low-cost means to create flexible electronics for numerous applications. the electrical conductivity and electrochemical reactivity of printed graphene has been shown to improve with post-print processing methods such as thermal, photonic, and laser annealing. however, to date no reports have shown the manipulation of surface wettability via post-print processing of printed graphene.


“herein, we demonstrate how the energy density of a direct-pulsed laser writing (dplw) technique can be varied to tune the hydrophobicity and electrical conductivity of the inkjet-printed graphene (ipg). experimental results demonstrate that the dplw process can convert the ipg surface from one that is initially hydrophilic (contact angle ∼47.7°) and electrically resistive (sheet resistance ∼21 mω ?−1) to one that is superhydrophobic (ca ∼157.2°) and electrically conductive (sheet resistance ∼1.1 kω ?−1).


“molecular dynamic (md) simulations reveal that both the nanoscale graphene flake orientation and surface chemistry of the ipg after dplw processing induce these changes in surface wettability. moreover, dplw can be performed with ipg printed on thermally and chemically sensitive substrates such as flexible paper and polymers.


“hence, the developed, flexible ipg electrodes treated with dplw could be useful for a wide range of applications such as self-cleaning, wearable, or washable electronics.”

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