College of Engineering News • Iowa State University

ECpE engineers publish tribocharge stability research findings in journal

Left: A schematic diagram of the experimental setup which utilizes Kelvin probe force microscopy (KPFM) to measure the triboelectric charge on nanostructured material surfaces. Right: A typical KPFM output and its analysis result.

Iowa State University Department of Electrical and Computer Engineering (ECpE) and Microelectronics Research Center (MRC) researchers Myung Gi Ji, Qiang Li, Rana Biswas and Jay Kim recently published the outcomes of their research in Nano Energy, a prestigious journal in the field of nanoscale harvesting, storage and utilization of energy, with its impact factor at 16.6.

“It was not easy to find the right journal to publish such a complex, mixed study,” Kim said.

“Publishing it in journals for very specialized areas would reduce the readership and impact. We were delighted to find a journal [Nano Energy] which is devoted to both nanoscale and energy with a larger readership and high impact.”

Their findings characterize and analyze the time-dependent behaviors of the triboelectric charge induced on nanotextured material surfaces. Triboelectric charging is a process in which two material bodies rub against each other and the friction will induce electric charges of opposite signs on their surfaces. The use of nanotextured material surfaces allows the researchers to control the shape and strength of the friction at the nanoscale and generate unusual nano-patterned tribocharges that can be utilized for nano-lithography and energy harvesting.

To precisely control both the nanotexture and the triboelectrification process, the Iowa State researchers have adopted the technique of replica molding, in which a liquid-phase elastomer is poured onto a nano-patterned master template and shaped conformally through its solidification. The friction occurring during the peel-off process will triboelectrically charge the surface of the elastomer replica in close relation with the nano-pattern on the master template.

For long-term applications, however, the generated tribocharges must be stable. Using various surface microscopic techniques, they found that the surface electric potential generated by tribocharges on the polymer surface undergoes a fast exponential decay during the initial 1-2 hours, which is followed by a slow exponential decay over about one day. The tribocharges and surface potential settles to a steady-state value that is 60-80 percent of its initial value and then becomes stable for weeks. The fast decaying component is mostly associated with tribocharges formed by the lateral sliding between surfaces, whereas the slow decay arises from regions where there was surface-normal separation during peel-off. The outcomes will help researchers studying the temporal behaviors of the tribocharge.

Tribocharging can also be used in the widely used facial masks for virus prevention, in which charged polymer fibers in the mask electrostatically trap small viruses and pathogens. The temporal behavior of such charged fibers is critical for long-term virus capture and prevention.

“It opens a new avenue for nanoscale lithography that can be very useful for microelectronics. It helps to understand the design and functioning of common fiber-blown face masks for virus protection,” Biswas said.