Nikolay Borodinov1 2 Anton Ievlev2 Jan-Michael Carrillo2 Andrea Calamari3 Marc Mamak3 John Mulcahy3 Bobby Sumpter2 Olga Ovchinnikova2 Petro Maksymovych2

1, Clemson University, Clemson, South Carolina, United States
2, Oak Ridge National Laboratory, Oak Ridge, Tennessee, United States
3, Procter & Gamble, Cincinnati, Ohio, United States

Triboelectric charging is one of the oldest manifestations of electricity known to mankind, however, its relevance for fundamental studies and applied research has rapidly increased in the recent years. Novel methods of energy harvesting such as triboelectric nanogenerators require strong ability to develop electrical charge while materials on the industrial production line should show the opposite trend to avoid handling issues and eliminate associated costs. Thus, practical applications prompt the development of techniques that can reliably identify the best candidates by their ability to develop tribological charge customized for a specific application.
Most prior works have explored the charging of the material with the localized probe. This approach has a general limitation that contact charging is convolved with the simultaneous discharging into the probe itself, as well as diffusion of static charge across the surface. Moreover, the rate of probe-surface motion is orders of magnitude smaller than the characteristic parameters of macroscopic triboelectric processes.
We developed a different approach that quantifies localized discharge of a previously charged surface. Force-distance curves acquired using scanning probe microscopy, were used to quantify the static charge density and observe its dynamics in real time. We demonstrate the capabilities of this methodology directly on industrial polymer samples – representing surfaces of commercial plastic bottles. Specifically, we investigate the efficiency of macroscopic charging, nanoscale discharging, and nanoscale recharging following a partial discharge. We directly observe the dynamics of the triboelectric charge and quantify its surface mobility, within the approximations of a continuum electrostatic model. At the same time, we show that it is possible to reliably differentiate polymer compositions based on their propensity to accumulate triboelectric charges. This is relevant to the handling of industrial bottles on production lines, where static charge can present significant challenges to handling and scale-up.

Acknowledgements: authors would like to thank Procter & Gamble Company for the funding of the project. The experiments have been carried at the Center for Nanophase Materials Sciences, Division of User Facilities, US Department of Energy.
Borodinov et al., submitted to Nano Lett. (2017)