Taming "Static Electricity" with Identical Materials

Dr. Scott Waitukaitis, Insitute of Science and Technology Austria

Contact electrification (CE) defies our best attempts to make sense of it. Commonly thought of as "static electricity," the effect seems straightforward—touch two neutral materials together, separate them, and they will have exchanged some electrical charge. Simple as this sounds, we don't even know what is transferred (e.g., ions vs. electrons), let alone why. In my group, we focus on CE between "identical" materials, which, though counterintuitive, has long been known to occur. I will discuss two sets of experiments on this same-material CE. In the first, we use acoustic levitation to study the charging of an SiO2 sphere as it bounces on an SiO2 plate. We test a leading hypothesis for same-material CE, i.e., that it is due to local variability in surface properties, and show that this is not the case. Going further, we reveal that there is a critical dependence on sample history, especially RH exposure, temperature, and surface treatment, which points to surface hydroxylation. In the second experiment, we study the charge exchange between soft polymers—identically prepared samples of PDMS. 

Measuring the charge exchange for all pair combinations of an ensemble, we find they begin charging randomly but over time evolve into a triboelectric series—i.e., a transitive ordering based on the polarity of the charge acquired. We test several symmetry-breaking parameters toward finding what creates the ordering, finding that changing virtually anything has an effect. However, to our surprise, we find that the biggest effect is caused by the act of contact itself; samples that have experienced more contacts in their history charge negatively compared to ones that have experienced less. Based on this observation, we develop a model that explains why our materials evolve into a series, and going further, allows us to leverage and control the charging behavior in experiments.

Hosted by Itai Cohen. 

Scott Waitukaitis was born in Phoenix, Arizona. He obtained his bachelor’s degree in physics (honors) from the University of Arizona. He then earned his Ph.D. in Physics from the University of Chicago, where he was a Robert Millikan Fellow and the inaugural recipient of the Bruce Winstein Prize for Instrumentation. He did his postdoctoral work at Leiden University and AMOLF in the Netherlands, where he was the winner of a prestigious Veni grant from the Dutch Organization for Scientific Research. In 2019 he became Assistant Professor at the Institute of Science and Technology Austria, where he runs the Soft & Electrified Materials Lab.