Studies of the Fundamental Mechanisms of Contact Electrification

We present results of investigations into the underlying mechanisms that drive the long observed phenomenon of contact electrification. Our experiments indicate identical single-crystal insulators are able to exchange charge at magnitudes comparable to charge transfer between dissimilar materials. Any complete theory of contact electrification must be held accountable to these observations, leading to significant constraints on possible underlying mechanisms of charge transfer between insulators. This self-charging behavior does not appear random when repeated contacts are made, suggesting the possibility of a nucleation-type event developing from seed charges. The confirmation of such a mechanism would require a probe capable of monitoring the charge distribution on the materials' surfaces without affecting the charge distribution. This effect could be direct (e.g. via polar interactions between the tip and sample or by encouraging discharges to the probe) or requiring substantial time to collect data between charging contacts, which could allow for charge redistribution or neutralization, obscuring information on the growth of charge patches.To this end, we demonstrate a novel non-destructive in-situ method of probing the charge distribution, including bipolar charging, on the surfaces of the contacting materials. This method also allows for determination of discharges and charge re-distribution during the experiment. This unprecedented understanding of charge carrier behavior immediately before and after contact provides key clues to the nature of the charge carriers in contact electrification and the underlying mechanism. These results provide constraints on both electron-dominant and ion-dominant theories of charge transfer and significantly narrows the field of possible mechanisms. Another significant aspect of this work is that it provides an explanation as to why a subject studied with so much interest for such a substantial period of time has failed to provide a definitive understanding of the topic. We find charge transfer is highly variable, even in the situation of like materials, and provides insight as to why the results of contact electrification experiments can have such high variation between runs or even individual contacts. We have found that the nature of the contact between two insulating materials, in terms of alignment and amount of rub, have dramatic effects on the charging behavior