Asperity shape in flexoelectric/triboelectric contacts

Triboelectric and flexoelectric phenomena have seen significant recent interest for energy harvesting. However, the underlying science responsible for triboelectricity has yet to be completely understood, both the funda-mentals and an understanding of how the energy output depends upon the shape of the interacting surface. Here, we investigate the role of the contacting shapes (asperities) in triboelectricity. We demonstrate that their shape and size is very important, obtaining qualitative agreement with experimental results. Further, we discuss how the impact of the shape depends on material, geometric, gradient elasticity and electronic transport details. We provide scaling rules which can be exploited to better design energy harvesting devices based upon either triboelectricity or flexoelectricity.