A quantitatively consistent, scale-spanning model for same-material tribocharging

Although tribocharging occurs ubiquitously and is widely studied, we still don't know how it works. It is not difficult to imagine why charge exchange might occur with different materials—any number of parameters (e.g. electron affinity, hydrophobicity, acidity/basicity) could break symmetry to drive transfer. Yet there is a little known but perfectly reproducible fact that makes tribocharging even more perplexing: even identical materials, when contacted together, still exchange electrical charge. It has been proposed that such 'same-material' tribocharging arises due to surface heterogeneity of some hereto unknown charge-driving parameter. This model correctly predicts that the scale of charge transfer grows with the square root of the contacting area. However, to reconcile it with experimental data, the size of individual donors/acceptors must be 1/100th the size of a hydrogen atom—a physical impossibility. To resolve this conundrum, we propose that charge donors/acceptors come in mesoscale patches. By accounting for the spatial correlations of these patches, we develop a model for same-material tribocharging that is able to make sense of several inconsistencies in the literature, including the impossibly small donors/acceptors previously mentioned, thus shedding potential light on this perplexing phenomenon.