Humidity transforms immobile surface charges into mobile charges during triboelectric charging

Triboelectric charging - which children see when they rub balloons on their hair - has important consequences in many industries and natural phenomena. Despite its importance, the identity of the charge carriers that lead to triboelectric charging is uncertain. For polymers, previous X-ray photoelectron spectroscopy studies definitively show that bonds break during triboelectric charging. Others have argued that a pair of co-located bond breaks release a charged fragment that acts as the charge carrier for triboelectric charging. We describe an alternative process based on density functional theory results showing that charged fragments, in the presence of water, will react to form neutral fragments and H⁺ or OH^- ions. These results show that a single bond break, which is more likely than a pair of co-located bond breaks, can then create tethered polymer fragments that in humidity will generate mobile H⁺ or OH^- charge carriers for triboelectric charging.