  Contact electrification, or tribocharging, is pertinent to a broad range of
industrial and natural processes involving dielectric materials. However, the
basic mechanism by which charge is transferred between insulators is still
unclear. Here, we use a simple apparatus that brings two macroscopic surfaces
into repeated contact and measures the charge on the surfaces after each
contact. We vary the temperature of the surfaces, and find that increasing
temperature leads to a decrease in the magnitude of charge transfer. When
paired with a Monte-Carlo simulation and TGA measurements, our results support
a mechanism where adsorbed surface water is crucial for charge exchange. Our
setup is easily extendable to a variety of industrially relevant materials.
