  Slide electrification is a spontaneous charge separation between a surface
and a sliding drop. Here, we describe this effect in terms of a voltage
generated at the three-phase contact line. This voltage moves charges between
capacitors, one formed by the drop and one on the surface. By introducing an
adaptation of the voltage upon water contact, we can model drop charge
experiments on many surfaces, including more exotic ones with drop-rate
dependent charge polarity. Thus, the adaptive two capacitor model enables new
insights into the molecular details of the charge separation mechanism.
