  Slide electrification - the spontaneous charge separation by sliding water
drops - can lead to an electrostatic potential of 1 kV and change drop motion
substantially. To find out, how slide electrification influences the contact
angles of moving drops, we analyzed the dynamic contact angles of aqueous drops
sliding down tilted plates with insulated surfaces, grounded surfaces, and
while grounding the drop. The observed decrease in dynamic contact angles at
different salt concentrations is attributed to two effects: An electrocapillary
reduction of contact angles caused by drop charging and a change in the free
surface energy of the solid due to surface charging.
