How Spontaneous Electrowetting and Surface Charge affect Drop Motion

It is unclear how this charge separation affects the contact angles of a sliding drop. We slide grounded and insulated drops on hydrophobic surfaces at low capillary numbers.

We find that the drop charge leads to spontaneous electrowetting which decreases the contact angles. The deposited charges lead to surface charge effect and decrease the contact angle. Both phenomena compensate each other at the receding contact line, resulting in an insignificant change in receding contact angle of a sliding drop.