Yeah, that seems possible too. So what are all the things which could be going on here?
Thinking out loud, at the interface we have:
- net positivity on the upswing side, as you point out
- differing net velocities of the droplet's sides w/r/t the electron rain
- viscous drag at the boundary with the oil
Outside the interface, the oil feels a field from the static charge on the disk in motion, like a current loop. So there's an induced magnetic field perpendicular to the rotation, which then let's us include the Lorentz force on the electron rain near the boundary.
...that's all I'm coming up with pre-coffee. I'll go poke at references later. Thanks for the puzzle 🙂