  While electrowetting has many applications, it is limited at large voltages
by contact angle saturation - a phenomenon that is still not well understood.
We propose a generalized approach for electrowetting that, among other results,
can shed new light on contact angle saturation. The model assumes the existence
of a minimum (with respect to the contact angle) in the electric energy and
accounts for a quadratic voltage dependence ~U^2 in the low-voltage limit,
compatible with the Young-Lippmann formula, and a ~1/U^2 saturation at the
high-voltage limit. Another prediction is the surprising possibility of a
reversed electrowetting regime, in which the contact angle increases with
applied voltage. By explicitly taking into account the effect of the
counter-electrode, our model is shown to be applicable to several AC and DC
experimental electrowetting-on-dielectric (EWOD) setups. Several features seen
in experiments compare favorably with our results. Furthermore, the AC
frequency dependence of EWOD agrees quantitatively with our predictions. Our
numerical results are complemented with simple analytical expressions for the
saturation angle in two practical limits.
