Uncovering molecular mechanisms of electrowetting and saturation with simulations.

Molecular dynamics simulations are used to explore the physical mechanisms of electrowetting and the limits of continuum theories. Nanoscale drops exhibit the same behavior seen in macroscopic experiments: The contact angle θ follows continuum theory at low voltages and then saturates. Saturation limits applications of electrowetting and its origin is of great interest. In the simulations, saturation occurs when ions are pulled from the drop by large local fields. Saturation can be controlled by changing temperature, screening, or the energy binding ions to the fluid. We show a local force balance equation for θ remains valid even after saturation and that the interface approaches the equilibrium contact angle within a few nanometers of the solid.