Electrostatic instability of liquid droplets on MEMS-based pillared surfaces

The electrostatic instability of the Cassie-state droplets for different pitches of pillared surfaces and various ion concentration of liquids has been investigated. MEMS-based pillar structures with well-defined geometrical parameters have been fabricated and wetting behaviors were characterized through systematic experiments. A mathematical model for estimating the critical voltage with which the Cassie-state liquid droplet collapses has been developed incorporating the pinning force and the surface tension under the electric field. The present model is found to be in good agreement with the experimental results, reproducing the electrostatic instability due to the pull-in of the liquid-air interface.