Electrostatic instability of liquid droplets on MEMS-based pillared surfaces

• MEMS-based pillared surfaces with well-defined solid fraction of 0.01 were microfabricated.
• The effect of the pitch with the constant solid fraction on the Cassie-to-Wenzel transition of different liquid properties is clarified.
• A mathematical model incorporating the pinning force is proposed to estimate the critical voltage of the Cassie-to-Wenzel transition.

sThe 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.