Resonance induced wetting state transition of a ferrofluid droplet on superhydrophobic surfaces

• We have analyzed wetting transition on a super-hydrophobic surface.
• We have carried experiments on a ferrofluid droplet in a oscillating magnetic field.
• We have shown that wetting transition occurs at the resonance conditions.
• Experiments suggest that when the external pressure overcomes the threshold pressure transition occurs.

We investigated manipulating wetting transitions of ferrofluid droplets on planar superhydrophobic surfaces by electromagnetic stimulation. We showed that even if magnetic forces are small at small liquid volumes (1–10 μl), they can be effectively used to induce Cassie to Wenzel transition when the exciting frequency is close to the resonant frequency. We related the wetting transition to the increase of the Laplace pressure as a consequence of the large deformation that occurs close to the resonant frequency; on the contrary, inertia forces were not able to induce such a transition. This study promises a new approach to manipulate ferrofluid droplets for various microfluidic and lab-on-chip technologies.