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Making superhydrophobic surfaces with magnetic elastomer : towards controlled droplet movement
In the field of superhydrophobic surfaces, natural surfaces exhibiting non-wetting filament networks remain a challenge to understand. Indeed, if classical superhydrophobic surfaces developed roughness at different scales, superhydrophobicity on hairy surfaces shows elastic behavior that is more difficult to model. Our approach was to elaborate model surfaces with high aspect ratio elastomeric pillars. By changing the geometry of the structures, we controlled stiffness and surface density to elucidate the role of elasticity upon wetting properties in the Cassie state. Using compliant pillars, we were able to measure the forces exerted by the contact line on the pillars. Unexpectedly, despite the deformations incurred by the pillars, the contact angle (either advancing or receeding ones) and the drop-sliding angle did not change significantly with the Young modulus of the pillars, in the range of 60 kPa to 2400 kPa.
Finally, we demonstrated that it is possible to induce the step by step motion of a droplet on a tilted surface by the application of a magnet above magnetically functionalized elastomeric pillars array (fig.1). The macroscopic movement of the droplet origins the microscopic depinning of the contact line at the rear of the droplet, comparable to a stick-slip dewetting phenomena.
- Fig. 1 : Step by step motion of a droplet on a tilted surface and corresponding snapshots. Each step is obtained by an individual magnet scan.