3D printing-assisted and magnetically-actuated superhydrophobic surfaces for droplet control

This paper presents a novel fabrication method for magnetically controllable micro-patterned wall arrays (MCMAs) for manipulating droplets. The MCMA films exhibited superhydrophobic properties (contact angle of 153.7 degrees) without additional post-treatment using the microstructure of the surface, which is a characteristic of fused-filament-fabrication-type additive manufacturing. To operate the MCMA films, the bending characteristics due to the magnetic force were analyzed, and the droplet transport pattern was verified under various conditions (e.g., structure height and droplet size). The droplet was rapidly manipulated on the MCMA films by using a magnet moved at a speed of 7.5 mm/s. The droplet showed a three-step transport pattern of backward move-ment, forward movement, and detachment depending on the relative position between the droplet and the magnet. A film composed of MCMAs with a high aspect ratio produced a continuous concave surface shape when driven by a magnetic force. The concave surfaces played an important role in the stable transport of droplets. MCMA films are expected to be applied in various scientific and industrial fields where droplet transport, mixing, and collection are used with careful droplet controlling is needed.