Anisotropic Droplet Motion on Ratcheted Hydrophobic Surfaces*

Anisotropic Droplet Motion on Ratcheted Hydrophobic Surfaces

Dillon Gagnon, Dhabin Park, Kevin Yim, Svetlana Morozova

Department of Macromolecular Science and Engineering, Case Western Reserve University, Cleveland OH 44106

Anisotropic wetting and droplet transport is well documented in nature, where it is observed in butterfly wing scales to direct water droplets away from the body. While it is known that surface geometry, specifically sawtooth ratcheted surfaces play a key role in these properties the ideal geometry has yet to be determined. To understand the role of geometry on anisotropic droplet transport, we have studied water droplet motion on hydrophobically-modified blazed surfaces. These surfaces have sawtooth patterns with angles (8.62-26.70 °) and lengths (0.56 - 1.67 um) that mimic butterfly scale geometry. The motion of water droplets across the surfaces are analyzed across the three primary directions of the blazes to determine the effects of surface geometry. The droplet velocities were tracked using high speed cameras. It was found that travel with the direction of the blaze is significantly faster than travel against or along the blazes. The surfaces most resembling natural analogs (butterfly wing scales) demonstrated the highest hysteresis.