Droplet transport on microstructured superhydrophobic surfaces

Systematic variation of microscale structures has been employed to create superhydrophobic tracks with varying contact angle. Droplets are propelled down these tracks, overcoming contact angle hysteresis using energy supplied by mechanical vibration. The rough hydrophobic surfaces have been designed to maintain air traps beneath the droplet by stabilizing its Fakir state. Dimensions and spacing of the microfabricated pillars in silicon control the solid-liquid contact area and are designed to create varying apparent contact angles. This work introduces the solid-liquid contact area fraction as a new control variable in any scheme of manipulating droplets, presenting theory, fabricated structures, and experimental results that validate the approach.