Deposition of micrometric water droplets on rough hydrophobic surfaces

In this talk, we present new experimental observations of a droplet sliding down an inclined, rough hydrophobic surface. Periodic micrometer-scale grooves were fabricated on smooth PDMS surfaces using a commercial laser cutter. A millimetric water droplet was then deposited on the inclined surface and the resulting contact-line dynamics were visualized using high-speed imaging.  We found that a micro-capillary bridge was formed at each structure, which ultimately ruptured at the trailing edge of the sliding water droplet.  This detachment mechanism resulted in the deposition of a trail of uniform micrometric droplets on top of the periodic substrate. The size of the isolated droplets was sensitive to both the droplet sliding velocity and the dimensions of the grooved structures; in particular, the size of the droplet increases with increasing droplet velocity as well as the spacing between the structures. Potential applications and future directions will be discussed.