Tiny bubble removal by gas flow through porous superhydrophobic surfaces: Ostwald ripening

The fact that tiny bubbles are easily formed on the rough, hydrophobic surface results in difficulties in bubble detachment and removal. We show that bubbles captured by porous superhydrophobic surfaces merge into larger ones, which can detach by buoyancy. The responsible mechanism is convective Ostwald ripening because networklike pores in the superhydrophobic film remain nonwetted and provide passage for gas flow between adhered bubbles. A large bubble grows spontaneously by absorbing all small adhered bubbles due to capillary pressure differences. Our results demonstrate that porous hydrophobic film can be an efficient, passive way of bubble removal in microfluidic systems. (c) 2008 American Institute of Physics.