Continuous flow switching by pneumatic actuation of the air lubrication layer on superhydrophobic microchannel walls

This paper introduces and experimentally verifies a method for robust, active control of friction reduction in microchannels, enabling new flow control applications and overcoming previous limitations with regard to sustainable liquid pressure. The air pockets trapped at a superhydrophobic micrograting during liquid priming are coupled to an actively controlled pressure source, allowing the pressure difference over the air/liquid interface to be dynamically adjusted. This allows for manipulating the friction reduction properties of the surface, enabling active control of liquid mass flow through the channel. It also permits for sustainable air lubrication at theoretically unlimited liquid pressures, without loss of superhydrophobic properties. With the non-optimized grating used in the experiment, a difference in liquid mass flow of 4.8% is obtained by alternatively collapsing and recreating the air pockets using the coupled pressure source, which is in line with a FE analysis of the same geometry. A FE analysis of a more optimized geometry predicts a mass flow change of over 30%, which would make possible new microfluidic devices based on local friction control. It is also experimentally shown that our method allows for sustainable liquid pressure 3 times higher than the Laplace pressure of a passive device.