Experimental pinning-depinning mechanism of the contact line on patterned surfaces

Abstract

We study the interface fluid-air of water in a patterned surface of a microchannel with a step. Our aim is to analyze how the advancement of the front is affected by local pinning-depinnig of the contact line between the fluid and the patterned surface. Microchannels with different patterns made of PDMS were fabricated in order to study the front behaviour. The interface moves forward due to a forced imbibition created by a water pressure on a reservoir at a known height. The fluid front is characterized by a constant velocity regime along the microchannel. We have observed that the pinning-depinning mechanism generates a local avalanche of the front, as well as it is concluded that this phenomenon produces an increase of the fluid velocity after the step. The front holds in a linear regime before and after the pattern. We also see that the avalanche effect is more relevant at low pressures or low velocity conditions