Implications of capillarity-wettability interaction on geometrically mediated droplet splitting mechanism

Abstract

The droplet splitting in a microchannel with different geometrical configurations viz., curved T-junction, flat T-junction and Y-shaped channel is investigated using a level set method for different wettability conditions of the wall surfaces and capillary number. The underlying physics is examined in terms of deformation of droplet, neck thickness, and the time that the droplet spends at the junction. For a Y-shaped channel, the droplet splitting takes place even for a small capillary number due to the presence of sharp bifurcating tip. On the other hand, the hydrophilic surfaces of channel wall yields into droplet splitting as compared to neutral and hydrophobic surfaces. In general, the droplet splitting is seen at higher capillary numbers whereas non-splitting and oscillating flow of droplet near the junction is observed at lower capillary number. The curved and flat T-junctions channels yield almost similar droplet splitting behaviour. In general, the Y-shaped channel with hydrophilic wall surfaces is found to be ideal configuration for droplet splitting to occur. Finally, the splitting, non-splitting and oscillating flow regimes are identified and its dependence on physicochemical parameters like wettability, capillary number and geometrical orientation are discussed. The present study establishes the significance and advancement on the droplet splitting mechanism prior to the previously reported investigations through the consideration of curve T-junction and surface wettability influence.