Effect of Intersection Angle and Wettability on Droplet Generation in Microfluidic Flow-Focusing Device

This article investigates the dynamics of droplet generation process in a microfluidic flow-focusing device under the effect of geometry altered by the intersection angle (phi), which the flanking inlets make with central inlet and wall wettability quantified by the contact angle (theta) using volume of fluid (VOF) model. These parameters have been found to alter the droplet shape and size greatly. The effect of intersection angles has been examined for phi = 15 deg, 30 deg, 45 deg, 60 deg, 90 deg, and 120 deg for generating size-controlled droplets. It was predicted that the diameter of droplet increased with the increase in intersection angle (phi = 15 deg, 30 deg, 45 deg, 60 deg, 90 deg, and 120 deg) and the maximum diameter has been generated at phi = 90. In addition, the wetting characteristics (hydrophilic to hydrophobic) have been studied numerically in detail by changing the contact angle of the dispersed phase with the channel wall ranging from 90 deg to 180 deg. It was indicated that the droplets of rectangular shape are formed in hydrophilic channel by completely wetting the wall when theta <= 90 deg. They transform their shape to slightly oval form with the increase in contact angle and start acquiring spherical shape when the channel becomes hydrophobic. Furthermore, Parameters such as dimensionless droplet diameter, droplet shape, and droplet breakup time have also been investigated extensively for flowrate ratios Q = 0.125, 0.25, 0.5, and 1, in order to optimize the microfluidic device.