Simulation studies on picolitre volume droplets generation and trapping in T-junction microchannels

Abstract

In this paper, we present simulation studies on the formation of water microdroplets in mineral oil in a T-junction Microfluidics device. We have studied the droplet generation in two different regimes, viz., squeezing and squeezing to dripping transition regime. The effect of fluid flow rates, and surfactant concentration on the droplet generation has been investigated. It is seen that a rise in the concentration of surfactant by 4%, increases the frequency of droplet generation by 16% at the higher capillary number (Ca= 0.02), whereas, there is only a marginal or no change in the case of squeezing regime (Ca = 0.0028–0.008). We have also studied the trapping of the generated microdroplets in microwells. It is observed that the trapping of the droplet is highly influenced by the viscous drag force, droplet length, the surface energy of the droplet, droplet speed, depth of the Well for trapping and alignment of the two plates constituting the device. Our studies reveal that the droplets travelling faster than a critical trapping velocity do not get trapped in the Well. Addition of a surfactant to the mineral oil is seen to lead to a significant reduction in the critical velocity for the droplet trapping. Trapping of droplets travelling at velocities close to the critical velocity for trapping depends strongly on the alignment of the two plats of the Slip-Chip device. © 2020, Springer Nature Switzerland AG.