Computational model and simulations of contact angle and geometry effects on centrifugal microfluidic step-emulsification

The generation of droplets in microfluidic systems is extensively applied in various chemical and biological applications. For two-phase immiscible micro-droplet formation, both actively and passively driven systems are being employed. Active systems typically include pump-based, magnetic actuation or centrifugal flow control-based methods that employ cross-flowing, flow-focusing or co-flowing microfluidic architecture to assist formation. Numerical modeling using Computational Fluid Dynamics (CFD) allows for an in-silico approach in the understanding of the micro-droplet formation behavior and the effect of several parameters on the size and rate of droplet formation. Although several such models have been presented previously for pump-driven cross-flowing, flow focusing or co-flowing microfluidic architectures, systems typically employing centrifugal actuation methods are limited. We investigate here a CFD method for modeling and simulating step-emulsification of water-in-oil, on a centrifugal microfluidics platform. The effects of contact angles, supply channel geometry, and capillary number were studied using the numerical model and compared to experimental data from previous work.