Formation of double emulsion droplets in flow-focusing microchips: a numerical parametric study

A microfluidic chip is introduced for generating double emulsion droplets, consisting of a coaxial focusing center structure combined with a flow-focusing structure. The volume of fluid method (VOF) was adopted to numerically simulate and validate the formation of double emulsion droplets in the device. The impact of microfluidics on the dimensions and molding position of double emulsion droplets was examined under varying flow parameters and physical properties. Results demonstrate that the impact of the alteration in the flow rate of the middle phase is pivotal in the droplet generation process in comparison to the outer phase. An increase in the flow rate of the middle phase results in a notable enlargement of the double emulsion droplets. An increase in viscosity affects the forming regime, causing a transition in the droplet regime. Furthermore, interfacial tension exerts a notable impact on the positioning of droplet formation. The microfluidic device outlined in this paper effectively generates double emulsion droplets characterized by high monodispersity and excellent stability, which serves as a new reference for the practical generation of double emulsion droplets.