Research of double emulsion formation and shell-thickness influence factors in a novel six-way junction microfluidic device

Abstract

The six-way junction microfluidic device has been widely used to prepare thin-shelled double emulsions as templates for liposomes. However, there is little numerical research of double emulsion formation in this device, and the influence factors of shell thickness still need to be further explored. In this paper, numerical simulations based on the VOF method are conducted to investigate double emulsion formation and shell-thickness influence factors in the six-way junction microfluidic device. Moreover, a new concept named relative shell thickness is proposed to intuitively reflect the relationship between the shell thickness and drop size. By the simulations, the double emulsion formation mechanisms at three typical flow regimes are revealed, including dripping, narrowing jetting, and widening jetting. The effects of operation parameters on the flow regime, double-emulsion droplet size and shell thickness are discussed. Results indicate that capillary numbers not only affect the flow regime but also the droplet size and shell thickness. It also finds that the effect of the middle fluid flow rate on the shell thickness is larger than the outer fluid flow rate and that the thin-shelled double emulsions are mainly generated in dripping. This paper reveals the change law of shell thickness with varied operation parameters and can guide for preparing double emulsions with controllable shell thickness in the six-way junction microfluidic device.