Microfluidic preparation of double emulsions using a high aspect ratio double co-flow device

Abstract

An innovative microfluidic device for one-step production of W/O/W and O/W/O double emulsions is introduced. The proposed geometry inspired by a combination of single and two-step methods consists of two same-level co-flow configurations with a high aspect ratio of height to the channel's width. The designed geometry offers a mechanism to generate double-emulsion drops without requiring regular partial surface modification methods. It offers a simple, robust, and permanent method to fabricate compound droplets in a profoundly controlled manner. Due to the high aspect ratio of the designed geometry, the inner phase jet stream remains enclosed to the middle phase jet, which prevents it from encountering microchannel walls. Hence, the wettability of the channels' surface does not influence the core droplet, implying the double emulsion formation can be achieved without requiring partial wettability treatment. The effects of continuous phase flow rate on the double emulsion size and formation frequency are experimentally investigated. The proposed microfluidic device is able to fabricate relatively high monodispersed and high throughput double emulsions successfully, i.e., the generation frequency can be reached up to 350 Hz while the monodispersity remains below 6%.