Controlled coalescence of two immiscible droplets for Janus emulsions in a microfluidic device

We developed a simple microfluidic device to prepare Janus emulsions by the controlled coalescence of two immiscible droplets. We could prepare Janus emulsions with different sizes and structures by changing three phase flow rates and the concentration of additives in different phases, and by controlling the equilibrium contact angle θ AB in the range of 120° to 190°. Furthermore, we firstly found that the coalescence process of two immiscible droplets would be quicker when the equilibrium structure of the Janus emulsion tends to be ‘complete engulfing’. The results will be helpful for preparing Janus emulsions with controlled structures in a microfluidic device.