Asymmetric generation and volume prediction of Janus droplet in microchannel

The behavior of neck breakup and the prediction of droplet volume during Janus droplet generation are investigated experimentally. The generation processes of Janus droplets can be divided into four distinct stages: the uniform extension stage, the accelerated extension stage, the radial necking stage and the rapid breakup stage, while the first two stages represent the filling stage of the droplet tip. Under varying continuous phase flow rates, the diameter of the droplet neck has the uniform evolution with time, and the droplet interface profiles exhibit self-similar characteristics. Differences in the physical properties of the two dispersed phases result in asymmetric contraction at the upper and lower interfaces of the Janus droplet neck, but this influence is reduced near the breakup time of the droplet in the way that the neck contraction tends to synchronize. The volume prediction model is proposed based on the local capillary number of the continuous phase, which demonstrates that the droplet volume consistently decreases as the continuous phase flow rate increases.