Dynamics of obstructed droplet breakup in microfluidic T-junction based on diffuse interface method

Gas-liquid two phases flow is common in microfluidics but still needs more study. Precise but efficient controlling the droplets volumes is important for subsequent reaction or processing. In this paper, the diffuse interface method and boundary condition equations are introduced at the beginning. Then, to validate the present phase-field model, three kinds of simulation results are shown and fitted well with the experiments. It indicates that this method can be used to simulate the droplet deformation process in the T-junction. Afterwards, the details about the three kinds of droplet behaviors are presented and due to the instability of droplet breakup with tunnels, we mainly focus on the droplet with t obstruction for the steady breakup process. By analyzing the sensitivity about capillary number and static contact angle, we find that they both have great influence on the breakup process. The fitted curve under a 45 degree contact angle agree well with the experiment of Fu et al. Chem Eng Sci 66(18) 4184-4195, [9] which verifies the accuracy of simulation again. Next, we fit the relation between scaled critical droplet length and the Ca number and the static contact angle. At last, the critical neck width observed in the experiment is discussed based on the minimum surface energy principle as supplementary to improve this two-dimensional formula.