Asymmetric breakup of double emulsion droplets in symmetric junctions

Abstract

The transportation behaviors of double emulsion droplets in symmetric microfluidic junctions are investigated experimentally, with much attention paid to the particular behavior of the asymmetric breakup. The dynamic processes of interface evolution in typical flow patterns are captured. In contrast to previous studies, the dynamic analysis is carried out with different combinations of the inner and outer droplet lengths, based on which new flow pattern maps are built. The evolutions of the interfacial parameters including the extension length, minimum neck width, gap width, deformation factor, and profile asymmetry are given thorough discussions to reveal the transition rules between neighboring flow patterns. Based on the typical feature of the breakup process, geometric expressions of the maximum extension length is proposed to quantify the critical threshold of droplet breakup, which also helps explain the different influences of the varied bifurcation junctions. Two thread pinch-off regimes in the final stage are identified and the different characteristics in terms of the thread position and satellite droplet size are discussed. The fixed pinch-off position is confirmed to be the reason why droplets are more easily broken in the Y-junction, which also results in the nearly unchanged small asymmetry. For the T-junction, the lateral bias of the neck thread is found to reversely rely on the shift of the inner core owing to the influence between interfaces and the profile asymmetry increases with the length ratio of the inner to outer droplet length.