Determining the Dynamic Interfacial Tension during Droplet/Bubble Generation Process in T-Junction and Co-Flowing Microchannels

The dynamic interfacial tension phenomenon caused by surfactant adsorption or mass transfer during droplet/bubble generation process is an assignable issue in the microfluidic studies. This phenomenon exhibits the variation of interfacial tension with operating conditions and channel structures as a dynamic character of interface evolution in microscaled space. This paper gives a summary of our studies focusing on determination of dynamic interfacial tension during droplet/bubble generation process in T-junction and co-flowing microchannels, including two determination methods basing on the droplet size and the pressure drop measurement, the effect study of microchannel size and structure, the comparison of different surfactants, as well as the dynamic interfacial tension in liquid-liquid and gas-liquid mass transfer processes. Experimental results showed almost 1~3 times higher dynamic interfacial tension than the static interfacial tension with saturated adsorbed surfactant could be measured in both T-junction and co-flowing microchannels, especial in the droplet generation process at high generation frequency. To the contrary, lower dynamic interfacial tension than the static interfacial tension without mass transfer was observed in the mass transfer process and the reducing rate of dynamic interfacial tension increased with the rising of concentration gradient. Some models of dynamic interfacial tensions in different microfluidic processes are suggested, which will be helpful for the in-depth understanding of multi-phase microfluidic processes.