The dynamic mass transfer of surfactants upon droplet formation in coaxial microfluidic devices

•Mass transfer in coaxial microfluidic devices was studied during droplet formation.•Dynamic adsorption of surfactants was used to evaluate mass transfer coefficient.•Mass transfer coefficient inner and external droplet were evaluated respectively.•Semi-empirical equations were developed to put into the effects of convection.

In this work, the dynamic adsorption of surfactants is used to evaluate the mass transfer coefficient during droplet formation. As surfactants exist in only one phase and at the interface, the resistance of mass transfer inside and outside the droplet can be decoupled. By exchanging the continuous phase and dispersed phase (N-hexane/water-Tween 80), the mass transfer coefficients inside and outside the droplet were evaluated. A semi-empirical equation with modified parameters was developed to incorporate the effects of convection and the experimental conditions on the mass transfer coefficient during droplet formation in micro-channels. The results presented in this work provide a more in-depth understanding of the dynamic mass transfer of surfactants inside and outside the droplet during the formation of a droplet in microfluidic devices.

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