Mehrnaz Oveysi - School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran;
Amin Zaker - School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran;
Vahid Bazargan - School of Mechanical Engineering, College of Engineering, University of Tehran, Tehran;

In this paper, we study alginate droplet formation in a flow-focusing microfluidic device with an orifice (۳۰*۱۰۰: width*depth) in the presence of surfactant in the continuous phase. The dispersed phase was ۰.۱wt% aqueous solution of alginate and the mixture of paraffin oil and the surfactant (Span ۸۰) with varying concentrations of ۱, ۳, and ۵wt%, was used as the continuous phase. The behavior of droplet formation under the impact of flow rate ratio alterations and surfactant addition was studied numerically and experimentally. To follow the two phases interface and examine droplet production, we employed the volume of fluid (VOF) approach. In the numerical simulation, applying surfactant reduces droplet diameter by lowering interfacial tension. Our numerical results agreed well with the experimental data. The flow rate ratio is increased to ۸ by keeping the dispersed flow rate to ۰.۹ μL/min. Surfactant addition and an increase in the flow rate ratio influence droplet size and frequency. The droplet size and frequency are influenced by surfactant addition and the increase in the flow rate ratio. The synergistic effect of these two parameters reduced droplet diameters by ۶۳.۸% and increased the droplet frequency production by ۸۰% in comparison to droplet formation in the surfactant-free outer phase. The smallest droplet (۶۱.۱μm diameter) was obtained at this flow rate ratio and ۵wt% Span ۸۰ concentration.

Droplet Microfluidics, Flow-focusing device, Surfactant Addition.