Effect of surfactant addition and viscosity of the continuous phase on flow fields and kinetics of drop formation in a flow-focusing microfluidic device

Droplet formation in a flow focusing microfluidic device was studied for capillary numbers between 10−4 and 10−1. The addition of cationic surfactant to the dispersed phase effect continuous viscosity on droplet size, neck kinetics fields inside drop investigated. size decreased with an increase number following power law exponent dependent confinement. At 1–3 ms before pinch-off, thinning rate is concentration increases closer pinch-off. For 96 mPa s phase, two-fluid Stokes regime observed effective interfacial tension smaller than equilibrium value, suggesting negative contribution Marangoni stresses. During necking, velocities along interface laden cases are due phenomena. expansion, increased fluid recirculation observed.