Pressure-driven microfluidic droplet formation in Newtonian and shear-thinning fluids in glass flow-focusing microchannels

Abstract

Pressure-driven microdroplet formation was experimentally investigated in glass flow-focusing devices using micro-imaging. The observations illustrated the effects of some important factors affecting the droplet formation, including the channel geometry, two-phase flow rates and non-Newtonian behavior of the continuous phase. Although the droplet formation dynamics showed some different characteristics in different geometries, self-similarities of the dispersed thread were found in both devices for various initial conditions by normalizing the thread length and time. When power-law shear-thinning fluids were used as the continuous phase, the growth of the dispersed thread was still self-similar, but the relationship became linear rather than power-law as with the Newtonian continuous phase. The droplet shape also changed for droplet generated in shear-thinning fluids, so a deformation index (D.I.) was defined to describe the shape differences. Finally, a previously presented prediction model was validated by the experimental data with good agreement.