Shear-Thinning Fluid Droplets Formation in Axisymmetric Flow-Focusing Microfluidics

The formation of shear-thinning fluid [sodium alginate (SA) solution] droplets in a continuous Newtonian fluid phase is studied numerically. The influences of shear thinning effects on the interface evolution, flow regimes, droplet size, and formation frequency are examined. A regime diagram is summarized in terms of the Capillary number of the continuous phase (Ca) and the concentration of the shear-thinning fluid (c(nN-f), the concentration of the SA solution). The results show that the regime transition from dripping to jetting caused by increasing Ca is delayed when the dispersed phase is a shear-thinning fluid, which is advantageous in the production of highly monodispersed droplets. Additionally, c(nN-f) shows a distinct influence on dripping and jetting regimes. In dripping regimes, increasing c(nN-f) results in decreased droplet size with a high formation frequency. This study provides a theoretical reference for the preparation of shear-thinning fluid droplets and is also helpful in clarifying the formation mechanism of non-Newtonian droplets.