Non-Newtonian effects on droplet breakup dynamics in a T-junction microfluidic channel

The non-Newtonian droplets formation in microfluidic systems constitutes an essential study for rheological applications in drug delivery systems. Most studies of droplet formation and pinch-off concern Newtonian liquids mainly in theoretical, experimental, and computational analysis. Nevertheless, the understanding of non-Newtonian droplet generation mechanism is still lacking under different flow conditions. As Reynolds number is typically small, viscosity plays a crucial factor influencing the physical process of droplet formation. The aim of the present paper is to systematically investigate the viscosity effect on the formation of shear-thinning nature of sodium carboxymethylcellulose (CMC) droplets. A two-phase conservative level-set formulation is adopted to capture the droplets breakup dynamics and relevant hydrodynamics. Liquid droplets comprising of 0.02wt% to 1.20wt% CMC solutions in a Newtonian continuum were employed in a microfluidic cell of T-junction configuration. Data for the rheological and physical properties of CMC polymer solution obeying Carreau-Yasuda constitutive model were empirically obtained to support the computational work. The simulation results predicted that the effect of non-Newtonian viscosity has profoundly changed the breakup time and generation frequency of the isolated CMC droplets in microfluidic flow. The droplet breakup time and generation frequency exhibits a striking non-monotonic relationship with the CMC viscosity in two distinct concentration regimes, namely dilute and semi-dilute. These numerical findings provide explicit information on the impact of viscosity on the motion and breakup of the non-Newtonian microdroplets. Present investigations on the relative importance of viscosity are working towards a conceptual framework to optimize the numerical and experimental studies and control droplet properties.