Shear-thinning droplets in abrupt contraction flow: transient deformation and interfacial instability

Chemical Engineering Sciences. 2026. Vol. 323. No. 15. Article 123203.

Patlazhan S. A., Kravchenko I. V., Vashchenko A. F., D.E. Roshchin, Kulichikhin V. G.

The dynamics of non-Newtonian droplets under strong confinement is critical for designing efficient droplet-based microreactors and multiphase chemical processes. This work combines systematic experiments with three-dimensional numerical simulations to investigate the transient deformation and interfacial stability of shear-thinning droplets in confined two-phase microchannel flow. Xanthan gum solution droplets were driven through a planar channel with an abrupt contraction while co-flowing with an immiscible Newtonian continuous phase. The dynamics of droplet deformation and breakup were characterized at various capillary numbers and confinement parameters. The critical capillary number for breakup was found to follow a robust power-law scaling with the confinement. Numerical simulations using a Carreau constitutive model revealed pronounced non-uniform viscosity fields within the droplets, coupled to the local strain rate distribution. A direct correlation was established between the deformation behavior and the onset of interfacial instability of the shear-thinning droplet and its volume-averaged viscosity ratio. The resulting scaling laws delineate stable and unstable deformation regimes and elucidate the pivotal role of internal viscosity gradients on droplet dynamics. These findings provide quantitative guidelines for the design of droplet-based microfluidic applications involving inelastic non-Newtonian dispersed phase under confined geometries.

Keywords: multiphase flows, Microfluidics, Shear-thinning fluids, droplet dynamics