Droplet breakup driven by shear thinning solutions in a microfluidic T-Junction

Droplet microfluidics is, like a miniaturized biomedical lab, efficient and adjustable for high throughput analysis, encapsulation of cells, drug formulation, polymerase chain reaction. Typically, for most biomedical applications, handling of complex, non-Newtonian fluids is involved, e.g. synovial and salivary fluids, collagen, gel scaffolds. The role of the corresponding rheology on the droplets breakup has not been accurately addressed so far. Here we suggest a novel approach to describe droplets formation occurring in a microfluidic T-shaped junction, either in Newtonian or non-Newtonian, shear thinning liquids. The non-Newtonian liquid carrying the droplets was made of Xanthan solutions, a stiff rod-like polysaccharide displaying a marked shear thinning rheology and weak elastic effects. The breakup process shows similar trends regardless of the nature of the surrounding liquid once the droplets size is assessed in terms of an effective Capillary number introduced to account for shear thinning effects. Experimental results are complemented with numerical simulations of pure power-law fluids with the lattice Boltzmann models, which are in good quantitative agreement with the experimental data and confirm the proposed scaling.