Marta Kasprzyk

Flow focusing with viscoelastic liquids

We present an experimental comparative study of the effect of elasticity of the continuous liquid in generation of droplets in microfluidic flow focusing devices. For a wide range of values of dynamic viscosity of the Newtonian droplet phase we compare the dynamics of the formation of droplets in three different Newtonian and non-Newtonian, viscoelastic (Boger) fluid pairs of the same (and nearly constant) shear viscosities. In both Newtonian and viscoelastic systems we find similar regimes of operation of the system: (i) dripping without satellites, (ii) dripping with single satellites, (iii) formation of multiple satellites, and (iv) jetting. We find that the elasticity of the focusing liquid stabilizes the jets facilitating formation of smaller droplets, and leads to transitions between various regimes at lower ratios of flow and at lower values of the capillary numbers in comparison to the Newtonian focusing liquids. We also show that the polydispersity of Newtonian droplets produced in non-Newtonian continuous phases depend significantly on the viscosity of the droplet phase while this dependence is minor when the continuous liquid is Newtonian.