BREAK-UP OF A NEWTONIAN DROP IN A VISCOELASTIC MATRIX UNDER SIMPLE SHEAR FLOW

The effect of matrix elasticity on the break-up of an isolated Newtonian drop under step shear flow is herein presented. Constantviscosity, elastic polymer solutions (Boger fluids) were used as matrix phase. Newtonian silicon oils were used as drop phase. Three viscosity ratios were explored (drop/matrix), i.e. 2, 0.6 and 0.04. Following the theoretical analysis of Greco [Greco F (2002) J Non-Newtonian Fluid Mech 107:111–131], the role of elasticity on drop fluid dynamics was quantified according to the value of the parameter p=s/sem, where s is a constitutive relaxation time of the matrix fluid and sem is the emulsion time. Different fluids were prepared in order to have p ranging from 0.1 to 10. At all the viscosity ratios explored, break-up was hindered by matrix elasticity. The start-up transient of drop deformation, at high, but sub-critical capillary numbers, showed an overshoot, during which the drop enhanced its orientation toward the flow direction. Both phenomena increase if the p parameter increases. Finally, the nondimensional pinch-off length and break-up time were also found to increase with p.