EXPERIMENTAL-STUDY ON THE BREAKUP OF MODEL VISCOELASTIC DROPS IN UNIFORM SHEAR-FLOW

The characteristics of deformation and breakup of model viscoelastic drops suspended in immiscible purely viscous Newtonian fluids undergoing simple shear flow were investigated. In this study the simple shear flow was generated by a counterrotating cone-and-plate device. The results were compared with data obtained on purely viscous Newtonian drops under similar conditions. The ratio of viscous forces to interfacial tension forces at breakup (epsilon(b)) was found to depend on the ratio of the viscosity of the dispersed phase to that of the continuous phase (p), the shear stress prevailing in the continuous phase at breakup, and the primary normal stress difference. At any given value of p, epsilon(b) was observed to increase with increasing shear rate, gamma(c), and with increasing weight fraction of the polymer in the droplet phase, i.e., with increasing degree of elasticity of the drop. Depending upon the value of p, a certain shear rate (gamma*) was found to exist below which model viscoelastic drops were easier to break up than purely viscous Newtonian drops. Similarly, at any fixed shear rate, a characteristic viscosity ratio (p*) was observed above which model viscoelastic drops were easier to break up than purely viscous Newtonian drops. The magnitudes of both gamma* and p* were found to depend upon the degree of elasticity of the dispersed drops.