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

The characteristics of deformation and breakup of model viscoelastic d rops suspended in immiscible purely viscous Newtonian fluids undergoin g simple shear flow were investigated. In this study the simple shear flow was generated by a counterrotating cone-and-plate device. The res ults were compared with data obtained on purely viscous Newtonian drop s under similar conditions. The ratio of viscous forces to interfacial tension forces at breakup (epsilon(b)) was found to depend on the rat io of the viscosity of the dispersed phase to that of the continuous p hase (p), the shear stress prevailing in the continuous phase at break up, 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. Depend ing upon the value of p, a certain shear rate (gamma) was found to ex ist 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 vis coelastic 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.