Pinch-off Dynamics of Non-Newtonian Fluids

The pinch-off dynamics of a variety of shear-thinning fluids (foams, concentrated emulsions, and slurries) were studied using high speed videography. The pinch was characterized by the variation of the minimum neck radius rmin as a function of the time to pinch $\tau$. For inviscid fluids, rmin scales as $\tau$ to the 2/3 power. We found that for all the shear-thinning fluids rmin scales with $\tau$ to a power in the range 0.2 to 0.5. To study the transition from conventional inviscid pinch, we systematically varied the concentration of a water-bentonite mixture. As the concentration increased the pinch event transitioned from a needle shape resulting in a satellite drop to a symmetric hyperbolic shape with no satellite drop. These results will be compared with the simulations of Suryo and Basaran (J. Non-Newtonian Fluid Mech. 138 (2006) 134-160).