Pinch-off dynamics in foams, emulsions and suspensions

Abstract

The break up of a non-Newtonian yield stress fluid bridge (acrylic paint, mayonnaise, hair gel, foam, and bentonite) was investigated. The minimum neck radius, h_min, was measured as a function of time and fit to a power law with exponent n₁. A rotational rheometer was used to measure the shear stress-rate of strain curve which was fit to a Herschel–Bulkley model with exponent n₂. For the pure, as purchased fluids, the exponent from the time dependence of h_min (n₁) and the rheology power law index (n₂) were quantitatively the same. These results provide the first experimental confirmation of this relationship predicted by Suryo and Basaran. In the pure fluids, the pinch-off did not produce a satellite drop. In contrast, when the non-Newtonian fluids were diluted with a Newtonian fluid, the relationship between n₁ and n₂ was more complicated even though the diluted fluids were still Herschel–Bulkley, and the pinch-off produced satellite drops whose size was a continuous function of dilution.