Pinch-off dynamics in foams, emulsions and suspensions

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 n(1). A rotational rheometer was used to measure the shear stress-rate of strain curve which was fit to a Herschel-Bulkley model with exponent n(2). For the pure, as purchased fluids, the exponent from the time dependence of h(min) (n(1)) and the rheology power law index (n(2)) 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 n(1) and n(2) 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.