prised of highly deformed droplets. Such emulsions exhibit We have measured the yield transition of monodisperse emula plastic-like response to shear deformations; for small deforsions as the volume fraction, f, and droplet radius, a, are varied. mations, they resist the shear elastically, with the stress, t, We study the crossover from the perturbative shear regime, which being linearly proportional to the strain, g; however, for reflects the linear viscoelastic properties, to the steady shear relarge enough deformations, they flow, offering comparagime, which reflects nonlinear, plastic flow. For small oscillatory tively much less additional resistance. For example, mayonstrains of peak amplitude g, the peak stress, t, is linearly propornaise maintains its shape under the relatively small stresses tional to g. As the strain is increased, the stress becomes nonlinear of gravity, but it can be easily spread with a knife with in g at the yield strain, g y . The f dependence of g y is independent of a and exhibits a minimum near the critical volume fraction, f c little more effort. By contrast, at dilute concentrations as Γ 0.635, associated with the random close packing of monodisfor example with milk, the droplets are undeformed, and perse spheres. We show that the yield stress, t y , increases dramatiemulsions exhibit simple viscous flow which closely resemcally as the volume fraction increases above f c ; t y also scales with bles that of the dominant continuous phase. Since nearly all the Laplace pressure, s/a, where s is the interfacial tension. For practical applications of emulsions require their transport, it comparison, we also determine the steady shear stress over a wide is important to establish how their flow behavior is influrange of strain rates, g g . Below f Γ 0.70, the flow is homogeneous enced by the properties of the constituent droplets, such throughout the sample, while for higher f, the emulsion fractures as their packing, their degree of deformation, their volume resulting in highly inhomogeneous flow along the fracture plane. fraction, f, and their radius, a.
Above f Γ 0.58, the steady shear stress exhibits a low strain rate
The flow properties of compressed, elastic emulsions can plateau which corresponds with the yield stress measured with the oscillatory technique. Moreover, t y exhibits a robust power law be broadly divided into two categories, yielding and steady dependence on g g with exponents decreasing with f, varying from shearing flow. The change from a linear to a nonlinear 2 3 to 1 2 . Below f Γ 0.58, associated with the colloidal glass transition, stress-strain relationship can be crudely characterized by a the plateau stress disappears entirely, suggesting that the equilibyield stress, t y , and a yield strain, g y , which mark the sigrium glassy dynamics are important in identifying the onset of the nificant departure of the microscopic droplet structure from yield behavior.