Yielding and Flow of Monodisperse Emulsions

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, gy . The f dependence of gy is independent of a and exhibits a minimum near the critical volume fraction, fc little more effort. By contrast, at dilute concentrations as É 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, ty , increases dramatiemulsions exhibit simple viscous flow which closely resemcally as the volume fraction increases above fc ; ty 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