SHEAR RUPTURING OF DROPLETS IN COMPLEX FLUIDS

We have experimentally studied the shear-induced rupturing of viscous droplets in viscoelastic complex fluids. Remarkably, a premixed emulsi on of large, polydisperse droplets can be ruptured into monodisperse e mulsions of uniform colloidal droplets. The monodispersity becomes mos t pronounced when the premixed emulsion is viscoelastic and has a shea r-thinning viscosity. Since viscoelastic materials may fracture, we re duce the gap of our shear cell to ensure a spatially uniform strain ra te for rupturing. We observe monodispersity whether the viscoelasticit y arises from the suspending fluid (e.g., concentrated surfactant solu tion) or droplet deformation as in compressed emulsions. Our observati ons suggest that the monodispersity results from droplet rupturing alo ne and that the capillary instability is inhibited by the partial elas ticity of the complex fluid. We use the monodispersity to study how th e droplet size depends upon the shear rate and composition.