Structure of concentrated nanoemulsions

Abstract

We use extreme shear to create a dispersion of nanoscale droplets of silicone oil in an immiscible water phase containing an anionic surfactant sodium dodecylsulfate. Using centrifugal size fractionation, we obtain nanoemulsions having a well-defined average radius of a=75 nm. We measure the structure of concentrated nanoemulsions over a wide range of volume fractions, 0<phi<0.6, using small angle neutron scattering, and we determine the structure factor S(q) of disordered glassy dispersions of uniform deformable droplets interacting through screened surface charge repulsions. Although the low-q behavior of S(q,phi) resembles that predicted for hard spheres, the height of the primary peak does not. Instead, it exhibits a maximum as phi is increased. This difference cannot be explained solely by the droplet size polydispersity and is likely related to the deformability of the droplets that have been locked into a glassy structure.