Emulsification

We study how strong mechanical shear is used to create emulsions, dispersions of droplets of one liquid (e.g. oil) in another immiscible liquid (e.g. water). These droplets are stabilized against coalescence (i.e. fusion) by a small quantity of surfactant. Our research focuses on how the non-Newtonian flow properties of concentrated emulsions having a high droplet volume fraction affect the ruptured droplet size distribution. We use an oscillatory controlled-strain plane-Couette shear cell with time-resolved small angle light scattering to study the droplet structure during the process of droplet stretching and rupturing.

We study how strong mechanical shear is used to create emulsions, dispersions of droplets of one liquid (e.g. oil) in another immiscible liquid (e.g. water). These droplets are stabilized against coalescence (i.e. fusion) by a small quantity of surfactant. Our research focuses on how the non-Newtonian flow properties of concentrated emulsions having a high droplet volume fraction affect the ruptured droplet size distribution. We use an oscillatory controlled-strain plane-Couette shear cell with time-resolved small angle light scattering to study the droplet structure during the process of droplet stretching and rupturing.
This images shows a small angle light scattering pattern from a concentrated emulsion that has been created using the plane couette. The presence of a ring and spots in the scattering pattern indicates that the droplets are uniform in size and have become ordered by the shear.
During the process of emulsification, the droplets are ruptured to smaller and smaller sizes, thereby increasing the Laplace pressure scale, given by the surface tension divided by the average droplet radius. Since the Laplace pressure scale is directly proportional to the shear modulus, G', of the concentrated emulsion, the emulsion becomes increasingly more elastic-- the emulsion irreversibly 'elastifies' as a result of the shear. This is possible because the total interfacial area of the droplets has increased and energy has effectively been stored in the droplet structures. We have invented a method, called Sinusoidal Amplitude Variation (SAV) Rheometry, to probe the process of shear-induced elastification in any type of complex fluid, including concentrated emulsions. Discreet oscillations of a large amplitude sinusoidal shear are applied and then a frequency sweep (FS) is performed to track how the linear viscoelasticity of the complex fluid changes as a result of the shear.