(184f) Controlled Generation of Monodisperse Particle-Stabilized Droplets With Arbitrary Interfacial Coverage

The complex interfaces of particle-stabilized drops and bubbles have a significant effect on the flow properties of bulk emulsions and foams. Common high-shear methods of generating stable emulsions have no direct control over the rate of droplet generation, the final droplet size distribution, or the composition of the interface, all of which are important to the interfacial and bulk rheology. In this talk, we present a method that allows for independent control over the droplet size generated and the degree of particle loading on the interface. Droplets are formed on demand at a T-junction with a desired size via a pressure-controlled generation scheme. Subsequently, the droplets travel along the axis of a circular capillary containing a surface-active particle suspension. We use a particle transport model that we have previously developed to estimate the particle coverage on the bubble surface as a function of residence time. We use light scattering methods to assess the degree of depletion of particles from the bulk and thus to verify that surface coverage is indeed a function of residence time, for two different systems: air-in-water foams stabilized by silica nanoparticles, and water droplets stabilized by silica in a continuous phase of cyclohexane. Thus, we show that by controlling channel geometry, applied inlet pressures, and residence time, we can directly control droplet size, volume fraction, and particle loading on the bubble interface, all of which are critical parameters relevant to the stability and rheology of a particle-stabilized emulsion or foam.