(353c) The Dynamics and Break-up of Confined Bubbles Translating in Surface-Active Colloidal Dispersions

The adsorption of particles to fluid-fluid interfaces is a key step in the generation of colloidosomes and particle-stabilized emulsions. Microfluidic channels are a promising tool for generating particle-stabilized drops and bubbles with independent control over the bubble size and the concentration of particles adsorbed at the fluid interface. In the first part of this presentation, we describe experimental observations of the adsorption of a nanoparticle-surfactant suspension to confined bubbles translating along a microchannel. Long bubbles exhibit a unique two-lobed shape that is linked to the adsorption of surface-active particles to the interface at a timescale comparable to the residence time in the channel. An accompanying decrease in the bubble velocity results from the added viscous drag at the bubble interface. We develop a transport model to describe the rate of particle adsorption to the interface and find good agreement between the model estimates of bubble shape changes and experimental observation. In the second part of this presentation, we focus on the bubble break-up that can occur in the microchannel during the particle adsorption process due to a significant difference in the front and rear bubble velocities. We describe the flow conditions necessary for bubble break-up and analyze the rate of neck thinning observed during the break-up process. The experimental thread break-up is compared to standard inviscid break-up models in order to determine the stabilizing effect of surface-active colloidal particles against rupture.