Formation, Development and Disruption of a Particle Coating on a Confined Bubble

Surface-active nanoparticles adsorb at fluid interfaces, imparting elasticity and stability against coalescence. Nanoparticles diffuse relatively slowly, desorb very slowly, and interact colloidally, allowing the coverage and mechanical properties of the interface to be manipulated in a fluid flow. We examine the coupling of hydrodynamics and particle adsorption for elongated bubbles translating along a capillary tube filled with surface-active nanoparticle suspension. Particle adsorption times are comparable to bubble residence times, and are controlled via flow rate, tube length, and suspension viscosity. Particles are convected to the trailing end of the bubble, yielding a rigid trailing cap. Short bubbles exhibit a uniform thickness Bretherton film. For longer bubbles the leading end thin film sharply transitions to a thick film at the trailing end, characteristic of a Marangoni stress on the interface. At higher speeds, the trailing cap appears to crumple, shedding layers of nanoparticles. We relate these observations to the interfacial hydrodynamics and the development of elasticity on the bubble interface. These observations highlight the critical role of processing history on formation of particle-stabilized interfaces.