(198w) Development of Interfacial Mechanical Strength for Armored Gas Filled Capsules

The fluid-fluid interface of an air bubble or oil droplet can be stabilized through the adsorption of surface active particles. If unconfined, the bubbles and droplets will assume spherical shapes to reduce their surface area and thus the interfacial energy. Within a confined geometry, adsorption and jamming of particles on an interface can lead to the retention of non-spherical shapes. Here, we examine the role of particle adsorption and interfacial compression in forming armored non-spherical air filled capsules. Capsules are generated by flowing an air bubble through a capillary filled with a suspension of surface active particle – surfactant complexes. Our work uses colloidal suspensions of silica nanoparticles coated with cetyltrimethylammonium bromide (CTAB). The complexes adsorb to the interface and are convected to the trailing end of the bubble, armoring the surface. The interface is compressed as the bubble exits the capillary resulting in the retention of a non-spherical shape. Time scale estimates and controlled interfacial measurements for a pinned air bubble are used to characterize particle adsorption to the interface. Controlled compressions are applied, and the interfacial rheology is compared before and after compression. Results from these experiments are combined with observations of changes in bubble shape in situ to characterize adsorption and compression during capsule generation. These results provide insight into the evolution of the interface’s mechanical strength to form the armored air-filled capsules.