| The interfaces of bubbles and droplets imbue foams and emulsions with extraordinary mechanical and chemical properties. The remarkably large interfacial area of these structures controls their thermodynamics and makes them practical and functional materials. When these interfaces are forced to touch, they can turn a dispersion of one fluid in another into a solid. These solid-like properties are evident in common household products such as shaving foam and mayonnaise, and our ability to control the fluid and solid properties of these materials is essential to their function.;Here we present results from three studies on the mechanical properties and applications of foams and emulsions. We describe experiments designed to probe the interplay between thermal fluctuations and interfacial energy in the liquid-to-solid transition of emulsions. We find a previously unknown elastic instability that makes emulsions susceptible to surprisingly small thermal perturbations, and describe some of its fascinating properties. We also investigate the effects of loading the interfaces of liquid droplets with solid nanoparticles; the dense packing solid particles on the droplet interfaces turns a soft and compliant material into a stiff yet fragile solid, whose Poisson's ratio may even become negative. Finally, we describe an application for the large specific surface area of polymer foams that improves the delivery poorly bioavailable pharmaceutical compounds. Here we dissolve hydrophobic drugs in a polymer melt and use the open, porous structure of a filled microcellular foam to quadruple the dissolution rate of active compounds over state-of-the-art formulations. |
