Adsorption of sub-micron amphiphilic dumbbells to fluid interfaces

We investigate the adsorption of submicrometer bulk-synthesized polymer dumbbells to oil-water interfaces using freeze-fracture, shadow-casting (FreSCa) cryo-scanning electron microscopy. We find that the dumbbells are amphiphilic and adsorb to the interface with a preferred orientation. Most particles adsorb in a tilted configuration, with the polar and apolar lobes intersecting the interface and pointing toward the water and oil, respectively. Some particles adsorb with only one lobe attached to the interface. Moreover, we find that each lobe has a preferred angle of contact with the interface, identical in all observed configurations. A simple geometrical calculation using these contact angles accurately predicts the dominant configuration of particles at the interface. This calculation provides insight into how the shape and composition of dumbbells can be tuned to stand upright and pack efficiently on curved interfaces.