General methodology of using oil-in-water and water-in-oil emulsions for coiling nanofilaments.

Hydrophobic carbon nanotubes (CNTs) and hydrophilic nanofilaments such as oxidized CNTs, Pd nanowires (NWs), and MnO(2) NWs are transformed from wires to rings by a general methodology. We show that both oil-in-water and water-in-oil emulsions, so long as their droplet size is sufficiently small, can exert significant force to the entrapped nanostructures, causing their deformation. This effect can be easily achieved by simply mixing a few solutions in correct ratios. Even preformed oil droplets can take in CNTs from the aqueous solution converting them into rings, indicating the important role of thermodynamics: The question here is not if the droplets can exert sufficient force to bend the nanofilaments, because their random vibration may be already doing it. As long as the difference in solvation energy is large enough for a nanofilament, it would "want" to move away from the bulk solution and fit inside tiny droplets, even at the cost of induced strain energy. That said, the specific interactions between a droplet and a filament are also of importance. For example, when an oil droplet rapidly shrinks in size, it can compress the entrapped CNTs in multiple stages into structures with higher curvatures (thus higher strain) than that of a circular ring, which has minimal induced strain inside a spherical droplet.