Science 342, 460–463 (2013)

The interface between two different liquids can be used to direct the assembly of nanoparticles. At sufficiently high nanoparticle concentrations such interfaces can lose mobility and start to exhibit solid-like properties, a process that is known as interfacial jamming. Thomas Russell and colleagues the University of Massachusetts Amherst and Tohoku University have now shown that an electric field can be used to manipulate this jamming process and stabilize liquid drops in different non-equilibrium shapes.

The researchers began by forming stable spherical liquid drops. Hydrophilic polystyrene nanoparticles were dispersed in water drops that were suspended in oil. An oleophilic molecule was added to the oil, which could interact with the nanoparticles and form nanoparticle surfactants. The surfactants self-assemble at the water/oil interface and create a disordered, jammed nanoparticle assembly. These spherical drops can then be deformed by applying an external electrical field, which increases the surface area of the drops and allows additional nanoparticle surfactants to form at the interface. When the field is removed, the drop is trapped in this non-equilibrium shape.

The deformation and jamming process can be repeated numerous times, and by applying electric fields in different directions a variety of unusual shapes can be created.