Adsorption and assembly of colloidal particles at the surface of liquid droplets are at the base of particle-stabilized emulsions and templating. Here we report that electrohydrodynamic and electro-rheological effects in leaky-dielectric liquid drops can be used to structure and dynamically control colloidal particle assemblies at drop surfaces, including electric-field-assisted convective assembly of jammed colloidal ‘ribbons’, electro-rheological colloidal chains confined to a two-dimensional surface and spinning colloidal domains on that surface. In addition, we demonstrate the size control of ‘pupil’-like openings in colloidal shells. We anticipate that electric field manipulation of colloids in leaky dielectrics can lead to new routes of colloidosome assembly and design for ‘smart armoured’ droplets.

We experimentally investigate the rotation of plate shaped aggregates of clay mineral particles immersed in silicone oil. The rotation is induced by an external electric field. The rotation time is measured as a function of the following parameters: electric field strength, the plate geometry (length and width) and the dielectric properties of the plates. We find that the plates always align with their longest axis parallel to the direction of the electric field (E), independently of the arrangement of individual clay mineral particles within the plate. The rotation time is found to scale as E −2 and is proportional to the viscosity (η), which coincides well with a model that describes orientation of dipoles in electric fields. As the length of the plate is increased we quantify a difference between the longitudinal and transverse polarizability. Finally, we show that moist plates align faster. We attribute this to the change of the dielectric properties of the plate due to the presence of water.

We study the behaviour of fluorohectorite synthetic clay particles dispersed in paraffin-wax. First, we report wide angle X-ray scattering related to electric-field-induced alignment of the embedded clay particles. Secondly, we provide observations of system anisotropy during melting and crystallization of clay/paraffin nanocomposites. Finally, the time evolution of the one-to-zero/zero-to-one water layer transition in paraffin embedded fluorohectorite clay galleries is presented, and we demonstrate that such particles can be used as 'meso-detectors' for monitoring the local water content in bulk carrier matrices, such as paraffin-wax.