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To realize new and directed self-assembly (SA) pathways, the focus in colloid science and nanoscience has shifted from spherical particles and interactions to increasingly more complex shapes and interparticle potentials. This field is fueled by recent breakthroughs in particle synthesis, such as particles with complementary shapes that allow for specific lock-and-key interactions induced by depletants. Here, we show that electric fields form an alternative route for directing the SA of convex and concave colloids, with the additional advantage that the system now becomes switchable by external conditions. Both experimental and theoretical results are presented that validate the electric-field-induced assembly mechanism and show that even irreversibly bound composites can be generated by tuning the force balance. The successful isolation of the irreversible composite particles, in combination with generalization to different materials, shows that the current mechanism provides a versatile new path not only toward complex-particle synthesis but also toward directed self-assembly.

Emulsions stabilized by solid particles, called Pickering emulsions, offer promising applications in drug delivery, cosmetics, food science and the manufacturing of porous materials. This potential stems from their high stability against coalescence and ‘surfactant-free’ nature. Generally, Pickering emulsions require that the solid particles are wetted by both phases and as a result, the adsorption free energy is often large with respect to the thermal energy (kBT). Here we provide the first experimental proof for an alternative scenario: non-touching (effectively non-wetting), charged, particles that are completely immersed in the oil phase through a balance of charge induced attractions and repulsions caused by van der Waals forces. These particles nonetheless stabilize the emulsion. The main advantage of this novel adsorption mechanism is that these particles can easily be detached from the interface simply by adding salt. This not only makes the finding fundamentally of interest, but also enables a triggered de-emulsification and particle recovery, which is useful in fields like enhanced oil recovery, heterogeneous catalysis, and emulsion polymerization.

We report several facile, surfactant-free methods to prepare monodisperse polydimethylsiloxane (PDMS) droplets in the size range 3–8 μm in water. These methods, of which the pros and cons are discussed, are extensions of a procedure described before by our group which focused on smaller droplet sizes. The PDMS oil droplets are formed by ammonia catalyzed hydrolysis and condensation of the monomer dimethyldiethoxysilane (DMDES) in water. One of the methods entails a seeded growth procedure in which other oils, such as lower molecular weight hydrocarbons, were found to be able to swell the PDMS droplets if their solubility in water was higher than that of the seed droplets. This way, larger droplets with mixed composition could be prepared. It also turned out to be possible to load the monodisperse droplets with an oil soluble dye. The droplets could be coated with an elastic, partially permeable, shell formed by cross-linking the PDMS with tetraethoxysilane (TES) in the presence of poly(vinylpyrrolidone) (PVP) that provided colloidal stability. Besides, the liquid interior of these shells could be changed by solvent exchange.