The application of ac electric fields in aqueous suspensions of anisotropic particles leads to unbalanced liquid flows and nonlinear, induced-charge electrophoretic motion. We report experimental observations of the motion of Janus microparticles with one dielectric and one metal-coated hemisphere induced by uniform fields of frequency 100 Hz–10 kHz in NaCl solutions. The motion is perpendicular to the field axis and persists after particles are attracted to a glass wall. This phenomenon may find applications in microactuators, microsensors, and microfluidic devices.

Microencapsulation is an advanced methodology for the protection, preservation, and/or delivery of active materials in a wide range of industrial sectors, such as pharmaceuticals, cosmetics, fragrances, paints, coatings, detergents, food products, and agrochemicals. Polymeric materials have been extensively used as microcapsule shells to provide appropriate barrier properties to achieve controlled release of the encapsulated active ingredient. However, significant limitations are associated with such capsules, including undesired leaching and the nonbiodegradable nature of the typically used polymers. In addition, the energy cost of manufacturing microcapsules is an important factor to be considered when designing microcapsule systems and the corresponding production processes. Recent factors linked to UN sustainability goals are modifying how such microencapsulation systems should be designed in pursuit of "ideal" microcapsules that are efficient, safe, cost-effective and environmentally friendly. This review provides an overview of advances in microencapsulation, with emphasis on sustainable microcapsule designs. The key evaluation techniques to assess the biodegradability of microcapsules, in compliance with recently evolving European Union requirements, are also described. Moreover, the most common methodologies for the fabrication of microcapsules are presented within the framework of their energy demand. Recent promising microcapsule designs are also highlighted for their suitability toward meeting current design requirements and stringent regulations, tackling the ongoing challenges, limitations, and opportunities.

We developed a novel method for preparation of asymmetrically coated colloid particles by using a microcontact printing technique. Films of water-insoluble ionic surfactants deposited on PDMS stamps were printed onto latex particle monolayers of opposite surface charge in order to produce spherical latex particles of dipolar surface charge distribution. We studied the effects of salt on the aggregation of such dipolar particles in aqueous suspensions. Upon addition of salt, dipolar colloid particles were found to give “linear” aggregates. We then extended this microcontact printing technique to the directed assembly of colloidal particles. Microcontact printing of one colloidal monolayer over a latex particle monolayer of opposite charge was used to fabricate particles of complex internal structure. We demonstrated that if the two colloid monolayers consist of particles of comparable sizes, this method allows fabrication of particle doublets. When the particle monolayer was stamped with another colloid monolayer of much smaller particle size complex structures as half-coated “raspberry”-like particles were obtained. Possible applications of these asymmetrically coated colloids include photonic crystals with novel symmetries, colloidal substitutes for liquid crystals and water-based electrorheological fluids.