Filled microcapsules made from double emulsion templates in microfluidic devices are attractive delivery systems for a variety of applications. The microfluidic approach allows facile tailoring of the microcapsules through a large number of variables, which in turn makes these systems more challenging to predict. To elucidate these dependencies, we start from earlier theoretical predictions for the size of double emulsions and present quantitative design maps that correlate parameters such as fluid flow rates and device geometry with the size and shell thickness of monodisperse polymer-based capsules produced in microcapillary devices. The microcapsules are obtained through in situ photopolymerization of the middle oil phase of water-in-oil-in-water double emulsions. Using polymers with selected glass transition temperatures as the shell material, we show through single capsule compression testing that hollow capsules can be prepared with tunable mechanical properties ranging from elastomeric to brittle. A quantitative statistical analysis of the load at rupture of brittle capsules is also provided to evaluate the variability of the microfluidic route and assist the design of capsules in applications involving mechanically triggered release. Finally, we demonstrate that the permeability and microstructure of the capsule shell can also be tailored through the addition of cross-linkers and silica nanoparticles in the middle phase of the double emulsion templates.

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The encapsulation of amines by emulsification and interfacial polymerization is important for smart adhesives and self-healing materials but has been challenging because of the reactive nature of amines and their wide miscibility range. In this study, we propose a new method to encapsulate amines using double-emulsion templates made in a microfluidic device. The double emulsions contain an aqueous solution of the amine of interest in the innermost phase and a reactive mixture of acrylic monomers and initiator in the middle phase. Polymerization of the middle phase leads to acrylic microcapsules containing highly concentrated nonvolatile amine upon removal of water via evaporation. The presence of the amine inside the capsules is confirmed with NMR spectroscopy, and their reactivity is demonstrated by showing their effectiveness as cross-linkers of liquid epoxy resins.

The feasibility of self-healing epoxy matrices using the same chemistry as the matrix material, namely a standard epoxy-amine system, is demonstrated. The two-component self-healing system is encapsulated in core-shell structures using standard in situ curing in a stirred emulsion and a novel microfluidic encapsulation technique for the epoxy monomer and the amine hardener, respectively. The recovery of fracture toughness after room temperature healing is above 50%, and increases to 100% when shape memory alloy wires are combined with a low temperature cure of the matrix to enhance crack closure. This healing ability is also preserved for higher curing temperatures, demonstrating the potential of this novel approach.

Ceramic thin films are used in various applications for their structural or functional properties. Below a thickness of approximately 25 μm, ceramic films are typically deposited, sintered, and used on a supporting substrate due to their fragility. Here, we present a set of easy and versatile green film deposition and sintering techniques that allow the fabrication of free‐standing micrometer‐thin alumina and yttria‐stabilized zirconia foils. Because of their extremely low thickness, the foils were transparent and flexible but still strong enough that they were self‐supporting and could be handled manually. The presented concepts are not limited to the materials used here and can potentially be extended to most ceramic materials and glasses. So prepared free‐standing ultrathin ceramic foils allow new assembly and fabrication methods of devices and novel materials that contain thin ceramic membranes.

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