Although strong and stiff human-made composites have long been developed, the microstructure of today's most advanced composites has yet to achieve the order and sophisticated hierarchy of hybrid materials built up by living organisms in nature. Clay-based nanocomposites with layered structure can reach notable stiffness and strength, but these properties are usually not accompanied by the ductility and flaw tolerance found in the structures generated by natural hybrid materials. By using principles found in natural composites, we showed that layered hybrid films combining high tensile strength and ductile behavior can be obtained through the bottom-up colloidal assembly of strong submicrometer-thick ceramic platelets within a ductile polymer matrix.

The unique structure and mechanical properties of platelet-reinforced biological materials such as bone and seashells have motivated the development of artificial composites exhibiting new, unusual mechanical behavior. On the basis of designing principles found in these biological structures, we combined high-performance artificial building blocks to fabricate platelet-reinforced polymer matrix composites that exhibit simultaneously high tensile strength and ductility. The mechanical properties are correlated with the underlying microstructure of the composites before and after mechanical loading using transmission electron microscopy. The critical role of the strength of the platelet-polymer interface and its dependence on the platelet surface chemistry and the type of matrix polymer are studied. Thin multilayered films with highly oriented platelets were produced through the bottom-up layer-by-layer assembly of submicrometer-thin alumina platelets and either polyimide or chitosan as polymer matrix. The tensile strength and strain at rupture of the prepared composites exceeded that of nacre, whereas the elastic modulus reached values similar to that of lamellar bones. In contrast to the brittle failure of clay-reinforced composites of similar or higher strength and stiffness, our composites exhibit plastic deformation in the range of 2-90% before failure. In addition to the high reinforcing efficiency and ductility achieved, several toughening mechanisms were identified in fractured composites, namely friction, debonding, and formation of microcracks at the platelet-polymer interface, as well as plastic deformation and void formation within the continuous polymeric phase. The combination of high strength, ductility, and toughness was achieved by selecting platelets that exhibit an aspect ratio high enough to carry significant load but small enough to allow for fracture under the platelet pull-out mode. At high concentrations of platelets, the ductility gets lost because of out-of-plane misalignment of the platelets and incorporation of voids in the microstructure during processing. The designing principles applied in this study can potentially be extended to other types of platelets and polymers to obtain new, hybrid materials with tunable mechanical properties.

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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.

We describe the preparation of nanocomposites which exhibit dichroism in the near infrared region (NIR). These materials consist of crosslinked poly(dimethylsiloxane) (PDMS) and gold nanoparticles, coated with 1-dodecanethiol or tert-tetradecanethiol. The alkanethiols improve dispersibility of the gold particles, and accordingly composites were manufactured by diffusion of the particles into swollen self-supporting PDMS elastomer films. After drying, the films were exposed to solvents for one minute, stretched in wet state, dried again and annealed. This procedure led to formation of oriented linear gold particle assemblies within stretched polymer. If the aspect ratio of the particle assemblies is high, the absorption of polarized light in the NIR region is expected to depend on the angle between the polarization plane and the orientation direction of the particle assemblies, and this was observed to be the case.

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