Mechanical behavior of bulk supercrystalline ceramic-organic nanocomposites
The proposed work aims at elucidating the mechanical behavior of bulk supercrystalline ceramic-organic nanocomposites. These are materials that consist of inorganic, usually crystalline, nanoparticles, surface-functionalized with organic ligands, and assembled into periodic structures, analogous to atomic lattices. They represent a rising field of materials science and nanoengineering, which has been finding applications in optoelectronics, plasmonics, magnetic materials, battery electrodes, catalysts and sensors. Their use for structural purposes is however largely unexplored, even if promising mechanical properties have started to emerge in bulk ceramics-based supercrystalline materials.An effective way to enhance their mechanical properties has been found in inducing crosslinking among the organic chains that are anchored to the ceramic nanoparticles’ surfaces. This limits the mobility of the inorganic building blocks with respect to each other, leading not only to high values of strength, hardness and stiffness, but also to significant changes in the materials’ behavior under loading. Preliminary work points towards the concurrent effects of material compaction, plastic-like deformation and extrinsic toughening mechanisms. Defects remindful of the ones typically observed in crystalline materials – such as interstitials, stacking faults, dislocations and shear bands – have also been detected.The interconnections among mechanical behavior and the local nanostructure deformations are yet to be clarified, and this is what the present proposal aims at tackling. For materials with various degrees of crosslinking of the organic ligands, the stress-strain relationships, creep and compressibility behavior are to be derived. In parallel, the defects and deformations induced by both material processing and mechanical loading will be characterized. The methods of choice involve nanoindentation with various tips, for the derivation of the materials’ constitutive response, and atomic force and electron microscopy for the visualization of imperfections, from point-defects to dislocations and inter-supercrystalline boundaries. Together with their empirical evaluation, the connections between supercrystalline deformations and overall mechanical behavior will be modeled by applying and adapting the classic theories from the literature on slip systems activation, strain and stress fields around line defects, and dislocation glide. The correlations between material processing, supercrystalline structure and mechanical properties will then be inferred.