Abstract
A key challenge in the development of inorganic-organic nanocomposites is the mechanical behavior identification of the organic phase. For supercrystalline materials, in which the organic phase ranges down to sub-nm areas, the identification of the organic materials' mechanical properties is however experimentally inaccessible. The supercrystalline nanocomposites investigated here are 3D superlattices of self-assembled iron oxide nanoparticles, surface-functionalized with crosslinked oleic acid ligands. They exhibit the highest reported values of Young's modulus, nanohardness and strength for inorganic-organic nanocomposites. A multiscale numerical modeling approach is developed to identify these properties using supercrystalline representative volume elements, in which the nanoparticles are arranged in a face-centered cubic superlattice and the organic phase is modeled as a thin layer interfacing each particle. A Drucker-Prager-type elastoplastic constitutive law with perfectly plastic yielding is identified as being able to describe the supercrystals' response in nanoindentation accurately. As the nanoparticles behave in a purely elastic manner with very high stiffness, the underlying constitutive law of the organic phase is also identified to be Drucker-Prager-type elastoplastic, with a Young's modulus of 13 GPa and a uniaxial tensile yield stress of 900 MPa, remarkably high values for an organic material, and matching well with experimental and DFT-based estimations. Furthermore, a sensitivity study indicates that small configurational changes within the supercrystalline lattice do not significantly alter the overall stiffness behavior. Multiscale numerical modeling is thus proven to be able to identify the nanomechanical properties of supercrystals, and can ultimately be used to tailor these materials' mechanical behavior starting from superlattice considerations.
Highlights
Structurally-ordered nanocomposites are emerging as key building blocks for the multiscale assembly of hierarchical materials systems with encoded functionality, amplified by new couplings between electrical, optical, transport, and mechanical properties [1]
A previous experimental nanoindentation campaign was used as reference to validate the proposed numerical approach and to extract additional information on the mechanical behavior of the homogenized supercrystalline nanocomposites [12]
A multiscale modeling strategy has been proposed to assess the mechanical behavior of bulk supercrystalline nanocomposites
Summary
Structurally-ordered nanocomposites are emerging as key building blocks for the multiscale assembly of hierarchical materials systems with encoded functionality, amplified by new couplings between electrical, optical, transport, and mechanical properties [1]. An elastoplastic material behavior of the homogenized (continuum) supercrystalline nanocomposites translates into an analogous mechani cal response at the local interphase level, while the stronger inorganic (iron oxide) phase behaves in a purely linear elastic fashion Together with these insights on the behavior of the supercrystalline nano composites’ phases, remarkable outcomes emerge on the stiffness and strength that the confined and crosslinked organic interphase can reach. This multiscale modeling approach is used to address another issue that typically affects supercrystalline materials, namely the very wide data scatter characteristic of micromechanical testing outcomes [8,11,12]. Composites Science and Technology 198 (2020) 108283 causes, among which the presence of supercrystalline defects and the size distribution of the constituent nanoparticles are numerically addressed in this work
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