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    Item type:Publication, Access status: with files ,
    Realistic microstructural modeling of supercrystalline oleic acid nanocomposites
    (Elsevier, 2025-06-10)
    Kolli, Vasu
    ;
    Scheider, Ingo
    ;
    Schneider, Konrad
    ;
    Giuntini, Diletta
    ;
    Cyron, Christian J.
    Supercrystalline nanocomposites, with their growing range of applications, present a significant challenge in understanding their structural behavior. These materials, composed of organically surface-functionalized inorganic nanoparticles arranged in periodic structures, exhibit superlattice imperfections, such as particle size scatter and superlattice vacancies, that emerge during fabrication. The mechanical effects of these defects, particularly particle size scatter and point defects, remain poorly understood due to experimental limitations. This study investigates these effects through advanced numerical modeling. A generalized Maxwell model is employed to model the oleic acid layer, with parameter values determined via inverse analysis. Subsequently, statistically equivalent periodic unit cells (SEPUCs) are used to simulate the impact of particle size scatter and point defects. Simulations reveal that nanocomposite mechanical properties, including stiffness, creep resistance, and plasticity, are highly influenced by particle distribution and the overlap volume of the organic interface. Conversely, point defects (superlattice vacancies) exhibit a negligible impact on the overall mechanical behavior. Furthermore, the material becomes increasingly isotropic with greater particle size scatter. These findings provide critical insights for the future design of these materials.
    Publicationtype: Journal Article
      72  21
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    Item type:Publication, Access status: with files ,
    Modeling of time-dependent mechanical behavior of oleic acid nanocomposites using nanoindentation
    (Elsevier, 2024-06-01)
    Kolli, Vasu
    ;
    Scheider, Ingo
    ;
    Ovri, Henry
    ;
    Giuntini, Diletta
    ;
    Cyron, Christian J.
    Supercrystalline nanocomposites are a burgeoning class of hybrid inorganic–organic materials. Studies showed that self-assembly of iron oxide particles surface-functionalized with organic (e.g. oleic acid) ligands produces a supercrystalline nanocomposite with exceptional mechanical properties. Consequently, significant research has been conducted on these materials to experimentally characterize the mechanical properties of such materials. However, so far all modeling studies used time and rate independent elastoplastic material models. In the light of new experimental results, we propose to extent this view and use time-dependent models to capture viscoelastic behavior. To this end, we quantified this behavior using nanoindentation creep experiments and modeled it using a rheological network model with several parallel Maxwell branches and an additional elasto-plastic branch. We demonstrate how the parameters of such a model can be found using inverse analysis. With the calibrated material model, a good agreement of the time dependent behavior between simulation and experimental results is achieved. Thus, a method is provided to model time dependent behavior using complex non-classical experiments like nanoindentation.
    Publicationtype: Journal Article
      25  78