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Item type:Publication, Access status: without files , 4D-Printing of Smart, Nacre-Inspired, Organic-Ceramic Composites(2023-09-05); ; ; ; Additive manufacturing of shape memory polymers has gained tremendous interest in recent years due to their versatile potential applications in various industries, such as biomedicine and aerospace. However, the polymers' mechanical properties, specifically stiffness and strength, often hinder their use in mechanically demanding applications, e.g. as structural materials. In this work we produced nacre-inspired composites with a covalent adaptable network, which enables fast and mechanically lossless self-healing, reshaping, and shape memory capabilities. We demonstrate a novel direct write 4D-printing strategy to print smart, nacre-inspired, organic-ceramic composites based on alumina platelets and vitrimers with up to 3.3 and 26.7 times higher tensile strength and stiffness, respectively, in comparison to the pristine vitrimer. To the best of our knowledge, we introduce for the first time a single step 4D-printing process for nacre-inspired composites, that exploits suspension spreading to align micron sized alumina platelets along a common plane, and which utilizes solvent evaporation to induce polycondensation of the monomers resulting in a vinylogous urethane vitrimer after extrusion of the suspension. This work presents a facile, direct write 4D-printing strategy at ambient printing conditions, establishing a foundation for adaptive additive manufacturing of smart organic-ceramic composites of interest to various industries.Publicationtype: Journal Article43 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Nanoindentation creep of supercrystalline nanocomposites(Elsevier, 2023-07); ; ; ; Supercrystalline nanocomposites (SCNCs) are inorganic-organic hybrid materials with a unique periodic nanostructure, and thus they have been gaining growing attention for their intriguing functional properties and parallelisms with hierarchical biomaterials. Their mechanical behavior remains, however, poorly understood, even though its understanding and control are important to allow SCNCs’ implementation into devices. An important aspect that has not been tackled yet is their time-dependent deformation behavior, which is nevertheless expected to play an important role in materials containing such a distribution of organic phase. Hereby, we report on the creep of ceramic-organic SCNCs with varying degrees of organic crosslinking, as assessed via nanoindentation. Creep strains and their partial recoverability are observed, hinting at the co-presence of viscoelasticity and viscoplasticity, and a clear effect of crosslinking in decreasing the overall material deformability emerges. We rationalize our experimental observations with the analysis of stress exponent and activation volume, resulting in a power-law breakdown behavior and governing deformation mechanisms occurring at the organic sub-nm interfaces scale, as rearrangement of organic ligands. The set of results is reinforced by the evaluation of the strain rate sensitivity via strain rate jump tests, and the assessment of the effect of oscillations during continuous stiffness measurement mode.Publicationtype: Journal ArticleScopus© Citations 4 20 320 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Solvent controlled 2D structures of bottom-up fabricated nanoparticle superlattices(Royal Society of Chemistry (RSC), 2023-02-08); ; ; ; We demonstrate that oleyl phosphate ligand-stabilized iron oxide nanocubes as building blocks can be assembled into 2D supercrystalline mono- and multilayers on flat YSZ substrates within a few minutes using a simple spin-coating process. As a bottom-up process, the growth takes place in a layer-by-layer mode and therefore by tuning the spin-coating parameters, the exact number of deposited monolayers can be controlled. Furthermore, ex situ scanning electron and atomic force microscopy as well as X-ray reflectivity measurements give evidence that the choice of solvent allows the control of the lattice type of the final supercrystalline monolayers. This observation can be assigned to the different Hansen solubilities of the solvents used for the nanoparticle dispersion because it determines the size and morphology of the ligand shell surrounding the nanoparticle core. Here, by using toluene and chloroform as solvents, it can be controlled whether the resulting monolayers are ordered in a square or hexagonal supercrystalline lattice.Publicationtype: Journal ArticleScopus© Citations 3 41 107 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Strengthening engineered nanocrystalt three-dimensional superlattices via ligand conformation and reactivity(American Chemical Society (ACS), 2022-08-23); ; ; ; Nanocrystal assembly into ordered structures provides mesostructural functional materials with a precise control that starts at the atomic scale. However, the lack of understanding on the self-assembly itself plus the poor structural integrity of the resulting supercrystalline materials still limits their application into engineered materials and devices. Surface functionalization of the nanobuilding blocks with organic ligands can be used not only as a means to control the interparticle interactions during self-assembly but also as a reactive platform to further strengthen the final material via ligand cross-linking. Here, we explore the influence of the ligands on superlattice formation and during cross-linking via thermal annealing. We elucidate the effect of the surface functionalization on the nanostructure during self-assembly and show how the ligand-promoted superlattice changes subsequently alter the cross-linking behavior. By gaining further insights on the chemical species derived from the thermally activated cross-linking and its effect in the overall mechanical response, we identify an oxidative radical polymerization as the main mechanism responsible for the ligand cross-linking. In the cascade of reactions occurring during the surface-ligands polymerization, the nanocrystal core material plays a catalytic role, being strongly affected by the anchoring group of the surface ligands. Ultimately, we demonstrate how the found mechanistic insights can be used to adjust the mechanical and nanostructural properties of the obtained nanocomposites. These results enable engineering supercrystalline nanocomposites with improved cohesion while preserving their characteristic nanostructure, which is required to achieve the collective properties for broad functional applications.Publicationtype: Journal ArticleScopus© Citations 9 58 417 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Nanoindentation of supercrystalline nanocomposites: linear relationship between elastic modulus and hardness(Springer, 2022-04-15); ; ; ; Supercrystalline nanocomposites (SCNCs) are a new category of nanostructured materials, with organically functionalized nanoparticles assembled into periodic structures, reminiscent of atomic crystals. Thanks to this nanoarchitecture, SCNCs show great promise for functional applications, and understanding and controlling their mechanical properties becomes key. Nanoindentation is a powerful tool to assess the mechanical behavior of virtually any material, and it is particularly suitable for studies on nanostructured materials. While investigating SCNCs in nanoindentation, a linear proportionality has emerged between elastic modulus and hardness. This is not uncommon in nanoindentation studies, and here we compare and contrast the behavior of SCNCs with that of other material categories that share some of the key features of SCNCs: mineral-rich biocomposites (where mineral building blocks are packed into a protein-interfaced network), ultrafine grained materials (where the characteristic nano-grain sizes are analogous to those of the SCNC building blocks), and face-centered cubic atomic crystals (which share the typical SCNC periodic structure). A strong analogy emerges with biomaterials, both in terms of the hardness/elastic modulus relationship, and of the correlation between this ratio and the dissipative mechanisms occurring upon material deformation. Insights into the suitability of SCNCs as building blocks of the next-generation hierarchical materials are drawn.Publicationtype: Journal ArticleScopus© Citations 10 63 102 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Constitutive and fracture behavior of ultra-strong supercrystalline nanocomposites(American Institute of Physics (AIP), 2021-09-09); ; ; ; Supercrystalline nanocomposites are a new class of hybrid and nanostructured materials that can reach exceptional mechanical strength and can be fabricated at low temperatures. Hierarchically arranged, they bridge the gap from the nano- to the macro-scale. Even though their mechanical properties are starting to be characterized, their constitutive behavior is still largely unexplored. Here, the mechanical behavior of supercrystalline nanocomposites of iron oxide nanoparticles, surface-functionalized with oleic acid and oleyl phosphate ligands, is investigated in both bending and compression, with loading-unloading tests. A new bar geometry is implemented to better detect deformation prior to unstable crack propagation, and notched bending bars are tested to evaluate fracture toughness. Micro-mechanical tests result in the values of strength and elastic modulus that are extremely high for supercrystals, reaching record-high numbers in the oleic acid-based nanocomposites, which also show a significant tension-compression asymmetry. The constitutive behavior of both materials is predominantly linear elastic, with some more marked nonlinearities arising in the oleyl phosphate-based nanocomposites. The fracture toughness of both types of nanocomposites, ∼0.3 MPa√m, suggests that extrinsic toughening, associated with both material composition and nanostructure, plays an important role. Fractographic observations reveal analogies with shear and cleavage in atomic crystals. The influence of material composition, nanostructure, and processing method on the mechanical behavior of the nanocomposites is analyzed.Publicationtype: Journal ArticleScopus© Citations 8 107 269 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Deformation behavior of cross-linked supercrystalline nanocomposites: an in situ SAXS/WAXS study during uniaxial compression(American Chemical Society (ACS), 2021-03-22); ; ; ; With the ever-expanding functional applications of supercrystalline nanocomposites (a relatively new category of materials consisting of organically functionalized nanoparticles arranged into periodic structures), it becomes necessary to ensure their structural stability and understand their deformation and failure mechanisms. Inducing the cross-linking of the functionalizing organic ligands, for instance, leads to a remarkable enhancement of the nanocomposites' mechanical properties. It is however still unknown how the cross-linked organic phase redistributes applied loads, how the supercrystalline lattice accommodates the imposed deformations, and thus in general what phenomena govern the overall material's mechanical response. This work elucidates these aspects for cross-linked supercrystalline nanocomposites through an in situ small- and wide-angle X-ray scattering study combined with uniaxial pressing. Because of this loading condition, it emerges that the cross-linked ligands effectively carry and distribute loads homogeneously throughout the nanocomposites, while the superlattice deforms via rotation, slip, and local defects generation.Publicationtype: Journal ArticleScopus© Citations 12 181 314 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Defects and plasticity in ultrastrong supercrystalline nanocomposites(2021-01-06); ; ; ; Supercrystalline nanocomposites are nanoarchitected materials with a growing range of applications but unexplored in their structural behavior. They typically consist of organically functionalized inorganic nanoparticles arranged into periodic structures analogous to crystalline lattices, including superlattice imperfections induced by processing or mechanical loading. Although featuring a variety of promising functional properties, their lack of mechanical robustness and unknown deformation mechanisms hamper their implementation into devices. We show that supercrystalline materials react to indentation with the same deformation patterns encountered in single crystals. Supercrystals accommodate plastic deformation in the form of pile-ups, dislocations, and slip bands. These phenomena occur, at least partially, also after cross-linking of the organic ligands, which leads to a multifold strengthening of the nanocomposites. The classic shear theories of crystalline materials are found to describe well the behavior of supercrystalline nanocomposites, which result to feature an elastoplastic behavior, accompanied by compaction.Publicationtype: Journal ArticleScopus© Citations 15 240 217 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Controlling the large-scale fabrication of supraparticlesControlling the nanoscale interactions of colloidal building blocks is a key step for the transition from single nanoparticles to tailor-made, architected morphologies and their further integration into functional materials. Solvent evaporation-induced self-assembly within emulsion droplets emerges as a fast, versatile, and low-cost approach to obtain spherical, complex structures, such as supraparticles. Nevertheless, some process-structure relationships able to describe the effects of emulsion conditions on the synthesis outcomes still remain to be understood. Here, we explore the effect of different physicochemical parameters of emulsion-templated self-assembly (ETSA) on supraparticles' formation. Supraparticle size, size dispersity, microporosity, and sample homogeneity are rationalized based on the used surfactant formulation, stabilization mechanism, and viscosity of the emulsion. We further demonstrate the significance of the parameters found by optimizing a transferable, large-scale (gram-size) ETSA setup for the controlled synthesis of spherical supraparticles in a range of defined sizes (from 0.1-10 μm). Ultimately, our results provide new key synthetic parameters able to control the process, promoting the development of supraparticle-based, functional nanomaterials for a wide range of applications.Publicationtype: Journal ArticleScopus© Citations 13 201 393 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Mapping the mechanical properties of hierarchical supercrystalline ceramic-organic nanocomposites(Multidisciplinary Digital Publishing Institute (MDPI), 2020-10-19); ; ; ; Multiscale ceramic-organic supercrystalline nanocomposites with two levels of hierarchy have been developed via self-assembly with tailored content of the organic phase. These nanocomposites consist of organically functionalized ceramic nanoparticles forming supercrystalline micron-sized grains, which are in turn embedded in an organic-rich matrix. By applying an additional heat treatment step at mild temperatures (250–350 °C), the mechanical properties of the hierarchical nanocomposites are here enhanced. The heat treatment leads to partial removal and crosslinking of the organic phase, minimizing the volume occupied by the nanocomposites’ soft phase and triggering the formation of covalent bonds through the organic ligands interfacing the ceramic nanoparticles. Elastic modulus and hardness up to 45 and 2.5 GPa are attained, while the hierarchical microstructure is preserved. The presence of an organic phase between the supercrystalline grains provides a toughening effect, by curbing indentation-induced cracks. A mapping of the nanocomposites’ mechanical properties reveals the presence of multiple microstructural features and how they evolve with heat treatment temperature. A comparison with non-hierarchical, homogeneous supercrystalline nanocomposites with lower organic content confirms how the hierarchy-inducing organic excess results in toughening, while maintaining the beneficial effects of crosslinking on the materials’ stiffness and hardness.Publicationtype: Journal ArticleScopus© Citations 10 291 331