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Item type:Publication, Access status: with files , A nanoporous gold-polypyrrole hybrid nanomaterial for actuationWe discuss actuation with a hybrid nanomaterial that is made by electro-polymerizing pyrrole on the internal surfaces of dealloying-derived nanoporous gold and then letting aqueous electrolyte be imbibed in the remaining pore space. In this way, active polypyrrole films are contacted by two separate but individually contiguous conduction paths, providing efficient transport of ions in the electrolyte channels and of electrons in the metal skeleton. The metal skeleton also serves to enhance the mechanical behavior of the actuator. Actuation exploits the dimension changes of the polymer when ions are exchanged with the electrolyte in a pseudo-capacitive way, at potentials negative of the classic oxidation/reduction of polypyrrole. Our experiments with millimeter-size bulk samples indicate fast switching and substantially larger strain amplitude than nanoporous metal actuators.Publicationtype: Journal ArticleScopus© Citations 30 289 474 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Silver-rich clusters in nanoporous gold(Taylor & Francis, 2017-01-17); ; ; ; Herein we report on how to render Ti3C2Tx (MXene) monolayers deposited on SiO2/Si wafers, with different SiO2 thicknesses, visible. Inputting the effective thickness of a Ti3C2Tx monolayer (1 ± 0.2 nm) measured by atomic force microscopy, and its refractive index into a Fresnel-law-based simulation software, we show that the optical contrast of Ti3C2Tx monolayers deposited on SiO2/Si wafers depends on the SiO2 thickness, number of MXene layers, and the light’s wavelength. The highest contrast was found for SiO2 thicknesses around 220 nm. Simulations for other substrates, namely, Al2O3/Si, HfO2/Si, Si3N4/Si and Al2O3/Al, are presented as supplementary information.Publicationtype: Journal ArticleScopus© Citations 59 460 804 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Local flow stresses in interpenetrating-phase composites based on nanoporous gold — in situ diffraction(Elsevier, 2016-09-23); ; ; ; We report a synchrotron in situ diffraction experiment exploring stress evolution during compression of interpenetrating-phase nanocomposites based on nanoporous gold and polymer.While previous experiments provided indirect indication of local flow conditions based on macroscopic effective flow stress and micromechanics models such as Gibson-Ashby scaling law, the lattice parameter data of our experiment access the flow stress directly. At small structure size we find excellent agreement with previous reports, supporting thematch between material andmodel of those studies. Yet, deviations at larger structure size suggest that coarsening generates defects in metal network structure that are ignored by standard models.Publicationtype: Journal ArticleScopus© Citations 4 329 334 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Nanoporous gold: 3D structural analyses of representative volumes and their implications on scaling relations of mechanical behaviourWe present a quantitative study of the salient structural parameters identified from so-called ‘representative volumes’ of the bicontinuous nanoporous gold (NPG) network, and examine the validity of self-similarity in describing its evolution. The approach is based on 3D-focused ion beam tomography applied to as-dealloyed and isothermally annealed NPG samples. After identifying sufficiently large representative volumes, we show that the ligament width distributions coarsen in a sufficiently self-similar, time-invariant manner, while the scaled connectivity density shows a self-similar ligament network topology. Using these critical parameters, namely mean ligament diameter and connectivity density, the Gibson–Ashby scaling laws for the mechanical response of cellular materials are revisited. The inappropriateness of directly applying the Gibson–Ashby model to NPG is demonstrated by comparing finite element method compression simulations of both the NPG reconstruction and that of the Gibson–Ashby solid model; rather than the solid volume fraction, we show that an effective load-bearing ring structure governs mechanical behaviour.Publicationtype: Journal Article86 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , A principle curvatures analysis of the isothermal evolution of nanoporous gold: Quantifying the characteristic length-scalesA study of the isothermal evolution of a nanoporous gold (npg) microstructure after dealloying has been performed. In order to adequately characterize its complex three-dimensional bicontinuous ligamentring structure, an analysis of the scaled principle curvatures k1 and k2 based on representative volumes of meshed 3D reconstructions was applied. Five npg samples, as obtained from an electrolytical dealloying process, with different mean ligament diameters ranging from ca. 25 nm (as-dealloyed) to ca. 420 nm (from annealing at 300 C) were analyzed. The results indicate that ligament surface flattening effects lead to small but distinct morphological changes during the investigated early and mid-stages of coarsening, visible in the scaled k1- and k2- marginal distributions. Thus, strictly speaking, self-similar evolution of npg cannot be confirmed, but dependent on the specific application, the evolution might be seen as “sufficiently” self-similar. Moreover, it is shown that the inverse mean principle curvatures from the marginal distributions can be used to identify the mean sizes of the two salient structural features, namely the ligaments and the rings. Both inverse mean principle curvatures scale linearly with the mean ligament diameter. Thus, for the material used in this study, one parameter is sufficient to characterize its microstructure. Finally, it is shown that rings resembling the ones from the real samples can be generated computationally by applying modified torus parameterizations. Surprisingly, a calculation of the curvature distribution of only one ”average” ring is sufficient to approximate the scaled kappa distributions accumulated from the ring distributions of the real samples.Publicationtype: Journal ArticleScopus© Citations 48 352 522 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Nanoporous gold : testing macro-scale samples to probe small-scale mechanical behavior(Taylor & Francis, 2015-10-16); ; ; ; Nanoporous gold made by dealloying exemplifies how the exciting mechanical properties of nanoscale objects can be exploited in designing materials from which macroscopic things can be formed. The homogeneous microstructure and the possibility of adjusting the ligament size, L, between few and few hundred nm, along with the high deformability and reproducible mechanical behavior predestine the material for model studies of small-scale plasticity using reliable macroscopic testing schemes on mm- or cm-size samples. Such experiments tend to agree with the Gibson-Ashby scaling relation for strength versus solid fraction, while suggesting an essentially L−1 scaling of the local strength of the ligaments. By contrast, the elastic compliance is dramatically enhanced compared to the Gibson-Ashby relation for the stiffness. Contrary to intuition, the anomalously compliant behavior of the nanomaterial goes along with a trend for more stiffness at smaller L. This article discusses surface excess elasticity, nonlinear elastic behavior and specifically shear instability of the bulk, network connectivity, and the surface chemistry as relevant issues which deserve further study.Publicationtype: Journal ArticleScopus© Citations 118 430 532 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Nanoporous-gold-based composites : toward tensile ductility(Macmillan Publishers Limited, part of Springer Nature, 2015-06-12); ; ; ; We report on mechanical tests on interpenetrating-phase nanocomposite materials made by vacuum impregnation of nanoscale metal networks with a polymer. The metal component is nanoporous gold made by dealloying, whereas two epoxy resins and polyurethane are explored as the polymer component. The composites are strong and deformable in compression. Although previous observations invariably indicate tensile brittleness for nanoporous gold, composite samples made from cm-sized nanoporous samples enable macroscopic tensile and four-point bending tests that show ductility. This implies that the high strength of individual metal objects such as nanowires can now be incorporated into a strong and ductile material from which macroscopic things can be formed. In fact, a rule-of-mixture-type analysis of the stresses carried by the metal phase suggests quantitative agreement with data reported from separate experiments on small-scale gold nanostructures.Publicationtype: Journal ArticleScopus© Citations 60 294 411 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Nanostructural changes in crystallizable controlling units determine the temperature-memory of polymers(Royal Society of Chemistry (RSC), 2015-03-03); ; ; ; Temperature-memory polymers remember the temperature, where they were deformed recently, enabled by broad thermal transitions. In this study, we explored a series of crosslinked poly[ethylene-co-(vinyl acetate)] networks (cPEVAs) comprising crystallizable polyethylene (PE) controlling units exhibiting a pronounced temperature-memory effect (TME) between 16 and 99 °C related to a broad melting transition (∼100 °C). The nanostructural changes in such cPEVAs during programming and activation of the TME were analyzed via in situ X-ray scattering and specific annealing experiments. Different contributions to the mechanism of memorizing high or low deformation temperatures (Tdeform) were observed in cPEVA, which can be associated to the average PE crystal sizes. At high deformation temperatures (>50 °C), newly formed PE crystals, which are established during cooling when fixing the temporary shape, dominated the TME mechanism. In contrast, at low Tdeform (<50 °C), corresponding to a cold drawing scenario, the deformation led preferably to a disruption of existing large crystals into smaller ones, which then fix the temporary shape upon cooling. The observed mechanism of memorizing a deformation temperature might enable the prediction of the TME behavior and the knowledge based design of other TMPs with crystallizable controlling units.Publicationtype: Journal ArticleScopus© Citations 17 367 214 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Composites of Nanoporous Gold and Polymer(2015); Nanoporous gold obtained by alloy corrosion was vacuum-impregnated with different polymers to produce interpenetrating phase nanocomposites that are reinforced by interconnected network of metal nanostructures. The interpenetrating phase composites were tested for microhardness, compressive stress-strain behavior, macroscopic tensile, and bending deformation. Mechanical tests demonstrate that impregnation with polymer is an efficient way of reducing the density change during plastic flow under uniaxial load. The composite has an isotropic microstructure, it is ductile in tension, it is strong and deformable in compression, and its strength considerably exceeds that of each of the constituent phases. Its electric conductivity reaches 1% of that of high-purity massive copper.Publicationtype: Doctoral Thesis815 1797 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Composites of nanoporous gold and polymerNanoporous gold made by alloy corrosion can be impregnated with epoxy resin to produce a novel, polymer-based nanocomposite material that is reinforced by an interconnected network of high-strength metal nanostructures. The composite has a near-metallic electric conductivity, is ductile in tension and compression and its strength considerably exceeds that of each of the individual constituent phases.Publicationtype: Journal Article106