In this report, we describe the use of several analytical techniques, including X-ray absorption spectroscopy (XAS), electron microscopy, and electron diffraction, as tools for characterizing the ...structural dynamics of supported Pt nanoscale particles. We examined several carbon-supported samples. Electron microscopy shows that the particles in these samples (S1−S3) have average particle diameters of roughly 20, 40, and 60 Å respectively, while electron microdiffraction data for these particles provided evidence of long-ranged ordering in the form of face centered cubic structures. This study highlights the use of advanced synchrotron X-ray absorption spectroscopies (XAS), in particular extended X-ray absorption fine structure (EXAFS) and X-ray absorption near-edge structure (XANES), as powerful tools for studying the structural habits and dynamics of these prototypical nanoscale materials. Using state-of-the-art methods of measurement and computational modeling, we demonstrate that it is possible to develop a detailed understanding of the shape and morphology of the nanoscale clusters. We use these techniques to provide information about the nature of their surface texturing, establishing that they preferentially adopt oblate (“hemispherical”) cuboctahedra cluster shapes truncated along the 111 basal plane. We further describe the use of temperature-dependent EXAFS measurements to investigate the nature of bond relaxation phenomenon occurring within the small metallic nanoparticles. To evaluate these complex structural behaviors, the disorder parameters are calculated from temperature-dependent EXAFS data and then subsequently compared to simple molecular graphics simulations of mechanisms involving either full cluster or surface relaxations. The average bond length and static disorder obtained by experiment appear to best fit a model involving dominant contributions made by surface atom bond relaxation.
Combining compliant electrode arrays in open‐mesh constructs with hydrogels yields a class of soft actuator, capable of complex, programmable changes in shape. The results include materials ...strategies, integration approaches, and mechanical/thermal analysis of heater meshes embedded in thermoresponsive poly(N‐isopropylacrylamide) (pNIPAM) hydrogels with forms ranging from 2D sheets to 3D hemispherical shells.
Recent work demonstrates that processes of stress release in prestrained elastomeric substrates can guide the assembly of sophisticated 3D micro/nanostructures in advanced materials. Reported ...application examples include soft electronic components, tunable electromagnetic and optical devices, vibrational metrology platforms, and other unusual technologies, each enabled by uniquely engineered 3D architectures. A significant disadvantage of these systems is that the elastomeric substrates, while essential to the assembly process, can impose significant engineering constraints in terms of operating temperatures and levels of dimensional stability; they also prevent the realization of 3D structures in freestanding forms. Here, we introduce concepts in interfacial photopolymerization, nonlinear mechanics, and physical transfer that bypass these limitations. The results enable 3D mesostructures in fully or partially freestanding forms, with additional capabilities in integration onto nearly any class of substrate, from planar, hard inorganic materials to textured, soft biological tissues, all via mechanisms quantitatively described by theoretical modeling. Illustrations of these ideas include their use in 3D structures as frameworks for templated growth of organized lamellae from AgCl–KCl eutectics and of atomic layers of WSe₂ from vapor-phase precursors, as open-architecture electronic scaffolds for formation of dorsal root ganglion (DRG) neural networks, and as catalyst supports for propulsive systems in 3D microswimmers with geometrically controlled dynamics. Taken together, these methodologies establish a set of enabling options in 3D micro/nanomanufacturing that lie outside of the scope of existing alternatives.
Direct‐ink writing (DIW), a rapidly growing and advancing form of additive manufacturing, provides capacities for on‐demand tailoring of materials to meet specific requirements for final designs. The ...penultimate challenge faced with the increasing demand of customization is to extend beyond modification of shape to create 4D structures, dynamic 3D structures that can respond to stimuli in the local environment. Patterning material gradients is foundational for assembly of 4D structures, however, there remains a general need for useful materials chemistries to generate gray scale gradients via DIW. Here, presented is a simple materials assembly paradigm using DIW to pattern ionotropic gradients in hydrogels. Using structures that architecturally mimic sea‐jelly organisms, the capabilities of spatial patterning are highlighted as exemplified by selectively programming the valency of the ion‐binding agents. Spatial gradients, when combined with geometry, allow for programming the flexibility and movement of iron oxide nanoparticle–loaded ionotropic hydrogels to generate 4D‐printed structures that actuate in the presence of local magnetic fields. This work highlights approaches to 4D design complexity that exploits 3D‐printed gray‐scale/gradient mechanics.
Patterning gradients is foundational for the development of 4D‐printed structures. A novel, simple materials assembly paradigm for direct‐ink writing is presented to translate design complexity to net form fabrication via embedding gray scale gradients of complex form.
Inorganic light-emitting diodes and photodetectors represent important, established technologies for solid-state lighting, digital imaging and many other applications. Eliminating mechanical and ...geometrical design constraints imposed by the supporting semiconductor wafers can enable alternative uses in areas such as biomedicine and robotics. Here we describe systems that consist of arrays of interconnected, ultrathin inorganic light-emitting diodes and photodetectors configured in mechanically optimized layouts on unusual substrates. Light-emitting sutures, implantable sheets and illuminated plasmonic crystals that are compatible with complete immersion in biofluids illustrate the suitability of these technologies for use in biomedicine. Waterproof optical-proximity-sensor tapes capable of conformal integration on curved surfaces of gloves and thin, refractive-index monitors wrapped on tubing for intravenous delivery systems demonstrate possibilities in robotics and clinical medicine. These and related systems may create important, unconventional opportunities for optoelectronic devices.
Al-ion batteries are a promising alternative to lithium-ion batteries because of the unique advantages of the Al anode, such as low cost and high specific capacities. Cathodes developed for these ...batteries, however, suffer from various problems, which include low discharge voltages with rapid capacity fade (e.g., V2O5) and unclear speciation of the Al intercalation mechanism with insufficient capacity (e.g., graphite). The lack of ideal cathode materials is currently a major challenge for Al-ion batteries. Here, a high-capacity layered organic cathode composed of graphitic carbon nitride (g-C3N4) is developed for Al-ion batteries. Full cells constructed using g-C3N4 paired with an Al metal in an AlCl3/EMImCl electrolyte showed an open-circuit potential of 1.9 V and a capacity of 90 mAh/g cycled at 0.1 C. This battery also exhibits a stable capacity of 75 mAh/g cycled at 0.2 C in a long-term test (500 cycles). The data show that the layered porous structure of the organic cathode material facilitates a reversible deintercalation of AlCl4− anions, substituting them for Cl– in a more oxidized form of the g-C3N4. The data further illustrate that the anion shuttle is associated with a conversion between N and N+· states at the tertiary N(C)3 positions of the g-C3N4 structure.
Understanding and controlling the interactions occurring between cells and engineered materials are central challenges toward progress in the development of biomedical devices. In this work, we ...describe materials for direct ink writing (DIW), an extrusion-based type of 3D printing, that embed a custom synthetic protein (RGD-PDL) within the microfilaments of 3D-hydrogel scaffolds to modify these interactions and differentially direct tissue-level organization of complex cell populations in vitro. The RGD-PDL is synthesized by modifying poly-d-lysine (PDL) to varying extents with peptides containing the integrin-binding motif Arg-Gly-Asp (RGD). Compositional gradients of the RGD-PDL presented by both patterned and thin-film poly(2-hydroxyethyl) methacrylate (pHEMA) substrates allow the patterning of cell-growth compliance in a grayscale form. The surface chemistry-dependent guidance of cell growth on the RGD-PDL-modified pHEMA materials is demonstrated using a model NIH-3T3 fibroblast cell line. The formation of a more complex cellular systemorganotypic primary murine dorsal root ganglion (DRG)in culture is also achieved on these scaffolds, where distinctive forms of cell growth and migration guidance are seen depending on their RGD-PDL content and topography. This experimental platform for the study of physicochemical factors on the formation and the reorganization of organotypic cultures offers useful capabilities for studies in tissue engineering, regenerative medicine, and diagnostics.
The development of methods to synthesize and physically manipulate extremely thin, single-crystalline inorganic semiconductor materials, so-called nanomembranes, has led to an almost explosive growth ...of research worldwide into uniquely enabled opportunities for their use in new “soft” and other unconventional form factors for high-performance electronics. The unique properties that nanomembranes afford, such as their flexibility and lightweight characteristics, allow them to be integrated into electronic and optoelectronic devices that, in turn, adopt these unique attributes. For example, nanomembrane devices are able to make conformal contact to curvilinear surfaces and manipulate strain to induce the self-assembly of various 3D nano/micro device architectures. Further, thin semiconductor materials (e.g., Si-nanomembranes, transition metal dichalcogenides, and phosphorene) are subject to the impacts of quantum and other size-dependent effects that in turn enable the manipulation of their bandgaps and the properties of electronic and optoelectronic devices fabricated from them. In this Perspective, nanomembrane synthesis techniques and exemplary applications of their use are examined. We specifically describe nanomembrane chemistry exploiting high-performance materials, along with precise/high-throughput techniques for their manipulation that exemplify their growing capacities to shape outcomes in technology. Prominent challenges in the chemistry of these materials are presented along with future directions that might guide the development of next generation nanomembrane-based devices.
We show that the noncrystalline-to-crystalline transition of supported Pt nanoparticles (NPs) in the subnanometer to nanometer size range is statistical in nature, and strongly affected by particle ...size, support, and adsorbates (here we use H2). Unlike in the bulk, a noncrystalline phase exists and is stable in small NPs, reflecting a general mesoscopic feature. Observations of >3000 particles by high-resolution transmission electron microscopy show a noncrystalline-to-crystalline transition zone that is nonabrupt; there is a size regime where disordered and ordered NPs coexist. The NP size at which this transition occurs is strongly dependent on both the adsorbate and the support, and this effect is general for late 5d transition metals. All results are reconciled via a statistical description of particle-support-adsorbate interactions.
3D printing is a rapidly growing field that requires the development of yield‐stress fluids that can be used in postprinting transformation processes. There is a limited number of yield‐stress fluids ...currently available with the desired rheological properties for building structures with small filaments (≤l00 µm) with high shape‐retention. A printing‐centric approach for 3D printing particle‐free silicone oil‐in‐water emulsions with a polymer additive, poly(ethylene oxide) is presented. This particular material structure and formulation is used to build 3D structure and to pattern at filament diameters below that of any other known material in this class. Increasing the molecular weight of poly(ethylene oxide) drastically increases the extensibility of the material without significantly affecting shear flow properties (shear yield stress and linear viscoelastic moduli). Higher extensibility of the emulsion correlates to the ability of filaments to span relatively large gaps (greater than 6 mm) when extruded at large tip diameters (330 µm) and the ability to extrude filaments at high print rates (20 mm s−1). 3D printed structures with these extensible particle‐free emulsions undergo postprinting transformation, which converts them into elastomers. These elastomers can buckle and recover from extreme compressive strain with no permanent deformation, a characteristic not native to the emulsion.
Particle‐free emulsions with polymer additives are examined to probe the critical relationship between the extensional rheology of yield‐stress fluid inks and 3D printing of buildable, gap spanning structures with small filament diameter (100 µm or less). The emulsions are transformed postprinting to produce 3D printed elastomer structures that are highly elastic and flexible, a property not inherent to the particle‐free emulsions.
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