Electrohydrodynamic redox 3D printing (EHD-RP) is an additive manufacturing (AM) technique with submicron resolution and multi-metal capabilities, offering the possibility to switch chemistry during deposition "on-the-fly". Despite the potential for...
Across disciplines and length scales, alloying of metals is a common and necessary strategy to optimise materials performance. While the manufacturing of alloys in bulk and thin film form is well understood, the fabrication of alloyed 3D nanostructures with precise control over the composition remains a challenge. Herein, we demonstrate that electrohydrodynamic redox printing from mixed metal salt solutions is a versatile approach for the 3D nanofabrication of alloys. We propose that the droplet-by-droplet nature of the electrohydrodynamic redox printing process allows straightforward electroplating of alloys with composition solely controlled by the composition of the electrolyte solution, independent of the reduction potential of the involved cations. As a demonstration of the direct control of composition, we deposit binary and ternary alloys of Ag, Cu and Zn. TEM microstructure analysis indicates homogeneous alloying at the nanoscale and the formation of a metastable solid-solution phase for Ag-Cu and a two phase system for Ag-Cu-Zn alloys. The straightforward approach to alloying with an electrochemical technique promises novel opportunities for optimisation of properties of 3D nanofabricated metals.
Agglomeration of copper nanowires (aspect ratios on the order of 1000) in polyethylene, commonly a major problem, could be prevented by modification of the nanowires with a surface layer of oleylamine. Nanocomposite films were prepared by mixing nanowire dispersions in organic solvents with polyethylene solutions followed by casting, drying, and sometimes hot pressing. Orientation of the copper nanowires by solid-state drawing of the composites at elevated temperatures led to preferential alignment of the nanowires in the drawing direction. This arrangement gave rise to a uniform dichroism in the near-infrared (NIR) region, which is uncommon in the case of the hitherto reported dichroic nanocomposites. The NIR dichroism is ascribed to the high aspect ratio of the metal wires. Hence, drawing of isotropic nanocomposites with metal wires may serve for the manufacture of NIR polarization filters.
Combining the unprecedented design freedom in microscale additive manufacturing (AM) with the ability to control the chemical nature of each printed voxel could unlock unique possibilities for tailoring mechanical, chemical, electrical, optical and magnetic properties of metal microstructures. A variety of techniques for micro- and nanoscale AM has been proposed for the fabrication of device-grade metals and alloys [1]. Electrochemical approaches to small-scale AM generally lead to superior microstructures (in terms of porosity and contamination) compared with techniques that transfer pre-synthesized materials [2]. The deposition of alloys with controlled composition, however, remains a challenge with electrochemical small scale AM techniques. In this talk, we will present our work on additive manufacturing of alloyed structures using electrohydrodynamic redox (EHD-RP) 3D printing [3]. EHD-RP is based on the deposition of solvent droplets containing metal ions onto a conductive substrate, where the solvent evaporates and the ions are reduced. In general, this technique allows the direct deposition of polycrystalline 3D metal structures with a resolution of approx. 250 nm and a feature size down to 100 nm. We will present our work in expanding the materials range of EHD-RP from the limited range reported previously to a wide range of metals and subsequently discuss in detail the direct deposition of alloys. As it will be shown, the approach of spatially confining electrodeposition enables the fabrication of multi-metal and alloyed structures with a chemical voxel size <400 nm, hence making a step towards chemically architected materials. We will show how we can control the composition of the deposited material and the challenges involved in its characterization. In summary, we present a novel approach to the bottom-up manufacturing of locally alloyed microstructures, adding an additional parameter in the design of novel nano- and microstructured inorganic materials. [1] L. Hirt, A. Reiser, R. Spolenak & T. Zambelli. Additive Manufacturing of Metal Structures at the Micrometer Scale. Adv. Mater., 29(17), 2017. [2] A. Reiser, R. Spolenak et al. Metals by Micro-scale Additive Manufacturing: Comparison of Microstructure and Mechanical Properties. Adv. Funct. Mater., 30, 1910491, 2020 [3] A. Reiser, M. Lindén, P. Rohner, A. Marchand, H. Galinski, A. S. Sologubenko, J. M. Wheeler, R. Zenobi, D. Poulikakos & R. Spolenak. Multi-metal electrohydrodynamic redox 3D printing at the submicron scale. Nat. Comm., 10(1):1-8, 2019. Figure 1
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