Inks containing metallic nanoparticles are among the most commonly used conductive materials for printed electronics. Inkjet layers of MNP materials enable unprecedented design flexibility, rapid processing and 3D printing of functional electronic devices such as sensors, solar panels, LED displays, transistors and smart textiles.
Inkjet 3D printing of metals typically forms a solid printed object via a two-step process: solvent evaporation during printing (pinning) and subsequent low-temperature consolidation of the nanoparticles (sintering). The low temperature is important because in many applications nanoparticles are co-imprinted with other functional / structural organic materials which are sensitive to higher temperatures.
However, the layers produced by inkjet printing of metal nanoparticles have different electrical conductivity between the horizontal and vertical directions. This effect is known as functional anisotropy and has been a long-standing problem in 3D printing of functional electronic devices, preventing its use for advanced applications.
It was previously believed that the reduction in vertical conductivity through a printed device is primarily caused by problems with shape and physical continuity at the interfaces of the constituent nanoparticles (at very small micro and nanoscale). However, the Nottingham researchers used silver nanoparticles to show, for the first time, that it is caused by organic chemical residues in inks.
These residues, which are added to inks to help stabilize nanomaterials, lead to the formation of very thin, low-conductive nanoscale layers that interfere with the electrical conductivity of the printed sample in the vertical direction.
With a better understanding of the distribution of residual organic additives in printed layers, researchers hope to continue to define new techniques and develop new ink formulations to overcome the functional anisotropy of 3D printed electronics. ink.
Lead author Dr Gustavo Trindade, CfAM researcher, said: “The conductivity of inkjet-printed metal nanoparticles is known to be temperature-dependent and has been previously attributed to changes in shape. and the porosity of nanoparticles in clusters, with the role of organic organs. residues are only speculated. “
“This new vision helps to develop pathways to overcome functional anisotropy in inkjet nanoparticles, and will therefore enhance the uptake of this potentially transformational technology, making it competitive with conventional manufacturing. Our approach is transferable to other nanomaterial-based inks, including those containing graphene and functionalized nanocrystals, and will enable the development and exploitation of 2D and 3D printed electronics such as flexible and portable sensors, panels solar panels, LED screens, transistors and smart textiles. “
The study was carried out by the Center for Additive Manufacturing (CfAM), as part of the £ 5.85million program grant funded by the EPSRC, enabling next generation additive manufacturing. Their results are published in a new article titled “ Residual Polymer Stabilizer Causes Anisotropic Electrical Conductivity When Inkjet Printing Metal Nanoparticles ” in the journal Nature Communication media.
The researchers used the unique chemical sensitivity of a state-of-the-art 3D orbiSIMS instrument belonging to the University of Nottingham. Nottingham’s orbiSIMS – the only one from a UK university – enables label-less 3D chemical imaging of materials at very high resolution, revealing information that informed this study.
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