Printable conductive inks used for the fabrication of electronics: an overview.

In recent years, a wide range of electronic materials with a great diversity in their chemical and physical properties has been patterned by printing techniques on a variety of substrates. Nanotechnology-based materials appear to be the most promising thereof, increasing the resolution of the printed raster and enhancing the electrical properties of the final patterns. Conductive nanoparticle inks are the main building block of all printed electronic devices and circuit boards, forming their fundamental structure and integrated low-resistance circuit interconnects, antennae, contact electrodes within transistors etc. A plethora of both conventional and novel printing techniques have been employed with nanoparticle-based inks for the fabrication of conductive patterns, dictating different limitations for the properties of the printed inks. Although several articles have reviewed printing techniques of nanomaterials, a comprehensive review on physicochemical properties that need to be considered in order to develop nanoparticle-based conductive inks, sufficiently compatible with each printing technique, is missing. This review firstly summarizes a wide range of printing techniques that are of high potential for printing electronics and then narrows them down to those applied with conductive nanoparticle inks. Next, it focuses on the typical properties of nanoparticle-based conductive inks (chemical composition, particle size and shape, solids loading, ink viscosity and surface tension) and suggests parameters that need to be taken into account when preparing conductive nanotechnology-based inks, corresponding the requirements of each printing technique. General principles that determine the electrical conductivity of the printed patterns are outlined. Lastly, future prospects on the development of novel printable materials are laid out.

Medical-Grade PLA Nanocomposites with Optimized Tungsten Carbide Nanofiller Content in MEX Additive Manufacturing: A Rheological, Morphological, and Thermomechanical Evaluation.

The goal of this paper is to investigate tungsten carbide (WC) as a reinforcement in the popular material extrusion (MEX) additive manufacturing (AM) procedure. The impressive characteristics of WC demonstrate its potential as a valuable additive for commonly used polymeric matrices in MEX 3D printing, offering reinforcement and stabilization properties. The mechanical properties of hybrid polymer/ceramic nanocomposites made up of various filler loadings (0-10 wt. %) of medical-grade polylactic acid (PLA) and WC were studied. The mechanical characteristics, structure, and thermomechanical properties of the resulting compounds were fully characterized following the respective standards. The fracture mechanisms were revealed with Scanning Electron Microscopy. Overall, a laborious effort was implemented with fifteen different tests to fully characterize the nanocomposites prepared. In comparison to the raw PLA material, the tensile strength of the 4.0 wt. % WC PLA/WC nanocomposite was improved by 42.5% and the flexural strength by 41.9%. In the microhardness test, a 120.4% improvement was achieved, justifying the properties of WC ceramic. According to these findings, PLA nanocomposites reach high-performance polymer specifications, expanding their potential use, especially in wear-related applications.

Optimizing the Rheological and Thermomechanical Response of Acrylonitrile Butadiene Styrene/Silicon Nitride Nanocomposites in Material Extrusion Additive Manufacturing.

The current research aimed to examine the thermomechanical properties of new nanocomposites in additive manufacturing (AM). Material extrusion (MEX) 3D printing was utilized to evolve acrylonitrile butadiene styrene (ABS) nanocomposites with silicon nitride nano-inclusions. Regarding the mechanical and thermal response, the fabricated 3D-printed samples were subjected to a course of standard tests, in view to evaluate the influence of the Si3N4 nanofiller content in the polymer matrix. The morphology and fractography of the fabricated filaments and samples were examined using scanning electron microscopy and atomic force microscopy. Moreover, Raman and energy dispersive spectroscopy tests were accomplished to evaluate the composition of the matrix polymer and nanomaterials. Silicon nitride nanoparticles were proved to induce a significant mechanical reinforcement in comparison with the polymer matrix without any additives or fillers. The optimal mechanical response was depicted to the grade ABS/Si3N4 4 wt. %. An impressive increase in flexural strength (30.3%) and flexural toughness (47.2%) was found. The results validate that these novel ABS nanocomposites with improved mechanical properties can be promising materials.

Temperature-Triggered/Switchable Thermal Conductivity of Epoxy Resins.

The pronouncedly low thermal conductivity of polymers in the range of 0.1-0.2 W m-1 K-1 is a limiting factor for their application as an insulating layer in microelectronics that exhibit continuously higher power-to-volume ratios. Two strategies can be applied to increase the thermal conductivity of polymers; that is, compounding with thermally conductive inorganic materials as well as blending with aromatic units arranged by the principle of π-π stacking. In this study, both strategies were investigated and compared on the example of epoxy-amine resins of bisphenol A diglycidyl ether (BADGE) and 1,2,7,8-diepoxyoctane (DEO), respectively. These two diepoxy compounds were cured with mixtures of the diamines isophorone diamine (IPDA) and o-dianisidine (DAN). The epoxy-amine resins were cured without filler and with 5 wt.-% of SiO2 nanoparticles. Enhanced thermal conductivity in the range of 0.4 W·m-1·K-1 was observed exclusively in DEO-based polymer networks that were cured with DAN (and do not contain SiO2 fillers). This observation is argued to originate from π-π stacking of the aromatic units of DAN enabled by the higher flexibility of the aliphatic carbon chain of DEO compared with that of BADGE. The enhanced thermal conductivity occurs only at temperatures above the glass-transition point and only if no inorganic fillers, which disrupt the π-π stacking of the aromatic groups, are present. In summary, it can be argued that the bisphenol-free epoxy-amine resin with an epoxy compound derivable from natural resources shows favorably higher thermal conductivity in comparison with the petrol-based bisphenol-based epoxy/amine resins.