Highly conductive electronics circuits from aerosol jet printed silver inks

Scientific Reports 11, 18141 (2021)

Recently, low-cost electronics printed on lightweight, flexible and 3D shaped substrates are gaining importance in the markets of wearables and smart packaging. However, printed electronics do not meet the electrical performance of subtractive techniques because the resistivity of metallic printed patterns is still much higher than that of bulk material. To fulfil this need, low-resistive and easy printable inks for high resolution printed electronics techniques are needed. In this work, parameters of silver nanoparticles ink for micro-scale printed electronics technique, Aerosol Jet Printing, are being enhanced. To increase electrical conductivity and enhance printability, surfactants and dispersing agents were used to increase ultrasonic atomisation efficiency, obtain a uniform structure of printed lines, and narrow the width of printed patterns. Electrical measurements show a decrease in resistivity value in samples enhanced by cationic and non-ionic surfactants, by 95%, compared to initially prepared inks. Surfactant additions to silver nanoparticles Aerosol Jet Printing ink show promising features for application in modern electronics.

Are We Able to Print Components as Strong as Injection Molded?—Comparing the Properties of 3D Printed and Injection Molded Components Made from ABS Thermoplastic

Applied Sciences 2021, 11(15), 6946

In this paper, we are focusing on comparing results obtained for polymer elements manufactured with injection molding and additive manufacturing techniques. The analysis was performed for fused deposition modeling (FDM) and single screw injection molding with regards to the standards used in thermoplastics processing technology. We argue that the cross-section structure of the sample obtained via FDM is the key factor in the fabrication of high-strength components and that the dimensions of the samples have a strong influence on the mechanical properties. Large cross-section samples, 4 × 10 mm2, with three perimeter layers and 50% infill, have lower mechanical strength than injection molded reference samples—less than 60% of the strength. However, if we reduce the cross-section dimensions down to 2 × 4 mm2, the samples will be more durable, reaching up to 110% of the tensile strength observed for the injection molded samples. In the case of large cross-section samples, strength increases with the number of contour layers, leading to an increase of up to 97% of the tensile strength value for 11 perimeter layer samples. The mechanical strength of the printed components can also be improved by using lower values of the thickness of the deposited layers.

Printed Flexible Thermoelectric Nanocomposites Based on Carbon Nanotubes and Polyaniline

Materials 2021, 14(15), 4122

A new era of composite organic materials, nanomaterials, and printed electronics is emerging to the applications of thermoelectric generators (TEGs). Special attention is focused on carbon nanomaterials and conducting polymers, and the possibility to form pastes and inks for various low-cost deposition techniques. In this work, we present a novel approach to the processing of composite materials for screen-printing based on carbon nanotubes (CNTs) and polyaniline (PANI), supported with a dielectric polymer vehicle. Three different types of such tailor-made materials were prepared, with a functional phase consisted of carbon nanotubes and polyaniline composites fabricated with two methods: dry mixing of PANI CNT powders and in situ polymerisation of PANI with CNT. These materials were printed on flexible polymer substrates, exhibiting outstanding mechanical properties. The best parameters obtained for elaborated materials were σ=405.45 S⋅m−1, S=15.4 μV⋅K−1, and PF=85.2 nW⋅m−1K−2, respectively.

Soldering of Electronics Components on 3D-Printed Conductive Substrates

Materials 2021, 14(14), 3850

Rapid development of additive manufacturing and new composites materials with unique properties are promising tools for fabricating structural electronics. However, according to the typical maximum resolution of additive manufacturing methods, there is no possibility to fabricate all electrical components with these techniques. One way to produce complex structural electronic circuits is to merge 3D-printed elements with standard electronic components. Here, different soldering and surface preparation methods before soldering are tested to find the optimal method for soldering typical electronic components on conductive, 3D-printed, composite substrates. To determine the optimal soldering condition, the contact angles of solder joints fabricated in different conditions were measured. Additionally, the mechanical strength of the joints was measured using the shear force test. The research shows a possibility of fabricating strong, conductive solder joints on composites substrates prepared by additive manufacturing. The results show that mechanical cleaning and using additional flux on the composite substrates are necessary to obtain high-quality solder joints. The most repeatable joints with the highest shear strength values were obtained using reflow soldering together with low-temperature SnBiAg solder alloy. A fabricated demonstrator is a sample of the successful merging of 3D-printed structural electronics with standard electronic components.

Printed Graphene, Nanotubes and Silver Electrodes Comparison for Textile and Structural Electronics Applications

Sensors 2021, 21(12), 4038

Figure 9. Scanning Electron Microscopy micrograph image presenting the morphology of the sample surface with printed graphene paste containing 10 wt.% GNP in PMMA organic vehicle.

Due to the appearance of smart textiles and wearable electronics, the need for electro-conductive textiles and electro-conductive paths on textiles has become clear. In this article the results of a test of developed textile electro-conductive paths obtained by applying the method of screen printing pastes containing silver nanoparticles and carbon (graphene, nanotubes, graphite) are presented. Conducted research included analysis of the adhesion test, as well as evaluation of the surface resistance before and after the washing and bending cycles. Obtained results indicated that the samples with the content of carbon nanotubes 3% by weight in PMMA on substrate made of aramid fibers (surface mass of 260 g/m2) were characterized by the best adhesion and the best resistance to washing and bending cycles. Such electro-conductive paths have potential to be used in smart clothing applications.

Carbon Nanotube-Based Composite Filaments for 3D Printing of Structural and Conductive Elements

Applied Sciences 2021, 11(3), 1272S

 

In this publication, we describe the process of fabrication and the analysis of the properties of nanocomposite filaments based on carbon nanotubes and acrylonitrile butadiene styrene (ABS) polymer for fused deposition modeling (FDM) additive manufacturing. Polymer granulate was mixed and extruded with a filling fraction of 0.99, 1.96, 4.76, 9.09 wt.% of CNTs (carbon nanotubes) to fabricate composite filaments with a diameter of 1.75 mm. Detailed mechanical and electrical investigations of printed test samples were performed. The results demonstrate that CNT content has a significant influence on mechanical properties and electrical conductivity of printed samples. Printed samples obtained from high CNT content composites exhibited an improvement in the tensile strength by 12.6 %. Measurements of nanocomposites’ electrical properties exhibited non-linear relation between the supply voltage and measured sample resistivity. This effect can be attributed to the semiconductor nature of the CNT functional phase and the occurrence of a tunnelling effect in percolation network. Detailed I–V characteristics related to the amount of CNTs in the composite and the supply voltage influence are also presented. At a constant voltage value, the average resistivity of the printed elements is 2.5 Ωm for 4.76 wt.% CNT and 0.15 Ωm for 9.09 wt.% CNT, respectively. These results demonstrate that ABS/CNT composites are a promising functional material for FDM additive fabrication of structural elements, but also structural electronics and sensors.

Additive manufacturing of electronics from silver nanopowders sintered on 3D printed low-temperature substrates

Advanced Engineering Materials 2021, 23(4), 2001085

Additive manufacturing is more widely used these days in aerospace, power industry, and automotive. The latest reports indicate that electronics can be produced with this technique. This approach requires the development of new materials for the fabrication of conductive metallic layers on polymers. Herein, a hybrid technique based on fused deposition modeling, direct‐write, and selective laser sintering is demonstrated, for the fabrication of structural electronics. Highly conductive paths are obtained with conductivity values up to 3.2·106 S m−1 in a single printing and sintering additive process. The influence of process parameters is evaluated with several 3D printed polymer substrates affecting the electrical conductivity of the printed conductive paths and circuits. The developed hybrid technique allows performing selective thermal sintering of metallic pastes on polymer substrates exhibiting the value of melting temperatures much lower than the sintering temperature of the silver paste. This phenomenon can be explained with the proposed hypothesis that the activation energy of the sintering process of metallic paste and degradation of polymer substrate plays a key role in obtaining functional conductive metallic paths on polymer substrates. Application of the developed process is demonstrated with a simple human interface device and a circuit with light‐emitting diodes and power source.

Carbon Nanotube Embedded Adhesives for Real-time Monitoring of Adhesion Failure in High Performance Adhesively Bonded Joints

Scientific Reports 10, 16833 (2020)

Carbon nanotubes (CNTs) embedded polymers are of increasing interest to scientific and industrial communities for multi-functional applications. In this article, CNTs have been introduced to high-strength epoxy adhesive for enabling in-situ strain sensing in adhesively bonded aluminium-to-aluminium single-lap joints to accurately indicate the onset and propagation of adhesion failure to the evolution of piezo-resistivity in varying mechanical loads. The CNT modified adhesive in bonded joints and the CNT modified adhesive alone have been tested under monothonic and cyclic tensile loads up to ultimate failure. The changes in the piezo-resistivity induced by the CNTs have been monitored in situ with respect to loading. A novel interpretation method has been developed for progressive, instantaneous adhesion failure estimation under cyclic tensile stresses from a resistivity baseline. The method indicates that the in-situ resistivity changes and the rate of the changes with strain, i.e. sensitivity, strongly correlate with the adhesion failure progression, irrespective of the CNT dispersion quality. Moreover, the effect of bond thickness on the evolution of piezo-resistivity and adhesion failure have been studied. It was observed that relatively thin adhesive bonds (0.18 mm thickness), possessing higher CNT contact points than thick bonds (0.43 mm thickness), provide 100 times higher sensitivity to varying cyclic loads.

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Flexible Gas Sensor Printed on a Polymer Substrate for sub-ppm Acetone Detection

Electronic Materials Letters (2020).

Graphical abstract

Gas sensors are widely used in many industrial and home applications. There is therefore continued need to develop novel gas sensor substrates which provide good mechanical and electrical stability, and good flexibility in comparison with the conventional alumina and silicon-based materials. In this paper, we present the experimental results on flexible gas sensors based on the Kapton foil and alumina substrate covered by copper oxide as a gas-sensitive layer. These sensors exhibited good mechanical stability and gas-sensing characteristics. The Kapton-based CuO gas sensors were tested under exposure to acetone in the 0.05–1.25 ppm range (150 °C, 50%RH). The results confirmed that sensors deposited on the flexible substrate such as Kapton can be used in the exhaled breath analyzers dedicated to diabetes biomarker detection or other applications for which the elastic substrate is needed.