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.

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.

Let’s get it started!

And it finally happened! After several months of a life-changing experience with the preparation of the idea that I want to dedicate a large part of my future life, I submitted ERC Consolidator Grant proposal. It is in line with the FNP strategy promoting PIs submitting ERC proposals – fingers crossed for the successful extension of the First Team realisation time.

Highly Conductive Carbon Nanotube-Thermoplastic Polyurethane Nanocomposite for Smart Clothing Applications and Beyond

Nanomaterials 2019, 9(9), 1287

The following paper presents a simple, inexpensive and scalable method of production of carbon nanotube-polyurethane elastomer composite. The new method enables the formation of fibers with 40% w/w of nanotubes in a polymer. Thanks to the 8 times higher content of nanotubes than previously reported for such composites, over an order of magnitude higher electrical conductivity is also observed. The composite fibers are highly elastic and both their electrical and mechanical properties may be easily controlled by changing the nanotubes content in the composite. It is shown that these composite fibers may be easily integrated with traditional textiles by sewing or ironing. However, taking into account their light-weight, high conductivity, flexibility and easiness of molding it may be expected that their potential applications are not limited to the smart textiles industry.

Electrical and rheological percolation threshold of graphene pastes for screen-printing

Circuit World, vol. 45, no. 1, pp. 26–30, 2019

A comparison of electric and viscosity percolation threshold is crucial from the scientific and technical points of view to understand the features and capabilities of heterogeneous graphene composite materials and properly select the functional phase volume. Therefore, the purpose of this paper is to present the analysis of the electrical and rheological percolation thresholds in the polymer–graphene screen printing pastes and the analysis of the relation between these two parameters.

In the paper, the properties of polymer-based pastes with graphene nanoplatelets were tested: paste viscosity and printed layers conductivity. The tests of pastes with different filler content allowed to determine both the electrical and rheological percolation thresholds using power law, according to Kirkpatrick’s percolation model.

The electrical percolation threshold for graphene nanoplatelets (GNPs) in the composite was 0.74 Vol.% when the rheological percolation threshold is observed to be at 1.00 Vol.% of nanoplatelets. The percolation threshold values calculated using the Kirkpatrick’s percolation model were 0.87 and 0.5 Vol.% of GNPs in the paste for electrical and rheological percolation thresholds, respectively.

Recently, GNPs are becoming more popular as the material of the functional phase in screen printing heterophase materials, because of their unique mechanical and electrical properties. However, till date no research presented in the literature is related to the direct comparison of both the electrical and rheological percolation thresholds. Such analysis is important for the optimization of the printing process toward the highest quality of printed conductive paths, and finally the best electrical properties.

Photonic curing of silver paths on 3D printed polymer substrate

Circuit World, Vol. 45 Issue: 1, pp.26-30, 2019

Despite almost limitless possibilities of rapid prototyping, the idea of 3D printed fully functional electronic device still has not been fulfilled – the missing point is a highly conductive material suitable for this technique. The purpose of this paper is to present the usage of the photonic curing process for sintering highly conductive paths printed on the polymer substrate.

This paper evaluates two photonic curing processes for the conductive network formulation during the additive manufacturing process. Along with the xenon flash sintering for aerosol jet-printed paths, this paper examines rapid infrared sintering for thick-film and direct write techniques.

This paper proves that the combination of fused deposition modeling, aerosol jet printing or paste deposition, along with photonic sintering, is suitable to obtain elements with low resistivity of 3,75·10−8 Ωm. Presented outcomes suggest the solution for fabrication of the structural electronics systems for daily-use applications.

The combination of fused deposition modelling (FDM) and aerosol jet printing or paste deposition used with photonic sintering process can fill the missing point for highly conductive materials for structural electronics.

Heterophase materials for fused filament fabrication of structural electronics

Journal of Materials Science: Materials in Electronics, vol. 30, no. 2, pp. 1236–1245, 2018

In this work, new electrically conductive composite filaments are developed for the fabrication of conductive paths, 3D printed with FDM technology. These composite materials consist of electrically conductive copper powder and a polymer matrix. The influence of three different polymers (ABS, PLA, PS) on the electrical properties of the composites was examined. Electrical measurements of the composite filaments with the increasing copper powder concentrations, allow identifying the percolation threshold for elaborated composites. Results show that the lowest resistivity (0.156 × 10−5 Ωm) was achieved for the ABS/Cu composite at the 84.6 wt% Cu concentration. The obtained resistivity values are much lower than for other conductive composites and nanocomposites filaments reported in the literature. Voltage-current characteristics determined for each composite material showed that composites have Ohmic characteristics in low voltage regime. At high voltage regime, the electrical power dissipated in the composites caused a rapid increase in temperature. It was discovered that a polymer matrix influences the maximum value of the electrical power that can be dissipated in the filament before losing electrical conductivity. Examples of conductive 3D printed structures made from elaborated composites are also presented.

Efficient Inkjet Printing of Graphene-Based Elements: Influence of Dispersing Agent on Ink Viscosity

Nanomaterials 2018, 8(8), 602

Inkjet printing is an excellent printing technique and an attractive alternative to conventional technologies for the production of flexible, low-cost microelectronic devices. Among many parameters that have a significant impact on the correctness of the printing process, the most important is ink viscosity. During the printing process, the ink is influenced by different strains and forces, which significantly change the printing results. The authors present a model and calculations referring to the shear rate of ink in an inkjet printer nozzle. Supporting experiments were conducted, proving the model assumptions for two different ink formulations: initial ink and with the addition of a dispersing agent. The most important findings are summarized by the process window regime of parameters, which is much broader for the inks with a dispersing agent. Such inks exhibit preferable viscosity, better print-ability, and higher path quality with lower resistivity. Presented results allow stating that proper, stable graphene inks adjusted for inkjet technique rheology must contain modifiers such as dispersing agents to be effectively printed.

Microscale Hybrid Flexible Circuit Printed with Aerosol Jet Technique

IEEE Transactions on Nanotechnology, 2018, V: 17, I:5.

Today, a microprinted electronics circuits are gaining more and more importance, but still printed electronic devices such as transistors or OLEDs are unstable in air and shows a poor performance. Moreover, printed microelectronic elements do not meet quality and high-reliability requirements, essential in electronics applications. To fulfill these needs, hybrid electronic circuits, combining printed technology, and surface-mount technology, are recommended. This approach gets advantages from both methods:Surface-mount devices (SMD) elements provide a high device functionality whereas a printed pattern ensures the device flexibility and efficiency. In this work, silver nanoparticle-based aerosol jet ink (AgNP ink) is used to realize the approach of a hybrid circuit with aerosol jet printed pads and surface-mount devices. The ultrasonic atomization process ensures the high printing resolution and appropriate line formation. Electrical and mechanical characterization was performed to present the connection performance and quality. Cross section view and morphological inspection explain the joint high quality and good performance. Resistance characterization presents the high current conductance comparable with connections made by silver epoxy or ink-jet printing. Shear test results show an excellent connection strength complying with USA Military Standard. Finally, a flexible hybrid conductance touch sensor is manufactured, demonstrating the feasibility of the presented assembling solution.