Graphene-based Conductive Inks Research Articles

Testing the Aquatic Toxicity of 2D Few-Layer Graphene Inks Using Rainbow Trout (Oncorhynchus mykiss): In Vivo and In Vitro Approaches to Support an SSbD Assessment.

Graphene-based conductive inks offer attractive possibilities in many printing technology applications. Often, these inks contain a mixture of compounds, such as solvents and stabilizers. For the safe(r) and sustainable use of such materials in products, potentially hazardous components must be identified and considered in the design stage. In this study, the hazards of few-layer graphene (FLG)-based ink formulations were tested in fish using in vitro (RTL-W1 cell line) and in vivo aquatic ecotoxicity tests (OECD TG 203). Five ink formulations were produced using different processing steps, containing varying amounts of solvents and stabilizers, with the end products formulated either in aqueous solutions or in powder form. The FLG ink formulations with the highest contents of the stabilizer sodium deoxycholate showed greater in vitro cytotoxic effects, but they did not provoke mortality in juvenile rainbow trout. However, exposure led to increased activities of the cytochrome P450 1a (Cyp1a) and Cyp3a enzymes in the liver, which play an essential role in the detoxification of xenobiotics, suggesting that any effects will be enhanced by the presence of the stabilizers. These results highlight the importance of an SSbD approach together with the use of appropriate testing tools and strategies. By incorporating additional processing steps to remove identified cytotoxic residual solvents and stabilizers, the hazard profile of the FLG inks improved, demonstrating that, by following the principles of the European Commission's safe(r) and sustainable by design (SSbD) framework, one can contribute to the safe(r) and sustainable use of functional and advanced 2D materials in products.

Cyclic Voltammetric-Paper-Based Genosensor for Detection of the Target DNA of Zika Virus.

Zika virus (ZIKV), a positive-sense single-stranded RNA virus, has been declared as the cause of a 'worldwide public health emergency' by the WHO since the year 2016. In cases of acute infections, it has been found to cause Guillain-Barre syndrome and microcephaly. Considering the tropical occurrence of the infections, and the absence of any proper treatments, accurate and timely diagnosis is the only way to control this infectious disease. Currently, there are many diagnostic methods under investigation by the scientific community, but they have some major limitations, such as high cost, low specificity, and poor sensitivity. To overcome these limitations, we have presented a low-cost, simple-to-operate, and portable diagnosis system for its detection by utilizing silver nanoparticles. silver nanoparticles were synthesized via chemical methods and characterization was confirmed by UV/TEM and XRD. The paper platform was synthesized using a graphene-based conductive ink, methylene blue as the redox indicator, and a portable potentiostat to perform the cyclic voltammetry to ensure true point-of-care availability for patients in remote areas.

Printed graphene and hybrid conductive inks for flexible, stretchable, and wearable electronics: Progress, opportunities, and challenges

Printed wearable electronics play a vital role in the electronics industry. Recently, there has been an increasing demand for printed wearable electronics. This necessitates the development of novel materials through a facile process to facilitate the fabrication of wearable devices with good electronic properties. Notably, conductive inks play a major role in printed electronics and even though there are various kinds of conductive inks in the market presently, there are certain challenges that still persist and need to be addressed. Some of these limitations include the use of toxic chemicals, low throughput and complicated fabrication processes, which often make the wider applications of conductive inks less economically feasible. Particularly, graphene-based conductive ink is widely investigated due to its excellent electrical conductivity. However, issues related to its stability, dispersion in water, and annealing temperature often limit its applications. Therefore, there are several attempts to formulate hybrid inks using graphene with metal nanoparticles or other conductive polymers. In this review, we present general important information and requirements of flexible electronics and stretchable electronics. Specifically, this article is focused on conductive ink based on graphene and its hybrid with other materials. A summary of previous studies on the formulations of conductive inks and hybrid conductive inks using solvents and water as greener alternatives is provided. Additionally, different printing methods used for the deposition of conductive inks and the various post-printing techniques for performance enhancement are extensively reviewed. Furthermore, different types of stretchable and flexible substrates used in wearable electronics are presented. Then, the prevailing challenges to the fabrication of printed wearable electronics and recommendations for subsequent research are covered in this review.

CuCl2-doped graphene-based screen printing conductive inks

The preparation of graphene-based conductive inks and their application in the field of flexible electronics have been extensively studied. However, improving the conductivity of the printed patterns always induces the neglect of the rheological properties of the graphene-based conductive inks or the mechanical properties of the as-printed patterns. In this study, the p-type doping of graphene with CuCl2 as the dopant is realized through liquid phase reaction, and the doped graphene powders are used to prepare the graphene-based conductive inks with a conductivity of 3.13 × 104 S m−1. Subsequently, to simplify the preparation of inks, CuCl2 is directly added into the graphene-based conductive inks, achieving the p-type doped graphene ink with the conductivity of 3.64 × 104 S m−1. The read range of ultrahigh-frequency radio frequency identification antenna and the temperature of the flexible electrothermal film printed with the CuCl2-doped graphene-based conductive inks can reach 7.15 m and 200°C, respectively when the equivalent isotropically radiated power is equal to 4 W and the input power density is 0.94 W cm−2. Moreover, good rheological properties of the conductive inks and high mechanical properties of the printed patterns are also obtained.

CircuitBot: Learning to survive with robotic circuit drawing.

Robots with the ability to actively acquire power from surroundings will be greatly beneficial for long-term autonomy and to survive in uncertain environments. In this work, a scenario is presented where a robot has limited energy, and the only way to survive is to access the energy from an unregulated power source. With no wires or resistors available, the robot heuristically learns to maximize the input voltage on its system while avoiding potential obstacles during the connection. CircuitBot is a 6 DOF manipulator capable of drawing circuit patterns with graphene-based conductive ink, and it uses a state-of-the-art continuous/categorical Bayesian Optimization to optimize the placement of conductive shapes and maximize the energy it receives. Our comparative results with traditional Bayesian Optimization and Genetic algorithms show that the robot learns to maximize the voltage within the smallest number of trials, even when we introduce obstacles to ground the circuit and steal energy from the robot. As autonomous robots become more present, in our houses and other planets, our proposed method brings a novel way for machines to keep themselves functional by optimizing their own electric circuits.

An Experimental Study of Graphene-Based Conductive Ink for Inkjet-Printable Electronics

The field of printable electronics and sensors has been experiencing increased interest and growth to meet the demands of low-cost, flexible, and lightweight devices. From this subset of devices, graphene-based printable electronics and sensors are of specific interest due to their transparency, flexibility, biocompatibility, and high conductivity. Among all modern ink printing technology, screen printing, spray coating, 3D printing, and inkjet printing are often utilized to fabricate flexible electronic applications from conductive ink. Compared with the other three, inkjet printing has received the most attention due to the simple printing process, high repeatability, economy, and time-savings compared to other printing techniques. However, inkjet printing often suffers from nozzle clogging due to aggregation of the particles in the conductive inks. In this research, a conductive graphene-based ink is developed to be used in a regular inkjet printer. Our goal is to fabricate this ink such that it is flexible, biocompatible, and easily manufacturable. This method seeks to create a low viscosity, high surface tension ink that addresses the clogging of the nozzle due to an aggregation of particles and is capable of being printed through a regular inkjet printer. By selectively choosing and modifying the composition and processes of ink formulation methodologies of past research, a graphene-based conductive ink that is compatible with inkjet printing is formulated. A flexible hydration sensor is printed out with this graphene-based conductive ink through which its conductivity and sensitivity are compared with the same sensor printed with commercially available graphene ink.

Flexible, graphene-based films with three-dimensional conductive network via simple drop-casting toward electromagnetic interference shielding

Fabricating flexible and large-scale graphene-based films through a simple process to achieve excellent electromagnetic interference (EMI) shielding performance is still a daunting challenge. Herein, the flexible and large-area EMI shielding films with ultrathin coating thickness (i.e., 10 μm) and low coating density (i.e., 2.4 mg/cm2) were fabricated through a simple drop-casting approach by using graphene-based conductive ink at room temperature. With the aid of electromagnetic simulation, the optimal square resistance of conductive film for desirable EMI shielding effectiveness is predicted, avoiding the unnecessary costs of error and trial. To solve the vital issue of poor conductivity of reduced graphene oxide (RGO) arising from defects and the serious agglomeration of each filler in ink, a three-dimensional network was constructed by connecting RGO with flexible one-dimensional (1D) conductive fibers (i.e., carbon nanotubes (CNT) and Ag nanowire (AgNW)). The square resistance of the RGO/CNT@Epoxy/AgNW composite film could reach as low as 1.94 ± 0.63 Ω/sq, which exhibited the shielding effectiveness value of 40 dB at a minimum in 8.2–12.5 GHz. These attributes could satisfy the EMI shielding and flexibly conformal demands of most communication equipment.

Preparation of Graphene-based Conductive Ink from Spent Zinc-carbon Batteries

Preparation of Graphene-based Conductive Ink from Spent Zinc-carbon Batteries

High conductivity and transparency of graphene-based conductive ink: Prepared from a multi-component synergistic stabilization method

Graphene-based conductive ink has been widely applied to printed electronics, which nevertheless faces several challenges, e.g., dispersion and stability of graphene flakes and ideal compromise between conductivity and transparency. This work reveals a multi-component synergistic stabilization method towards a well-dispersed and stable graphene-based conductive ink with high conductivity and transparency. Commercially available graphene (<10 layers) material (KNG®-G2) was selected and ethanol/water (2/1, v/v) was used as co-solvent to disperse the graphene flakes. Multi-walled carbon nanotubes, providing network for attaching of graphene through π-π force and amphipathic polymer polyvinylpyrrolidone, acting as a surfactant were indispensable to stabilize conductive ink. The as-prepared graphene-based ink can be deposited on different substrates through drop-casting, spin-coating and inkjet-printing and the sheet resistance of the deposited films was tested as low as 180 Ω/sq with the optical transmittance of 90%. The method reported in this work is potential for industrial production toward a graphene composite conductive ink with high conductivity and transparency for printing electronic applications.

Multimode-Inspired Low Cross-Polarization Multiband Antenna Fabricated Using Graphene-Based Conductive Ink

In this letter, a dual-port antenna for multiband operation is reported. The prototype of the proposed design is fabricated using graphene-based conductive ink printed textile showing the surface resistance of 2.7 $\Omega /\square$ , and conductivity of $\text{0.37}\times \text{10}^5$ S/m. The microstructural analysis of the conductive ink printed cotton fabric is done by field emission scanning electron microscopy (FESEM) and electric characteristic is extracted using a four-probe measurement. The proposed antenna resonates at a triple-band and dual-band mode through two different feeding locations. Through Port-1, the antenna resonates only at higher order TM $_{02}$ and TM $_{20}$ modes, whereas through Port-2 three TM $_{10}$ , TM $_{02}$ , and TM $_{20}$ modes are excited. Thereafter, the Co- and Cross-Polarization (CP-XP) isolation of each band is investigated identifying only two useful frequency bands TM $_{10}$ , 2.9 GHz, and TM $_{20}$ , 6 GHz. A defected ground structure (DGS) technique is deployed to improve the CP-XP isolation of TM $_{m0}$ modes achieving CP-XP isolation better than 30 and 15 dB in both useful bands. The measured results have a fairly good agreement with simulated results.

Graphene-based surface heater for de-icing applications.

Graphene-based de-icing composites are of great interest due to incredible thermal, electrical and mechanical properties of graphene. Moreover, current technologies possess a number of challenges such as expensive, high power consumption, limited life time and adding extra weight to the composites. Here, we report a scalable process of making highly conductive graphene-based glass fibre rovings for de-icing applications. We also use a scalable process of making graphene-based conductive ink by microfluidic exfoliation technique. The glass fibre roving is then coated with graphene-based conductive inks using a dip-dry-cure technique which could potentially be scaled up into an industrial manufacturing unit. The graphene-coated glass roving demonstrates lower electrical resistances (∼1.7 Ω cm−1) and can heat up rapidly to a required temperature. We integrate these graphene-coated glass rovings into a vacuum-infused epoxy–glass fabric composite and also demonstrate the potential use of as prepared graphene-based composites for de-icing applications.

Microfluidization of Graphite and Formulation of Graphene-Based Conductive Inks.

We report the exfoliation of graphite in aqueous solutions under high shear rate [∼ 108 s–1] turbulent flow conditions, with a 100% exfoliation yield. The material is stabilized without centrifugation at concentrations up to 100 g/L using carboxymethylcellulose sodium salt to formulate conductive printable inks. The sheet resistance of blade coated films is below ∼2Ω/□. This is a simple and scalable production route for conductive inks for large-area printing in flexible electronics.

Inkjet Printing of Graphene Inks for Wearable Electronic Applications

Inkjet printing of graphene-based conductive inks is an encouraging research approach in the field of printed electronics as both the benefits of inkjet printing and extraordinary electronic, optical and mechanical properties of graphene can be exploited [1]. Inkjet printing is one of the most promising techniques for the fabrication of wearable electronics due to number of advantages over conventional manufacturing techniques such as digital and additive patterning, reduction in material waste, deposition of controlled amount of materials and compatibility with various substrates [2]. In addition, graphene is a single atom thick two-dimensional closely packed honeycomb lattice of sp2 carbon allotropes, which has been focus of mass investigations in recent years because of its unique physical and chemical properties [3].Currently silver nanoparticles (NPs) as inkjet printing inks are the most reported and utilised conductive inks because of their excellent electrical conductivity and strong antioxidant characteristics [4]. However higher concentration of NPs and higher sintering temperatures are required in order to obtain continuous metallic phase, with numerous percolation paths between metal particles within the printed pattern [5], which increased processing cost and limited the choice of substrates to be printed because of their heat sensitivity. Inkjet printing of reduced graphene oxide (rGO) are reported in several studies as a popular choice to fabricate wearable devices due its advantages such as readily dispersible in water and high volume production at lower cost [6]. However large number of unreduced oxygen-containing functional groups and inter-sheet junctions between the graphene domains limits the conductivity achieved with rGO [7]. In order to overcome the limitations associated with rGO inkjet inks, pristine graphene inks were developed and printed.Herein we report exfoliation of pristine graphene dispersions produced in gram scale quantities based on literature review [8, 9]. Liquid phase exfoliation method was used by shear mixing in the presence of a polymer stabilizer, ethyl cellulose which enhances the ink stability as well as printing performance [2, 10]. To formulate ink for inkjet printing graphene/ethyl cellulose powder was directly dispersed in a mixture of solvents by bath sonication. Then the formulated inks were successfully inkjet printed onto textile substrate in order to fabricate an Electro-Oculogram (EOG) device for healthcare applications, Figure 1. &lt;fig position="float" id="s121_f.1"&gt; &lt;label&gt;Figure 1&lt;/label&gt; &lt;caption&gt;Graphene printed electrodes on textile substrates for bio-sensing without requiring a fixed connection to the body&lt;/caption&gt; &lt;graphic mime-subtype="tif" xlink:href="Images\s121_f01.tif" xmlns:xlink="http://www.w3.org/1999/xlink"/&gt; &lt;/fig&gt

Barytes fillers

Fabricating flexible and large-scale graphene-based films through a simple process to achieve excellent electromagnetic interference (EMI) shielding performance is still a daunting challenge. Herein, the flexible and large-area EMI shielding films with ultrathin coating thickness (i.e., 10 μm) and low coating density (i.e., 2.4 mg/cm2) were fabricated through a simple drop-casting approach by using graphene-based conductive ink at room temperature. With the aid of electromagnetic simulation, the optimal square resistance of conductive film for desirable EMI shielding effectiveness is predicted, avoiding the unnecessary costs of error and trial. To solve the vital issue of poor conductivity of reduced graphene oxide (RGO) arising from defects and the serious agglomeration of each filler in ink, a three-dimensional network was constructed by connecting RGO with flexible one-dimensional (1D) conductive fibers (i.e., carbon nanotubes (CNT) and Ag nanowire (AgNW)). The square resistance of the RGO/[email protected]/AgNW composite film could reach as low as 1.94 ± 0.63 Ω/sq, which exhibited the shielding effectiveness value of 40 dB at a minimum in 8.2–12.5 GHz. These attributes could satisfy the EMI shielding and flexibly conformal demands of most communication equipment.