Study of Single and Multipass f-rGO Inkjet-Printed Structures with Various Concentrations: Electrical and Thermal Evaluation.

Reduced graphene oxide (rGO) is a derivative of graphene, which has been widely used as the conductive pigment of many water-based inks and is recognized as one of the most promising graphene-based materials for large-scale and low-cost production processes. In this work, we evaluate a custom functionalised reduced graphene oxide ink (f-rGO) via inkjet-printing technology. Test line structures were designed and fabricated by the inkjet printing process using the f-rGO ink on a pretreated polyimide substrate. For the electrical characterisation of these devices, two-point (2P) and four-point (4P) probe measurements were implemented. The results showed a major effect of the number of printed passes on the resulting resistance for all ink concentrations in both 2P and 4P cases. Interesting results can be extracted by comparing the obtained multipass resistance values that results to similar effective concentration with less passes. These measurements can provide the ground to grasp the variation in resistance values due to the different ink concentrations, and printing passes and can provide a useful guide in achieving specific resistance values with adequate precision. Accompanying topography measurements have been conducted with white-light interferometry. Furthermore, thermal characterisation was carried out to evaluate the operation of the devices as temperature sensors and heaters. It has been found that ink concentration and printing passes directly influence the performance of both the temperature sensors and heaters.

Flexible Inkjet-Printed Heaters Utilizing Graphene-Based Inks.

Thermal sensors are mainly based on the selective heating of specific areas, which in most cases is a critical feature for both the operation and the performance of the thermal device. In this work, we evaluate the thermoelectrical response of two graphitic materials, namely (a) a commercial 2.4%wt graphene-ethyl cellulose dispersion in cycloxehanone and terpineol (G) and (b) a custom functionalized reduced graphene oxide (f-rGO) ink in the range of -40 to 100 °C. Both inks were printed on a flexible polyimide substrate and the Thermal Coefficients of Resistance (TCR) were extracted as TCRG = -1.05 × 10-3 °C-1 (R2 = 0.9938) and TCRf-rGO = -3.86 × 10-3 °C-1 (R2 = 0.9967). Afterward, the inkjet-printed devices were evaluated as microheaters, in order to exploit their advantage for cost-effective production with minimal material waste. f-rGO and G printed heaters reached a maximum temperature of 97.5 °C at 242 mW and 89.9 °C at 314 mW, respectively, applied by a constant current source and monitored by an infrared camera. Repeatability experiments were conducted, highlighting the high robustness in long-term use. The power-temperature behavior was extracted by self-heating experiments to demonstrate the ability of the devices to serve as heaters. Both static and dynamic evaluation were performed in order to study the device behaviors and extract the corresponding parameters. After all the experimental processes, the resistance of the samples was again evaluated and found to differ less than 13% from the initial value. In this work, fabrication via inkjet printing and demonstration of efficient and stable microheaters utilizing a custom ink (f-rGO) and a commercial graphene ink are presented. This approach is suitable for fabricating selectively heated geometries on non-planar substrate with high repeatability and endurance in heat cycles.

Highly Conductive Water-Based Polymer/Graphene Nanocomposites for Printed Electronics.

The preparation and characterization of highly conductive carbon inks is described based on nanocomposites that combine a polystyrene-acrylic resin or water-soluble polymers with a hydrophilic graphene/carbon nanotube hybrid. The water-based carbon inks showed high electrical conductivity and could be effectively used in advanced technologies such as gravure printing for printed electronics. Moreover, the conductivity was shown to be increased with a power law of the nanohybrid volume fraction, with an exponent close to that predicted from the percolation theory, indicating a limited impact of the polymer tunneling barrier on the electrical conductivity of such nanocomposites.

One-Pot Synthesis of Functionalised rGO/AgNPs Hybrids as Pigments for Highly Conductive Printing Inks.

This work provides a method for the development of conductive water-based printing inks for gravure, flexography and screen-printing incorporating commercial resins that are already used in the printing industry. The development of the respective conductive materials/pigments is based on the simultaneous (in one step) reduction of silver salts and graphene oxide in the presence of 2,5-diaminobenzenesulfonic acid that is used for the first time as the common in-situ reducing agent for these two reactions. The presence of aminophenylsulfonic derivatives is essential for the reduction procedure and in parallel leads to the enrichment of the graphene surface with aminophenylsulfonic groups that provide a high hydrophilicity to the final materials/pigments.

Graphene-Based Composites with Silver Nanowires for Electronic Applications.

Graphene/metal nanocomposites have shown a strong potential for use in electronic applications. In particular, the combination of silver nanowires (AgNWs) with graphene derivatives leads to the formation of an efficient conductive network, thus improving the electrical properties of a composite. This work focused on developing highly conductive hydrophilic hybrids of simultaneously functionalized and reduced graphene oxide (f-rGO) and AgNWs in different weight ratios by following two different synthetic routes: (a) the physical mixture of f-rGO and AgNWs, and (b) the in situ reduction of GO in the presence of AgNWs. In addition, the role of AgNWs in improving the electrical properties of graphene derivatives was further examined by mixing AgNWs with a hybrid of few-layered graphene with functionalized multiwalled carbon nanotubes (FLG/MWNT-f-OH). The studied materials showed a remarkable improvement in the overall electrical conductivity due to the synergistic effect of their components, which was proportional to the percentage of Ag and dependent on the procedure of the hybrid formation. One of the f-rGO/AgNWs composites was also selected for the preparation of gravure printing inks that were tested to determine their rheological and printing properties. All of the f-rGO/AgNWs composites were shown to be very promising materials for use as conductive inks for flexible electronics.

Evaluation of Inkjet-Printed Reduced and Functionalized Water-Dispersible Graphene Oxide and Graphene on Polymer Substrate-Application to Printed Temperature Sensors.

The present work reports on the detailed electro-thermal evaluation of a highly water dispersible, functionalized reduced graphene oxide (f-rGO) using inkjet printing technology. Aiming in the development of printed electronic devices, a flexible polyimide substrate was used for the structures' formation. A direct comparison between the f-rGO ink dispersion and a commercial graphene inkjet ink is also presented. Extensive droplet formation analysis was performed in order to evaluate the repeatable and reliable jetting from an inkjet printer under study. Electrical characterization was conducted and the electrical characteristics were assessed under different temperatures, showing that the water dispersion of the f-rGO is an excellent candidate for application in printed thermal sensors and microheaters. It was observed that the proposed f-rGO ink presents a tenfold increased temperature coefficient of resistance compared to the commercial graphene ink (G). A successful direct interconnection implementation of both materials with commercial Ag-nanoparticle ink lines was also demonstrated, thus allowing the efficient electrical interfacing of the printed structures. The investigated ink can be complementary utilized for developing fully printed devices with various characteristics, all on flexible substrates with cost-effective, few-step processes.

Photocatalytic degradation of Reactive Red 195 using anatase/brookite TiO2 mesoporous nanoparticles: optimization using response surface methodology (RSM) and kinetics studies.

In the present study, the photocatalytic degradation of Reactive Red 195 (RR195) from aqueous samples under UV-A irradiation by using anatase/brookite TiO2 (A/B TiO2) mesoporous nanoparticles has been investigated. Batch experiments were conducted to study the effects of the main parameters affecting the photocatalytic process. The effects and interactions of most influenced parameters, such as substrate concentration and catalyst load, were evaluated and optimized by using a central composite design model and a response surface methodology. The results indicated that the dye degradation efficiency in the experimental domain investigated was mainly affected by the tested variables, as well as their interaction effects. Analysis of variance showed a high coefficient of determination value (R(2) = 0.9947), thus ensuring a satisfactory adjustment of the first-order regression model (2FI model) with the experimental data. The obtained results also indicate that catalyst loading plays an important role in determining the removal efficiency of RR195 attributable to both photodegradation and adsorption process. Under optimal conditions (initial dye concentration (50 mg/L) and catalyst loading (2,000 mg/L), A/B TiO2 showed similar removal efficiency compared to that of commercial titania (Degussa P25). Also, at these conditions, complete degradation of RR195 can be achieved by both catalysts within 15 min under UV-A irradiation. The experiments demonstrated that dye removal on the prepared A/B TiO2 was facilitated by the synergistic effects between adsorption and photocatalysis. Photocatalytic mineralization of RR195 was monitored by total organic carbon. The recycling experiments confirmed the stability of the catalyst.

Nanobiotechnology for the prevention of dialysis-related amyloidosis.

Dialysis-related amyloidosis is related to the inefficient removal of beta(2)-microglobulin (beta(2)-m) that is mainly responsible for the formation of amyloid fibrils deposited on the joints and in the heart, blood vessels and digestive system. Magnetically assisted hemodialysis (MAHD) can be used for the prevention of dialysis-related amyloidosis. MAHD is based on ferromagnetic nanoparticle-targeted binding substance conjugates (FN-TBS Cs) that should be administered to the patient before the dialysis session. The TBS should have a high affinity for beta(2)-m so that the conjugates bind with the beta(2)-m in the bloodstream. The complex FN-TBS-beta(2)-m will be selectively removed during dialysis by means of a "magnetic dialyzer" that is installed at the dialysis machine in series to the conventional dialyzer. We have examined the in vitro applicability of MAHD by employing biocompatible Fe(3)O(4) and bovine serum albumin (BSA) as constituents of the FN-TBS Cs. We evaluated the binding capacity of both bare Fe(3)O(4) FNs and Fe(3)O(4)-BSA Cs for beta(2)-m concentrations ranging from mild to severe conditions. Finally, we conducted mock-dialysis experiments for the evaluation of several technical issues related to MAHD. beta(2)-m is adsorbed onto the Fe(3)O(4)-BSA Cs not only almost instantly, but also very efficiently. The employed Cs do not chemically interact with the materials used in standard dialyzers, as agglomerates were not observed in the capillaries of the conventional dialyzers. MAHD may become an efficient modality for the prevention of dialysis-related amyloidosis because beta(2)-m concentrations ranging from mild to severe conditions can be adequately handled.