The effect of graphene dispersion on the mechanical properties of graphene/epoxy composites

Field electron emission from protruded GO and rGO sheets on CuO and Cu nanorods

Graphene oxide (GO), an oxidized form of graphene, has various advantages in the preparation of functional nanocomposites because it can be easily modified and can be produced in large quantity. Moreover, the reduction of GO sheets produces reduced GO (rGO) sheets, which provide a highly electro-conductive pathway and robust electrochemical reaction sites as an electrode material. Moreover, due to the presence of those functional groups, GO can be utilized as a novel platform for hybrid nanocomposites in chemical synthetic approaches. In this presentation, we demonstrate a straightforward strategy to prepare nanohybrids of rGO-metal oxide nanoparticles, such as SnO2 and Cu2O, via simple solution mixing. When precursor solutions and GO suspension were simply mixed, precursor ions were spontaneously formed into nanoparticles upon the deoxygenation of GO. This method anchored nanoparticles on the rGO sheets, preventing the re-stacking of rGO. Our investigation for the electrocapacitive properties of hybrid electrode showed the highly enhanced performance, compared with rGO-only electrode. Our straightforward route for preparing this graphene-based hybrid provides a high-throughput and scalable strategy to synthesize active electrode materials for highly efficient graphene-based supercapacitors.

Non-covalent functionalized reduced graphene oxide (rGO) with l-tryptophan was rapidly fabricated by reducing graphene oxide (GO), using l-ascorbic acid as reducer under microwave heating. Atomic force microscope, scanning electron microscope, ultraviolet–visible spectroscopy, X-ray diffraction, Raman spectroscopy and Fourier transform infrared spectroscopy were employed to investigate the morphologies and structures of the samples. The average particle sizes and zeta potentials of rGO were measured by means of dynamic light scattering spectroscopy. Furthermore, the maximum dispersibility of rGO dispersion was calculated from Lambert–Beer law. It was shown that oxidative debris of GO were cleaned after ammonia wash process, and ultimately improving the water dispersibility through enhancing the π–π interaction between l-tryptophan molecules and rGO sheets. The maximum dispersibility of the functionalized rGO dispersion with cleaning oxidative debris was increased by 95 % (from 0.44 to 0.86 mg mL−1) compared to that without cleaning oxidative debris. This investigation proposed an effective method to fabricate the non-covalent functionalized rGO, as well as the method to improve its water dispersibility.

Graphene oxide (GO) and reduced graphene oxide (rGO) sheets have usually been synthesized through Hummers' method by using highly pure graphite (HPG) as the main starting material. However, HPG can be relatively expensive for mass production of high-quality graphene. In this work, a general method for synthesis of high-quality GO and rGO sheets from various natural and industrial carbonaceous wastes such as vegetation wastes (wood, leaf, bagasse, and fruit wastes), animal wastes (bone and cow dung), a semi-industrial waste (newspaper), and an industrial waste (soot powders produced in exhaust of diesel vehicles) was developed. Based on atomic force microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy, and current–voltage characteristics of the synthesized sheets, the single- and multi-layer properties, chemical state, carbonaceous structure, and electrical properties of the graphene sheets synthesized from various waste materials (with ≤4-monolayer thicknesses and electrical sheet resistance of ∼105 MΩ sq−1 for GO and ∼1 MΩ sq−1 for rGO sheets) were found to be nearly independent of the starting materials used; moreover, they were comparable to those of the high-quality graphene sheets achieved using HPG. These results provide a possible route for inexpensive mass production of high-quality graphene sheets from natural and industrial carbonaceous wastes.

Impact of enhanced interfacial strength on physical, mechanical and tribological properties of copper/reduced graphene oxide composites: Microstructural investigation

Graphene is prized for its large surface area and superior electrical properties. Efforts to maximize the electrical conductivity of graphene commonly result in the recovery of sp2-hybridized carbon in the form of reduced graphene oxide (rGO). However, rGO shows poor dispersibility and aggregation when mixed with other materials without hydrophilic functional groups, This could lead to electrode delamination, agglomeration, and reduced efficiency. This study focuses on the impact of solvothermal reduction on the dispersibility and capacitance of rGO compared with chemical reduction. The results show that the dispersibility of rGO-D obtained through solvothermal reduction using N,N-dimethylformamide improved compared to that obtained through chemical reduction (rGO-H). Furthermore, when utilized as a material for CDI, an improvement in deionization efficiency was observed in the AC@rGO-D-based CDI system compared to AC@rGO-H and AC. However, the specific surface area, a key factor affecting CDI efficiency, was higher in rGO-H (249.572 m2 g−1) than in rGO-D (150.661 m2 g−1). While AC@rGO-H is expected to exhibit higher deionization efficiency due to its greater specific surface area, the opposite was observed. This highlights the effect of the improved dispersibility of rGO-D and underscores its potential as a valuable material for CDI applications.

Natural rubber (NR) has poor mechanical properties, which limits its practical application. Filler blending is a simple method that improves the inherent properties of natural rubber and expand its applicability. Using the mechanical mixing process, the effects of graphene oxide (GO) and redox graphene (rGO) on the physical properties, electrical conductivity, thermal conductivity, and air permeability of styrene-butadiene rubber (SSBR)/NR composites were studied. The results show that rGO exhibits efficient filler properties in various aspects, for example, the optimal filling amount of rGO and GO was 1.5 phr. In addition, rGO filled SSBR/NR composites showed satisfactory filler dispersibility. Notably, the better dispersibility of rGO was because of fewer hydrophilic functional groups on the surface which were difficult to agglomerate. The increase of rGO and GO content increased the maximum torque (MH) and minimum torque (ML) of the composite material, and decreases tc90 and tc10. The Payne effect of GO/SSBR/NR composites is more obvious than that of rGO/SSBR/NR composites. In addition, we found that the content of rGO (GO) reached saturation at 2phr. Notably, rGO and GO improved the properties of rGO filled SSBR/NR composites such as the tensile strength of rGO/SSBR/NR composites to 23.9 MPa. This shows the potential application of SSBR/NR composites in wearable electronic devices.

In this study, the graphene oxide synthesized by the Hummers method was carried out using the thermal reduction under the vacuum and atmospheric pressure was carried out by the design of the Taguchi experiment. The thermal reduction under vacuum and atmospheric pressure has a higher ID/IG value (D peak intensity to G peak intensity ratio) at 36.84% and 42.31%, respectively, with respect to the chemical reduced oxide of the graphene oxide. If the chemical graphene oxide is thermally reduced under vacuum and atmospheric pressure, it has a higher ID/IG value, with 36.17% and 43.93%, respectively, with respect to the reduced graphene oxide. The thermal reduction under vacuum and atmospheric pressure has a higher carbon to oxygen ratio value (in other words higher reduction rate) at 72.19% and 74.58%, respectively, with respect to the chemical reduced oxide of the graphene oxide. If the chemical graphene oxide is thermally reduced under vacuum and atmospheric pressure, it has a higher carbon to oxygen ratio, with 74.56% and 78.92%, respectively, with respect to the reduced graphene oxide. The results showed that to obtain the highest reduction rate of graphene oxide; the thermal and H2 gas reduction process should be monitored under the atmospheric pressure of the chemically reduced graphene oxide.

Various approaches have been employed to disperse graphene in polymers. We introduce a new method which takes advantage of the amphiphilic nature of graphene oxide (GO). This feature results in the spontaneous self-assembly of monolayers at the oil–water interface. Thermodynamically favorable adsorption of GO sheets on the liquid droplets serves as the first step in the fabrication of well-dispersed composites. It eliminates the need for sonication and further compounding, which can destroy the structure of the graphene layers. Another equally important consideration is how to vaporize the liquid medium to preserve appropriate dispersion in the dried masterbatch. Microwave radiation is employed to vaporize the liquids and also to partially reduce GO while keeping it well-dispersed in the polymer. As a challenging matrix, the dispersion of GO in natural rubber is studied here. XRD and SEM results confirm appropriate dispersion of the particles. Improvements in the modulus and ultimate strength were observed without any significant reduction in elongation at break.

A well-dispersed phase of exfoliated graphene oxide (GO) nanosheets was initially prepared in water. This was concentrated by centrifugation and was mixed with a liquid epoxy resin. The remaining water was removed by evaporation, leaving a GO dispersion in epoxy resin. A stoichiometric amount of an anhydride curing agent was added to this epoxy-resin mixture containing the GO nanosheets, which was then cured at 90 °C for 1 h followed by 160 °C for 2 h. A second thermal treatment step of 200 °C for 30 min was then undertaken to reduce further the GO in situ in the epoxy nanocomposite. An examination of the morphology of such nanocomposites containing reduced graphene oxide (rGO) revealed that a very good dispersion of rGO was achieved throughout the epoxy polymer. Various thermal and mechanical properties of the epoxy nanocomposites were measured, and the most noteworthy finding was a remarkable increase in the thermal conductivity when relatively very low contents of rGO were present. For example, a value of 0.25 W/mK was measured at 30 °C for the nanocomposite with merely 0.06 weight percentage (wt%) of rGO present, which represents an increase of ~40% compared with that of the unmodified epoxy polymer. This value represents one of the largest increases in the thermal conductivity per wt% of added rGO yet reported. These observations have been attributed to the excellent dispersion of rGO achieved in these nanocomposites made via this facile production method. The present results show that it is now possible to tune the properties of an epoxy polymer with a simple and viable method of GO addition.

2019 Innovations in Intelligent Systems and Applications Conference, ASYU 2019; 31 October 2019 through 2 November 2019

In this work, a new melt blending method under the synergy of in‐situ ball milling (ISBM) and extensional flow field are reported. The corresponding equipment and processing mechanism of this new method are introduced in detail. The improvement in the dielectric properties of polyvinylidene fluoride (PVDF)/reduced graphene oxide (rGO)/hollow glass beads (HGBs) composites are experimentally investigated. Benefit from uniform dispersion and reduced shattered rate of HGBs, the effect of ISBM on the rGO is strengthened. The results of SEM, TEM, XRD, and Raman spectra show that HGBs promote the exfoliation and dispersion of rGO in PVDF matrix. The addition of HGBs not only increases the dielectric constant of the composites, but also reduces the dielectric loss. When the content of rGO is 3.5 wt%, the dielectric constant of PVDF/rGO/HGBs (PRH) composites reaches 132.7, which is 63.2% higher than that of PVDF/rGO (PR) composites without HGBs. Moreover, the dielectric loss ofPRHcomposites is 0.3, which is 23.3% lower than that ofPRcomposites. To sum up, the new processing method is a simple, green and efficient way to enhance the dielectric properties of PVDF/rGO composites by improving the exfoliation and dispersion of rGO in PVDF.

Three-dimensional (3D) graphene networks are performance boosters for functional nanostructures in energy-related fields. Although tremendous intriguing nanostructures-decorated 3D graphene network...

Graphene oxide (GO) is an important precursor in the production of chemically derived graphene. During reduction, GO's electrical conductivity and band gap change gradually. Doping and chemical functionalization are also possible, illustrating GO's immense potential in creating functional devices through control of its local hybridization. Here we show that laser-induced photolysis controllably reduces individual single-layer GO sheets. The reaction can be followed in real time through sizable decreases in GO's photoluminescence efficiency along with spectral blueshifts. As-produced reduced graphene oxide (rGO) sheets undergo additional photolysis, characterized by dramatic emission enhancements and spectral redshifts. Both GO's reduction and subsequent conversion to photobrightened rGO are captured through movies of their photoluminescence kinetics. Rate maps illustrate sizable spatial and temporal heterogeneities in sp(2) domain growth and reveal how reduction "flows" across GO and rGO sheets. The observed heterogeneous reduction kinetics provides mechanistic insight into GO's conversion to chemically derived graphene and highlights opportunities for overcoming its dynamic, chemical disorder.

Room temperature in situ chemical synthesis of Fe3O4/graphene