Graphene Oxide Fillers Research Articles

Effect of graphene on polar and nonpolar rubber matrices

BackgroundSo far, the effect of graphene oxide (GO) and reduced graphene oxide (rGO) in rubber matrix has not been well established.MethodsThe effects of graphene oxide (GO) and reduced graphene oxide (rGO) on the physical properties of polar acrylonitrile-butadiene rubber (NBR) and non-polar Ethylene-propylene-diene terpolymer rubber (EPDM) matrix have been investigated and their properties compared. NBR vulcanizates exhibited higher cure rates compared to the EPDM systems.ResultsEffective dispersion of the nanosheets within the different matrices was observed to be a reason for the improvement in properties, but the effective nanosheets-matrix interactions played a key role in reinforcing action. This was noticeable in the various properties (crosslinking density, tensile properties, and dynamical mechanical analysis) evaluated. Typically, the polar NBR matrix was observed to show about 461 and 405% higher interactions parameter with GO and rGO fillers (loaded from 0.1~1phr) than composites of EPDM based on Kraus model.ConclusionsWhile this present work has confirmed the significance of considering the polarities of graphene sheets or derivative graphene (GSD) and their respective polymers matrices for effective property enhancement for specific applications, it has also demonstrated the future prospects of rubber-graphene nanocomposites for several applications which include structural, barrier, and dielectric energy storage materials.

Preparation and characterization of cross-linked poly (vinyl alcohol)-graphene oxide nanocomposites as an interlayer for Schottky barrier diodes

Cross-linked polyvinyl alcohol (PVA) graphene oxide (GO) nanocomposites were prepared by simple solution-mixing route and characterized by Raman, UV–visible and fourier transform infrared (FT-IR) spectroscopy analysis, X-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. The XRD pattern and SEM analysis showed significant changes in the nanocomposite structures, and the FT-IR spectroscopy results confirmed the chemical interaction between the GO filler and the PVA matrix. After these morphological characterizations, PVA-GO-based diodes were fabricated and their electrical properties were characterized using current–voltage (I–V) and impedance-voltage-frequency (Z-V-f) measurements at room temperature. Semilogarithmic I–V characteristics of diode showed a good rectifier behavior. The values of C and G/[Formula: see text] increased with decreasing frequency due to the surface/interface states (N[Formula: see text]) which depend on the relaxation time and the frequency of the signal. The voltage, dependent profiles of N[Formula: see text] and series resistance (R[Formula: see text]) were obtained from the methods of high-low frequency capacitance and Nicollian and Brews, respectively. The obtained values of N[Formula: see text] and R[Formula: see text] were attributed to the use of cross-linked PVA-GO interlayer at the Au/n-Si interface.

Novel hydroxylated boron nitride functionalized p-phenylenediamine-grafted graphene: an excellent filler for enhancing the barrier properties of polyurethane

A hydroxylated boron nitride (BN(OH)x) functionalized p-phenylenediamine modified reduced graphene oxide (rGO) filler (BN(OH)x–PrGO) is prepared for the first time using a facile and novel strategy.

Graphene Oxide Filled Lignin/Starch Polymer Bionanocomposite: Structural, Physical, and Mechanical Studies.

In this study, graphene oxide (GO) was investigated as a potential nanoreinforcing agent in starch/lignin (ST/L) biopolymer matrix. Bionanocomposite films based on ST/L blend matrix and GO were prepared by solution-casting technique of the corresponding film-forming solution. The structures, morphologies, and properties of bionanocomposite films were characterized by Fourier transform infrared (FTIR), thermal gravimetric analysis (TGA), ultraviolet-visible (UV-vis), SEM, and tensile tests. The experimental results showed that content of GO have a significant influence on the mechanical properties of the produced films. The results revealed that the interfacial interaction formed in the bionanocomposite films improved the compatibility between GO fillers and ST/L matrix. The addition of GO also reduced moisture uptake (Mu) and water vapor permeability of ST/L blend film. In addition, TGA showed that the thermal stability of bionanocomposite films was better than that of neat starch film. These findings confirmed the effectiveness of the proposed approach to produce biodegradable films with enhanced properties, which may be used in packaging applications.

Improved mechanical performance of bisphenol-A graphene-oxide nano-composites

Epoxy resins have been extensively utilized for mechanical strength applications in the field of aerospace, automobiles, marine, defence, etc. Improving the strength as well as fracture behaviour of the light weight materials is challenging. Present work is an attempt to enhance elastic modulus, hardness and fracture resistance simultaneously by reinforcing the epoxy (bisphenol-A) matrix with a new-age two-dimensional atomically thin graphene oxide filler. Wet chemical oxidation method was used to prepare graphene oxide sheets. Morphological study of the synthesized graphene oxide was carried out using scanning electron microscopy. Fourier-transformed infrared, ultraviolet–visible and Raman spectroscopic techniques were also employed to ascertain the synthesis of graphene oxide. The results confirmed the synthesis of well oxidized graphene oxide sheets. The prepared graphene oxide sheets were then sonicated in acetone solution to ensure better dispersion in the bisphenol-A graphene oxide nano-composite using 0.25, 0.5, 1.0 and 1.5 wt.% graphene oxide reinforcement. Solution mixing method was used to synthesize the polymer nano-composite. Scanning electron microscopy results revealed the smooth dispersion of graphene oxide in the bisphenol-A matrix. Nano-indentation of the bisphenol-A graphene oxide nano-composite showed a considerable jump in elastic modulus at 1 wt.% and hardness at 0.50 wt.% of graphene oxide reinforcement. Fracture resistance of bisphenol-A graphene oxide composite as represented by ratio of elastic modulus to hardness was enhanced by 24% as compared to the pristine bisphenol-A. Our results demonstrate a promising way to improve the mechanical characteristics of epoxy resins through graphene oxide reinforcement at low weight percentages.

The Impact of Polymer Grafting from a Graphene Oxide Surface on Its Compatibility with a PDMS Matrix and the Light-Induced Actuation of the Composites.

Poly(dimethyl siloxane) (PDMS)-based materials with improved photoactuation properties were prepared by the incorporation of polymer-grafted graphene oxide particles. The modification of the graphene oxide (GO) surface was achieved via a surface initiated atom transfer radical polymerization (SI ATRP) of methyl methacrylate and butyl methacrylate. The modification was confirmed by thermogravimetric analysis, infrared spectroscopy and electron microscopy. The GO surface reduction during the SI ATRP was investigated using Raman spectroscopy and conductivity measurements. Contact angle measurements, dielectric spectroscopy and dynamic mechanical analyses were used to investigate the compatibility of the GO filler with the PDMS matrix and the influence of the GO surface modification on its physical properties and the interactions with the matrix. Finally, the thermal conductivity and photoactuation properties of the PDMS matrix and composites were compared. The incorporation of GO with grafted polymer chains, especially poly(n-butyl methacrylate), into the PDMS matrix improved the compatibility of the GO filler with the matrix, increased the energy dissipation due to the improved flexibility of the PDMS chains, enhanced the damping behavior and increased the thermal conductivity. All the changes in the properties positively affected the photoactuation behavior of the PDMS composites containing polymer-grafted GO.

Rheological and physical characterization of PEDOT: PSS/graphene oxide nanocomposites for perovskite solar cells

In this work, the influence of graphene oxide (GO) doped poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) thin nanocomposite on an indium–tin‐oxide (ITO) anode, as hole transport layer (HTL) in perovskite solar cells, was investigated. Different concentrations of GO were added into the PEDOT:PSS in order to enhance its conductivity. In particular, the influence of GO content on the rheological and thermal properties of poly(3,4‐ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GO nanocomposites was initially examined. The GO filler was prepared by using modified Hummers method and dispersed into PEDOT:PSS in different quantity (ranging from 0.05 to 0.25%wt/wt). The obtained nanocomposite solutions were analyzed by rheological characterizations in order to evaluate the influence of the GO filler on the viscosity of the PEDOT:PSS matrix. The wettability of solutions was evaluated by Contact Angle (CA) measurements. The quality of GO dispersion into the polymer matrix was studied using Scanning electron microscopy (SEM) and X‐ray diffraction (XRD). Thermal characterizations (DSC and TGA) were, finally, applied on nanocomposite films in order to evaluate thermal stability of the films as well as to indirectly comprehend the GO influence on PEDOT:PSS‐water links. POLYM. ENG. SCI., 57:546–552, 2017. © 2017 Society of Plastics Engineers

Pressure-sensitive adhesive composites with a hydrophobic form of graphene oxide for enhanced thermal conductivity

Pressure-sensitive adhesive (PSA) composites containing oleylamine functionalized graphene oxide (OA-f-GO) fillers were prepared. The effects of the surface modification of graphene oxide (GO) on the morphology of the PSA composites and on its thermal and adhesive properties were investigated. In contrast to GO fillers, the OA-f-GO fillers were found to be uniformly dispersed in the PSA matrix without any agglomeration and voids. The hydrophobization of GO resulting from the oleylamine functionalization improved the compatibility of the GO sheets with the PSA matrix. The thermal conductivity of the OA-f-GO (5 wt%)/PSA composites at UV energy of 2,000 mJ/cm2 was 55%, 140%, and 300% greater than the thermal conductivities of the OA-f-GO (5 wt%)/PSA composites, GO (5 wt%)/PSA composites, and bare PSA at UV energy of 800 mJ/cm2, respectively. In addition, the higher peel strength of the OA-f-GO/PSA composites compared to that of the GO/PSA composites was explained by the better wetting of hydrophobic OA-f-GO fillers in the PSA matrix.

Enhancing mechanical properties of polyelectrolyte complex nanofibers with graphene oxide nanofillers pretreated by polycation

The wide application of polyelectrolyte complex (PEC) nanofibers has been restrained by their unsatisfactory mechanical properties due to high porosity. In this study, we proposed a strategy for improving the mechanical properties of PEC nanofibers using graphene oxide (GO) fillers pretreated by polycation. Chitosan/gelatin (CS/GE) was adopted as the PEC model system. Through the proposed preparation procedure, GO/CS/GE nanofibers can be obtained successfully by electrospinning. Fourier transform infrared spectroscopy (FITR) and differential scanning calorimetry (DSC) results revealed the strong interactions between GO and PEC matrix, which resulted from the synergistic effect of electrostatic attraction and hydrogen bonding. The effective dispersion of GO in CS/GE matrix was verified through TEM and XRD analysis. As demonstrated by the results of tensile testing, mechanical properties of CS/GE can be effectively enhanced with the addition of GO fillers. At 1.5 wt% filler content, GO/CS/GE nanofiber membranes achieved 358% augment of tensile strength, 175% improvement of Young's modulus and 460% boost of toughness compared with neat CS/GE, which were attributed to effective filler-matrix interactions and good dispersion of fillers. Therefore, the inclusion of GO fillers into PEC through the procedure proposed in this study is a promising strategy for mechanical enhancement of PEC nanofibers.

Novel Electrospun Polylactic Acid Nanocomposite Fiber Mats with Hybrid Graphene Oxide and Nanohydroxyapatite Reinforcements Having Enhanced Biocompatibility.

Graphene oxide (GO) and a nanohydroxyapatite rod (nHA) of good biocompatibility were incorporated into polylactic acid (PLA) through electrospinning to form nanocomposite fiber scaffolds for bone tissue engineering applications. The preparation, morphological, mechanical and thermal properties, as well as biocompatibility of electrospun PLA scaffolds reinforced with GO and/or nHA were investigated. Electron microscopic examination and image analysis showed that GO and nHA nanofillers refine the diameter of electrospun PLA fibers. Differential scanning calorimetric tests showed that nHA facilitates the crystallization process of PLA, thereby acting as a nucleating site for the PLA molecules. Tensile test results indicated that the tensile strength and elastic modulus of the electrospun PLA mat can be increased by adding 15 wt % nHA. The hybrid nanocomposite scaffold with 15 wt % nHA and 1 wt % GO fillers exhibited higher tensile strength amongst the specimens investigated. Furthermore, nHA and GO nanofillers enhanced the water uptake of PLA. Cell cultivation, 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) and alkaline phosphatase tests demonstrated that all of the nanocomposite scaffolds exhibit higher biocompatibility than the pure PLA mat, particularly for the scaffold with 15 wt % nHA and 1 wt % GO. Therefore, the novel electrospun PLA nanocomposite scaffold with 15 wt % nHA and 1 wt % GO possessing a high tensile strength and modulus, as well as excellent cell proliferation is a potential biomaterial for bone tissue engineering applications.

Fabrication and tribological properties of copper matrix composite with short carbon fiber/reduced graphene oxide filler

Copper matrix composite with short carbon fiber(CF)/reduced graphene oxide(rGO) hybrid filler have been fabricated by freeze-drying and spark plasma sintering. Microstructure and tribological properties of as-prepared composites were characterized. The microstructural observation shows that the rGO exhibits both agglomerated and dispersed states, and the uniform CF presents the various space orientations in the Cu matrix. The composite with CF/rGO hybrid filler exhibited the lower friction coefficient (0.32), and whose wear rates decreased respectively by 45.3% and 86.0% in comparison with pure Cu and the composite with rGO filler. The CF/rGO hybrids act as solid lubricant and play the major role in the improved tribological performance. The formation, friction-reducing and anti-wear mechanisms of the composite were discussed.

Influence of temperature on the confinement effects of micro and nano level graphite filled poly(isoprene-co-isobutylene) composites

Electrically conducting elastomer composites using nanocarbon fillers have utmost significance in the current scenario of flexible electronics. Though a large number of reports have come out in this topic, the influence of temperature on the nano reinforcement is little addressed. Here we aim at deducing the confinement effects occurring in the micro and nano composites of poly(isobutylene-co-isoprene) rubber (IIR) under different temperatures. For this various composite samples of IIR were prepared with expanded graphite (micro-sized) and reduced graphene oxide (nano-sized) fillers and the structure and morphology were characterized by Raman spectroscopy, X-ray diffraction studies and scanning electron microscopy. We could observe greater influence of temperature on the properties of rubber nanocomposites compared to the micro and anticipate the applicability of such materials in temperature sensors. With 25–45 °C rise in temperature, the current increases and the sample shows deviations from the non-linear behavior. However at 45 °C, non-linear property is seen as the conducting particles gap increases with temperature. The temperature variation influences the modulus (stiffness) of the polymeric material as well. Finally a correlation is drawn between their electrical and dielectric characteristics and the molecular level interactions from Payne effect at different temperatures.

Strong and ductile graphene oxide reinforced PVA nanocomposites

Graphene oxide (GO) and its derivatives have been widely used as reinforcement in polymer matrices for enhanced mechanical and electrical properties. While graphene has higher elastic modulus and tensile strength than that of graphene oxide, it is the latter’s hydrophilic nature that provides a distinct advantage as a filler in the aqueous processing of polymer nanocomposites. In this work, we have tried to disseminate the effects of GO and reduced graphene oxide (rGO) as fillers in polyvinyl alcohol (PVA) matrix. At a loading of only 0.3 wt% GO in PVA, we observed ∼150% increment both in elastic modulus and tensile strength, which is unprecedented. The property enhancement was attributed to the homogeneous distribution of fillers, and strong interfacial interactions (hydrogen bonds) between the fillers and the matrix. Composites fabricated after in-situ reduction of GO fillers had elastic modulus comparable to that of pure PVA, but had considerably improved tensile strength. The failure strain of rGO based composites was much higher than that of both pure PVA and GO reinforced PVA composites, thus showing enhanced ductility. The microstructure of the PVA-rGO composites exhibited alignment of the fillers in the plane of the polymer film, with interfacial bonds between the fillers and matrix only at the rGO sheet edges. The distribution of GO fillers in the PVA-GO composites, however, was random with no preferred orientation. A higher degree of interfacial interactions and the homogeneous distribution of the fillers led to enhanced elastic modulus and strength, along with considerable ductility for the PVA-GO composites.

High Performance of Alkaline Anion-Exchange Membranes Based on Chitosan/Poly (vinyl) Alcohol Doped with Graphene Oxide for the Electrooxidation of Primary Alcohols

Mixed matrix membranes (MMM) based on chitosan (CS) and poly (vinyl) alcohol (PVA) with a 50:50 w/w ratio doped with graphene oxide (GO) are prepared by solution casting and characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), water uptake, alcohol permeability, ion exchange capacity (IEC) and OH− conductivity measurements. The SEM analysis revealed a dense MMM where the GO nanosheets were well dispersed over the entire polymer matrix. The incorporation of GO increased considerably the thermal stability of the CS:PVA membrane. The GO-based MMM exhibited a low conductivity of 0.19 mS·cm−1 in part because the GO sheets did not change the crystallinity of the CS:PVA matrix. The reinforced structure created by the hydrogen bonds between the GO filler and the CS:PVA matrix resulted to be a good physical barrier for alcohol permeability, achieving a coefficient of diffusion of 3.38 × 10−7 and 2.43 × 10−7 cm2·s−1 after 60 and 120 min, respectively, thus avoiding additional alcohol crossover. Finally, the electrochemical performance of the GO-based MMM in the electrooxidation of propargyl alcohol was investigated in a Polymer Electrolyte Membrane Electrochemical Reactor (PEMER) under alkaline conditions, through the polarization curve and the electrolysis reactions, showing a performance comparable to anion-exchange commercial membranes.

Performance of “Polymer-in-Salt” Electrolyte PAN-LiTFSI Enhanced by Graphene Oxide Filler

Exploring solid state electrolytes with high ionic conductivity and good electrochemical stability is of prime importance for the development of safe batteries. In this study, we prepare a high-performance “polymer-in-salt” solid polymer electrolyte (SPE) by using polyacrylonitrile (PAN) as a host polymer, bistrifluoromethanesulfonimide lithium salt (LiTFSI) as an electrolyte salt, and different loading graphene oxide (GO) as a nano-filler. PAN-LiTFSI electrolyte filled with 0.9 wt% GO nanosheet exhibits an ionic conductivity of 1.1 × 10−4 S cm−1 at 30°C, which is almost one order of magnitude higher than that of the filler-free one. In addition, the anodic potential and the lithium ion transference number also increase to 5 V and 0.4, respectively. The enhancement on ionic conductivity is attributed to a 3D fast ion transport network constructed by GO nanosheets and a further decoupling of ion transport from segmental dynamics.

Structure and electrical properties of silicone rubber filled with thermally reduced graphene oxide

Graphene oxide (GO) was heat treated at different temperatures between 120 and 220 °C and the structural changes were assessed by thermogravimetry, infrared spectroscopy, X-ray photoelectron spectroscopy and scanning electron microscopy (SEM). The resulting reduced graphene oxide (rGO) fillers showed markedly lower oxygen contents (primarily by reduction of epoxide and hydroxyl groups) than GO. SEM of silicone rubber composites containing 3 wt.% rGO or GO filler showed that the nanoparticles were uniformly distributed in the polymer. The rGO-filled composites exhibited electric field-dependent resistivity; the resistivity decreased from 1014 to 1011 ohm m as the electric field was increased from 0.2 to 6 kV (mm)−1. The composites exhibited an increased resistivity after being exposed to a combined thermal cycling and electrical field. An increase in the resistivity of samples aged at 120 °C for more than 17 h was observed; the resistivity-electric field behavior and the dielectric constant of the aged composite resembled that of GO-filled composite. The composites exhibited dielectric constant values between 4.0 and 5.2 and a low tan delta (≤ 0.015) at frequencies between 10−2 and 104 Hz. The results suggest that the resistivity of the composites can be tuned by adjusting the degree of reduction of GO. The low rGO-filler content that was required to achieve this adequate property profile is attractive, which makes these composites potentially useful as electric field-grading material in HVDC cable accessories. However, this requires that the long-term stability problem can be sensible addressed.

Enhanced thermal properties for epoxy composites with a three-dimensional graphene oxide filler

In this study, we report a simple and efficient method to prepare three-dimensional graphene oxide (3DGO) network by freeze drying and investigate the effect of 3DGO network on thermal properties of epoxy composites. It was found that the 3DGO network not only improved thermal conductivity, thermal stability, glass transition temperature and storage modulus of epoxy composites, but also reduced the thermal expansion properties of epoxy composites. For instance, the thermal conductivity value of epoxy composite with only 1.3 wt% 3DGO is 0.62 Wm-1K-1, increased by 148 % in comparison with that of the neat epoxy (0.25 Wm-1K-1).

An All‐Solid‐State Flexible Piezoelectric High‐k Film Functioning as Both a Generator and In Situ Storage Unit

An all‐solid‐state flexible generator–capacitor polymer composite film converts low‐frequency biomechanical energy into stored electric energy. This design, which combines the functionality of a generator with a capacitor, is realized by employing poly(vinylidene fluoride‐co‐hexafluoropropylene) (PVDF‐HFP) in the simultaneous dual role of piezoelectric generator and polymer matrices of the flexible capacitor. Proper surface modification of the reduced graphene oxide (rGO) fillers in the polymeric matrices is indispensable in achieving the superior energy storage performance of the composite film. The heightened dielectric performance stems from enhanced compatibility of the rGO fillers and PVDF‐HFP matrices, and a microcapacitor model properly explains the dielectric behaviors. A device that is easily fabricated using our film allows timely decoupled motion energy harvest and output of the motion‐generated electricity. This report opens new design possibilities in the fields of motion sensors, information storage and high‐voltage output by accumulating low‐frequency random biological motions.

Effect of the C/O ratio in graphene oxide materials on the reinforcement of epoxy‐based nanocomposites

ABSTRACTThe effect of the C/O ratio of graphene oxide materials on the reinforcement and rheological percolation of epoxy‐based nanocomposites has been studied. As‐prepared graphene oxide (GO) and thermally‐reduced graphene oxide (TRGO) with higher C/O ratios were incorporated into an epoxy resin matrix at loadings from 0.5 to 5 wt %. Tensile testing revealed good reinforcement of the polymer up to optimal loadings of 1 wt %, whereas agglomeration of the flakes at higher loadings caused the mechanical properties of the composites to deteriorate. The level of reduction (C/O) of the graphene oxide filler was found to influence the mechanical and rheological properties of the epoxy composites. Higher oxygen contents were found to lead to stronger interfaces between graphene and epoxy, giving rise to higher effective Young's moduli of the filler and thus to superior mechanical properties of the composite. The effective modulus of the GO in the nanocomposites was found to be up to 170 GPa. Furthermore, rheological analysis showed that highly oxidized graphene flakes did not raise the viscosity of the epoxy resin significantly, facilitating the processing considerably, of great importance for the development of these functional polymeric materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 281–291

Robust ultraviolet shielding and enhanced mechanical properties of graphene oxide/sodium alginate composite films

To enhance the mechanical performance and ultraviolet shielding property, graphene oxide was incorporated as the functional nanofiller into a sodium alginate matrix to form a composite film via a solvent-casting method. The as-obtained films were characterized by scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, and thermal gravimetric; their mechanical and ultraviolet blocking properties were also systemically evaluated and compared. The results showed that the maximum tensile strength increased to 84 MPa at 6 wt.% graphene oxide loading, nearly 265% greater than that of pure sodium alginate film. The increased tensile strength may have resulted from the existence of hydrogen bonding and high interfacial adhesion between graphene oxide filler and sodium alginate matrix. Furthermore, the sodium alginate/graphene oxide films also demonstrated robust ultraviolet shielding capacity; the corresponding ultraviolet protection factor reached up to 133.61 at 8 wt.% graphene oxide loading.