Effect of electrostatic forces control on the structure and properties of polyaniline/graphene oxide nanocomposite

The effects of electrostatic forces (EF), control on the morphology, structure, and electrochemical properties of polyaniline, PANI/graphene oxide (GO), nanocomposites prepared by interfacial electropolymerization (IEP), are studied in this work. FESEM images showed that the IEP method can form the PANI/GO nanocomposites when the EF-control has been found mainly on the PANI nanofibers formation and growth on the GO film surface; and the EF-enhancement can form PANI nanofibers with small nano-diameter, longer length, uniform morphology, high order and well orientation as compared with the EF-reduction-formed sample. The EF-enhancement-formed PANI/GO nanocomposite showed improved electrochemical properties than that of the EF-reduction-formed sample due to the EF-enhancement that enhances the C–N structure for PANI/GO nanocomposite.     

Click coupled graphene for fabrication of high‐performance polymer nanocomposites

An effective technique of using click coupled graphene to obtain high‐performance polymer nanocomposites is presented. Poly(ε‐caprolactone) (PCL)‐click coupled graphene sheet (GS) reinforcing fillers are synthesized by the covalent functionalization of graphene oxide with PCL, and subsequently the PCL‐GS as a reinforcing filler was incorporated into a shape memory polyurethane matrix by solution casting. The PCL‐click coupled GS has shown excellent interaction with the polyurethane matrix, and as a consequence, the mechanical properties, thermal stability, thermal conductivity, and thermo‐responsive shape memory properties of the resulting nanocomposite films could be enhanced remarkably. In particular, for polyurethane nanocomposites incorporated with 2% PCL‐GS, the breaking stress, Young's modulus, elongation‐at‐break, and thermal stability have been improved by 109%, 158%, 28%, and 71 °C, respectively. This click coupling protocol offers the possibility to fully combine the extraordinary performance of GSs with the properties of polyurethane. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Studies on the mechanism for the sudden mechanical property drops of graphene/polymer nanocomposites

Graphene/polymer nanocomposites (GPNCs) have gained intense research interest in recent years. Graphene can improve the properties of the nanocomposites at low loadings, but usually causes sudden drops in the mechanical properties of the nanocomposites at similarly low loadings, risking the performance, reproducibility, and batch stability of the nanocomposites. This problem has been troubling the GPNCs field for years, but it is difficult to solve mainly because the mechanism of the sudden mechanical property drops has not been well documented yet. Here, we present a systematic study on this problem. At first, a statistical study was made to provide an overview of the sudden mechanical property drops. It was found that the sudden mechanical property drops were almost independent of the surface modification of graphene, and the in situ polymerization method sometimes leads to lower critical concentration than the solvent blending and melt blending methods. Then, we demonstrated a cutting‐off mechanism which unveiled that the formation of a continuous or semicontinuous network of graphene throughout the polymeric matrix was the main cause of the sudden mechanical property drops, and the low critical concentration of the sudden mechanical property drops was mainly due to the large aspect ratio of graphene. Finally, future research prospects were proposed. Overall, our work has provided new understandings and insights to the mechanical properties of GPNCs.     

Model for anomalous moisture diffusion through a polymer–clay nanocomposite

Experimental data are reported on moisture diffusion and the elastoplastic response of an intercalated nanocomposite with vinyl ester resin matrix and montmorillonite clay filler at room temperature. Observations in diffusion tests showed that water transport in the neat resin is Fickian, whereas it becomes anomalous (non‐Fickian) with the growth of the clay content. This transition is attributed to immobilization of penetrant molecules on the surfaces of hydrophilic clay layers. Observations in uniaxial tensile tests demonstrate that the response of vinyl ester resin is strongly elastoplastic, whereas an increase in the clay content results in a severe decrease of plastic strains observed as a noticeable reduction in the curvatures of the stress‐strain diagrams. This is explained by slowing down the molecular mobility in the host matrix driven by confinement of chains in galleries between platelets. Constitutive equations are developed for moisture diffusion through and the elastoplastic behavior of a nanocomposite. Adjustable parameters in these relations are found by fitting the experimental data. Fair agreement is demonstrated between the observations and the results of numerical simulation. A striking similarity is revealed among changes in diffusivity, ultimate water uptake, and the rate of plastic flow with an increased clay content. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 476–492, 2003     

Possible causes for rippling in a multivacancy graphene system

The occurrence of ripples in an eight‐atom vacancy graphene system was analyzed through first principles calculations based on density functional theory. The study focuses on the conditions that should be considered in order that ripples could occur in the single layer defected graphene. The vacancies concentration, especially the pentagonal figures formed after relaxation of the vacant system, and the distances between neighbor pentagons, are found to be key aspects for rippling occurrence, with no charge distribution consequence. Two different configurations of rippling have been found where the position of the pentagonal figures is discussed as the driving force for any of them to occur.     

A first principle study of adsorption of two proximate nitrogen atoms on graphene

Different possible configurations of two nitrogen‐adatoms on graphene are studied using density functional theory. Adsorption of single nitrogen atom on the bridge site of graphene is accompanied by distortion of the sheet. Electronically, this case amounts to p‐type doping. Two N atoms adsorbed on the graphene sheet can share a bond in two ways. They acquire positions either just above two adjacent carbon atoms or they form a bridge across opposite bonds of a hexagon in the sheet. Both these configurations also induce structural distortion of the sheet. Another stable configuration consists of two N atoms bonded as an N₂ molecule physisorbed on the graphene sheet. It is also possible to adsorb two N atoms on opposite sides of the graphene sheet, bonded to the same two C atoms. Moreover, two N atoms can be individually adsorbed on alternate bridge sites of neighboring hexagons experiencing a repulsion, the energy for which arises from the additional distortion of the graphene sheet. The densities of states near the Fermi level are found to be dependent on the adsorption configurations of two nitrogen atoms on graphene. Thus the electronic properties of graphene can be controlled by the selective adsorption of two nitrogen atoms. © 2014 Wiley Periodicals, Inc.     

Physical and mechanical properties of graphene oxide/polyethersulfone nanocomposites

The aim of this study was to investigate physical and mechanical properties of graphene oxide (GO)/polyethersulfone (PES) nanocomposite films. The films were produced by solution casting method. The mechanical properties of composite films were evaluated by tensile test. A significant enhancement in the mechanical properties of neat PES films was obtained incorporating a small amount of GO loading (0.05–1 wt.%). The highest tensile strength was observed at 1 wt.% of GO. Comparisons were made between experimental data and the Halpin–Tsai model predictions for the tensile strength and modulus of GO/PES composites. The effect of an orientation factor on model predictions was also acquired. The hydrophilicity of the nanocomposite was evaluated by assessing contact angle and enhanced wet ability of the films was obtained with increasing the amount of GO up to 1%. The morphology of the nanocomposites was investigated using scanning electron microscopy and transmission electron microscopy and the results revealed a good dispersion of GO in the PES matrix. The thermal behavior of the composite was also studied. Thermal stability of composites was increased by adding the GO. Copyright © 2013 John Wiley & Sons, Ltd.     

Reinforcing epoxy resin through covalent integration of functionalized graphene nanosheets

A chemically converted graphene/epoxy (EP) resin nanocomposite has been developed through the use of the functionalized graphene nanosheets (FGNs). The FGNs were prepared via the reaction of amines with alkylcarboxyl groups attached to the graphite oxides in the course of a dicarboxylic acid acyl peroxide treatment. FGNs/EP composites were prepared by dissolving the FGNs in organic solvent followed by mixing with EP and curing agent. In this composite, the FGNs were able to create molecular entanglement with EP matrix by taking advantage of the reactions between amine groups of FGNs and EP groups of EP, thus the FGNs could be covalently integrated into the EP matrix and became part of the cross‐linked network structure rather than just a separated component. Great enhancement in the mechanical properties of the epoxy composite, such as the ultimate tensile strength and toughness, had been achieved with small loading (0.1 wt%) of FGNs by 17.0% and 262.2%, respectively. However, the FGNs reinforced EP composites showed a slight decrease in glass transition temperature (Tg). Copyright © 2014 John Wiley & Sons, Ltd.     

Combined molecular and periodic DFT analysis of the adsorption of co macrocycles on graphene

The molecular doping of graphene with π‐stacked conjugated molecules has been widely studied during the last 10 years, both experimentally or using first‐principle calculations, mainly with strongly acceptor or donor molecules. Macrocyclic metal complexes have been far less studied and their behavior on graphene is less clear‐cut. The present density functional theory study of cobalt porphyrin and phthalocyanine adsorbed on monolayer or bilayer graphene allows to compare the outcomes of two models, either a finite‐sized flake of graphene or an infinite 2D material using periodic calculations. The electronic structures yielded by both models are compared, with a focus on the density of states around the Fermi level. Apart from the crucial choice of calculation conditions, this investigation also shows that unlike strongly donating or accepting organic dopants, these macrocycles do not induce a significant doping of the graphene sheet and that a finite size model of graphene flake may be confidently used for most modeling purposes. © 2017 Wiley Periodicals, Inc.     

Effect of graphene quantum dots on photoluminescence property of polyvinyl butyral nanocomposite

Design and development of new photoluminescence system are much in demand for various engineering and technological applications. The present investigation focused on the influence of graphene quantum dots (GQDs) dispersion in the polyvinyl butyral (PVB) matrix. The structural and chemical interaction of GQD‐dispersed PVB composites was confirmed by X‐ray diffraction (XRD), Fourier transform infrared (FTIR), micro‐Raman spectroscopy, ultraviolet and visible (UV‐Vis), and photoluminescence (PL) techniques. Chemical interaction between the functional groups leads to PL quenching at 455 nm. Changes on crystallite size and interplanar spacing hinders on the structural properties of the nanocomposite. Raman spectroscopy reveals the decrease in D/G intensity ratio influenced by GQD loading wt% in the polymer system. The dispersion and occupied network of GQD in the PVB matrix was confirmed by optical polarizing microscopy (OPM), atomic force microscopy (AFM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Effect of electrical conductivity of composites as a function of temperature has been verified. Decrease in direct bandgap as a function of GQD loading confirms the promising PL properties of the prepared composite system. Thus GQD‐derived composites may further be developed as a membrane for improved PL property.     

Fabrication of highly catalytic silver nanoclusters/graphene oxide nanocomposite as nanotag for sensitive electrochemical immunoassay

Silver nanoclusters and graphene oxide nanocomposite (AgNCs/GRO) is synthesized and functionalized with detection antibody for highly sensitive electrochemical sensing of carcinoembryonic antigen (CEA), a model tumor marker involved in many cancers. AgNCs with large surface area and abundant amount of low-coordinated sites are synthesized with DNA as template and exhibit high catalytic activity towards the electrochemical reduction of H₂O₂. GRO is employed to assemble with AgNCs because it has large specific surface area, super electronic conductivity and strong π-π stacking interaction with the hydrophobic bases of DNA, which can further improve the catalytic ability of the AgNCs. Using AgNCs/GRO as signal amplification tag, an enzyme-free electrochemical immunosensing protocol is designed for the highly sensitive detection of CEA on the capture antibody functionalized immunosensing interface. Under optimal conditions, the designed immunosensor exhibits a wide linear range from 0.1 pg mL⁻¹ to 100 ng mL⁻¹ and a low limit of detection of 0.037 pg mL⁻¹. Practical sample analysis reveals the sensor has good accuracy and reproducibility, indicating the great application prospective of the AgNCs/GRO in fabricating highly sensitive immunosensors, which can be extended to the detection of various kinds of low abundance disease related proteins.     

LDPE/EVA/graphene nanocomposites with enhanced mechanical and gas permeability properties

In the present work, graphene oxide (GO) and reduced graphene oxide (RGO) were incorporated at low‐density polyethylene (LDPE)/ethylene vinyl acetate (EVA) copolymer blend using solution casting method. Monolayer GO with 1‐nm thickness and good transparency was synthesized using the well‐known Hummers's method. Fourier transform infrared and X‐ray photoelectron spectroscopy data exhibited efficient reduction of GO with almost high C/O ratio of RGO. Scanning electron microscopy showed the well distribution of GO and RGO within LDPE/EVA polymer matrix. The integrating effects of GO and RGO on mechanical and gas permeability of prepared films were examined. Young's modulus of nanocomposites are improved 65% and 92% by adding 7 wt% of GO and RGO, respectively. The tensile measurements showed that maximum tensile strength emerged in 3 wt% of loading for RGO and 5 wt% for GO. The measured oxygen and carbon dioxide permeability represented noticeably the attenuation of gas permeability in composite films compared with pristine LDPE/EVA blend. Copyright © 2015 John Wiley & Sons, Ltd.     

Facile synthesis of wide-bandgap fluorinated graphene semiconductors

The bandgap opening of graphene is extremely important for the expansion of the applications of graphene-based materials into optoelectronics and photonics. Current methods to open the bandgap of graphene have intrinsic drawbacks including small bandgap openings, the use hazardous/harsh chemical oxidations, and the requirement of expensive chemical-vapor deposition technologies. Herein, an eco-friendly, highly effective, low-cost, and highly scalable synthetic approach is reported for synthesizing wide-bandgap fluorinated graphene (F-graphene or or fluorographene) semiconductors under ambient conditions. In this synthesis, ionic liquids are used as the only chemical to exfoliate commercially available fluorinated graphite into single and few-layer F-graphene. Experimental and theoretical results show that the bandgap of F-graphene is largely dependent on the F coverage and configuration, and thereby can be tuned over a very wide range.     

Ionic liquid functionalized graphene oxide for enhancement of styrene‐butadiene rubber nanocomposites

Ionic liquid 1‐allyl‐3‐methyl‐imidazolium chloride (AMICl) is used to fine‐tune the surface properties of graphene oxide (GO) sheets for fabricating ionic liquid functionalized GO (GO‐IL)/styrene‐butadiene rubber (SBR) nanocomposites. The morphology and structure of GO‐IL are characterized using atomic force microscope, X‐ray diffraction, differential scanning calorimetry, X‐ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, UV‐vis spectra and Raman spectra. The interaction between GO and AMICl molecules as well as the effects of GO‐IL on the mechanical properties, thermal conductivity and solvent resistance of SBR are thoroughly studied. It is found that AMICl molecules can interact with GO via the combination of hydrogen bond and cation–π interaction. GO‐IL can be well‐dispersed in the SBR matrix, as confirmed by X‐ray diffraction and scanning electron microscope. Therefore, the SBR nanocomposites incorporating GO‐IL exhibit greatly enhanced performance. The tensile strength, tear strength, thermal conductivity and solvent resistance of GO‐IL/SBR nanocomposite with 5 parts per hundred rubber GO‐IL are increased by 505, 362, 34 and 31%, respectively, compared with neat SBR. This method provides a new insight into the fabrication of multifunctional GO‐based rubber composites. Copyright © 2016 John Wiley & Sons, Ltd.     

Effects of hydroxyl group on H2 dissociation on graphene: A density functional theory study

Graphene-based materials are promising for hydrogen production and storage. In this work, using density functional theory calculations, we explored how a hydroxyl group influences H₂ dissociation on graphene. Presence of the hydroxyl group makes the binding of H atom with graphene stronger, as the binding energy of H atom with the hydroxyl-modified graphene is higher than that with the pristine graphene. The para-site is the most favorable site for H₂ dissociation on both the pristine and hydroxyl-modified graphene. The energy barrier of H₂ dissociation at para-site on the pristine graphene is 3.10 eV whereas that on the hydroxyl-modified graphene is 2.46 eV, indicating a more facile H₂ dissociation on the hydroxyl-modified graphene.     

氧化石墨烯和石墨烯在催化领域中的应用研究进展

石墨烯具有独特的二维平面结构,其导电性能好,比表面积大,耐酸碱,耐高温.基于石墨烯的优异特性,本文作者从材料的合成和结构等方面对石墨烯基催化剂的研制及其催化性能进行了评述.介绍了石墨烯催化体系的类型和机理,对石墨烯催化中存在的问题进行了简单分析,并对石墨烯在催化领域的应用前景进行了展望.     

Synthesis,characterization and optical properties of graphene oxide–polystyrene nanocomposites

The synthesis of graphene oxide (GO)–polystyrene (PS) Pickering emulsions, as environment‐friendly nanostructures suitable for novel applications, has received significant attention in recent years. In this work, the synthesis and characterization of GO–PS nanocomposites through seeded emulsion polymerization and the selective light reflection properties of dry films have been reported. Amphiphilic molecule sulfonated 3‐pentadecyl phenol was used as a co‐surfactant to stabilize GO dispersions during the emulsion polymerization process. The particle size of the dispersions as measured by dynamic light scattering decreases from 540 nm, for PS without any GO, to 88 nm with 1 wt% GO content. Scanning electron microscopy studies show a uniform size distribution of the composite particles prepared with GO. The dried films show a structural color that varies with the GO content. The self‐assembly behavior of the dried film was further studied using reflectance spectroscopy, which shows a red shift of the reflectance maximum from 440 to 538 nm as the GO loading was increased from 0.2 to 0.5 wt%, respectively, indicating a different microstructure. X‐ray diffraction, transmission electron microscopy (TEM) and atomic force microscopy (AFM) were used to study the morphology and structure of the composite particles on drying. The AFM study confirms the non‐spherical shape of the particles. Thermogravimetric analysis shows improved thermal decomposition characteristics of the nanocomposite films. Copyright © 2015 John Wiley & Sons, Ltd.     

Improved interfacial properties of PI composites through graphene oxide and carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs) have been identified as excellent nanoreinforcements for carbon fiber (CF)–reinforced polymers regarding a wide range of engineering applications. The outstanding properties of CNTs, such as their large surface area, high mechanical strength, and low manufacturing cost bring them to be distinguished nanoreinforcements for carbon fiber–reinforced polymers to form multifunctional and multiscale composites. Electrophoretic deposition of graphene oxide for CNTs onto the CF surface was conducted. The presence of graphene oxide–CNTs may effectively increase both the roughness and wettability of the CF surface, resulting in an improvement to the interfacial bonding strength between the CF and the polyimide (PI).     

Orientation of platelets in multilayered nanocomposite polymer films

The orientation of platelets in micro-meter-thick polymer-clay nanocomposite films was investigated with small-angle neutron scattering (SANS), small-angle X-ray scattering (SAXS), and wide-angle X-ray diffraction (WAXD). The films with various clay contents (15–60% by mass fraction) were prepared by a layer-by-layer approach from polymer-clay solutions that led to the formation of a high degree of orientation in both polymer and clay platelets. Shear-induced orientation of polymer-clay solutions is compared with the orientation of polymer-clay films. SANS, SAXS, and WAXD, with beam configurations in and perpendicular to the spread direction of the film, were used to determine the structure and orientation of platelets. In all films, the clay platelets oriented preferentially in the plane of the film. The observed differences in semidilute solutions, with clay surface normal parallel to the vorticity direction, versus bulk films and with clay surface normal parallel to the shear gradient direction at clay mass fractions of 40 and 60%, were attributed to the collapses of clay platelet during the drying process. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 3237–3248, 2003     

Enhanced interfacial interaction by grafting carboxylated‐macromolecular chains on nanodiamond surfaces for epoxy‐based thermosets

A novel core‐shell‐structured carboxylated‐styrene butadiene rubber (XSBR)‐functionalized nanodiamond (ND‐XSBR) was synthesized and characterized. Epoxy (EP) nanocomposites toughened by pristine ND and ND‐XSBR were investigated and compared. The ND‐XSBR‐reinforced nanocomposite exhibited mechanical properties superior to those of the one filled by pristine ND. At a low‐filler loading, the ND‐XSBR exhibited an impressive toughening effect. The maximum flexural strength was shown when the filler loading was as low as 0.1 wt % for the EP/ND‐XSBR nanocomposite. Furthermore, enhanced fracture toughness and fracture energy were shown by surface functionalization, representing enhanced compatibility between the ND‐XSBR and EP matrix. The glass transition temperature (T_g) and storage modulus of the nanocomposites were studied, and the EP/ND‐XSBR0.1 nanocomposite exhibited the highest T_g owing to the stronger interfacial interaction. The EP/ND‐XSBR0.2 exhibited higher storage modulus and T_g than the EP/ND0.2, because the higher interfacial interaction can restrict the molecular mobility of the EP by the functionalized ND‐XSBR. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1890–1898