Highly conductive graphene oxide/polyaniline hybrid polymer nanocomposites with simultaneously improved mechanical properties

Graphene oxide (GO) was added to a polymer composites system consisting of surfactant-wrapped/doped polyaniline (PANI) and divinylbenzene (DVB). The nanocomposites were fabricated by a simple blending, ultrasonic dispersion and curing process. The new composites show higher conductivity (0.02–9.8 S/cm) than the other reported polymer system filled with PANI (10⁻⁹–10⁻¹ S/cm). With only 0.45 wt% loading of GO, at least 29% enhancement in electric conductivity and 29.8% increase in bending modulus of the composites were gained. Besides, thermal stability of the composites was also improved. UV–Vis spectroscopy, X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM) revealed that addition of GO improves the dispersion of PANI in the polymer composite, which is the key to realize high conductivity.     

Novel surfactant-stabilized graphene-polyaniline composite nanofiber for supercapacitor applications

In this work, we present a new synthesis method for surfactant stabilized graphene (SSG) combined with polyaniline nanofiber (PANI-Nf) and apply the composite material as supercapacitor (SC) electrodes by screen-printing technique. Surfactant stabilized graphene polyaniline nanofiber composite (PANI-SSG) was synthesized by electrolytic exfoliation of graphite and subsequent interfacial polymerization. Firstly, graphite was electrolytically exfoliated in an electrolyte containing anionic surfactant. Next, ammonium peroxydisulfate initiator and hydrochloric acid were added to the graphene dispersion to form the aqueous phase for interfacial polymerization of polyaniline nanofiber. This dispersion was then added to the water-insoluble solvent phase containing aniline monomer. The polymerization only occurred at the interface of the two immiscible phases leading to polyaniline nanofiber decorated graphene structures. Characterizations by scanning electron microscopy, transmission electron microscopy, atomic force microscopy and Raman spectroscopy suggested nanocomposite formation with intermolecular π-π bonding of graphene with polyaniline nanofibers. Pastes of the materials were screen printed on stainless steel current collectors and tested for SC performance by cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) measurements with 2 M H₂SO₄ electrolyte using a home-built two-electrode test-cell. CV results showed redox peaks of polyaniline with wide cyclic loop, indicating large pseudocapacitance of the nanocomposite. From GCD measurement, a high specific capacitance of 690 Fg⁻¹ at 1 Ag⁻¹ was achieved. Therefore, PANI-SSG nano-composite prepared by electrolytic exfoliation and interfacial polymerization is a promising candidate for SC applications.     

Deformation and fracture in graphene nanosheets

Graphene nanosheets (GNSs) are flake-like materials composed of few-layer graphene sheets. GNSs are similar to multi-walled carbon nanotubes (CNTs) in graphene structures and in layer numbers. However, GNSs and CNTs behave very differently in deformation and fracture. In this study, natural graphite flakes were employed to make expanded graphite (EG), which is composed of partially connected GNSs. Both sonication and three-roll milling were used to separate the GNSs and to disperse them into an epoxy resin. By compacting EG, the GNSs inside were compressed and deformed. By breaking the GNS/epoxy composite, most GNSs on the cracked surfaces were fractured. Both SEM and TEM have been used for microscopic observations. The micrographs revealed that folding and wrinkling are the major modes of deformation, while tearing and peeling are the dominant modes of fracture. These modes are virtually non-existent in CNTs. The factors to cause the different behavior are discussed.     

Effect of graphene oxide nanosheets on the physico-mechanical properties of chitosan/bacterial cellulose nanofibrous composites

In this work, novel chitosan/bacterial cellulose (CS/BC) nanofibrous composites reinforced with graphene oxide (GO) nanosheets are introduced. As cell attachment and permeability of nanofibrous membranes highly depend on their fiber diameter, the working window for successful electrospinning to attain sound nanofibrous composites with a minimum fiber diameter was determined by using the response surface methodology. It is shown that the addition of GO nanosheets to CS/BC significantly reduces the average size of the polymeric fibers. Their mechanical properties are also influenced and can be tailored by the concentration of GO. Fourier transform infrared spectroscopy reveals hydrogen bonding between the GO nanosheets and the polymer matrix. A decrease in the hydrophilicity of the electrospun nanofibers and their water vapor permeability with the addition of GO are also reported. The prepared nanofibrous composites are potentially suitable candidates for biomedical applications such as skin tissue engineering and wound dressing.     

Preparation and properties of reduced graphene oxide/polyacrylonitrile nanocomposites using polyvinyl phenol

Nanocomposites of polyacrylonitrile (PAN) with reduced graphene oxide (rGO) were prepared using a solution mixing technique employing polyvinyl phenol (PVP) as a compatibilizer. The PVP can facilitate composite formation by interacting with both rGO and PAN via π-π and H-bonding respectively. Various amounts of rGO were used to prepare PAN nanocomposites. The cross-sectional morphology of the composite films shows a uniform dispersion of rGO sheets in the PAN matrix. The Fourier transform infrared (FT-IR) studies revealed that good interaction of the rGO/PVP hybrid with PAN. The wide angle x-ray diffraction (WAXS) study confirms that the rGO sheets were uniformely dispersed as individual sheets in the PAN matrix. Thermogravimetric analysis shows enhanced thermal stability of the composite compared to pure PAN. The tensile strength and elastic modulus of the nanocomposites increased with increasing rGO content. A 102% enhancement in tensile strength and a 62.9% enhancement in elastic modulus were observed in the nanocomposite with 5% rGO.     

Preparation of reduced graphene oxide-NiFe2O4 nanocomposites for the electrocatalytic oxidation of hydrazine

A reduced graphene oxide (RGO)-NiFe₂O₄ nanocomposite was synthesized by a simple one step hydrothermal approach and its application in the electrocatalytic oxidation of hydrazine was demonstrated. The as-synthesized nanocomposite was characterized by X-ray diffraction, Fourier transform infrared spectroscopy, UV–visible spectroscopy, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, Thermogravimetric analysis, Field emission-scanning electron microscopy (FE-SEM), and Transmission electron microscopy (TEM). The FE-SEM and TEM image analyses revealed that the NiFe₂O₄ nanoparticles were uniformly distributed on the RGO sheets with a diameter and length of ∼10 and ∼100 nm, respectively. The XPS analysis confirmed the ionic states of Ni and Fe to be Ni³⁺ and Ni²⁺, and Fe²⁺ and Fe³⁺, respectively. Further, the electrochemical activity of the RGO-NiFe₂O₄ nanocomposite was investigated by studying the oxidation of hydrazine. The RGO-NiFe₂O₄ modified glassy carbon electrode (GCE) showed an outstanding electrocatalytic activity towards the oxidation of hydrazine as compared to the NiFe₂O₄ and RGO modified electrodes. The enhanced electrocatalytic activity is due to the synergistic effect between RGO and NiFe₂O₄. Using amperometry, the lowest detection limit of 200 nM was achieved with the RGO-NiFe₂O₄ modified GCE. Therefore, the RGO-NiFe₂O₄ modified GCE can be used for the electrochemical oxidation of hydrazine.     

Enhanced microwave absorption properties of flake-shaped FePCB metallic glass/graphene composites

A novel kind of composite absorber, i.e. FePCB/graphene composite, with excellent microwave absorption properties was successfully fabricated by a simple and scalable ball milling method. After being milled, the FePCB particles displayed flaky morphology with large aspect ratio. The complex permittivity and permeability of the flaky FePCB distinctly increased compared with those before milling. Furthermore, with the introduction of graphene, the flaky FePCB/graphene composite exhibited excellent microwave absorption performance with strong absorption and wide absorption band. In particular, for FePCB/graphene composite with an absorber thickness of 2 mm, the reflection loss (RL) reached a minimum of −45.3 dB at 12.6 GHz and the effective absorption bandwidth (RL < −10 dB) covered 5.4 GHz. The enhanced microwave absorption performance of the FePCB/graphene composite was attributed to the high magnetic loss and improved impedance matching which were closely related to the flake-shaped FePCB particles and the introduction of graphene sheets.     

Transparent and flexible ultraviolet photodetectors based on colloidal ZnO quantum dot/graphene nanocomposites formed on poly(ethylene terephthalate) substrates

Transparent colloidal ZnO quantum-dot (QD)/graphene nanocomposites were formed on poly(ethylene terephthalate) (PET) substrates. Ultraviolet (UV)–visible absorption spectra showed a shoulder peak around 350 nm corresponding to the absorption of ZnO QDs. Optical transmittance of the ZnO QD/graphene/PET multilayer was approximately 80%. High-resolution transmission electron microscopy images showed that the ZnO QDs were distributed along the circumferences of the surfaces on the graphene layers. Current–voltage and current–time measurements on the UV photodetector after bending at 300 K exhibited the ON/OFF switching states and stability resulting from the light-induced conductivity of the flexible graphene layer.     

Enhanced thermal conductivity and retained electrical insulation for polyimide composites with SiC nanowires grown on graphene hybrid fillers

Polyimide (PI) composites containing one-dimensional SiC nanowires grown on two-dimensional graphene sheets (1D–2D SiC_NWs-GSs) hybrid fillers were successfully prepared. The PI/SiC_NWs-GSs composites synchronously exhibited high thermal conductivity and retained electrical insulation. Moreover, the heat conducting properties of PI/SiC_NWs-GSs films present well reproducibility within the temperature range from 25 to 175 °C. The maximum value of thermal conductivity of PI composite is 0.577 W/mK with 7 wt% fillers loading, increased by 138% in comparison with that of the neat PI. The 1D SiC nanowires grown on the GSs surface prevent the GSs contacting with each other in the PI matrix to retain electrical insulation of PI composites. In addition, the storage modulus and Young’s modulus of PI composites are remarkably improved in comparison with that of the neat PI.     

Photochemical performance and electrochemical capacitance of titania nanocomplexes

Titania nanocomplexes, comprising the disordered nanoribbons or nanowires on the top surface and highly ordered nanotube array on the underlaying layer, has been fabricated by longitudinally splitting off nanotubes in a controlled anodization process. Anatase titania nanocomplexes show higher photovoltage and photocurrent responses and photocatalysis activity than titania nanotube array due to the enhanced light harvesting caused by nanoribbons and nanowires. Furthermore, titania nanowire-nanotube demonstrates a higher photoelectrical performance than nanoribbon-nanotube due to its thicker space charge layer caused by long nanotubes and more effective surface area contributed by nanowires. Cyclic charge-discharge measurements show that titania nanotube array exhibits a much higher electric double layer capacitance than titania nanocomplexes because the surface nanoribbons or nanowires inhibit the free diffusion and transportation of electrolyte ions into the underlaying nanotubes. Therefore, titania nanocomplexes can act as a photoactive material for photocatalysis applications and titania nanotube array can act as an electrode substrate for electrochemical supercapacitor applications.     

Facile coordinating decoration of salophen Al on graphene nanosheet: Salophen Al complex functionalized graphene nanocomposite with electrochemical properties

Salophen Al complex functionalized graphene (SCFG) nanocomposite was synthesized by simple coordination of phenol functionalized graphene (PFG) and as-prepared salophen Al complex. This process is facile, convenient and high efficient. We also investigated the structure, optical properties and electrochemical properties of the obtained SCFG composites. The results showed that salophen Al conjugated and incorporated onto the graphene sheet surface and the composites maintained the micro-structure of graphene sheets without agglomeration. The photoluminescence of salophen Al was completely quenched by graphene, due to the charge transfer between the salophen Al and the graphene nanosheets. Moreover, a significant electrochemical signal emerged on the SCFG modified electrodes compared with those of the graphene sheets or salophen Al complex. Owing to preliminary results of the excellent electrochemical property, SCFG nanocomposite is a promising electrochemical redox probe material.     

Electrical conductive and graphitizable polymer nanofibers grafted on graphene nanosheets: Improving electrical conductivity and flame retardancy of polypropylene

Polyaniline (PANI) nanofibers grafted reduced graphene oxide (PANI–RGO) is prepared using the “grafting-from” strategy and then is incorporated into polypropylene (PP) matrix by way of the master batch-based melt mixing method. Grafted PANI nanofibers can improve the dispersion and electrical conductivity of reduced graphene oxide (RGO). The electrical conductivity of the modified RGO and its composites is not impaired by the grafted polymer, due to the conductive characteristics of PANI. The barrier action of PANI–RGO can greatly inhibit the release of flammable pyrolysis products of PP. PANI–RGO exhibits a marked flame retardancy effect on PP. The smoke release of the composites is slightly retarded. Transmission electron microscopy image and Raman spectrum of the char residue for PANI–RGO based composite indicate the formation of carbon nanofibers during combustion. The in situ formed carbon nanofibers on graphene nanosheets can enhance barrier performance against heat and mass transfer, resulting in enhanced flame retardancy.     

Flow-induced crystallization of polypropylene in the presence of graphene nanoplatelets and relevant mechanical properties in nanocompsoite fibres

Flow-induced crystallization of polypropylene (PP) in the presence of graphene nanoplatelets (GnPs) was experimentally observed for the first time. Monofilaments of PP and PP/GnPs in the presence and absence of polypropylene grafted maleic anhydride (PP-g-MA) as a compatibilizer were produced via masterbatch dilution technique. Morphology, crystalline and super molecular structures, thermal and mechanical characteristics of the nanocomposite fibres were investigated by means of SEM, WAXD, DSC, DMTA, TGA, polarized light microscopy and tensile testing. The fractured cross-section images indicated a reasonably good GnPs dispersion in the compatibilized nanocomposite fibres since a few large GnPs aggregates were observed. Based on DSC, XRD, and polarizing optical microscopy results, it can say that GnPs acted as a nucleating agent and increased the crystallization temperature and simultaneously acted as a physical barrier, reducing crystallite growth of PP. The introduction of PP-g-MA into PP/GnPs nanocomposite fibre increased storage modulus. Upon inclusion of PP-g-MA, the most significant improvement of 48% was observed for tensile modulus with the incorporation of 0.5 wt.% GnPs. The observed results suggested that the presence of PP-g-MA changed the internal structure and morphology of PP/GnPs nanocomposite fibres rather than improving the interface of PP/GnPs. We concluded that using extensional flow and having proper dispersion of GnPs, flow-induced crystallization could be occurred in PP/GnPs nanocomposite fibres. About 20% increase in crystallinity was found for the compatibilized PP/GnPs nanocomposite fibres as compared to that of the virgin PP.     

Synergy in hybrid polymer/nanocarbon composites. A review

The aim of this review article is to report the most recent developments in the understanding of and beliefs about the properties of polymer hybrid composites that are reinforced with various combinations of nanometer-sized carbon and mineral fillers. The discussions are primarily focused on an analysis and comparison of the electrical, thermal, and mechanical properties. It is shown that the introduction of a mixed (hybrid) system of filler nanoparticles into polymer matrices enhances the macro- and microproperties of the composites as a result of the synergistic interactions between the fillers and the simultaneous creation of a unique filler network in the polymer. The synergy of various types of carbon nanofillers and combinations of nanocarbon materials with inorganic fillers manifests itself as modifications of most of the properties of hybrid polymer composites relative to the properties of a polymer system containing a single filler. The reinforcing effect is related to the structure and particle geometry of the hybrid fillers, the interactions between the fillers, the concentrations and the processing methods.The existence of synergy between different types of carbon nanofillers, as well as with mineral fillers, shows great potential and could significantly increase applications of carbon-based nanomaterials.     

Preparation and properties of novel epoxy/graphene oxide nanosheets (GON) composites functionalized with flame retardant containing phosphorus and silicon

2-(Diphenylphosphino)ethyltriethoxy silane (DPPES) was grafted onto the surface of graphene oxide nanosheets (GON) via a condensation reaction. X-ray photoelectron spectroscopy, X-ray diffractometry, Fourier transform infrared spectroscopy and Raman spectroscopy verify that DPPES did not only covalently bond to GON as a functionalization moiety, but partly restored its conjugated structure as a reducing agent. DPPES on graphene sheets oxide was observed by transmission electron microscopy, and contributed to the favorable dispersion of DPPES-GON in nonpolar toluene. Additionally, the flame retardancy and thermal stability of epoxy/DPPES-GON nanocomposites that contain various weight fractions of DPPES-GON were studied using the limiting oxygen index test, UL-94 test and by thermogravimetric analysis in nitrogen. The composites containing 10 wt% DPPES-GON can pass V-0 rating in UL-94 test. Adding 10 wt% DPPES-GON in epoxy greatly increased the char yield and LOI by 42% and 80%, respectively. Epoxy/DPPES-GON nanocomposites with phosphorus, silicon and graphene layer structures were found to exhibit much greater flame retardancy than neat epoxy. The synergistic effects among silicon, phosphorus and GON can improve the flame retardancy of epoxy resin.     

Influence of multi-walled carbon nanotubes on electrochemical performance of transparent graphene electrodes

In this work, carbon-carbon nanocomposites as transparent electrodes were prepared by a chemical reduction of graphite oxide (GO) and multi-walled carbon nanotubes (MWNTs). The electric, optical, and electrochemical properties of graphene-MWNT nanocomposites (G-MCs) were investigated as a function of the MWNT content. It was found that chemically bonded G-MCs were successfully formed with a reduction of the functional groups of the GO and acid-treated MWNTs, resulting in the conjugation of 1D MWNTs onto a 2D graphene surface. The electrical conductivity of the graphene was significantly enhanced by introducing the MWNTs. In addition, the G-MCs showed improved current density and high efficiency compared with graphene alone. This indicated that the improved electrochemical performance of the G-MCs can be attributed to the increase in the activity and electrical conductivity enhanced by π-π interaction between graphene and MWNTs.     

Evaluation of the chemical interaction between carbon nanotubes functionalized with TGDDM tetrafunctional resin and hardener DDS

In this work, the chemical interaction between carbon nanotubes (MWCNT) functionalized with acyl chloride (SOCl₂) and polymer chain tetrafuncional N,N,N′,N′-tetraglycidyl-4,4′-diaminodiphenylmethane (TGDDM) and hardener 4,4′diaminodiphenyl sulfone (DDS) has been monitored by Fourier transform infrared spectroscopy (FTIR) with a attenuated total reflectance (ATR) coupled. MWCNT were obtained from the pyrolysis of a mixture of camphor and ferrocene into a oven. The functionalization process was done by oxidative treatment in order to incorporate carboxylic group over the walls of MWCNT, before to be used SOCl₂. The functionalized carbon nanotubes were evaluated by X-ray photoelectron spectroscopy (XPS), Raman and transmission electron microscopy (TEM). Nanostructured composites were processed by using epoxy resin with MWCNT in varying percentages. In this work it was observed that different percentages of functionalized nanotubes modify the interaction between the composite matrix and curing agent, where can be observed that in specimens with content less than 1 wt% MWCNT the chemical bond occurs preferentially from the opening of the SO double bond of the hardener and when is used MWCNT content higher than 1 wt% there is little chemical interaction with the SO bond of the hardener and most MWCNT binds to amine.     

Enhanced electrical conductivity and mechanical properties of ABS/EPDM composites filled with graphene

Acrylonitrile–butadiene–styrene (ABS)/ethylene–propylene–diene monomer (EPDM) composites reinforced with graphene nanoplatelets (GN) were fabricated by the direct melt blending, dried premixing and wet premixing process, respectively. The electrical resistivity, tensile strength, impact strength, microstructure, thermal stability, glass transition temperature and morphology of fracture surface of composites were investigated. In case of direct melt blending process, the maximum tensile strength with minimum impact strength is obtained. But this result is reversed while the fabrication of composites by wet premixing process. SEM results show that GN is prior to distributing in the continuous ABS phase. The percolation threshold could be significantly decreased from 11.8 wt% to 6.6 wt% when prepare composites by wet/dried premixing process instead of melt blending.     

Enhanced crack detection sensitivity of carbon fiber composites by carbon nanotubes directly grown on carbon fibers

The ability of highly conductive hybrid carbon–fiber/carbon nanotube loaded epoxy composites to sense matrix cracking damage in situ is demonstrated. Multi-walled carbon-nanotubes (MWCNTs) are grown perpendicular to and on the surface of a woven carbon–fiber fabric using a chemical vapor deposition process. An increase in sensitivity of resistance change under interlaminar fracture is shown through a series of double cantilever beam (DCB) tests on samples prepared with MWCNTs grown on both sides of carbon–fiber fabric lamina placed at the top and bottom surfaces of an 8-layer test panel whereas samples with MWCNTs inside the samples did not show much increase in sensitivity of resistance change compared with the baseline samples without MWCNTs. The results suggest that the addition of surface positioned hierarchical carbon-nanotube lamina on composite structures has the potential for autonomic sensing of internal matrix damage.     

Processing of graphene nanoribbon based hybrid composite for electromagnetic shielding

The advent of graphene heralded by the recent studies on carbon based conducting polymer composites has been a motivation for the use of graphene as an electromagnetic interference (EMI) shielding material. One of the variants of graphene, graphene nanoribbon (GNR) shows remarkably different properties from graphene. The EMI shielding effectiveness of the composite material mainly depends on fillers’ intrinsic conductivity, dielectric constant and aspect ratio. We have synthesized graphene nanoribbon (GNR) – Polyaniline (PANI) – epoxy composite film for effective shielding material in the X-band frequency range of 8.2–12.4 (GHz). We have performed detailed studies of the EMI shielding effect and the performance of the composite and found that the composite shows ∼−40 dB shielding which is sufficient to shield more than 95% of the EM waves in X Band. We checked the shielding effectiveness of the composite film by varying the GNR percentage and the thickness of the film. The strength properties of the synthesized composited were also studied with a aim to have a material having both high strength and EMI shielding properties.