Graphene In Poly Research Articles

Highly sensitive and disposable screen-printed ionic liquid/graphene based electrochemical sensors

In this work, a highly sensitive and disposable screen-printed ionic liquid-graphene electrode (SPIL-GE) was developed for electrochemical sensing. The paste for screen printing was facilely prepared by mixing IL with electrolytically exfoliated graphene in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (GP/PEDOT/PSS) and carbon paste (CP) via ball milling. The IL-GP paste was then screen printed to form working and counter electrodes (WE & CE) followed by screen printing of Ag/AgCl reference electrode and insulator layer on a polyethylene substrate. Electrode geometries were optimized for electrochemical sensing, arriving at an optimal design with an overall electrode length of 25 mm, and CE and WE active areas of 15.70 and 12.57 mm2, respectively. SPIL-GEs employing six ILs with imidazolium and pyridinium cations were assessed for electrochemical sensing of K3Fe(CN)6. The pyridinium-type IL, namely 3-methyl-1-propylpyridinium bis(trifluoromethyl sulfonyl)imide (PMPlm), was found to exhibit the highest CV peak currents compared with other ILs at an optimal PMPlm content of 1.0% (w/w). Characterization with scanning electron microscopy and Fourier-transform infrared spectroscopy confirmed the presence of PMPlm, GP/PEDOT/PSS and CP in SPIL-GEs. The electrochemical performance of the optimal SPIL-GE towards the three common analytes including ferri/ferro cyanide (Fe(CN)6)3-/4- redox couple, dopamine and hydroquinone were compared with the screen-printed carbon and graphene electrodes (SPCE & SPGE). From the results, the SPIL-GE demonstrated larger anodic currents with lower oxidation potentials for the three analytes than SPGE and SPCE, respectively. Therefore, the SPIL-GE could be a potential candidate for advanced electrochemical sensing applications.

Understanding the Reinforcement of Graphene in Poly(Ether Ether Ketone)/Carbon Fibre Laminates.

PEEK appears as an excellent candidate to substitute epoxy resins in carbon fibre laminates for high-performance aeronautical applications. The optimization of the properties and, in particular, of the transition region between the fibres and the matrix appear as a major issue prior to serial production. Graphene, modified with two compatibilizers, has been incorporated in the polymer layer with the purpose of imparting additional functionalities and enhancing the matrix-fibre interaction. It is found that both carbon fibres and modified graphene significantly influence the crystallization behaviour and smaller, and/or more imperfect crystals appear while the degree of crystallinity decreases. Despite this, nanoindentation studies show that the PEEK layer exhibits significant modulus improvements (≈30%) for 5 wt.% of graphene. Most importantly, the study of the local mechanical properties by nanoindentation mapping allows the identification of remarkably high modulus values close to the carbon fibre front. Such a relevant mechanical enhancement can be associated with the accumulation of graphene platelets at the polymer–fibre boundary, as revealed by electron microscopy studies. The results offer a feasible route for interlaminar mechanical improvement based on the higher density of graphene platelets at the fibre front that should promote interfacial interactions. Concerning electrical conductivity, a large anisotropy was found for all laminates, and values in the range ~10−4 S/cm were found for the through-thickness arrangement as a consequence of the good consolidation of the laminates.

Good dispersion of poly(δ-gluconolactone)-grafted graphene in poly(vinyl alcohol) for significantly enhanced mechanical strength

Here, we presented a straight forward and new approach for designing the interfacial compatibility between polyvinyl alcohol (PVA) and graphene sheets. The synthesis of poly(delta-gluconolactone) grafted from reduced graphene oxide (PGL-g-rGO) has been primarily developed by the ring-opening polymerization (ROP) of the green delta-gluconolactone monomer. The structure of PGL-g-rGO was fully confirmed using 1HNMR, XRD, FTIR, UV/Vis spectroscopy, TGA, and SEM. Poly(delta-gluconolactone) was expected to have a dual function of an efficacious modifier and a reducing agent for graphene oxide. Hence, the addition of PGL-g-rGO as a filler into PVA polymer was done into different mass ratios to obtain high-performance polymer nanocomposites. The dispersion and interfacial interaction of PGL-g-rGO sheets with the PVA matrix were studied. The thermal behavior, mechanical properties, and surface wettability of the final PVA nanocomposites were also evaluated. It can be observed that the char yield and the initial decomposition temperature of PVA were considerably enhanced after the addition of PGL-g-rGO to the polymer besides, the mechanical properties were totally improved. The use of PGL-g-rGO with only a mass ratio of 1.5% results in increasing the tensile strength and Young's modulus of PVA polymer by 124 and 121%, respectively. The elongation at break was uncommonly increased from 93 to 251% because of the formed strong hydrogen bonding between the filler and the polymer which can't only work on the efficacious convey of stress from PVA to reduced graphene sheets but also facilitate the polymer crystallization.

Fabrication of poly(ethylene glycol) hydrogels containing vertically and horizontally aligned graphene using dielectrophoresis: An experimental and modeling study

We incorporated bovine serum albumin (BSA)-functionalized graphene in poly(ethylene glycol) diacrylate (PEG) hydrogels. The graphene alignment in PEG hydrogels was changed using dielectrophoresis (DEP) forces. Effect of graphene concentration (2.55 and 5.1 mg/mL) and alignment (vertical and horizontal) on electrical and mechanical properties of hybrid graphene-PEG gels was evaluated. In addition, the molecular interaction of BSA peptides with graphene in the presence and absence of an electric field was assessed. The incorporation of graphene in PEG improved mechanical properties of hybrid gels. Dielectrophoretically aligned graphene-PEG hydrogels showed an anisotropic electrical conductivity. Young's modulus of 5.1 mg/mL graphene-PEG was almost three times higher than that of pristine PEG. Viability and proliferation of mouse embryonic stem cells on graphene-PEG gels were comparable with control PEG hydrogels. Ab initio calculations showed longer peptides had higher binding affinity towards graphene and caused a change in dipole moment due to the presence of electric field. The electric field also expanded graphene and peptide chains, which confirms the graphene alignment using DEP forces. Hybrid aligned graphene-PEG hydrogels may serve as functional biomaterials to engineer biological tissues and fabricate biomedical devices.

Integration of graphene in poly(lactic) acid by 3D printing to develop creep and wear‐resistant hierarchical nanocomposites

Polylactic acid (PLA) and graphene reinforced polylactic acid (PLA‐graphene) composites have been fabricated by three‐dimensional (3D) fused deposition modeling (FDM) printing. Indentation creep resistance was analyzed in terms of the strain‐rate sensitivity index of PLA (0.11) and PLA‐graphene (0.21). Enhanced creep resistance in PLA‐graphene is attributed to the restriction of the polymeric chains by graphene, caused by low strain rates identified during secondary creep. The tribological properties of PLA and PLA‐graphene composites were evaluated by ball‐on‐disk wear tests. Wear resistance was increased by a 14% in PLA‐graphene as compared to PLA. A two‐stage coefficient of friction (COF) behavior has been observed for PLA‐graphene. Initially, PLA‐graphene exhibits a 65% decrease in COF as compared to PLA. During the second stage, PLA‐graphene approached similar COF behavior and value of PLA (∼0.58). PLA‐graphene composites have shown significant improvement in creep and wear resistance demonstrating 3D printing to be a novel manufacturing route. POLYM. COMPOS., 39:3877–3888, 2018. © 2017 Society of Plastics Engineers

Interlayer Polymerization in Chemically Expanded Graphite for Preparation of Highly Conductive, Mechanically Strong Polymer Composites

The large-scale application of graphene–polymer composites needs a simple, low-cost method that simplifies the preparation process of graphene and optimizes the structure and properties of composites. We propose the first interlayer polymerization in chemically expanded graphite (CEG) with large specific surface areas, which allows CEG to be spontaneously exfoliated into single- and few-layer graphene in poly(methyl methacrylate) (PMMA). Our results demonstrate that besides weakened interlayer interactions, the surface wettability of CEG to monomers is a critical prerequisite for the desired graphene exfoliation, dispersion, and performance optimization of composites. The slightly oxidized CEG (LCEG) improved to some extent the affinity for the monomer but is not sufficient to achieve complete exfoliation of LCEG, so that the resulting composites reveal the mechanical and electrical properties that are far poorer than those of the surface-modified LCEG-based composites. The latter not only exhibit a signi...

Interfacial interactions of thermally reduced graphene in poly(trimethylene terephthalate)-epoxy resin based composites

Nanocomposites containing thermally reduced graphene (TRG) have been prepared with poly(trimethylene terephthalate) (PTT) plasticized with (bisphenol-A diglycidyl ether) (BADGE), a cross-linkable additive. Morphology of the PTT–BADGE blend was dependent on preference for interaction of TRG with PTT or BADGE and nucleation activity of TRG toward PTT. PTT-TRG and PTT-BADGE-TRG nanocomposites with different BADGE-TRG ratios were prepared by a melt mixing technique facilitated by miscibility of PTT and BADGE. The influence of TRG on crystallization nucleation, kinetics and morphology was measured using differential scanning calorimetry and wide-angle X-ray scattering. Crystallization of PTT caused phase separation of BADGE, though PTT–BADGE remained miscible in PTT amorphous regions. BADGE created increased flexibility of PTT though dynamic mechanical properties were moderated by TRG, both directly as a filler and as a result of enhanced crystallization. Synergistic improvement in modulus was observed at particular compositions attributed to a change in morphology of an immobilized zone consisting of BADGE and TRG within amorphous fractions of PTT. The results are of consequence for design of materials using a semi-crystalline polymer, for applications where simultaneous use of a processing aid, plasticizer and nano-reinforcement.

Interface engineering of ionic liquid integrated graphene in poly(vinylidene fluoride) matrix yielding magnificent improvement in mechanical, electrical and dielectric properties

Graphene oxide(GO) functionalized with imidazolium ionic liquid(IL) is characterized from spectroscopic and microscopic techniques. Poly(vinylidene fluoride)(PVDF)/ionic liquid functionalized graphene oxide(GO-IL) composite(PGL) films are flexible, and exhibit fibrillar network morphology. Transmission electron microscopy indicates dendritic morphology at 3%(w/w) GO-IL and the formation of piezoelectric β-polymorph PVDF is evidenced from wide angle x-ray scattering. PGL composites exhibit a gradual increase of melting, crystallization, glass transition (Tg) and other relaxation temperatures with increasing GO-IL concentration. The maximum increases of storage modulus (73%), Young's modulus (333%) and tensile strength (628%) occur at 3% filler concentration. Halpin–Tsai equation suggests GO sheets are randomly distributed at low GO-IL concentration but they are unidirectional at higher concentration. A sharp increase of dc-conductivity of PGL composite to ∼10−2 S/cm occurs with a percolation threshold of 0.1% (w/w). The dielectric permittivity increases from 7.5 for PVDF to 13.5 for 3% filler with a percolation threshold at 0.1% (w/w) filler.

Novel Method for the Fabrication of Flexible Film with Oriented Arrays of Graphene in Poly(vinylidene fluoride-co-hexafluoropropylene) with Low Dielectric Loss

Carbon–polymer nanocomposites with good dielectric properties have potential applications in the electronic and electrical industry because of their good mechanical properties and low cost. The morphology, structure, dielectric properties, and mechanical strength of reduced-graphene oxide nanosheet/poly(vinylidene fluoride-co-hexafluoropropylene) nanocomposites (rGO/PVDF-HFP) were investigated. The rGO nanosheets were well dispersed and strongly oriented in the matrix, thanks to the unique spin-assistant preparation process. A dielectric constant of 54 (100 Hz) which was four times higher than that of pure PVDF-HFP was obtained when the concentration of rGO was 0.7 vol % and the dielectric loss was as low as 0.27. The good dielectric performance of the nanocomposites was attributed to the homogeneous dispersion and good alignment of rGO. The shear force provided by spin-coating, the thickness decreasing process, and thickness control were assumed to be key factors in the alignment of rGO nanosheets in the...

Synthesis of well dispersed graphene in conjugated poly(3,4-ethylenedioxythiophene):polystyrene sulfonate via click chemistry

Abstract The well dispersed graphene in poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) composites was achieved by chemical modification via click chemistry under mild condition in order to improve the electrical conductivity of polymer. Graphene sheets were prepared from natural graphite flake by a modified Hummers method followed by reducing with hydrazine. Graphene and PEDOT:PSS were functionalized with alkyne and azide, respectively followed by reacting via click chemistry at room temperature for 48 h using copper sulfate as catalyst. The successful functionalization and click reaction between terminal alkyne groups ( C C) on graphene sheets and terminal azide groups ( N3) of PEDOT:PSS were confirmed by Fourier Transform Infrared (FTIR), Raman and X-ray photoelectron (XPS) spectroscopy. The preliminary test to check the dissimilar dispersibility between graphene oxide and alkyne-modified graphene oxide in mixed water/hexane solvent was performed. Thermogravimetric analysis result exhibited the composites having excellent thermal stabilities due to the incorporation of graphene in PEDOT:PSS; however, clicked composites showed slightly lower thermal stabilities than unclicked ones as a result of cleavages of amide linkages and remaining oxygen-containing functionalities. It was also found that the surface morphologies observed by scanning electron microscope of clicked composites were smoother than those of unclicked composites because of the enhancement of interfacial interaction between graphene sheets and PEDOT:PSS matrix, resulting in a decrease in graphene agglomeration and, in turn, an increase in electrical conductivity.

PEDOT:PSS/Graphene Nanocomposite Hole-Injection Layer in Polymer Light-Emitting Diodes

We report on effects of doping graphene in poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate), PEDOT:PSS, as a PEDOT:PSS/graphene nanocomposite hole injection layer on the performance enhancement of polymer light-emitting diodes (PLEDs). Graphene oxides were first synthesized and then mixed in the PEDOT:PSS solution with specifically various amounts. Graphenes were reduced in the PEDOT:PSS matrix through thermal reduction. PLED devices with hole-injection nanocomposite layer containing particular doping concentration were fabricated, and the influence of doping concentration on device performance was examined by systematically characterizations of various device properties. Through the graphene doping, the resistance in the hole-injection layer and the turn-on voltage could be effectively reduced that benefited the injection and transport of holes and resulted in a higher overall efficiency. The conductivity of the hole-injection layer was monotonically increased with the increase of doping concentration, performance indices from various aspects, however, did not show the same dependence because faster injected holes might alter not only the balance of holes and electrons but also their combination locations in the light-emitting layer. Results show that optimal doping concentration was the case with 0.03 wt% of graphene oxide.

Effective Reinforcement of Graphene in Poly (vinyl alcohol) Nanocomposites at Low Loading via Enhanced Interfacial Interaction

The graphene/poly(vinyl alcohol) nancomposites with enhanced filler-matrix interfacial interaction were fabricated via water-blending partially reduced graphene oxide (PRGO) and poly(vinyl alcohol)(PVA). The nanocomposites were characterized by X-ray Diffraction(XRD), Fourier transform infrared spectroscopy(FTIR), Scanning Electron Microscopy(SEM), thermogravimetry(TG). The results showed that the graphene nanosheets were homogeniously dispersed in the PVA matrix and enhanced interfacial adhesion was greatly enhanced due to new covalent linkage and hydrogen-bonding between graphene and PVA backbone. The mechanical and thermal properties of the nanocomposites were significantly improved at low graphene loadings. An 116% increase in tensile strength and a 19°C improvement of onset thermal degradation temperature were achieved by the addition of only 0.8 wt% graphene.