Electrically and thermally conductive elastomer/graphene nanocomposites by solution mixing

The greatest challenge in developing polymer/graphene nanocomposites is to prevent graphene layers stacking; in this respect, we found effective solution-mixing polymers with cost-effective graphene of hydrophobic surface. Since graphene oxide is hydrophilic and in need of reduction, highly conducing graphene platelets (GnPs) of ∼3 nm in thickness were selected to solution-mix with a commonly used elastomer – styrene–butadiene rubber (SBR). A percolation threshold of electrical conductivity was observed at 5.3 vol% of GnPs, and the SBR thermal conductivity enhanced three times at 24 vol%. Tensile strength, Young's modulus and tear strength were improved by 413%, 782% and 709%, respectively, at 16.7 vol%. Payne effect, an important design criteria for elastomers used in dynamic loading environment, was also investigated. The comparison of solution mixing with melt compounding, where the same starting materials were used, demonstrated that solution mixing is more effective in promoting the reinforcing effect of GnPs, since it provides more interlayer spacing for elastomer molecules intercalating and retains the high aspect ratio of GnPs leading to filler–filler network at a low volume fraction. We also compared the reinforcing effect of GnPs with those of carbon black and carbon nanotubes.     

Synthesis and interfacial properties of montmorillonite/polypyrrole nanocomposites

Montmorillonite/polypyrrole (MMT/PPy) nanocomposites were prepared by the in situ polymerization of pyrrole in the presence of MMT. The morphology of the MMT/PPy nanocomposites as examined by scanning electron microscopy differs slightly from that of the untreated MMT but markedly from that of polypyrrole. X-ray photoelectron spectroscopy (XPS) showed that the materials have MMT-rich surfaces, an indication that polypyrrole is essentially intercalated in the host clay galleries. The transmission electron microscopy showed, that the interlamellar spacing of the untreated MMT increased from 1.25 to 18.9 nm, when compared to nanocomposite MMT/10.8% PPy. Moreover, XPS highlighted the cation exchange of Na⁺ from montmorillonite by K⁺ (from the oxidant) and by the positively charged polypyrrole chains. Inverse gas chromatography indicated that the nanocomposites are high surface energy materials with a dispersive contribution to the surface energy reaching 200 mJ/m² at 150 °C, for a PPy loading of 21.4 wt%. The values of the MMT/PPy nanocomposites were correlated to the changes in the specific surface area of the MMT induced by the intercalation of polypyrrole.     

Preparation and characterization of coaxial halloysite/polypyrrole tubular nanocomposites for electrochemical energy storage

Halloysite nanotubes/polypyrrole (HNTs/PPy) nanocomposites with coaxial tubular morphology for use as electrode materials for supercapacitors were synthesized by the in situ chemical oxidative polymerization method based on self-assembled monolayer amine-functionalized HNTs. The HNTs/PPy coaxial tubular nanocomposites were characterized with transmission electron microscope (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), electrical conductivity measurement at different temperatures, cyclic voltammetry (CV), and galvanostatic charge-discharge measurements. The coaxial tubular nanocomposites showed their greatest conductivity at room temperature and a weak temperature dependence of the conductivity from 298 K to 423 K. A maximum discharge capacity of 522 F/g after correcting for the weight percent of the PPy phase at a current density of 5 mA cm⁻² in a 0.5 M Na₂SO₄ electrolyte could be achieved in a half-cell setup configuration for the HNTs/PPy composites electrode, suggesting its potential application in electrode materials for electrochemical capacitors.     

Synthesis and characterization of electrically conductive polyethylene-supported graphene films

We describe a simple mechanical approach for low-density polyethylene film coating by multilayer graphene. The technique is based on the exfoliation of nanocrystalline graphite (few-layer graphene) by application of shear stress and allows to obtain thin graphene layers on the plastic substrate. We report on the temperature dependence of electrical resistance behaviors in films of different thickness. The experimental results suggest that the semiconducting behavior observed at low temperature can be described in the framework of the Efros-Shklovskii variable-range-hopping model. The obtained films exhibit good electrical conductivity and transparency in the visible spectral region.

PACS

72.80.Vp; 78.67.Wj; 78.66.Qn; 85.40.Hp     

Solvothermal synthesis of SnO2/graphene nanocomposites for supercapacitor application

A facile solvent-based synthesis route based on the oxidation–reduction reaction between graphene oxide (GO) and SnCl₂·2H₂O has been developed to synthesize SnO₂/graphene (SnO₂/G) nanocomposites. The reduction of GO and the in situ formation of SnO₂ nanoparticles were achieved in one step. Characterization by X-ray diffraction (XRD), ultraviolet-visible (UV–vis) absorption spectroscopy, Raman spectroscopy, and field emission scanning electron microscopy (FESEM) confirmed the feasibility of using the solvothermally treated reaction system to simultaneously reduce GO and form SnO₂ nanoparticles with an average particle size of 10 nm. The electrochemical performance of SnO₂/graphene showed an excellent specific capacitance of 363.3 F/g, which was five-fold higher than that of the as-synthesized graphene (68.4 F/g). The contributing factors were the synergistic effects of the excellent conductivity of graphene and the nanosized SnO₂ particles.     

Potentiostatically deposited polypyrrole/graphene decorated nano-manganese oxide ternary film for supercapacitors

A simple method based on potentiostatic polymerization was developed for the preparation of ternary manganese oxide-based nanocomposite films. The ternary nanocomposites, which were characterized using x-ray diffraction spectroscopy and x-ray photoelectron spectroscopy, showed that the manganese oxide within the film consisted of MnO₂ and Mn₂O₃. Electrochemical measurements showed that the ternary nanocomposite electrode exhibited high specific capacitance (up to 320.6 F/g), which was attributed to the morphology of a polypyrrole/graphene/manganese-oxide (PPy/GR/MnO_x) ternary nanocomposite. The experimental approach maximized the pseudocapacitive contribution from redox-active manganese oxide (MnO_x) and polypyrrole (PPy), as well as the electrochemical double layer capacitive (EDLC) characteristic from graphene (GR) sheets. Long cyclic measurements indicated that the specific capacitance of the ternary nanocomposite film could retain 93% of its initial value over 1000 charge/discharge cycles, in the potential range of −0.2 to 0.7 V versus silver/silver chloride electrode (Ag/AgCl).     

Synthesis and properties of magnetite/polypyrrole core–shell nanocomposites and polypyrrole hollow spheres

In this work a new route for preparation of core–shell nanoparticles composed of an iron oxide core and a polypyrrole (PPy) shell is explored. During the preparation procedure the initially formed iron(0) core is converted to magnetite. It is demonstrated, that the magnetite cores can completely be dissolved by reaction with acid. Furthermore the dissolution of iron oxide cores by electrolysis also is possible. The resulting PPy hollow spheres as well as the core–shell nanocomposites are electrochemically active.     

Graphene/polypyrrole nanocomposites with high negative permittivity and low dielectric loss tangent

Graphene (GNs)/ polypyrrole (PPy) nanocomposites with different content of GNs prepared by in-situ polymerization possess negative permittivity in the range of test frequency. Importantly, the GNs/PPy nanocomposites also have low dielectric loss tangent. ATR and XRD tests showed that no significant change in chemical bond and crystallization is found in GNs/PPy nanocomposites. SEM analysis indicated that GNs/PPy nanocomposites form different morphologies with the increase of GNs content. The negative permittivity of GNs/PPy nanocomposites is mainly caused by the plasmon resonance of the free electrons. The variation of resistivity and negative permittivity are basically consistent, which reflects that the good conductivity of the nanocomposites is attribute to the plasmon resonance of free electrons. The moderate addition of GNs is beneficial to the development of permittivity to a great negative value and decrease the dielectric loss tangent. The negative permittivity is up to ?1.226?×?10⁵ and the dielectric loss tangent is reduce to 0.32 in GNs/PPy nanocomposites with 10?wt% GNs content. The negative permittivity and the low dielectric loss tangent in GNs/PPy nanocomposites is achieved in a wider frequency range 1–1000?MHz.     

Vertically aligned,polypyrrole encapsulated MoS2/graphene composites for high-rate LIBs anode

Ultrathin MoS₂ nanosheets were vertically anchored on the reduced graphene oxide (MoS₂/rGO) via hydrothermal method. To further engineering the surface conductivity, ultrathin polypyrrol (PPy) layer was coated on the MoS₂/rGO composite via in situ polymerization to form a bi-continuous conductive network with a sandwich-like structure. The graphene nanosheets and the PPy coating can facilitate the electrons transfer rate, while the ultrathin MoS₂ nanosheets can enhance the utilization efficiency of the active materials. The obtained MoS₂/rGO-10 composite exhibits high reversible specific capacity (970?mAh?g^?1 at 0.1?A?g^?1) and rate capability (capacity retention of 64% at 3.2?A?g^?1). Moreover, the PPy@MoS₂/rGO hybrids reveal lower specific capacity but better rate capability, and a “trade-off” effect between electrons and ions transfer resistance was observed. This easy-scalable PPy surface conductivity engineering strategy may be applied in the preparation of high-performance LIBs active materials.     

Electrically conductive polyethylene terephthalate/graphene nanocomposites prepared by melt compounding

Graphene nanosheets were prepared by complete oxidation of pristine graphite followed by thermal exfoliation and reduction. Polyethylene terephthalate (PET)/graphene nanocomposites were prepared by melt compounding. Transmission electron microscopy observation indicated that graphene nanosheets exhibited a uniform dispersion in PET matrix. The incorporation of graphene greatly improved the electrical conductivity of PET, resulting in a sharp transition from electrical insulator to semiconductor with a low percolation threshold of 0.47 vol.%. A high electrical conductivity of 2.11 S/m was achieved with only 3.0 vol.% of graphene. The low percolation threshold and superior electrical conductivity are attributed to the high aspect ratio, large specific surface area and uniform dispersion of the graphene nanosheets in PET matrix.