Electrical and mechanical properties of PMMA/reduced graphene oxide nanocomposites prepared via in situ polymerization

We report the effect of filler incorporation techniques on the electrical and mechanical properties of reduced graphene oxide (RGO)-filled poly(methyl methacrylate) (PMMA) nanocomposites. Composites were prepared by three different techniques, viz. in situ polymerisation of MMA monomer in presence of RGO, bulk polymerization of MMA in presence of PMMA beads/RGO and by in situ polymerization of MMA in presence of RGO followed by sheet casting. In particular, the effect of incorporation of varying amounts (i.e. ranging from 0.1 to 2 % w/w) of RGO on the electrical, thermal, morphological and mechanical properties of PMMA was investigated. The electrical conductivity was found to be critically dependent on the amount of RGO as well as on the method of its incorporation. The electrical conductivity of 2 wt% RGO-loaded PMMA composite was increased by factor of 10⁷, when composites were prepared by in situ polymerization of MMA in the presence of RGO and PMMA beads, whereas, 10⁸ times increase in conductivity was observed at the same RGO content when composites were prepared by casting method. FTIR and Raman spectra suggested the presence of chemical interactions between RGO and PMMA matrix, whereas XRD patterns, SEM and HRTEM studies show that among three methods, the sheet-casting method gives better exfoliation and dispersion of RGO sheets within PMMA matrix. The superior thermal, mechanical and electrical properties of composites prepared by sheet-casting method provided a facile and logical route towards ultimate target of utilizing maximum fraction of intrinsic properties of graphene sheets.     

One-step synthesis of conductive graphene/polyaniline nanocomposites using sodium dodecylbenzenesulfonate: preparation and properties

The preparation of conducting graphene/polyaniline–sodium dodecylbenzenesulfonate (PANI–SDBS) nanocomposites using synthesised graphene as the starting material is successfully conducted in the present study. The effect of the anionic surfactant SDBS on the properties of the graphene/PANI–SDBS nanocomposites is studied. The structure and morphology of the synthesised nanocomposites are characterised by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–vis) spectrophotometry, X-ray diffraction and atomic force microscopy (AFM). The electrical conductivity properties of the resulting nanocomposites are determined using a resistance meter measurement system. The FESEM and TEM images reveal that the addition of SDBS surfactant to the PANI transforms the nanofibers of the PANI to a nanosphere morphology of PANI–SDBS. FTIR and UV–vis studies reveal that the conductive graphene/PANI–SDBS nanocomposites are successfully synthesised. AFM characterisation shows that the addition of graphene reduces the root mean square roughness of the surface of the PANI. The electrical conductivity and thermal stability of the PANI are improved after the introduction of SDBS. The nanocomposites containing a 5 wt% graphene loading exhibit the highest electrical conductivity of 2.94?×?10^?2 S/cm, which is much higher than that of PANI (9.09?×?10^?6 S/cm).     

An investigation on the effect of sintering mode on various properties of copper-graphene metal matrix composite

The present work investigates the effect of sintering mode and graphene addition on the microstructural, mechanical and electrical properties of copper–graphene metal matrix composites reinforced with varying amounts (0.9, 1.8, 2.7 and 3.6 vol%) of graphene particles fabricated through powder metallurgy route. Sintering was carried out at 900 °C in 95%N₂-5%H₂ (forming gas) atmosphere with a heating rate of 5°/min for conventional and 20 °C/min for microwave with a holding time of 60 min in both cases. All the composites were found to couple well with microwave field and had resulted in 63% reduction in the processing cycle time as compared to the conventional process. Micro-structural analysis revealed the homogeneous distribution of graphene in copper matrix. Copper-graphene composites exhibited excellent wear resistance due to higher hardness and excellent lubricating nature of graphene. It was observed that porosity has a significant effect on the electrical conductivity values.     

Characterization and properties of in situ emulsion polymerized poly(methyl methacrylate)/graphene nanocomposites

Poly(methyl methacrylate) (PMMA)/graphene nanocomposites were prepared by in situ emulsion polymerization. Raman and Fourier transform infrared spectra showed that PMMA polymer contained partially reduced graphite oxide. Dynamic mechanical analysis and differential scanning calorimetry analysis showed that graphene in the PMMA matrix acted as reinforcing filler; it enhanced the storage moduli and glass transition temperatures of the nanocomposites. Thermogravimetric analysis showed that the thermal stability of the nanocomposites increased by ca. 35 °C. The electrical conductivity of nanocomposite with 3 wt.% graphite oxide was 1.5 S m⁻¹ at room temperature.     

Enhanced electrical and thermal conductivity of modified poly(acrylonitrile-co-butadiene)-based nanofluid containing functional carbon black-graphene oxide

Solution refluxing and high-pressure homogenization technique were reported for synthesizing nanofluids based on modified poly(acrylonitrile-co-butadiene) (M-PANB) as base fluid and carbon black (CB)/carbon black-graphene oxide (CB-GO) as filler. The physiochemical properties were studied to analyze the structure, morphology, thermal and electrical conductivity. FTIR analysis corroborated the structure of CB-GO nanobifiller and nanocomposite. Microstructure analysis of M-PANB/CB-GO revealed good dispersion of CB-GO nanosheets, while CB series showed granular distribution. XRD studies confirmed amorphous structure of M-PANB/CB-GO nanocomposite. Thermal conductivity of nanofluid was found to increase upto 1.41 W/mK for 10 wt.% CB-GO loading and electrical conductivity was increased to 2.5 × 10^?3 Scm^?1.     

Enhancement of thermal and electrical conductivities of cyanoacrylate by addition of carbon based nanofillers

Nanocomposites with addition of graphite nanoparticles, multi-walled carbon nanotubes (MWCNTs), and graphene in cyanoacrylate from 0.1 to 0.5 or 0.6 vol% were fabricated. The influences of morphology towards thermal and electrical conductivities of cyanoacrylate nanocomposites were studied. Microstructure based on field emission scanning electron microscopy and transmission electron microscopy images indicated that nanofillers have unique morphologies which affect the thermal and electrical conductivities of nanocomposites. The maximum thermal conductivity values were measured at 0.3195 and 0.3500 W/mK for 0.4 vol% of MWCNTs/cyanoacrylate and 0.5 vol% of graphene/cyanoacrylate nanocomposite, respectively. These values were improved as high as 204 and 233% as compared with the thermal conductivity of neat cyanoacrylate. Nanocomposites with 0.2 vol% MWCNTs/cyanoacrylate fulfilled the requirement for ESD protection material with surface resistivity of 6.52?×?10⁶ Ω/sq and volume resistivity of 6.97?×?10⁹ Ω m. On the other hand, 0.5 vol% MWCNTs/cyanoacrylate nanocomposite can be used as electrical conductive adhesive. Compared with graphene and graphite nanofillers, MWCNTs is the best filler to be used in cyanoacrylate for improvement in thermal and electrical conductivity enhancement at low filler loading.     

Supercapacitive performance of chemically synthesized polypyrrole thin films: effect of monomer to oxidant ratio

Polypyrrole (PPY) thin films with different PPY monomer to ammonium peroxidisulphate (APS) oxidant molar ratios have been synthesized using simple and inexpensive chemical oxidative polymerization method. An interrelation between the monomer to oxidant molar ratio, morphology and supercapacitive performance of PPY thin films is studied. Initial polymerization conditions strongly affect the morphology and electrical properties of PPY thin films. Thermo-gravimetric and differential scanning calorimetric curves show the thermal stability of PPY up to 483 K. The supercapacitive performance of PPY films is studied using cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy techniques. In the present work, PPY films deposited with 0.1:0.2 monomer to oxidant molar ratio (pyrrole:APS) show maximum specific capacitance of 754 F g^?1 in 1 M H₂SO₄ electrolyte at the scan rate 5 mV s^?1 in potential window of ?0.4 to +0.6 V/SCE.     

Conductivity improvement of silver flakes filled electrical conductive adhesives via introducing silver–graphene nanocomposites

In this study, silver–graphene nanocomposites (SGNs) were successfully prepared by spontaneous reduction of silver ions and graphene oxide. Silver nanoparticles (about 30 nm) with narrow size distribution were distributed randomly on the surface of graphene. Different amounts of SGNs were introduced into silver flakes filled electrical conductive adhesives (ECAs) to study the effect of SGNs on the properties of the ECAs. The results showed that the volume resistivity of the ECAs decreased first and then increased with the increase of weight ratios of SGNs to silver flakes. While the weight ratio of SGNs to silver flakes was 20:80 (%), the resistivity reached the lowest value of 2.37 × 10^?4 Ω cm. The lap shear strength decreased with the increase of the content ration of SGNs. And when the weight ratio of SGNs to silver flakes was 20:80 (%), the lap shear strength of ECA was about 10 MPa. According to the thermogravimetric analysis, the addition of SGNs can cause a slight decrease in the thermal stability of the ECA. In summary, SGNs are the promising candidates for the conductivity improvement of silver flakes filled electrical conductive adhesives.     

Topological Design of Ultrastrong and Highly Conductive Graphene Films

Nacre‐like graphene films are prepared by evaporation‐induced assembly of graphene oxide dispersions containing small amounts of cellulose nanocrystal (CNC), followed by chemical reduction with hydroiodic acid. CNC induces the formation of wrinkles on graphene sheets, greatly enhancing the mechanical properties of the resultant graphene films. The graphene films deliver an ultrahigh tensile strength of 765 ± 43 MPa (up to 800 MPa in some cases), a large failure strain of 6.22 ± 0.19%, and a superior toughness of 15.64 ± 2.20 MJ m^?3, as well as a high electrical conductivity of 1105 ± 17 S cm^?1. They have a great potential for applications in flexible electronics because of their combined excellent mechanical and electrical properties.     

Designed fabrication of hierarchical porous carbon nanotubes/graphene/carbon nanofibers composites with enhanced capacitive desalination properties

Carbonaceous materials, one of the most important electrode materials for sea water desalination, have attracted tremendous attention. Herein, we develop a facile and effective two-step strategy to fabricate hierarchical porous carbon nanotubes/graphene/carbon nanofibers (CNTs/G/CNFs) composites for capacitive desalination application. Graphite oxide (GO), Ni²⁺, and Co²⁺ are introduced into polyacrylonitrile (PAN) nanofibers by electrospinning method. During the annealing process, the PAN nanofibers are carbonized into CNFs felt, while the CNTs grow in situ on the surface of CNFs and graphite oxide are reduced into graphene simultaneously. Benefiting from the unique hierarchical porous structure, the as-prepared CNTs/G/CNFs composites have a large specific surface area of 223.9 m² g^?1 and excellent electrical conductivity. The maximum salt capacity of the composites can reach to 36.0 mg g^?1, and the adsorbing capability maintains a large retention of 96.9% after five cycles. Moreover, the effective deionization time of the CNTs/G/CNFs composites lasts more than 30 min, much better than the commercial carbon fibers (C-CFs) and graphene/carbon nanofibers (G/CNFs) composites. Results suggest that the designed hierarchical porous CNTs/G/CNFs architecture could enhance the capacitive desalination properties of electrode materials. And the possible adsorption mechanism of the novel electrode materials is proposed as well.     

Conductive,self-cleaning,and short-circuit proof multi-functional graphene aerogel composite fibers

This work reports the superior properties of flexible multi-functional composite fibers based on graphene aerogel fibers. With the addition of phase change materials, the graphene aerogel fibers were synthesized by wet spinning and supercritical drying. The phase change materials can improve the structural uniformity and thermal stability of the composite fibers. The fibers coated with polydimethylsiloxane and fluorocarbon can respond to various external stimuli (e.g., electrons, photons, and heat), as well as have excellent properties of shape compliance, self-cleaning, and insulated surfaces. After coating fluorocarbon, the maximum water contact angle of graphene aerogel fibers increases from 132.18° to 151.77°. It is worth mentioning that adding an insulation layer of polydimethylsiloxane avoids the high-temperature problem caused by the short circuit of graphene aerogel fibers. The short-circuit temperature of graphene aerogel fibers is as high as 65 °C, while that of the composite fiber is only 41.5 °C after coating with polydimethylsiloxane. The temperature of graphene aerogel fibers with polyethylene glycol can increase to 39.3 °C under simulated sunlight. In addition, graphene aerogel fibers have excellent electrical conductivity (4.85?×?10³ S m^?1) at 300 K. After coating with polyethylene glycol, its electrical conductivity is still as high as 2.95?×?10³ S m^?1. The good electrical conductivity makes the aerogel fibers have promising application in advanced wearable systems.

     

Intumescent flame retardant polyurethane/reduced graphene oxide composites with improved mechanical, thermal, and barrier properties

Intumescent flame retardant polyurethane (IFRPU) composites were prepared in the presence of reduced graphene oxide (rGO) as synergism, melamine, and microencapsulated ammonium polyphosphate. The composites were examined in terms of thermal stability (both under nitrogen and air), electrical conductivity, gas barrier, flammability, mechanical, and rheological properties. Wide-angle X-ray scattering and scanning electron microscopy indicated that rGO are well-dispersed and exfoliated in the IFRPU composites. The limiting oxygen index values increased from 22.0 to 34.0 with the addition of 18 wt% IFR along with 2 wt% rGO. Moreover, the incorporation of rGO into IFRPU composites exhibited excellent antidripping properties as well as UL-94 V0 rating. The thermal stability of the composites enhanced. This was attributed to high surface area and good dispersion of rGO sheets induced by strong interactions between PU and rGO. The oxygen permeability, electrical, and viscoelasticity measurements, respectively, demonstrated that rGO lead to much more reduction in the gas permeability (by ~90 %), high electrical conductivity, and higher storage modulus of IFRPU composites. The tensile strength, modulus, and shore A remarkably improved by the incorporation of 2.0 wt% of rGO as well.     

Graphene/PANI hybrid film with enhanced thermal conductivity by in situ polymerization

Heat dissipation in time is essential for long-term reliability of electrical devices. Graphene, with superior thermal conductivity and excellent flexibility, exhibits a potential to substitute currently used graphite film for thermal management. In this work, a free-standing film with enhanced thermal conductivity and better flexibility was achieved by a facile and environmentally friendly in situ polymerization. The ‘molecular welding’ strategy was introduced for preparation of graphitized graphene oxide/polyaniline (gGO/PANI) hybrid film, and the uniformly distributed PANI, serving as a solder, connected adjacent graphene sheets and filled in air voids of GO films. Scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction and Raman spectroscopy were used to determine the structure of PANI and the interaction between GO and PANI. The in-plane thermal conductivity of gGO/PANI film is enhanced by 38% to 1019.7 ± 0.1 W m^?1 K^?1 with addition of 12 wt% PANI, compared with that of pristine gGO film. Besides, the gGO/PANI film shows better flexibility than gGO film after 180° bending for 500 times.     

3D-assembled graphene–LiFePO4 frameworks with enhanced electrochemical performance

In the on-going development of power sources and energy-storage devices, achieving both high power and large energy capacity with a high discharge rate is still a great challenge. In this paper, three dimension assembled graphene–LiFePO₄ (G–LFP) composites were prepared by one-step hydrothermal method. LiFePO₄ (LFP) particles became smaller and were dispersed uniformly on the graphene sheets after compositing with graphene. Compared to the pristine LFP, the electrochemical properties of the G–LFP are greatly improved, especially the rate capability and the cyclic performance. At 10 C, the G–LFP holds nearly 80 % of the initial capacity and has a flat voltage platform, while for the LFP, its capacity drops down to 65 % and its voltage platform is not noticeable. After 600 cycles at 10 C, the specific capacity of the G–LFP decreases from 135 to 125 mA hg^?1 with a capacity loss of 5.1 %, while it drops from 105  to 86  mA hg^?1 with a capacity loss of 30 % for the LFP. The reason for the improvement of the electrochemical performances could be ascribed to the introduction of graphene which enhances the conductivity and diminishes the LFP size which improves the diffusion of lithium ions.     

Preparation of flexible graphene@SnO2 composite fiber via in situ chemical reduction and self-assembly method

A facile in-situ chemical reduction and self-assembly method was developed to prepare graphene and tin oxide (graphene@SnO₂) composite fibers. The obtained graphene@SnO₂ fiber exhibits excellent tensile mechanical performance with high mechanical strength and superior plastic deformation (mechanical strength up to 65 MPa with an ultimate elongation about 7%). The electrical resistance of the graphene@SnO₂ fiber holds steady and has a negligible change in either the bent or straight status over 100 cycles. In the prepared composite fibers, SnO₂ nanoparticles with sizes of 3–5 nm homogeneously dispersed on the graphene sheets. The conductivity of GF@SnO₂ was about 6.0–2.5 S/cm with the increase content of Sn⁴⁺ due to the tin oxide semiconductor doping.     

Characterization of epoxy functionalized graphite nanoparticles and the physical properties of epoxy matrix nanocomposites

This work presents a novel approach to the functionalization of graphite nanoparticles. The technique provides a mechanism for covalent bonding between the filler and matrix, with minimal disruption to the sp² hybridization of the pristine graphene sheet. Functionalization proceeded by covalently bonding an epoxy monomer to the surface of expanded graphite, via a coupling agent, such that the epoxy concentration was measured as approximately 4 wt.%. The impact of dispersing this material into an epoxy resin was evaluated with respect to the mechanical properties and electrical conductivity of the graphite–epoxy nanocomposite. At a loading as low as 0.5 wt.%, the electrical conductivity was increased by five orders of magnitude relative to the base resin. The material yield strength was increased by 30% and Young’s modulus by 50%. These results were realized without compromise to the resin toughness.     

Effect of Multiwalled Carbon Nanotubes on the Conductivity and Swelling Properties of Porous Polyacrylamide Hydrogels

Multiwalled carbon nanotubes (MWCNTs) were added to polyacrylamide (PAM) hydrogels in different proportions to tune their electrical and mechanical properties. The choice of MWCNTs as a reinforcement is justified by the fact that these are highly conducting, fairly stable and flexible particles. A series of MWCNT/PAM hydrogels were prepared by freezing method. The characteristic absorption peaks at 1480 and 1213 cm^?1 in the FTIR spectra reveal that MWCNTs are embedded in the PAM hydrogels. Powder x-ray diffractograms and thermogravimetric analysis (TGA) images show that the MWCNT/PAM hydrogels are crystalline, more thermally stable and have a higher electrical conductivity than a traditional PAM hydrogel. Scanning electron micrographs reveal about reduced pore size, homogeneous and denser texture. The swelling properties of all these hybrid hydrogels were found to be better than those of the parent PAM hydrogel. The Li–Tanaka equation was employed to produce the swelling parameters. The diffusion coefficients (D _c ) of PAM hydrogel is 10 times higher than the literature value. 0.8% MWCNTs reinforced PAM hydrogel has excellent τ_c and electrical conductivity (0.76 mS/cm) with improvements in all properties. Lower D _c of 0.8% MWCNTs/PAM hydrogel reveal that extent of crosslinking is much important than density of the system for a better collective diffusion of the respective solvent.     

The role of ferrocene on the enhancement of the mechanical and electrochemical properties of coal tar pitch-based carbon foams

In the present study, the role of ferrocene on mechanical and electrochemical properties of coal tar pitch (CTP)-based carbon foam (CFoam) was investigated. The different weight fractions of ferrocene were mixed with CTP and foam was developed from the mixture of CTP and ferrocene by sacrificial template technique. Before the characterisation of foams, it was heat treated at 1000 and 2500 °C in inert atmosphere. It was observed that the bulk density of CFoam increased with the increase in ferrocene content and as a consequence of an improvement of structural properties of the CFoam. The compressive strength increased by 60 and 62 % of 1000 and 2500 °C heat-treated CFoam with 5 wt% of ferrocene content. However, higher content of ferrocene had negative effect on the compressive strength. The electrical and thermal conductivity increased with the increasing ferrocene content and as a result of catalytic graphitization of ligaments in CFoam. The current density increased with the increasing electrical conductivity of CFoam, and it was 102 mA/cm² at 10 wt% ferrocene. The specific capacitance was 865 μF/cm² at scan rate 10 mV/s, which was due to the higher conductivity and surface area of CFoam. This demonstrated that ferrocene could be useful for improving the properties of CFoam.     

Ternary polyurethane nanocomposites with remarkable electrical conductivity

ABSTRACT

A series of polyurethane composites with constant 5 wt-% loading of 2D graphene nanosheets and varying levels of 1D silver nanowire (AgNW) were prepared by a solution mixing method. The electrical conductivity of composite films was measured using a 4-point probe method. An extremely high conductivity of 3,657?S?cm^–1 was achieved with a polyurethane composite containing 25?wt-% AgNW and 5?wt-% graphene, confirming that a combination of AgNW and graphene is very effective in producing conducting pathways to achieve high conductivity. The incorporation of AgNW and graphene was confirmed by scanning electron microscopy and energy dispersive spectrometry. Additionally, the results of tensile strengths and thermogravimetric analysis showed that the as-prepared polyurethane composite films possessed good mechanical properties and stable thermal properties.     

Graphene and carbon black filled conductive nanocomposite films for heating element applications

Graphene has ultra-high electrical and thermal conductivity, which makes graphene as the most encouraging fillers for thermally conductive composites. Graphene and/or carbon black filled conductive polymer composite (CPC) films used as heating element are smarter than the traditional heating elements due to less environmental pollution, ease of application on many surfaces and possess the merits of lightweight. In this study, we investigated mainly the production, characterization and industrial application of graphene/carbon black reinforced styrene acrylic copolymer emulsion matrix composite films deposited on polyvinyl chloride for flexible heating element. After that, the films were dried at room temperature for 24 h in air. Structural and surface properties of the CPC films were characterized by X-ray diffraction and scanning electron microscopy. Temperature, time and voltage relation of the produced composite films were investigated. Heating and electrical properties of the CPC films were determined by using a thermal camera and 4-point probe measurement system, respectively. The electrical resistivity of the CPC films decreases from ~?10⁸ to 10¹ Ω cm with increasing the filler content or using a combination of two fillers. Graphene and carbon black filled conductive polymer composites to be considered as candidates for flexible heating element applications exhibited good electrical and heating properties thanks to synergistic effect of fillers.