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.     

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).     

Controlling the shapes and electrical conductivities of polyaniline-wrapped MWCNTs

Nanocomposites of carbon nanotubes with polyaniline (PANI) constitute promising conducting nanomaterials, due to their ease of synthesis, electrical conductivity, and environmental stability. Variously shaped multi-walled carbon nanotube (MWCNT)-PANI nanocomposites were synthesized, and their electrical conductivities were compared. This study shows that new synthetic methods were able to control the shapes and electrical conductivities of MWCNT-PANI nanocomposites. The shapes of the MWCNT-PANI nanocomposites were changed by altering the reactant concentrations and the sequence of adding the initiator, ammonium persulfate (APS). The use of surface-modified MWCNTs instead of pristine MWCNTs is also an important factor determining the shapes of the nanocomposites. It was found that the electrical conductivity is strongly dependent on the shape and PANI content. The electrical conductivities of the MWCNT-PANI nanocomposites increased when the PANI/MWCNT ratio was decreased. The nanocomposites were characterized via field emission transmission electron microscopy (FE-TEM), Fourier-transform infrared (FT-IR) and ultraviolet-visible (UV-Vis) spectroscopy, and elementary analysis of the MWCNT-PANI nanocomposites.     

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.     

Polyaniline–sodium montmorillonite clay nanocomposites: effect of clay concentration on thermal, structural, and electrical properties

A simple and facile method was used to synthesize polyaniline (PANI) nanocomposites with sodium montmorillonite clay (Na⁺-MMT) using in situ intercalative oxidative polymerization. Aniline was admixed with Na⁺-MMT at various concentrations, keeping the aniline monomer in the reaction mixture constant. The intercalation of PANI into the clay layers was confirmed by X-ray diffraction studies in conjugation with electron microscope techniques and FTIR spectra, particularly by the narrowing of the Si–O stretching vibration band confirmed the interaction between PANI and the clay. The employed route offers the possibility to improve the thermal properties with simultaneously controlled electrical conductivity. Thermal studies show an improved thermal stability of the nanocomposites relative to the pure PANI. Depending on the loading of the clay, the room temperature conductivity values of these nanocomposites varied between 2.0 × 10⁻⁴ and 7.4 × 10⁻⁴ S cm⁻¹, with the maximum at 44 wt% PANI concentration. The decrease of electrical conductivity at high PANI concentration was ascribed to the decrease of the structural ordering of PANI in the nanocomposite.     

Graphene oxide reinforced polyimide nanocomposites via in situ polymerization

Graphene oxide (GO) reinforced polyimide nanocomposites were synthesized by in situ polymerization of monomers in the presence of GO sheets dispersed in N,N-Dimethylacetamide (DMAc). The functional groups (e.g., hydroxyl, epoxide, and carboxyl groups) associated with the GO make GO excellent dispersion in the organic solvent, which benefits the subsequent in situ polymerization. This process enabled uniform dispersion of GO sheets in the polymer matrix. The resultant GO-polyimide nanocomposite films were studied by tensile test, TGA and SEM. The results showed that the GO sheets incorporated in the polymer matrix exhibited a layer-aligned structure without destruction of the thermal stability of the polymer matrix, and a loading of GO (10 wt%) resulted in a significant enhancement in elastic modulus (86.4%).     

Graphene oxide-filled conducting polyaniline composites as methanol-sensing materials

Polyaniline/graphene oxide (PANI/GO) composites were prepared by polymerization of aniline monomer in the presence of GO under acidic conditions. The synthesized samples were characterized by Fourier transform infra red spectroscopy, ultraviolet–visible absorption, Raman spectroscopy, X-ray diffraction, scanning electron microscopy, transmission electron microscopy and thermogravimetric analysis. The direct current electrical conductivity of the composite was calculated by a four-probe technique. It is found that the conductivity dramatically increased to 241 S m^?1 for PANI/GO (5 wt%) composite at 110 °C compared to pure PANI (7.5 S m^?1). The composite material was investigated as a methanol vapour sensor and compared with pure PANI. The methanol-sensing characteristics of the prepared composite was monitored by measuring the change in electrical resistivity on exposure to methanol vapour at different concentrations. The resistivity of PANI increases on exposure to methanol vapour because of strong hydrogen bonding between methanol with the polymer chain. A density functional theory study was carried out to verify the proposed concept of hydrogen bonding between the polymer chains and methanol. The presence of GO in PANI/GO composite increases the sensitivity towards methanol as compared with the pure PANI.     

A new strategy to prepare polyethylene nanocomposites by using a late-transition-metal catalyst supported on AlEt3-activated organoclay

A new strategy for in situ polymerization was developed to prepare the polyethylene nanocomposites, in which a nickel α-diimine late-transition-metal catalyst supported on the AlEt₃-activated organoclay was adopted to initiate the ethylene polymerization and to provide the reinforcement materials after the polymerization. It was found that the polymerization conditions such as reaction time, Al/Ni molar ratio, and reaction temperature affected the polymerization activity and the clay loading. The nanoscale dispersion of the clay layers in the polyethylene matrix was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). From the thermogravimetric analyses (TGA), it was found that the decomposition temperature of the nanocomposite with the organoclay of 11.91 wt% could be 46.8 °C higher than that of pure polyethylene when 30% weight loss was selected as a measuring point, showing enhanced thermal oxidation stability of this kind of polyolefin nanocomposites.     

Preparation and characterization of conducting polyaniline/silica nanosheet composites

A series of polyaniline/silica nanosheet composites (PANI/SNS) with different contents of the silica nanosheets derived from vermiculite via acid-leaching were prepared via the in situ chemical oxidation polymerization. The PANI/SNS composites were characterized with Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), and electrical conductivity measurement. It is interesting that the electrical conductivities of the PANI/SNS composites increased with the increasing of the contents of the silica nanosheets added because of the moisture absorption. It was confirmed by the TGA analysis.     

Thermal and electrical conductivity of Al(OH)<Subscript>3</Subscript> covered graphene oxide nanosheet/epoxy composites

Al(OH)₃ functionalized graphene composites (Al–GO) were prepared using a simple sol–gel method. In this protocol, graphene oxide (GO) was prepared according to the Hummers method and functionalized to enhance its reactivity with aluminum isopropoxide by a LiAlH₄ treatment. The functionalized graphene sheets were characterized by X-ray photoelectron spectroscopy, field emission scanning electron microscopy, and transmission electron microscopy. These analyses confirmed that GO had been fabricated and the Al(OH)₃ layer could have a homogeneous distribution with large and dense coverage onto GO sheets. In addition, the thermal and electrical conductivity of the epoxy composites with GO and Al–GO fillers were measured. The thermal conductivities of the composites with graphene-based fillers were enhanced by the addition of fillers. In particular, the thermal conductivity of GO/epoxy composite containing 3 wt% was approximately two times higher than that of pure epoxy resin. In addition, the electrical conductivity of Al–GO embedded composites degenerated compared to GO composites.     

In situ thermal reduction of graphene oxide for high electrical conductivity and low percolation threshold in polyamide 6 nanocomposites

Electrically conductive and thermally stable polyamide 6 (PA 6) nanocomposites were prepared through one-step in situ polymerization of ε-caprolactam monomer in the presence of electrically insulating and thermally unstable graphene oxide (GO) nanosheets. These nanocomposites show a low percolation threshold of ∼0.41 vol.% and high electrical conductivity of ∼0.028 S/m with only ∼1.64 vol.% of GO. Thermogravimetric analysis and X-ray photoelectron spectroscopy results of GO before and after thermal treatment at the polymerization temperature indicate that GO was reduced in situ during the polymerization process. X-ray diffraction patterns and scanning electron microscopy observation confirm the exfoliation of the reduced graphene oxide (RGO) in the PA 6 matrix. The low percolation threshold and high electrical conductivity are attributed to the large aspect ratio, high specific surface area and uniform dispersion of the RGO nanosheets in the matrix. In addition, although GO has a poor thermal stability, its PA 6 nanocomposite is thermally stable with a satisfactory thermal stability similar to those of neat PA 6 and PA 6/graphene nanocomposite. Such a one-step in situ polymerization and thermal reduction method shows significant potential for the mass production of electrically conductive polymer/RGO nanocomposites.     

Effect of different carbon fillers and dopant acids on electrical properties of polyaniline nanocomposites

Electrically conducting nanocomposites of polyaniline (PANI) with carbon-based fillers have evinced considerable interest for various applications such as rechargeable batteries, microelectronics, sensors, electrochromic displays and light-emitting and photovoltaic devices. The nature of both the carbon filler and the dopant acid can significantly influence the conductivity of these nanocomposites. This paper describes the effects of carbon fillers like carbon black (CB), graphite (GR) and muti-walled carbon nanotubes (MWCNT) and of dopant acids like methane sulfonic acid (MSA), camphor sulfonic acid (CSA), hydrochloric acid (HCl) and sulfuric acid (H₂SO₄) on the electrical conductivity of PANI. The morphological, structural and electrical properties of neat PANI and carbon–PANI nanocomposites were studied using scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FT–IR), UV–Vis spectroscopy and the four-point probe technique, respectively. Thermogravimetric analysis (TGA) and X-ray diffraction (XRD) studies were also conducted for different PANI composites. The results show that PANI and carbon–PANI composites with organic acid dopants show good thermal stability and higher electrical conductivity than those with inorganic acid dopants. Also, carbon–PANI composites generally show higher electrical conductivity than neat PANI, with highest conductivities for PANI–CNT composites. Thus, in essence, PANI–CNT composites prepared using organic acid dopants are most suitable for conducting applications.     

Facile preparation,characterization and performance of noncovalently functionalized graphene/epoxy nanocomposites with poly(sodium 4-styrenesulfonate)

Graphene was noncovalently functionalized with poly(sodium 4-styrenesulfonate) (PSS) and then successfully incorporated into the epoxy resin via in situ polymerization to form functional and structural nanocomposites. The morphology and structure of PSS modified graphene (PSS-g) were characterized with transmission electron microscopy, X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy. The effects of PSS-g additions on tensile, electrical and thermal properties of the epoxy/graphene nanocomposites were studied. Noncovalent functionalization improved interfacial bonding between the epoxy matrix and graphene, leading to enhanced tensile strength and modulus of resultant nanocomposites. The PSS-g additions also enhanced electrical properties of the epoxy/PSS-g nanocomposites, resulting in a lower percolation threshold of 1.2 wt%. Thermogravimetric and differential scanning calorimetric results showed the occurrence of a two-step decomposition process for the epoxy/PSS-g nanocomposites.     

Fe(3)O(4)@Au/polyaniline multifunctional nanocomposites: their preparation and optical, electrical and magnetic properties

Fe(3)O(4)@Au/polyaniline (PANI) nanocomposites were fabricated by in situ polymerization in the presence of mercaptocarboxylic acid. The mercaptocarboxylic acid was used to introduce hydrogen bonding and/or electrostatic interaction; it acts as a template in the formation of Fe(3)O(4)@Au/PANI nanorods. The morphology and structure of the resulting nanocomposites were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy, x-ray diffraction and x-ray energy dispersion spectroscopy (EDS). It was found that the nanocomposites were rod-like with an average diameter of 153?nm, and they exhibited a core-shell structure. A UV-visible spectrometer, semiconductor parameter analyzer and vibrating sample magnetometer (VSM) were used to characterize the optical, electrical and magnetic properties of the Fe(3)O(4)@Au/PANI nanocomposites. It was interesting to find that these properties are dependent on the molar ratio of Au to Fe(3)O(4) when the molar ratio of Fe(3)O(4)@Au to PANI is fixed. The magnetic property of the Fe(3)O(4)@Au/PANI nanocomposite is very close to superparamagnetic behavior.     

Improved optical and electrical response in metal–polymer nanocomposites for photovoltaic applications

Hybrid nanocomposites based on polyethylene glycol (PEG) embedded with nanoscopic Ag particles were prepared by two distinct approaches: in situ and ex situ chemical processing routes. The effect of Ag loading on tailored optical and electrical responses in the two classes of metal–polymer nanocomposites (MPNs) was investigated. Transmission electron microscopy of the in situ MPN sample revealed core–shell-type combination comprising Ag nanoparticles lying at the core surrounded by polymeric (PEG) shell. On the other hand, ex situ MPNs exhibited dispersed phase microstructure with uneven distribution of Ag nanoparticles in the PEG matrix. Comparison of the thermal properties of in situ and ex situ MPNs confirmed that the MPN obtained through in situ process with 2 wt% of Ag contents displayed higher thermal stability (≈18%) relative to ex situ MPN of the same composition. The absorption spectrum confirmed clear, blue shift with enhanced band gap in the case of in situ MPN relative to its ex situ counterpart. The Ag–PEG nanocomposites prepared by both the processes exhibited metallic I–V response. Electrical transport observed in terms of resistivity variation with temperature confirmed typical semiconducting behavior in the composite phase in sharp contrast to the insulating property of the host PEG. A large decrease (≈65%) in activation energy was observed in the case of in situ MPN at higher loading of Ag possibly because of the higher mobility assisted by tunneling of charge carriers through polymeric spacers in the composite phase. The drastic improvement in optical and electrical responses of the nanocomposites indicated the suitability for photovoltaic and optoelectronic applications.     

Crystallization,mechanical performance and hydrolytic degradation of poly(butylene succinate)/graphene oxide nanocomposites obtained via in situ polymerization

Poly(butylene succinate) (PBS)/graphene oxide (GO) nanocomposites were fabricated via in situ polymerization with very low GO content (from 0.03 to 0.5 wt%). The microstructures of the nanocomposites were characterized with Raman spectroscopy, fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), sedimentation experiments and atomic force microscopy (AFM). The results showed that PBS chains have been successfully grafted onto GO sheets during in-situ polymerization, accompanied by the thermo-reduction from GO to graphene. The grafted GO displayed a great nucleating effect on PBS crystallization, resulting in largely improved crystallization temperature and decreased spherules size. A simultaneous enhancement in tensile strength and elongation was achieved for PBS/GO nanocomposites fiber. Meanwhile, increase in hydrolytic degradation rate was also observed for these nanohybrids. Our result indicates that using very low content GO is a simple way to achieve good dispersion yet with remarkable property enhancement for polymer/GO nanocomposites.     

Conducting nanocomposites of poly(N-vinylcarbazole) with single-walled carbon nanotubes

The in situ solid-state polymerization of N-vinylcarbazole (NVC) at an elevated temperature in the presence of single-walled carbon nanotubes (SWCNTs) leads to the formation of new types of composite materials, the morphology and properties of which were characterized by field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), and electrical property measurements. FTIR spectroscopy and XPS studies confirmed the ability of SWCNTs to initiate the in situ polymerization of NVC monomers. FE-SEM and TEM results showed the coating of the outer surfaces of SWCNTs by the PNVC hompolymer with separation of individual SWCNTs from the bundles. Thermogravimetric analysis revealed a moderate improvement in the thermal stability of the nanocomposites at a higher temperature region relative to the base polymer. The electrical conductivity of neat polymer dramatically improved in the presence of SWCNTs. For example, dc electrical conductivity increased from 10(-16)-10(-12) S x cm(-1) for neat PNVC to approximately 10(-6) S x cm(-1) for nanocomposite containing 9 wt% SWCNTs.     

Thermoelectric properties of porous multi-walled carbon nanotube/polyaniline core/shell nanocomposites

Porous polyaniline (PANI)-coated multi-walled carbon nanotube (MWNT) core/shell nanohybrids were fabricated through in situ polymerization and subsequently assembled into macroscopic composites. N(2) adsorption/desorption analysis indicated that the volume of nanopores increased significantly, which could make a significant contribution to phonon scattering. Thermal annealing was also carried out to improve the Seebeck coefficient of the as-produced nanocomposites. The optimal sample showed electrical conductivity of 14.1?S?cm(-1), a Seebeck coefficient of 79.8?μV K(-1) and thermal conductivity of 0.27?W?mK(-1), resulting in a highest figure of merit (ZT) of 0.01 at a very low loading of MWNTs (<1?wt%). These results will provide a potential direction to enhance thermoelectric performance of organic materials and also facilitate the application of organic materials in thermal energy harvesting or cooling.     

Synthesis and characterization of polyaniline nanorods/Ce(OH)3-Pr2O3/montmorillonite composites through reverse micelle template

Polyaniline (PANI) nanorods/Ce(OH)₃-Pr₂O₃/montmorillonite (MMT) nanocomposites were synthesized via in situ polymerization of aniline monomer through reverse micelle template (RMT) in the presence of montmorillonite and Ce(OH)₃, Pr₂O₃. In the experiment, sulphosalicylic acid was used as dopant, aniline was designated as oil phase and the aqueous solution comprising Ce³⁺ and Pr³⁺ as water phase. The nanocomposites were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) analysis, Fourier transform infrared (FT-IR) spectroscopy and thermogravimetry-differential thermal analysis (TG-DTA). The results showed that PANI nanorods were synthesized in the interlayer spaces of MMT with uniform spherical rare earth nanoparticles. The thermal stability of the nanocomposites prepared was enhanced drastically compared with pure polyaniline.     

Novel polyacrylonitrile/Na-MMT/silica nanocomposite: Co-incorporation of two different form nano materials into polymer matrix

Polyacrylonitrile (PAN)/Na-montmorillonite (Na-MMT)/SiO₂ nanocomposites were synthesized via in-situ emulsion polymerization. The X-ray diffraction (XRD) measurements and transmission electron microscopy (TEM) observations show that the Na-MMT layers were exfoliated in polymerization and the nano materials are well dispersed in the polymer matrix. The thermogravimetric analysis (TGA) suggests that co-incorporating Na-MMT and SiO₂ into the polymer matrix significantly enhances the thermal stability of the polymer. At same nano material loading, the PAN/Na-MMT/SiO₂ nanocomposites show superior thermal stability with respect to the PAN/Na-MMT and PAN/SiO₂ nanocomposites. The mechanical properties of the nanocomposites were also examined. It was found that the PAN/Na-MMT/SiO₂ nanocomposites exhibit considerably enhanced moduli compared with the PAN/Na-MMT and PAN/SiO₂ nanocomposites due to the synergistic reinforcing effect.