Electromagnetic interference shielding behavior of polyaniline/graphite composites prepared by in situ emulsion pathway

Polyaniline–graphite composites were prepared via in situ emulsion pathway, using different weight ratios of aniline to graphite. These composites were characterized for thermal, electrical, and spectral attributes. The thermal stability (～ 230°C) and electrical conductivity (67.9 S/cm) were improved significantly as compared with polyaniline doped with conventional inorganic dopants such as HCl (140°C and 10 S/cm). Scanning electron micrographs indicated a systematic change in morphology from globular to flaky with increasing amounts of graphite. The relative shifting of UV–visible bands indicates that some interactions exist between doped polyaniline and graphite. Absorption‐dominated total electromagnetic interference shielding effectiveness of the order of ?33.6 dB suggests that these materials can be used as futuristic microwave shielding materials. The good electrical conductivity and thermal stability make them ideal candidates for preparing conducting composites by melt blending with conventional thermoplastics such as polyethylene, polypropylene, and polystyrene, etc. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Dielectric properties of polymers at microwave frequencies: a review

A review of the dielectric loss spectra of polymers at microwave frequencies has been carried out. While the main focus of attention is the frequency range from 100 MHz to 100 GHz, loss spectra outside this region are also reviewed because variations in temperature can cause a shift of dielectric loss into or out of the microwave range. A large volume of data for low loss polymers (polyethylene, polypropylene and poly(tetrafluoroethylene)), which are used in the communications industry, was available for review. Other polymers, for which data were available and which have significant loss at microwave frequencies are: polystyrene, poly(vinylchloride), poly(vinylidene chloride), poly(vinylidene fluoride), poly(methyl-methacrylate), poly(methyl acrylate), poly(oxymethylene), poly(ethylene oxide), poly(propylene oxide), polyacetylene, and poly(sulphur nitride). Also, the microwave dielectric properties of engineering thermoplastics such as poly(phenylene oxide), polycarbonate and polysulphane have been reviewed. The origins of microwave dielectric loss in polymers are categorized as: (a) dipolar absorption dispersions in both crystalline and amorphous polymers; (b) dipolar losses due to impurities, additives or fillers in a polymer material; (c) microwave absorption in conducting polymers (polyacetylene and poly(sulphur nitride)) for which the current carriers are electrons; and (d) photon-phonon absorption spectra corresponding to the density of states in amorphous regions of a polymer material.     

A novel method for synthesis of water‐soluble polypyrrole with horseradish peroxidase enzyme

A novel water‐soluble, conducting polypyrrole was synthesized by horseradish peroxidase (HRP), in the presence of sulfonated polystyrene, as a polyanionic template. The HRP is an effective catalyst for the oxidative polymerization of pyrrole in the presence of hydrogen peroxide at room temperature. The reaction is sensitive to solution pH and it is performed in pH 2 aqueous solutions. Polymerization of pyrrole by this biological route produced a conducting water‐soluble polypyrrole for the first time. The reaction is benign and in one pot, and the product requires minimal purification. The reversible redox activity of the polypyrrole displays a hystersis loop with pH changes. FT‐IR, UV‐vis absorption spectroscopy, and cyclic voltammetry are used in the characterization of the synthesized polypyrrole. These studies confirm the electroactive and conducting form of polypyrrole, similar to that which has been traditionally synthesized, chemically and electrochemically. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 254–258, 2004     

Electrochemical synthesis of sulfonated polypyrrole in FSO3H/acetonitrile solution

The incorporation of SO₃^? groups into a polypyrrole backbone was successfully carried out using FSO₃H/acetonitrile medium. The degree of sulfonation (sulfonation or sulfur‐to‐nitrogen ratio) of polymer was controlled by varying FSO₃H concentration while the film was being electrodeposited. The cyclic voltammograms of the electrodeposited films were taken between ?1.00 and +2.00 V (versus Ag/AgCl) in blank solution. A substantial effect on the electrical conductivity was observed upon the incorporation of SO₃^? groups in the polypyrrole polymeric chain. The elemental analysis results of the freshly prepared and reduced films give independent evidence that the SO₃^? groups are covalently bound to the structure. FTIR, UV‐Vis, spectroscopy and SEM techniques were used to characterize the electrosynthesized polypyrrole films. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 93: 526–533, 2004     

Preparation of fine Ni particles and their shielding effectiveness for electromagnetic interference

Fine Ni particles with sphere‐like architecture were synthesized via a wet chemical route in distilled water. The resulting fine Ni particles and/or commercial microsized Ni particles were then added to a mixed resin solution to fabricate resin‐based conductive composites. The shielding effectiveness (SE) of the resultant conductive composites for electromagnetic interference was measured as a function of nickel mass fraction. The results indicated that the SE values of the two kinds of Ni‐containing resin‐based composites increased with increasing loading of Ni filler. Moreover, the fine Ni particles, in the absence of any protective agents, were liable to aggregate for the sake of decreasing surface energy, which could be well avoided by ultrasonic disposal. The resin‐based conductive composites containing a low concentration (33.3 wt %) of the ultrasonically disposed fine Ni particles recorded an SE value as much as above 22 dB in a frequency range of 130 MHz to 1.5 GHz, which could not be realized for the composites filled with microsized nickel particles unless the mass fraction of the Ni filler in this case was as high as 50.0 wt %. In other words, the ultrasonically disposed fine Ni particles could be used as efficient lightweight filler for shielding of electromagnetic interference. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Facile fabrication of polyaniline/polypyrrole copolymer nanofibers with a rough surface and their electrorheological activities

Hierarchical polyaniline/polypyrrole (PANI/PPy) copolymer nanofiber was prepared via a two‐step method and adopted as dispersing materials for electrorheological (ER) fluids. The first step was used to synthesize PANI nanofibers by a rapid mixing method. Subsequently, the PANI/PPy copolymer nanofibers with a rough surface were obtained using an in situ polymerization method continuously. The morphology of the resultant PANI/PPy copolymer nanofibers can be controlled by varying the amount of Py monomer in the secondary in situ polymerization method. The rough surface of PANI/PPy copolymer nanofibers were confirmed by scanning electron microscopy and transmission electron microscopy. The diameter of PANI/PPy nanofiber is within the range 100–200 nm. The obtained PANI/PPy copolymer particles all exhibit amorphous structure through X‐ray diffraction measurement. We also demonstrated that the hierarchical PANI/PPy copolymer nanofibers exhibited characteristic ER behaviors, which were investigated using a Haake rotational rheometer at various electric field strengths. The ER efficiency e for PANI‐1mLPPy and PANI‐2mLPPy ER fluids at shear rate 0.1 s⁻¹ is 36.6 and 28.5 under electric field strength E = 3 kV/mm, respectively. Low leaking current density is observed even at high electric field strength and wide plateau region appeared, which show a strong ER activity for the PANI/PPy composite nanofibers. The results also indicate that the PANI/PPy composite particles have distinctly enhanced ER effect compared with the pure PANI and PPy particles under electric stimuli. The significantly improved ER property of PANI/PPy‐based ER fluid is ascribed to the enhanced interfacial polarization. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46289.     

Poly(vinylidene fluoride-co-hexafluorpropylene)/polyaniline conductive blends: Effect of the mixing procedure on the electrical properties and electromagnetic interference shielding effectiveness

Poly(vinylidene fluoride-co-hexafluoropropylene)/polyaniline (PVDF-co-HFP/PAni) conductive blends were prepared by two methodologies involving the in situ polymerization in two different media and dry blending approach using ball milling. Dodecylbenzenesulfonic acid (DBSA) was used both as surfactant and as protonating agent in PAni synthesis. X-ray diffraction (XRD), scanning electron microscopy (SEM), ultraviolet–visible (UV–Vis) spectroscopy, and thermogravimetric analysis were used for characterizing the blends. PAni and PVDF/PAni prepared by in situ polymerization in H₂O/toluene medium exhibited superior electrical conductivity, higher thermal stability and significantly higher electromagnetic interference shielding effectiveness (EMI SE) than those prepared in H₂O/dimethylformamide (DMF) medium. PVDF/PAni with high-PAni content (>40%) prepared by the dry blend approach presented higher conductivity and EMI SE than those prepared by in situ polymerization. The molding temperature exerted significant influence on the conductivity and EMI SE for the blend containing higher amount of PAni. The free-solvent dry blending approach using ball milling presented similar conductivity value but the higher EMI SE when compared with in situ polymerization, and is considered environmentally and technologically interesting.     

Facile synthesis of graphene/polypyrrole 3D composite for a high‐sensitivity non‐enzymatic dopamine detection

One kind of nanocomposite consisting of graphene and polypyrrole was synthesized via a facile and mild way with the assistant of microwave irradiation. The synthesis route was embedding the polypyrrole into the graphene flakes to form a 3D structure, to achieve larger active surface and higher electro‐catalysis property. Structures and components of the composite were measured by X‐ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared spectroscopy. A stronger electrochemical response of electrode with modified resultant was observed in the electrochemical test. Dopamine sensor based on the composite showed a sensitivity of 363 μA mM ^?1 cm^?2, a linear range of 1 × 10^?4 M to 1 × 10^?3 M , and a detection limit of 2.3 × 10^?6 M (S/N = 3). © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44840.     

Dielectric properties and electromagnetic interference shielding studies of nickel oxide and tungsten oxide reinforced polyvinylchloride nanocomposites

ABSTRACT

Polyvinylchloride (PVC)/nickel oxide (NiO)/tungsten oxide (WO₃) nanocomposite films were prepared via solution casting technique. The crystallinity, morphology, and the analysis of dispersion state of PVC/NiO/WO₃ nanocomposite was carried out using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The dielectric studies of nanocomposite films were investigated and a maximum dielectric constant of 2.3 with dielectric loss (tan δ) of 2.4 was attained. The EMI shielding studies were carried out in the X and Ku-band frequency range (8 GHz-18 GHz). The maximum SE of 15.78 dB in X-band and 12.05 dB in Ku-band was achieved for 75/20/5 compositions of the PVC/NiO/WO₃ nanocomposite.     

Novel V‐shaped negative temperature coefficient of conductivity thermistors and electromagnetic interference shielding effectiveness from butyl rubber–loaded boron carbide ceramic composites

The presentation of a new conductive composite with good effective applications like negative and positive temperature coefficient of conductivity thermistors (i.e., V‐shaped thermistors) and electromagnetic interference shielding effectiveness (EMI) was the aim of this study. The effect of boron carbide (B₄C) contents on the vulcanization characteristics and network structure of butyl rubber (IIR) composites were analyzed in detail. The prediction of the type of crosslinks based on the affine and phantom network theory was also analyzed. The influence of the volume fraction of B₄C on the dc conductivity and thermoelectric power was investigated. The electrical and dielectric properties of IIR composites were investigated. The results suggest that the conduction occurs by a tunneling mechanism and behaves as a p‐type semiconductor. Isothermal resistance at different temperatures, as a function of B₄C content, was displayed. The current–voltage characteristics showed properties of switches, which were explained by coulombic repulsive force. For practical applications, as self‐electrical heating the temperature–time cycles were investigated under certain applied power. It was found that increasing the B₄C content increases the thermal stability of the composite. However, the theoretical modeling of the current–voltage characteristic is very useful for planning groups in industrial applications of conducting polymer composites. Furthermore, the endurance test under applied power indicates that the proposed composites could be useful as temperature sensors with good reliability. Specific heat as a function of B₄C contents was evaluated by experimental and various energy balance models. Furthermore, the temperature dependency of thermal conductivity and thermal diffusivity were investigated. Finally, the standing wave ratio, reflection coefficient, return loss, and attenuation of IIR/B₄C composites were studied in the 1‐ to 4‐GHz frequency range. The resulting values of electromagnetic interference shielding effectiveness were compared with theoretical models. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:2756–2770, 2004