S. K. Dhawan

Shielding of electromagnetic interference using polyaniline

Since the discovery in 1977 of the metallic properties of molecularly doped polyacetylene, there has been rapid growth in the field of electronically conducting polymers [1-5]. The interest in this area is mainly due to the numerous technological applications of conducting polymers as active electrode materials in energy storage [6], opto-electronic devices [7], display devices [8, 9 ] and their envisaged application for the control of electromagnetic radiation (EMR) and dissipation of electrostatic charge [10-12]. Polyaniline (PAn) is particularly interesting because of the presence of the chemically flexible N H group in the polymer backbone which not only takes part in the protonation/deprotonation but also contributes to 7r-band formation [13], thus ensuring greater environmental stability. PAn can be obtained either by chemical or electrochemical method and does not involve any special precautions [14-16[. Although it is easily synthesized in bulk, its use is restricted due to its unprocessibility by normal melt or solution techniques. For many applications, such as in the control of electromagnetic interference (EMI), dissipation of electrostatic charge (ESD) requires a thin conducting coating on a flexible surface. Polyaniline, unlike metallic coating, is free from corrosion and is very suitable under a highly corrosive atmosphere where other conducting coatings fail. Due to the reactivity of synthetic fabrics like Nylon, Terylene and glass fabric towards mineral acids, we have used organic acids like benzenesulfonic acid (BSA), para-toluenesulfonic acid (PTSA), 5-sulfosalicylic acid (SSA) and 4-hydroxybenzenesulfonic acid as media for grafting PAn. The detailed study using these acids on the properties of polyaniline has been reported elsewhere [8, 9, 17]. The effect of these acids on charge transport, optical and magnetic properties which are quite different to those of mineral acids (like persistence

Graphene oxide/ferrofluid/cement composites for electromagnetic interference shielding application

This paper deals with the preparation of graphene oxide-ferrofluid-cement nanocomposites to evaluate the electromagnetic interference (EMI) shielding effectiveness (SE) in the 8.2-12.4 GHz frequency range. It has been observed that incorporation of graphene oxide (30 wt%) along with an appropriate amount of ferrofluid in the cement matrix leads to a shielding effectiveness of 46 dB (>99% attenuation).The presence of graphene oxide and ferrofluid in the cement leads to strong polarizations and magnetic losses that consequently result in higher shielding effectiveness compared to pristine cement. The resulting nanocomposites have shown Shore hardness of 54 and dc conductivity of 10.40 S cm( - 1). SEM reveals the homogeneous dispersion of graphene oxide and ferrofluid in the cement matrix.

Microwave absorption properties of conducting polymer composite with barium ferrite nanoparticles in 12.4–18GHz

Conducting polymer nanocomposites of polyphenyl amine with barium ferrite nanoparticles (50–70nm) have been synthesized via emulsion polymerization. The complex permittivity, permeability, and microwave absorption properties of the composite were studied in the 12.4–18GHz (Ku band) frequency range. The composite has shown high shielding effectiveness due to absorption (SEA) of 28.9dB (∼99.9%), which strongly depends on dielectric loss, magnetic permeability, and volume fraction of barium ferrite nanoparticles. The high value of SEA suggests that these composites can be used as a promising radar absorbing materials.

Investigations on the effect of 5-sulfosalicylic acid on the properties of polyaniline

Abstract Results of the investigation of the chemical and electrochemical polymerization of aniline in 5-sulfosalicylic acid medium and its characterization by electrochemical and spectroscopic techniques are presented. The investigation reveals that 5-sulfosalicylic acid as a dopant not only enhances electrochemical stability of polyaniline at higher potentials but also yields a polymer which is soluble to the extent of 11 g/l in DMSO. The characterization of conducting polyaniline thus obtained was carried out by electronic and vibrational spectra, 1 H NMR in DMSO-d 6 , X-ray powder diffraction, thermal analysis and by electrochemical techniques.

Shielding effectiveness of conducting polyaniline coated fabrics at 101 GHz

Conducting polyaniline coated fabrics can be used as a shield material for the control of electromagnetic interference at 101 GHz. The conducting fabrics can also be used for the dissipation of electrostatic charge. The conducting fabric shows a shielding effectiveness of 35.61 dB. The characterization of the conducting polymer polyaniline and conducting fabrics was carried by spectroscopic techniques and thermogravimetric analysis. Static charge measurements of the conducting fabrics show a complete removal of static charge.

Polyaniline as an electrode material for magnesium reserve battery

Abstract The results of the investigation on the use of polyaniline (PANI) as a cathode material in a battery configuration, having magnesium as anode and a neutral aqueous solution of one of the magnesium salts such as perchlorate, chloride and bromide as an electrolyte, are presented. This system shows a open circuit voltage in the range 1.6–1.8 V. The study indicates that the capacity of the system largely depends upon the anion present in the electrolyte.

Grafting of electronically conducting polyaniline on insulating surfaces

A method is described to graft conducting polyaniline onto glass fabric, glass wool and nylon cloth to impart flexibility and mechanical strength to the polyaniline, which is otherwise powdery and untracable. These flexible conductive surfaces can find application as antistatic shields.

Memory effect in cadmium telluride quantum dots doped ferroelectric liquid crystals

A pronounced memory effect has been observed in cadmium telluride quantum dots (CdTe-QDs) doped ferroelectric liquid crystals (FLCs) by using dielectric and electro-optical methods. The memory effect has been attributed to the charge storage on the CdTe-QDs upon the application of dc bias across the sample cell. The FLC molecules remain in the switched state in vicinity of the charge stored on QDs even after removal of bias. It has been observed that the memory effect depends on doping concentrations of CdTe-QDs and the FLC material used.

Conduction mechanism in Polyaniline-flyash composite material for shielding against electromagnetic radiation in X-band & Ku band

β–Naphthalene sulphonic acid (β–NSA) doped polyaniline (PANI)–flyash (FA) composites have been prepared by chemical oxidative polymerization route whose conductivity lies in the range 2.37–21.49 S/cm. The temperature dependence of electrical conductivity has also been recorded which shows that composites follow Motts 3D–VRH model. SEM images demonstrate that β–NSA leads to the formation of the tubular structure with incorporated flyash phase. TGA studies show the improvement in thermal stability of composites with increase in loading level of flyash. Complex parameters i.e. permittivity (ɛ* = ɛ′- iɛ″) and permeability (μ*=μ′- iμ″) of PANI-FA composites have been calculated from experimental scattering parameters (S11 & S21) using theoretical calculations given in Nicholson–Ross and Weir algorithms. The microwave absorption properties of the composites have been studied in X-band (8.2 – 12.4 GHz) & Ku–Band (12.4 – 18 GHz) frequency range. The maximum shielding effectiveness observed was 32dB, which strongly depends on dielectric loss and volume fraction of flyash in PANI matrix.

ZnO anchored graphene hydrophobic nanocomposite-based bulk heterojunction solar cells showing enhanced short-circuit current

Hydrophobic and surfactant-free ZnO nanoparticles and ZnO decorated graphene nanocomposite (Z@G) with narrow and uniform size distribution were synthesized by a time-efficient microwave-assisted hydrothermal reaction that can be used specifically for application in hybrid photovoltaics. The synthesized ZnO nanoparticles and Z@G nanocomposite showed stable and clear dispersion in chloroform and methanol (with volume ratio of 9:1) and chloroform and ethanol (volume ratio 9:1). Being hydrophobic, these inorganic samples blend very well with organic polymer solution in chlorobenzene, which is a prerequisite to cast smooth and undisrupted film for hybrid solar cell application. The introduction of these hydrophobic nanoparticles into PCPDTBT:PCBM-based bulk-heterojunction polymer solar cells resulted in significant improvement in solar cell J–V characteristics with enhancement in open circuit voltage (VOC), short circuit current density (JSC) and thereby overall improvement in cell efficiency. With the optimization of the weight ratio of polymer, fullerene and synthesized ZnO nanoparticles/Z@G nanocomposite, the power conversion efficiencies 1.76% and 3.65% were achieved.