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.     

Conducting polymer embedded with nanoferrite and titanium dioxide nanoparticles for microwave absorption

The present paper deals with the synthesis of conducting ferrimagnetic polyaniline nanocomposite embedded with γ-Fe₂O₃ (9–12 nm) and titanium dioxide (70–90 nm) nanoparticles via a micro-emulsion polymerization. The microwave absorption properties of nanocomposite in 12.4–18 GHz (Ku-band) frequency range shows shielding effectiveness due to absorption (SE_A) value of ?45 dB, which is much higher than polyaniline composite with iron oxide and polyaniline–TiO₂ composites. The higher EMI shielding is mainly arising due to combined effect of γ-Fe₂O₃ and TiO₂ that leads to more dielectric and magnetic losses which consequently contributed to higher values of shielding effectiveness. XRD analysis of the nanocomposite reveals the incorporation of nanoparticles in the conducting polymer matrix while the thermal gravimetric analysis (TGA) demonstrates that the nanocomposite is stable up to 250 °C.     

Enhanced microwave absorption properties in polyaniline and nano-ferrite composite in X-band

Highly conducting polyaniline (PANI) nanocomposite with Mn_0.2Ni_0.4Zn_0.4Fe₂O₄ ferrite was prepared by mechanical blending. The present work reports the EMI shielding characteristics of the ferrite-Pani nanocomposite with different thickness. The saturation magnetization (Ms) for pure MnNiZn ferrite (52 emu/g) and composite (41 emu/g) was measured by VSM at room temperature. The crystalline size of MnNiZn ferrite was found in the range of 25–30 nm as analyzed by TEM and XRD. The complex permittivity, permeability and shielding effectiveness of the composite for different thicknesses were measured in the 8–12 GHz (X-band) frequency range. The composite of 2.5 mm thickness has shown high shielding effectiveness (49.2 dB) due to absorption (SE_A). The high value of SE_A suggests that this composite can be used as a promising absorbing material for X-band frequency range.     

Enhanced microwave absorption behavior of polyaniline-CNT/polystyrene blend in 12.4–18.0 GHz range

Blends of polystyrene with polyaniline (PANI) coated multiwalled carbon nanotubes (MWCNTs) were designed which inherit dielectric and magnetic attributes from PANI and MWCNT respectively. The high resolution transmission electron microscopy image shows the PANI coating over MWCNT containing entrapped Fe catalyst. These blends show absorption dominated total shielding effectiveness (SE_T) of ?45.7 dB (>99.99% attenuation) in the 12.4–18.0 GHz range, suggesting their utility for making efficient microwave absorbers. The enhanced SE_T was ascribed to optimization of conductivity, skin-depth, complex permittivity and permeability. A good agreement between theoretical and experimental shielding measurements was also observed.     

Microwave study of chemically synthesized conducting polyaniline on alumina

Polyaniline (PANI) thin film on alumina was prepared by the chemical oxidation of aniline with ammonium peroxydisulphate in acidic aqueous medium. DC conductivity, microwave transmission and reflection, microwave conductivity, shielding effectiveness and microwave dielectric constant of the conducting PANI films are reported. DC conductivity was between 0.15 × 10^?3 and 3.13 × 10^?3 S/cm. Microwave conductivity was between 0.2 and 10 S/cm. The PANI films coated on alumina gave shielding effectiveness value of ?1 to ?4 db. The ?′ was between 2 and 350 whereas ?″ was between 437 and 60. Measurements have been carried over the frequency range of 8.2–18 GHz.     

Electro/magnetic shielding effectiveness of soft magnetic Fe80Nb6B14 amorphous alloy

Application of the Fe₈₀Nb₆B₁₄ amorphous alloy to electromagnetic shielding was examined in detail using different experimental techniques. For shields made of the optimized (annealing at 700 K/1 h) amorphous ribbons the shielding effectiveness b was measured versus frequency f and shield thickness h. It was shown that for h = 200 μm in the frequency range 2 MHz < f < 15 MHz (the near-zone, electric field) b decreases from 55 dB to 20 dB. In the frequency range 0.2 kHz < f < 10 kHz (the near-zone, magnetic field) b > 20 dB. The best shielding effectiveness, i.e. b > 100 dB was obtained for electromagnetic field in the frequency range 200 MHz < f < 1000 MHz (the far-zone).     

Preparation of conductive wool fabrics and adsorption behaviour of Pd (II) ions on chitosan in the pre-treatment

In this study, an effective deposition of Ni–P alloy on wool fabric is proposed by a chemical plating approach with PdCl₂ solution and a carrier agent chitosan (CTS). CTS possesses strong ability to absorb metal ions through several mechanisms, such as electrostatic attraction and chelation, depending on the pH of the solution. The lowest surface resistance of the wool fabric is achieved when Pd (II) ions are absorbed in acid condition (around pH = 2.5). Sorption isotherms are obtained and modeled using Langmuir and Freundlich model and kinetic curves nicely fitted to the pseudo-first-order equation. Also, isotherms have been introduced to obtain the thermodynamic parameters, such as Gibbs free energy, enthalpy and entropy. The resulting positive value of the enthalpy indicates that the adsorption is an endothermic process. Conductive wool fabrics are characterized by scanning electron microscopy (SEM), Fourier transform-infrared (FT-IR) spectroscopy. Evidenced by SEM, CTS–Pd is found on the surface of fabrics and effectively activated the chemical plating. FT-IR shows the adsorption of Pd (II) ions on CTS is mainly controlled by physical adsorption. Mechanical and physical tests were investigated and the encouraging results show no significant modification and open new perspectives for future application of wool fabrics.     

Antistatic coating and electromagnetic shielding properties of a hybrid material based on polyaniline/organoclay nanocomposite and EPDM rubber

Thermal, mechanical, electrical and microwave radiation absorbing properties of conductive composites based on dodecylbenzenesulfonate doped polyaniline/organoclay nanocomposites and propylene–ethylidene–norbornene rubber have been investigated with special interest on the effect of the nanocomposite concentration. Composites were prepared by melt blending using an internal mixer. Morphology studies by scanning electron microscopy of cryofractured surfaces indicated that the conducting nanocomposites produced heterogeneously distributed aggregates in the continuous elastomeric matrix. The composites exhibit high conductivities, up to 10⁻³ S cm⁻¹ for 40 wt.% of conducting nanocomposite, and good mechanical properties. They also present high microwave attenuation values, in the frequency range of 8–12 GHz. This property depends on the concentration of the conductive nanocomposite and on the film thickness. The composites can be used for antistatic coatings or for electromagnetic shielding.     

Electromagnetic interference shielding effectiveness of electroless Cu-plated PET fabrics

In order to develop the high quality electromagnetic interference (EMI) shielding textiles for protective clothing, polyester fabrics were electroless copper-plated. Effects of pretreatment conditions such as scouring, etching, and catalyzation on electromagnetic interference shielding effectiveness (EMISE) and physical properties of treated fabrics were investigated.High EMISE of fabrics over the wide range of frequency level were obtained when fabrics were scoured with 0.3% NaOH and 1.0% Triton X-100, and etched with the mixture of HCl/HNO₃ at 25°C for 30 min before activation. We found that KCl was the better catalyst activator than commonly used SnCl₂. EMISE of copper-plated fabrics increased as the concentration of KCl increased up to 1:8 molar ratio of PdCl₂:KCl then decreased with further addition. As the catalyzation temperature increased from 25 to 40°C, the EMISE of copper-plated fabrics increased, whereas their EMISE reduced to about zero when the activation temperature exceeded over 40°C. Physical properties including tensile extension and drape stiffness of copper-plated fabrics are higher than those of the untreated PET, but tensile strength was slightly decreased. By scanning electron microscope (SEM), we found special fracturing behavior of the copper-coated PET fabrics due to the ductility and brittleness of copper film on the PET fabric.     

Near infrared electrochromism of lutetium phthalocyanine

The near infrared (NIR) electrochromism of lutetium phthalocyanine (LuPc₂) is studied both in its solution and vacuum deposited thin film. The LuPc₂ in neutral state has near infrared absorption in the region from 1100 nm to 1600 nm. In electrochemical oxidized state (+1.0 V), it has an absorption peak at 880 nm. In electrochemical reduced state (−1.0 V), it shows no absorption in the near IR region. The attenuation at 1300 nm of electrochromic (EC) devices based on solution and thin film of LuPC₂ was also studied. Attenuation of 0.31 dB and 0.28 dB was achieved respectively and the response time was 24 s and 1 s, respectively. These results demonstrate that LuPc₂ is a kind of NIR EC material and it has potential application for variable optical attenuator.     

Characterization of conducting polymer coated synthetic fabrics for heat generation

Heat generation in fabrics coated with the conductive polymer polypyrrole was investigated. The PET fabrics were coated by chemical synthesis using four different oxidizing agent–dopant combinations. The samples from the four different dopant systems all show an increase in temperature when a fixed voltage is applied to the fabric. The antraquinone-2-sulfonic acid (AQSA) sodium salt doped polypyrrole coating was the most effective in heat generation whereas the sodium perchlorate dopant system was the least effective. The power density per unit area achieved in polypyrrole coated polyester–Lycra® fabric with 0.027 mol/l of AQSA acting as dopant was 430 W/m². The power density per unit area achieved for the sodium perchlorate system, using the same synthesis conditions, was 55 W/m².     

Development of a cooling fabric from conducting polymer coated fibres: Proof of concept

It is supposed that there should be a thermal electric effect if a dc current is applied across two dissimilar conducting polymers, similar to so called “Peltier effect” in metals or semiconductors. However, this hypothesis has not been tested on conducting polymers and using these materials to make cooling fabrics has never been attempted before. Polypyrrole coated fabrics were used to test the hypothesis in this preliminary study. Seebeck and the Peltier effects were proven to exist. However, thermoelectricity effect between two conducting polymer coated fabric samples was only about 10 μV/°C. Cooling effect by conductive polymer powder was achieved but performance was unsteady due to electrical degradation of the conducting polymer. Nevertheless, the concept was demonstrated and the development of a cooling fabric is possible.     

Pure carbon microwave absorbers from anion-exchange resin pyrolysis

A series of carbon materials [C_F-x (where x denotes carbonization temperature)] have been prepared by pyrolysis of an anion-exchange resin at different temperatures (500–700 °C). X-ray diffraction and Raman spectroscopy suggest the presence of tiny crystalline domains in these materials, whose content is strongly determined by carbonization temperature. The microwave absorption of these materials is examined in the frequency range of 2–18 GHz, and it is found that the reflection loss characteristics are highly sensitive to the carbonization temperature. At a thickness of 2 mm, C_F-600 exhibits the best microwave absorbing ability with a maximum reflection loss of ?20.6 dB at 16 GHz, and a bandwidth exceeding ?10 dB in the range 13.5–18 GHz. It is concluded that dielectric loss in cooperation with better matched characteristic impedance results in the excellent microwave absorption of C_F-600. Furthermore, a reflection loss exceeding ?10 dB can be obtained in the range of 7–18 GHz by manipulating the thickness from 2 to 3.5 mm, and the maximum can reach ?37.0 dB at 10.8 GHz with a thickness of 2.8 mm. These materials may be used as light-weight and highly effective microwave absorbers over a wide frequency range.     

Electrical,structural, photoluminescence and optical properties of p-type conducting,antimony-doped SnO2 thin films

P-type transparent conducting antimony-doped tin oxide (ATO) films were successfully fabricated on quartz glass substrates by radio-frequency magnetron sputtering using a 20 mol.% Sb-doped SnO₂ ceramic target. The deposited films were annealed at different temperatures for different durations. Hall effect results indicated that 973 K was the optimum annealing temperature to get p-type ATO films with the highest hole concentration (5.83 × 10¹⁹ cm^–3). X-ray diffraction studies indicated that the preferred (1 0 1) orientation favored the formation of p-type conducting films. Photoluminescence spectra showed an intense UV luminescence peak near 362 nm resulting from the band-edge exciton transition observed for p-type ATO films. UV–visible transmission spectra showed that p-type ATO films had high transparence. In addition, p-type conductivity was also confirmed by the non-linear characteristics of a p-type ATO/n-type ATO structure; the diode structure has an optical transmission of ～60–85% in the visible light range.     

Development of electroless (Ni-P)/BaNi0.4Ti0.4Fe11.2O19 nanocomposite powder for enhanced microwave absorption

Ni-, Ti-substituted nanocrystalline M-type barium hexaferrite powder (BaNi_xTi_xFe_12?2xO₁₉ (x = 0.4) of size ～10 nm) was coated with Ni-P by electroless (EL) coating technique to form EL Ni-P/BaNi_0.4Ti_0.4Fe_11.2O₁₉, a radar absorbing material (RAM) nanocomposite powder. Under TEM, the particle size of RAM powders before and after Ni-P coating were found to be in the range of 10–15 nm and 15–25 nm respectively. A uniform layer of 5–10 nm thick coating is deposited due to the controlled growth of EL Ni-P nanoglobules onto the powder. A growth mechanism was proposed to understand the deposition of EL Ni-P layer onto the RAM powder. The reflection loss (RL) of the EL (Ni-P)/RAM nanocomposite powder in Ku band (12.4 ?18 GHz) was evidently enhanced to ?28.70 dB, as compared to the EL Ni-P nanoglobules (?16.20 dB) and nanocrystalline RAM powder (?24.20 dB). After annealing at 400 °C for 4 h, the RL and bandwidth of EL (Ni-P)/RAM nanocomposite powder was further improved from ?24.20 to ?35.90 dB and 1.50 to 4.00 GHz respectively. The RL enhancement mechanism was explained on the basis of VSM study (hysteresis loops) and electromagnetic theory.     

Properties of composite films of titania nanofibers and Safranin O dye

Titania (TiO₂) nanofibers and composite thin films of titania nanofibers and Safranin O dye (SAF) were studied. TiO₂ nanofibers were prepared by electrospinning technique from titanium tetra-isopropoxide precursor solution in ethanol. Surface topology of the nanofibers was observed using scanning electron microscopy (SEM), their crystal structure was studied by X-ray diffraction (XRD) and the chemical composition by X-ray photoelectron spectroscopy (XPS). Properties of the TiO₂ nanofibers were studied in dependence on the values of relative air humidity in the range from 15% to 55%. It was necessary to maintain the relative humidity lower than 30% during electrospinning in order to obtain high quality nanofiber films. The average minimum diameter of the as-prepared TiO₂ nanofibers was found to be around 100 nm. Nanofiber diameter diminishes to about 50 nm after annealing at 420 °C for 1 h. The as-prepared titania nanofiber films were completely amorphous while anatase crystal phase was detected in the films after annealing. In order to prepare the composite films, solution of SAF dye with poly(vinylpyrrolidone) in ethanol/water was dropped off on the prepared titania nanofibers surface. Opto-electrical properties of SAF dye and the resulting nanocomposite films were studied by UV–Vis spectroscopy and current–voltage characteristics. Safranin O is characterized by two strong absorption peaks; one at 274 nm and a wide band with splitting between 420 nm and 600 nm. The optical energy band gap of titania nanofibers was estimated from the UV–Vis measurements to be 3.4 eV. The charge transport in the composite films is influenced by the space charge limited currents due to the very high resistance of the materials.     

Polymer infrared photo-detector with high sensitivity up to 1100 nm

We reported a low band-gap conjugated polymer, poly[2,3-bis(4-(2-ethylhexyloxy)phenyl)-5,7-di(thiophen-2-yl)thieno[3,4-b]pyrazine] (PDTTP), was studied for the near infrared (NIR) photo-detector application. PDTTP shows intense absorption in NIR wavelength (to 1000 nm) and the estimated optical and electrochemical band-gaps of PDTTP are quite small around 1.15 eV and 1.08 eV, respectively. The low band-gap and the extended long wavelength absorption originates from the introduction of alternating TP units when its parent polythieno[3,4-b]pyrazine shows excellent narrow band-gap properties. Therefore, the relatively low band-gap and intense absorption in long wavelength of PDTTP make itself a promising candidate for near-infrared photo-detector. The hole mobility of the PDTTP measured from the bottom contact field effect transistor is around 1.40 × 10^?3 cm²/V s with a on/off ratio of 2100. The photo-detector based on bulk hetero-junction PDTTP and (6,6)-phenyl-C61-butyric acid methyl ester blend (PCBM) has the incident photon-to-electron conversion efficiency 28.9% at 1000 nm (?5 V) and 6.2% at 1100 nm (?5 V). This photo-detector can be operated at a high-speed of 1 MHz. The experimental result suggests the potential applications of low band-gap conjugated polymers on near-infrared photo-detectors.     

A study of optical properties and annealing effect on the absorption edge of pristine- and iodine-doped polyazomethine thin films

Aromatic polyazomethine (PPI) thin film have been obtained by chemical vapor deposition (CVD) method, via polycondensation process and characterized by X-ray diffraction, AFM, FTIR and detailed UV–Vis–NIR studies. Optical transmission and fundamental reflectivity spectra of the film have been examined within the spectral range 200–2500 nm. The refractive index (n), film thickness (d) and parameters of the absorption edge i.e. the optical gap (E_G) and the Urbach energy (E_U) have been found for the PPI film before and after iodine (I₂) doping. Then the annealing effect (from 25 °C every 25 °C up to 225 °C) on the absorption edge have been investigated during “in situ” spectral measurements. Amorphous character of the films allowed us to obtain the E_G and E_U values, in the way typical for amorphous semiconductors. As a result of iodine doping, the energy gap of the PPI film (2.19 eV) distinctly reduces to 1.73 eV, due to the polaron states and, simultaneously, the Urbach energy decreases. Thermal stability of the pure PPI film, being the typical feature of polyazomethines, was confirmed, while after iodine doping the film turned out to be thermo-stable only below 100 °C; then the distinct changes of the optical gap and the Urbach energy, connected with the iodine releasing process, have been presented and discussed.     

Influence of the scan rate on the morphology of polyaniline grown on conducting fabrics. Centipede-like morphology

We report the apparition of different polyaniline (PANI) morphologies when different scan rates were employed in the electrochemical deposition of PANI on conducting fabrics. The most impressive structure obtained was the centipede-like morphology. PANI was deposited on conducting textiles of polyester covered with polypyrrole (PPy)/anthraquinone sulphonic acid (AQSA) by means of cyclic voltammetry. With the scan rates of 50 mV s^?1 and 5 mV s^?1 PANI with centipede-like morphology was obtained in the first scans. Globular PANI gained importance for higher number of scans due to the formation of new nucleation sites. When a scan rate of 1 mV s^?1 was employed a variety of different morphologies were observed, such as: fibrillar, stalagmite-like, coral-like and plain irregular forms. Such variety of morphologies is due to the slow growth that allowed different types of morphologies.     

Highly efficient synthesis of thieno[3,4-b]thiophene derivatives and (opto)electrochemical properties of new low bandgap conjugated polymers

Various thieno[3,4-b]thiophene derivatives functionalized by n-octyl, 4-tert-butylphenyl, 4-n-butylphenyl, and 4-n-pentylphenyl were synthesized in a concise and efficient way. Previously reported synthetic processes were modified to produce target molecules in relatively high yields. Electrochemical and optical properties of polymers were examined by cyclic voltammetry and Vis–NIR spectrophotometry. The bandgap of electrochemically prepared polymers varied with substituents, ranging from 0.91 eV to 0.98 eV. While HOMO of conjugated polymers was raised by inductive effect of alkyl substituents, the bandgap was mainly determined by resonance stabilization of phenyl substituents.