The reduction of silver nitrate to metallic silver inside polyaniline nanotubes and on oligoaniline microspheres

Polyaniline (PANI) reduces silver nitrate to metallic silver. Composites based on conducting polymer and silver have been prepared with equimolar proportions of reactants. Polyaniline bases having different morphologies – granular or nanotubular – and oligoaniline microspheres have been left to react with silver nitrate in acidic, neutral, and alkaline media. The content of silver, typically 20–30 wt.%, was determined by thermogravimetric analysis. Clusters of 40–80 nm silver particles are produced in the granular form of PANI. The formation of silver inside PANI nanotubes has been observed. With oligoaniline microspheres, silver was produced on their surface, and on PANI agglomerates accompanying them. The highest conductivity, 943 S cm^?1, was found with silver reduced by nanotubular PANI base in 0.1 M nitric acid at 17.3 wt.% silver content. The standard granular PANI, used as a reference material, yielded a composite having a much lower conductivity of 8.3 × 10^?5 S cm^?1 at 24.3 wt.% Ag. There is no simple correlation between the conductivity and silver content. Infrared and Raman spectroscopies have been used to study the changes in the molecular structure of the PANI bases of various morphologies before and after reaction with silver nitrate.     

Characteristics of nano-sized silver–glass composite powders prepared by flame spray pyrolysis

Nano-sized silver–glass composite powders were directly prepared by high-temperature flame spray pyrolysis applying ultrasonic spray generator. The silver–glass composite powders with various glass contents had nanometer size, spherical shape and non-aggregation characteristics. The mean size of the silver–glass composite powders was 56 nm. The nano-sized silver–glass composite powders had pure Ag crystal structures irrespective of adding amounts of glass. The silver conducting films formed from the nano-sized silver–glass composite powders had dense structures at firing temperatures between 400 and 500 °C. The silver conducting films formed from the nano-sized silver–glass composite powders had lower sheet resistivities than those formed from the nano-sized silver powders irrespective of the firing temperatures. The sheet resistivities of the silver conducting films formed from the nano-sized silver–glass composite powders with 1 wt% glass content were 53, 16 and 11 mΩ/sq at firing temperatures of 400, 450 and 500 °C, respectively.     

Preparation and dispersive properties of Ag colloid by electrical explosion of wire

In this work, Ag colloid was prepared by electrical explosion of wire in deionized water with 0.2 mm and 0.3 mm wire diameter. The temperature of water used for medium of explosion process was change from 20 °C to 80 °C. Morphology and particle size of nanoparticles was observed by transmission electron microscope. The particle size and size distribution of nanoparticles was found to shift to a smaller size with a decrease of temperature and smaller wire diameter. Surface plasmon resonance of the silver colloids was studied by UV–vis spectroscopy. Stability of silver colloids was investigated by zeta-potential and Turbiscan techniques. The results indicated that temperature of medium during explosion affects much on the stability of Ag colloid. The silver colloidal stability prepared at lower temperature and smaller wire diameter was more stable.     

Transparent conductive Sb-doped SnO2/Ag multilayer films fabricated by magnetron sputtering for flexible electronics

The effects of an embedded silver layer and substrate temperature on the electrical and optical properties of Sb-doped SnO₂ (ATO)/silver (Ag) layered composite structures on polyethylene naphthalate substrates have been investigated. The highest conductivity of ATO/Ag multilayer films was obtained with a carrier concentration of 1.5 × 10²² cm^?3 and a resistivity of 2.4 × 10^?5 Ω cm at the optimum Ag layer thickness and substrate temperature. The photopic averaged transmittance and Haacke figure of merit are 81.7%, and 21.7 × 10^?3 Ω^?1, respectively. In addition, a conduction mechanism is proposed to elucidate the mobility variation with increased Ag thickness. We also describe the influence of substrate temperature on the structural, electrical and optical properties of the ATO/Ag multilayer films, and propose a mechanism for the changes in electrical and optical properties at different substrate temperatures.     

Preparation of poly (hydroxymethyl EDOT)/nano-silver composite films by oxidative polymerization with low-baking temperature,low resistance and good adhesion on PET substrate

Low-resistance films were prepared by polymerization of hydroxymethyl EDOT along with nano-Ag at low-baking temperature (below 120 °C) and low-silver contents (below 20 wt%) on PET substrate. The poly (hydroxymethyl EDOT)/nano-Ag composite films showed low resistance at 21 Ω/□ by spin-coating and at 196 m Ω/□ by drop-casting. We also compared the conductive inks of EDOT, AI4083, nano-Ag and hydroxymethyl EDOT/nano-Ag, and investigated their conductivity, film-forming property and adhesion property. The viscosity of hydroxymethyl EDOT/nano-Ag conductive ink was 12.2 cP at 25.9 °C and suitable for application in flexible plastic devices and inkjet printing technology.     

Composites of low bandgap conducting polymer-wrapped MWNT and poly(methyl methacrylate) for low percolation and high transparency

The composites of multi-walled carbon nanotubes (MWNT) wrapped with low bandgap conjugated polymer and poly(methyl methacrylate) (PMMA) were prepared for transparent conductive films. NIR-absorbing poly(ethyl thieno[3,4-b]thiophene-2-carboxylate) (PTTEt) with E_g of 1.0 eV was used in this study. Upon hybridization with MWNT, PTTEt in an insulating state became partially conductive due to electron transfer from PTTEt to MWNT, meaning that PTTEt can function as conductive glue interconnecting MWNT in a PMMA matrix. The electrical conduction of the composites (PTTEt-MWNT/PMMA), consisting of PTTEt-wrapped MWNT (PTTEt-MWNT/PMMA) and PMMA, showed the percolation at 0.10 wt% MWNT loading, which was ca. 0.18 wt% lower than the composites of MWNT and PMMA (MWNT/PMMA). The maximum conductivity of PTTEt-MWNT/PMMA, on the other hand, was one order of magnitude lower than that of MWNT/PMMA, suggesting that PTTEt incorporation onto MWNT for transparent conductive films is effective within a specific range of MWNT loadings (i.e., between percolation thresholds of MWNT/PMMA and PTTEt–MWNT/PMMA). The comparison of transmittance of PTTEt–MWNT/PMMA (0.18 wt% MWNT) with MWNT/PMMA (0.32 wt% MWNT), possessing the same conductivities (3 × 10^?3 S cm^?1), showed ca. 10% enhanced transmittance at 550 nm. These results imply that hybridization of low bandgap conjugated polymers with carbon nanotubes can be utilized for the reduction of percolation threshold and the increase of optical transparency without sacrificing conductivities at low MWNT loadings.     

Effect of adding 1 wt% Bi into the Sn–2.8Ag–0.5Cu solder alloy on the intermetallic formations with Cu-substrate during soldering and isothermal aging

Intermetallic compound (IMC) formations of Sn–2.8Ag–0.5Cu solder with additional 1 wt% Bi were studied for Cu-substrate during soldering at 255 °C and isothermal aging at 150 °C. It was found that addition of 1 wt% Bi into the Sn–2.8Ag–0.5Cu solder inhibits the excessive formation of intermetallic compounds during the soldering reaction and thereafter in aging condition. Though the intermetallic compound layer was Cu₆Sn₅, after 14 days of aging a thin Cu₃Sn layer was also observed for both solders. A significant increase of intermetallic layer thickness was observed for both solders where the increasing tendency was lower for Bi-containing solder. After various days of aging, Sn–2.8Ag–0.5Cu–1.0Bi solder gives comparatively planar intermetallic layer at the solder–substrate interface than that of the Sn–2.8Ag–0.5Cu solder. The formation of intermetallic compounds during aging for both solders follows the diffusion control mechanism and the diffusion of Cu is more pronounced for Sn–2.8Ag–0.5Cu solder. Intermetallic growth rate constants for Sn–2.8Ag–0.5Cu and Sn–2.8Ag–0.5Cu–1.0Bi solders were calculated as 2.21 × 10⁻¹⁷ and 1.91 × 10⁻¹⁷ m²/s, respectively, which had significant effect on the growth behavior of intermetallic compounds during aging.     

Facile one-step route to polyaniline–silver nanocomposite particles and their application as a colored particulate emulsifier

Polyaniline–silver nanocomposites were synthesized in the form of colloidal particles by the facile one-step aqueous chemical oxidative dispersion polymerization of aniline using silver nitrate as an oxidant and poly(vinyl alcohol) as a colloidal stabilizer. Aniline monomer was oxidized by silver ions, yielding polyaniline and elemental Ag simultaneously. The synthesized nanocomposite particles were colloidally stable over 2 years and transmission electron microscopy studies indicated the production of spherical, plate and rod-shaped polyaniline–silver nanocomposite particles with a silver core–polyaniline shell morphology. The conductivity of a pressed pellet of the nanocomposite particles using the conventional four-point probe technique was 1.4 × 10^?2 S/cm at 25 °C. The nanocomposite particles behaved as a ‘colored’ particulate emulsifier for the stabilization of transparent oil-in-water emulsions.     

Mechanism of polypyrrole and silver nanorod formation in lauric acid–cetyl trimethyl ammonium bromide coacervate gel template: Physical and conductivity properties

Polypyrrole (PPy) and silver (Ag) nanorods are synthesized in cetyl trimethylammonium bromide–lauric acid (CTAB–LA) complex coacervate gel template. When PPy–CTAB–LA system is polymerized with AgNO₃, Ag nanorods are produced while use of ammonium persulphate (APS) as initiator yields PPy nanorods. Ag-nanorods are produced from the initial stage while PPy nanorods take a longer time. The average diameter of Ag nanorods varies from 60 to 145 nm by increasing AgNO₃ concentration from 0.27 M to 1.08 M and that of PPy varies from 145 nm to 345 nm by changing pyrrole concentration from 1 × 10^?4 to 2 × 10^?4 M, respectively. Fourier transformed infrared (FTIR) spectra indicate stabilization of Ag nanorods through complexation of PPy with adsorbed Ag⁺ ions. PPy nanoparticles are stabilized by adsorbed sulphate ions and lauric acid, both are acting as dopant to it. FFT pattern and EDX spectra clearly indicate the presence of Ag nanocrystals and PPy on the surface of Ag nanorods, respectively. The mechanism of nanorod formation is attributed from UV–Vis spectra showing a red shift of surface plasmon band of Ag and π–π* transition band of PPy with time. The highest dc conductivity of PPy–Ag composite is found to be 414.2 S/cm, 7 orders higher than that of PPy nanorods (9.3 × 10^?4 S/cm). PPy–Ag systems show Ohmic behavior while PPy nanorods exhibit semi-conducting behavior. The preferential formation of Ag nanorod in AgNO₃ initiated polymerization is attributed to the higher cohesive force of Ag than that of PPy. With two times higher LA and CTAB concentration in the gel the Ag nanorod diameter decreases only 12% while that of PPy nanorod decreases by 50%. Possible reasons are discussed from the hard and soft nature of the two nanorods and from the elasticity of the gel template.     

Micropatterning of conducting polymer tracks on plasma treated flexible substrate using vapor phase polymerization-mediated inkjet printing

A facile strategy to pattern a conducting polymer on various flexible substrates is reported using vapor phase polymerization-mediated inkjet printing. Complex polypyrrole patterns were obtained via oxidation polymerization of vaporized monomer on the inkjet-printed oxidant patterns. The patterned lines are readily controlled by inkjet printing with the high resolution of micrometer scale. FT-IR attenuated total reflection analysis and X-ray photoelectron spectroscopy were conducted in order to confirm the polymerization of pyrrole monomer. This process provided highly conductive polymer patterns of polypyrrole with the sheet resistance of 2.8 × 10³ Ω/□, the minimum line width of ca. 60 μm and the film thickness of ca. 450 nm. Furthermore, metallic copper pattern was prepared on previously patterned polypyrrole architectures by electroless plating as a practical application.     

Synthesis of conductive adhesives based on epoxy resin and polyaniline.DBSA using the in situ polymerization and physical mixing procedures

Electrically conductive adhesives based on epoxy-anhydride system containing polyaniline (PAni) doped with dodecylbenzenesulfonic acid (DBSA) have been successfully developed and characterized. The blends were prepared by physical mixing and by in situ polymerization of aniline within epoxy matrix. The in situ polymerization procedure contributes for the formation of a conducting pathway with lower amount of PAni.DBSA. A conductivity as low as 10^?3 S cm^?1 with 12 wt% of PAni and excellent adhesion properties were achieved with these systems. The microstructure of the conductive adhesives was studied by means of scanning electron microscopy (SEM). In the case of blends prepared by in situ polymerization, PAni.DBSA is dispersed within the epoxy matrix in the form of microtubules. Dielectrical properties as a function of frequency and temperature have also indicated a great interaction between polyaniline and epoxy matrix by in situ polymerization procedure.     

Supercapacitor performance of porous carbon nanofiber composites prepared by electrospinning polymethylhydrosiloxane (PMHS)/polyacrylonitrile (PAN) blend solutions

Porous carbon nanofiber composites (NFCs) were prepared by electrospinning blended solutions of polyacrylonitrile (PAN) and polymethylhydrosiloxane (PMHS) in N,N-dimethylformamide (DMF). A PMHS concentration of 5 wt% was regarded as the optimum concentration to obtain fibers of a uniform size with a homogeneous dispersion of silica, the maximum specific surface area and the highest conductivity (4.91 S cm^?1) after heat treatment at 800 °C. The supercapacitor electrode prepared with 5 wt% PMHS had the highest specific capacitance, 126.86 F/g, and the highest energy density, 17.0–10.0 Wh/kg, in the range of 400–20,000 W/kg in a 6 M KOH aqueous solution.     

Effect of impingement angle and WC content on high temperature erosion behavior of SiC-WC composites

Hot pressed dense SiC-(0, 10, 30 or 50 wt%)WC composites were subjected to erosion against SiC particles at 800 °C. Effects of WC content and angle of impingement (30°, 60° or 90°) on the erosion performance of composites were evaluated. Erosion rate ranged from 2.1 × 10² mm³/kg to 7.7 × 10² mm³/kg with varying WC content or angle of impingement. The erosion rate of the composites increased with increasing the impingement angle from 30° to 90°, and decreased with WC content up to 30 wt%. Minimum and maximum erosion wear rates were obtained for SiC-30 wt% WC composites at 30° and for SiC-50 wt% WC composites at normal impact, respectively. Grain fracture and pull-out were observed as major mechanisms of material removal for the composites. Decreased angle of impingement led to reduced grain fracture and pull-out, and hence reduction in material removal. Owing to increased fracture toughness with incorporation of WC particles, the composites showed less fracture and removal of WC particles up to 30 wt% reinforcement.     

Solid-state oxidation of aniline hydrochloride with various oxidants

Aniline hydrochloride was oxidized in the solid state with three different oxidants: ammonium peroxydisulfate, iron(III) chloride, and silver nitrate. Polyaniline salt was obtained after a few hours when ammonium peroxydisulfate was used as an oxidant. The polymerization of aniline hydrochloride with silver nitrate leads to polyaniline only after several days; in the case of iron(III) chloride, aniline oligomers were obtained. The conductivity of the polyaniline was 0.21 S cm^?1 when ammonium peroxydisulfate was applied; it is comparable with the conductivity of a ‘standard’ polyaniline. The oxidation with silver nitrate yields a composite material, polyaniline salt and silver particles, with conductivity 1.5 × 10^?3 S cm^?1. Photoacoustic spectroscopy was employed to study the kinetics of the oxidation reaction. Infrared and UV–vis spectra were efficient tools to characterize the final products, and to compare their molecular structure with that of the polyaniline prepared under ‘standard’ conditions in aqueous medium.     

Interfacial behavior in the brazing of silicon nitride joint using a Nb-foil interlayer

Silicon nitride (Si₃N₄) samples prepared the spark plasma sintering (SPS) technique, which had different amounts of oxide additives, were used as disc-preforms. The surfaces of the materials to be bonded during the brazing process (ceramic, metal and filler alloys) were previously coated with thin layer of silver and then stacked together with these preforms. Sandwich-like specimens of Si₃N₄/Cu–Zn/Nb/Cu–Zn/AISI-304 combinations were joined at 1000 °C using 5, 20, and 40 min holding times under an inert atmosphere. Analysis by scanning electron microscopy revealed un-joined zones between the ceramic and metallic parts after 5 min of treatment. For holding times >20 min, homogenous and non-porous Si₃N₄/Cu–Zn/Nb interfaces were obtained. The thicknesses of the resulting ceramic–metal interfaces increased from ～10 to >25 μm as the holding time was increased. The amount of additives used during the preparation of the Si₃N₄ ceramics had a direct effect on the decomposition rate of Si₃N₄ during the joining process. The largest decomposition of Si₃N₄ was observed at 1000 °C/40 min from the less dense ceramic preforms (4 wt% of additives in this case), which in turn induced the migration of Si atoms through the interface to promote the formation of Si-based components. In contrast, when using larger amounts of additives (8 wt%) during sintering of the ceramic performs, it becomes more difficult for N and Si to dissociate upon brazing. When the diffusion rate of Si is low, it migrates toward the metal part, which limits the formation of Si-based components.     

Superplastic deformation of a heat-resistant Al–Cu–Mg–Ag–Mn alloy

The superplastic behavior and deformation mechanism of a heat-resistant Al–Cu–Mg–Ag–Mn alloy prepared by ingot metallurgy was investigated by using optical microscopy, scanning electron microscopy and transmission electron microscopy. It is shown that the Al–Cu–Mg–Ag–Mn alloy shows good superplastic properties at temperatures higher than 450 °C and strain rates lower than 10^?2 s^?1. A maximum elongation-to-failure of 320% was observed at 500 °C and 5 × 10^?4 s^?1, where the corresponding strain rate sensitivity index m is 0.58 and the flow stress σ is 5.7 MPa. Microstructure studies revealed that the observed superplastic behavior resulted from severe grain elongation rather than grain boundary sliding. It is suggested that this phenomenon may provide a new concept for developing superplastic materials.     

Preparation of silver nanostructure from silver(I) coordination polymer and fabrication of nano silver(I) bromide by reverse micelles technique

A new one-dimensional silver(I) coordination polymer, [Ag(μ-bpfb)(NO₃)]_n (1); bpfb = N,N′-bis(4-pyridylformamide)-1,4-benzene, has been synthesized and characterized by IR, ¹H NMR and ¹³C NMR spectroscopy. The single crystal X-ray data show that the silver(I) 1D coordination polymer grows into a three-dimensional network by hydrogen bonding and π–π stacking interactions. Compound 1 with nanorod morphology was also prepared by sonochemical method. The cetyltrimethylammonium bromide (CTAB) as a cationic surfactant was used in reverse micelles technique to obtain spongy silver(I) bromide nanoparticles from compound 1. Also, different silver nanoparticles have been prepared via direct calcination at 673 K and thermal decomposition in oleic acid from compound 1. The nanostructures of [Ag(μ-bpfb)(NO₃)]_n (1), silver and silver(I) bromide were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive X-ray (EDAX) analysis. Thermal stability of compound 1 in both bulk and nano-sized form was studied by thermal gravimetric (TG) and differential thermal (DT) analyses.     

Effects of Y2O3 on SiC/MoSi2 composite by mechanical-assistant combustion synthesis

MoSi₂ based materials are considered as a potential high temperature structural parts. In this work, a 0.5 wt% Y₂O₃–20 vol% SiC/MoSi₂ composite was successfully prepared by pressureless sintering from mechanical-assistant combustion synthesized powders. Adding a small amount of Y₂O₃ to the SiC/MoSi₂ composite decreased the apparent activation energy of sintering by 10.4%, resulting in a denser composite with finer grains. The relative density, flexural strength, Vickers hardness and fracture toughness of 0.5 wt% Y₂O₃–20 vol% SiC/MoSi₂ increased by 5.3%, 27.7%, 27.2% and 35.8% as compared to 20 vol% SiC/MoSi₂, respectively. The oxidation mass gain of Y₂O₃–20 vol% SiC/MoSi₂ at 1200 °C was higher than that of 20 vol% SiC/MoSi₂ for 16.9%, while it still exhibited very good oxidation resistance at this temperature.     

Effect of SPFGraphene dopant in MEH–PPV organic light-emitting devices

In this paper, graphene acts as the acceptor material in the luminous layer. The doping behavior of graphene in MEH–PPV has improved the device performance due to the efficient electron injection and transport through highly conductive graphene. When the graphene content is 0.02 wt%, the highest EL brightness reaches 1960 cd/m² and the threshold voltage declines from 8 V to 5 V. When the graphene content is 0.02 wt%, the device has the highest EL brightness compared with the devices of other graphene content at the same current density. The doping graphene into MEH–PPV results in the best luminous efficiency and balanced electron and hole mobilities in the active layer.