Conducting polyaniline composite for ESD and EMI at 101 GHz

Conducting polyaniline forms an important family of electronic polymers with a developed potential application for a number of areas because of their flexible chemistry, processibility, environmental stability and ease of forming composites. The electromagnetic interference shielding effectiveness of conducting polyaniline (PANI)–ABS composites was studied at 101 GHz. It was observed that shielding effectiveness of the PANI–ABS composites increases with the increase in the loading levels of the conducting polymer doped with hybrid dopants. The lower loading of PANI doped with hybrid dopants in the moulded conducting composites can be effectively used for the dissipation of electrostatic charge. However, with higher loadings, a shielding effectiveness of 60 dB has been achieved which makes the conducting composites a potential EMI shielding material for its application in encapsulation of electronic equipments in electronic and in high tech applications.     

Controlled growth of hollow polyaniline structures: From nanotubes to microspheres

Homogeneous and fairly monosized microspherical structures of polyaniline has been synthesized using a simple soft template method with β-naphthalene sulfonic acid (β-NSA) as both the surfactant and dopant, and ammonium persulfate (APS) as the oxidant at 2–5 °C. The morphology of PANI-NSA was successfully controlled from nanotubes to microsphere, by changing the synthesis conditions (i.e. pH, the concentration of surfactant and monomer, and temperature). Some mechanistic aspects of the formation of nanotubes and hollow spheres have been discussed precisely based on SEM, TEM, DLS, FTIR and UV-visible results. Moreover, synthesis was performed under acidic environment to obtain further understanding about the formation mechanisms.     

Inherently fluorescent polyaniline nanoparticles in a dynamic landscape

In this paper we report for the first time on the emissive behavior of two polyaniline (PANI) nanoparticle systems produced via oxidative chemical polymerization in the presence of either poly(vinyl alcohol) (PVA) or chitosan as polymeric stabilizers in water. The emission from PANI nanoparticles is irreversibly quenched by an increase of pH of the suspending medium from acid to neutral (chitosan-PANI) or alkaline (PVA-PANI). Conversely, PANI nanorods synthesized in the same conditions of the above, but in presence of poly(N-vinyl pyrrolidone), is not emissive at any pH. The role of the polymeric surfactant as a soft template is key in controlling the morphology and the properties of the obtained PANI dispersions. FTIR, UV-Vis absorption and photoluminescence excitation (PLE) spectra studies suggest that the emissive properties are related to the establishment of strong, non-covalent interactions between nanoscalar PANI particles and the polymeric surfactant at the pH of synthesis. Morphology examination of the three systems, by both dynamic light scattering (DLS) and Transmission Electron Microscopy (TEM), reveal that photoluminescence is associated to the presence of a genuinely 3D nanoscalar morphology, together with an ordered disposition of PANI chains into aligned crystal planes. Concomitant to the irreversible quenching of the emission signal with increasing pH, there is an evolution of the morphology leading to particle coalescence, coarsening and ultimately phase-separation, with consequent modification of PANI-polymeric surfactant interactions, PANI chains supra-molecular organization and optical properties of the PANI nanoparticles dispersion.     

Recent progress in chemical modification of polyaniline

Polyaniline (PANI) has been the subject of considerable recent interest because of their unique electrical behavior, good environmental stability in doped and neutral states, ease of synthesis and wide applications in different fields. However, the main drawback of PANI is lack of solubility, which explains its limited processability due to a rigid backbone. Various procedures have been adapted to improve its processability. The major part of this review is a discussion of some of the methods employed for chemical modification of PANI, including doping via Acid–Base chemistry, sulfonation of PANI or copolymerization of aniline with sulfonated aniline derivatives, synthesis of PANI composites with processable polymers, copolymerization of aniline with substituted corresponding monomers, incorporation of polymeric chains or long and flexible alkyl chains in the PANI backbone, and enzymatic polymerization of aniline during the last decade.     

Conducting polyaniline film from aqueous dispersion: Crystallizable side chain forced lamellar structure for high conductivity

Aqueous conducting polyaniline dispersion was prepared employing acidic phosphate ester bearing hydrophilic ethylene glycol segment as dopant, and conducting film with electrical conductivity of 25 S/cm was obtained from the dispersion. Ordered self-assembly lamellar structure with interlamellar distance of 1.2 nm was observed in the film, which consisted of alternating layers of rigid polyaniline chain and flexible phosphate ester side chains, where the phosphate side chain layer was separated by two rigid polyaniline layers. The lamellar structure leading to high conducting film was formed due to the confinement of polyaniline chain by crystallizable phosphate side chain, since the electrical conductivity decreased by four orders of magnitude once the dopant side chain crystalline was destroyed. The crystallizable side chain forced lamellar structure is expected to be a new chance for highly conducting polyaniline.     

Conducting polymer-noble metal nanoparticle hybrids: Synthesis mechanism application

Recent research has established growing research interest in subject of conducting polymer (CP)-based hybrids due to their novel properties and potential applications in diverse fields. The incorporation of CPs with other materials can produce new hybrids showing distinct properties that are not observed in the individual components. Among numerous CP-based hybrids, CP and noble metal nanoparticle (NMNP) hybrids have attracted the most intensive attention in the past few years. The numerous functional groups and tunable chemical structures through redox in the main chains of CPs, make them as ideal supporters for NMNPs. The compact interactions and synergistic effects between CPs and NMNPs contribute to the increased performances in diverse applications. The purpose of this review focuses on state-of-the-art synthetic strategies, mechanisms and applications involved in CP-NMNP hybrids. Herein, CPs used are polyaniline (PANI), polypyrrole (PPY), polythiophene (PTH) and their derivatives; while NMNPs mainly refer to Au, Ag, Pt and Pd nanoparticles. Specifically, the topics include: 1) strategies and mechanisms involved in the synthesis of CP-NMNP hybrids; 2) potential applications of CP-NMNP hybrids in fields of catalysis, sensor, surface-enhanced Raman scattering (SERS), device and others. Finally, prospects and challenges for making advanced CP-NMNP hybrids are discussed.     

Conducting polymer gel: formation of a novel semi-IPN from polyaniline and crosslinked poly(2-acrylamido-2-methyl propanesulphonicacid)

In the present article, a simple two-step technique for synthesis of electrically conducting hydrogel is described. The synthesized hydrogel is originally a semi-interpenetrating polymer network (IPN) in which conducting polyaniline (linear) is entrapped within a crosslinked polyelectrolyte gel viz. poly(2-acrylamido-2-methyl propane sulphonic acid) (PAMPS). A conventional photo-polymerization technique was followed for synthesis of the PAMPS gel while aniline is in situ polymerized within the gel, giving rise to the desired semi-IPN. For comparison, a neutral gel based semi-IPN PAn-PAAm (polyaniline-polyacrylamide) was also prepared following the similar route. PAn imparts appreciable electrical conductivity to both PAMPS and PAAm based gels without hampering their existing properties that indicates the success of the work. Synthesis of the gel was studied in detail and different experimental conditions were optimized. Different physical properties of the gel viz. its degree of swelling, electrical conductivity, mechanical strength, etc were also studied. The resultant semi-IPN or the composite hydrogel was found to possess appreciable electrical conductivity, good swellability and mechanical strength. The electro-driven volume contraction of the composite gel was found to occur at sufficiently lower voltage compared to the pure PAMPS gel, which indicates its promising application aspect in fabrication of chemomechanical devices.     

Reprotonation of polyaniline: A route to various conducting polymer materials

Polyaniline (PANI) is one of the most studied conducting polymers. Its properties can be modified by controlling the way of protonation. Polyaniline base was immersed in aqueous solutions of 42 inorganic or organic acids in order to find out, which is able to constitute a salt with the PANI base and what are the properties of products. The conductivity of the reprotonated PANI bases is determined especially by the pH of acid solutions. The highest conductivity, 1.22 S cm⁻¹, was found after reprotonation of PANI base with 50% tetrafluoroboric acid. The reaction with most strong inorganic acids yielded samples with a conductivity of 10⁻¹ S cm⁻¹. Sulfonic acids gave products having conductivity of the order of 10⁻²–10⁻¹ S cm⁻¹. Carboxylic acids were less efficient in protonation, and their ability to produce a conducting polymer depended on increasing the acid concentration. Acids containing an acidic hydroxyl group, like picric acid, also protonated PANI to a good level of conductivity. The lowest conductivity, 1.8 × 10⁻¹⁰ S cm⁻¹, was observed in the absence of any acid. The density of reprotonated PANI varied between 1.19 and 2.06 g cm⁻³, the contact angle between 29° and 102°, and volume change between −14% and +33%, depending of the acid used. The reprotonation of PANI base with various acids offers the opportunity to prepare materials with great variability and versatility in properties.     

Amperometric ascorbate sensor based on conducting polymer: Poly(N-methylaniline) versus polyaniline

Electrocatalytic oxidation of ascorbate (vitamin C) at poly(N-methylaniline) modified electrode has been studied and compared with that proceeding at polyaniline modified sensor. A sigmoid-shaped anodic current transient as a response to addition of ascorbate was found for polyaniline modified electrode in pH-neutral solution, whereas a ‘normal-shaped’ current transient was found to be characteristic for poly(N-methylaniline) modified electrode. Based on this, a hypothesis on the autocatalytic mechanism for electrochemical oxidation of ascorbate was confirmed. It has been shown that poly(N-methylaniline) modified electrode can be used as an amperometric ascorbate sensor, operating in slightly acidic or pH-neutral buffer solutions at a controlled potential of 0.1-0.5 V versus Ag/AgCl, and the dependencies of current response on ascorbate concentration, the thickness of a polymer layer, and operating potential have been analyzed.     

Optically active fluoro-substituted polyaniline prepared in organic media: The synthesis, chiroptical properties, and comparison with optically active non-substituted polyaniline

Optically active polyaniline (PANI) bearing an electron-withdrawing fluorine substituent, poly(2-fluoroaniline) (F-PANI), was synthesized in organic solvents by using (+)- or (−)-camphorsulfonic acid (CSA) as a chiral dopant, in which 2,3-dichloro-5,6-dicyanobenzoquinone (DDQ) was used as an electron acceptor. Formations of the optically active (chiral) F-PANI/(+)- or (−)-CSA, the dedoped F-PANI, and the redoped F-PANI/CSA were confirmed by the FT-IR, UV/vis/near-IR, and/or circular dichroism (CD) spectroscopy. The CD spectra of the chiral F-PANIs/(+)- and (−)-CSA were investigated in various organic solvents and compared with those of non-substituted PANI/(+)- or (−)-CSA. The F-PANI/(+)-CSA and PANI/(+)-CSA interestingly indicated almost mirror-imaged CD spectra in the visible region, although CD absorptions of the F-PANI/CSA were slightly blue shifted compared with those of PANI/CSA. The chiral F-PANI/CSA was unexpectedly confirmed to remain the initial chiral conformation during reversible dedoping/redoping cycles in solution state. The chiroptical properties of F-PANI/(+)-CSA in organic solvents were found to be affected by the solvent, probably due to the solvent effect to the polymer backbone, and the helical conformation was drastically reversed by change of the solvent. Furthermore, the conformation of F-PANI/CSA in m-cresol can be significantly changed when the F-PANI/CSA was dissolved in cosolvent of m-cresol and DMSO at various volume ratios, in which the sign inversions of CD absorption bands were caused when the ratio of DMSO in the m-cresol/DMSO cosolvent exceeded 10%. On the other hand, in the case with PANI/(+)-CSA, the similar sign inversions of CD absorption bands were not observed under the similar conditions, and then the helical conformation of chiral F-PANI/CSA was supposed to be rather flexible compared with that of chiral PANI/CSA, presumably due to relatively weak interaction among F-PANI backbone, CSA, and m-cresol.     

Photo-induced polymerization in ionic liquid medium: 1. Preparation of polyaniline nanoparticles

Photo-induced polymerization is employed to prepare polyaniline (PAN) nanoparticles in ionic liquid for the first time. Photons and photoactive ionic liquid cations replace conventional oxidants and metal complexes to promote the polymerization of aniline monomer. The diameter of the resulted PAN is confirmed in nano-scale by SEM. With increase of protonic acid in medium, the yield of the PAN increased, the UV absorption of the PAN strengthened, and a blue shift of the π-polaron absorption was observed. And the conductivity of the PAN also increased with the acid content in medium. The potential mechanism of photo-induced polymerization of aniline is proposed. Moreover, after the ionic liquid is separated from the reaction mixture and reused for five times, no obvious decrease in catalytic activity could be found in photo-induced polymerization of aniline. The method may open a new pathway to prepare nano-scale conducting polymers with sunlight.     

Fabrication of paper based carbon/graphene/ZnO aerogel composite decorated by polyaniline nanostructure: Investigation of electrochemical properties

The cellulose derived carbon/graphene/ZnO aerogel composite was prepared as an electrode in order to investigate the electrochemical properties. Carbon aerogel was synthesized using paper as an available cellulose source, and the composite was obtained through a new and simple preparation method including the immersion of monolithic carbon aerogel in graphene oxide/Zn²⁺ suspension and subsequent chemical reduction and freeze drying. The morphology, functional groups and crystalline structure of the samples were studied with Scanning Electron Microscopy (SEM), Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction Spectroscopy (XRD), respectively. Electrochemical performance of the prepared binder free electrodes was examined using Cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The data revealed that flexible carbon/graphene/ZnO composite resulted in a low density (0.035 g cm⁻³) electrode with the capacitance of 900 mF cm⁻² at a high current density of 10 mA cm⁻², lower IR drop and high cyclic stability (capacitance retention of 96%) after 1000 cycles, at 10 mA cm⁻². These features were due to the presence of 3D porous conductive network, highly reduced graphene oxide, and the formation of ZnO nanoparticles on graphene sheets. Moreover, polyaniline (PANI) was introduced to carbon/graphene/ZnO composite electrode using electro-oxidation method at different reaction time and aniline concentration in order to achieve remarkably improved capacitance of 2500 mF cm⁻² (at 10 mA cm⁻²) and low charge transfer resistance. Also, after the supercapacitor device assembly, the capacitance was retained. Based on the results, the synthesized composite is a promising material for new generation of lightweight freestanding electrodes with the high electrochemical performance.     

Influence of added surfactant on particle flocculation in waterborne polymer–particle systems

Polymer–particle interactions can cause particle flocculation and phase separation problems in waterborne coatings. The problems can be the result of interactions that are either too weak or too strong. It is known by empirical work that addition of surfactants can minimize these problems. In this study, the authors have investigated how different types of surfactants influence the polymer–particle interactions. Both hydrophobic and hydrophilic particles were included in the study, and nonionic, anionic, and cationic surfactants were used. A simple model is suggested that can be used to predict the surfactant concentration needed to stabilize the system. The model considers the cmc (critical micelle concentration) of the surfactant, the adsorption to the polymer, and the adsorption to the particles.     

Correlation between mobility enhancement and conformational change in polyaniline and its derivatives: Polaron lattice formation

Conformational changes in polyaniline, poly(methylaniline), and poly(methoxyaniline) are studied in perchloric acid and acetonitrile by means of an in situ reflection technique with oxidation level as a parameter. Stretching of polymer chains leading to enhancement of specular reflection at the polymer-coated electrodes is found to be well correlated with the increase in carrier mobility. The concomitant change in mobility and chain conformation observed with the polyaniline family is explained in terms of the formation of polaron lattice at increased oxidation levels.     

Effects of polyaniline nanoparticles in polyethersulfone ultrafiltration membranes: Fouling behaviours by different types of foulant

Polyethersulfone (PES) was modified by blending it with polyaniline (PANI) nanoparticles to improve the membrane performance. Three types of membranes: PES (controlled sample), PES-PANI self-synthesised, and PES-PANI (commercial), were evaluated by direct interaction with BSA, humic acid, silica nanoparticles, Escherichia coli and Bacillus bacteria. The surface hydrophilicity of the modified PES membranes was enhanced by the addition of PANI nanoparticles and showed improved fouling resistance and a high flux recovery ratio as well as improvement in BSA and humic acid rejection even with higher pore sizes. The modified membrane also showed less attack from the bacteria, demonstrating improved biofouling activity.     

Electroless versus electrodriven deposition of silver crystals in polyaniline: Role of silver anion complexes

Electrocrystallization of silver is studied at polyaniline-coated electrodes using silver cations and two silver anion complexes (silver thiosulfate and silver–EDTA) as reducing species. Use of the silver thiosulfate complex results in a significant shift of the silver deposition potential window in the negative direction and highly impeded metal crystallization. The silver cation and silver–EDTA plating solutions allow to perform both electrodriven and electroless metal deposition. Number and size of silver crystals obtained by the two deposition methods in the different plating solutions are compared. Electroless precipitation in the silver–EDTA solution results in the highest number (10⁸ cm⁻²) of small-sized crystals. This result is discussed in terms of the special role of the EDTA anions for the redox state of the polyaniline layers. It is demonstrated that factors such as polyaniline redox charge, concentration of reducing ions and dipping time allow effective control over the amount of electroless deposited metal.     

Synthesis by in situ chemical oxidative polymerization and characterization of polyaniline/iron oxide nanoparticle composite

Polyaniline (PANI) is a well‐studied material and is the pre‐eminent electrically conducting organic polymer with the potential for a variety of applications such as in batteries, microelectronics displays, antistatic coatings, electromagnetic shielding materials, sensors and actuators. Its good environmental as well as thermal stability and electrical conductivity tunable by appropriate doping make PANI an ideal active material for several applications. In this paper, we report the synthesis of water‐dispersible colloidal PANI/iron oxide composite nanoparticles using an in situ chemical oxidation polymerization method in a micellar medium of sodium dodecylsulfate, where the cores (iron oxide) are embedded in a PANI matrix layer. Transmission electron micrographs showed evidence of the formation of an iron oxide core/PANI shell composite with a thin layer of PANI over the iron oxide cores. The results of thermogravimetric, Fourier transform infrared and UV‐visible analysis indicated that the iron oxide nanoparticles could improve the composite thermal stability possibly due to the interaction between iron oxide particles and PANI backbone. We believe that the synthetic route described can also be adapted for the assembly of hierarchical structures of other metal oxides or hydroxides onto various cores. Copyright © 2010 Society of Chemical Industry     

Emulsifiers with high chemical resistance: a key to high performance waterborne coatings

A powerful way to coatings with low volatile content are waterborne systems. They are an important alternative to high solid- and powder coatings. It is essential, that waterborne coatings should not have a lower property level compared with conventional systems. A novel type of emulsifier allows the preparation of non-ionic stabilized aqueous emulsions. The main advantage of this new type of emulsifier consists in improving the chemical resistance of the resulting crosslinked films, especially against acids. There upon they show no discoloring even at high staving temperatures and a very good emulsifying behavior. The base type can be easily functionalized with a multitude of chemical functionalities like -OH, -COOH or vinyl groups. That means the emulsifier can be incorporated in the film during the crosslinking reaction. A migration to the coating surface can be avoided under these conditions. The different synthesis routes will be described in detail. A comparison of three non-ionic stabilized waterborne automotive coating systems with different crosslinking reactions (polyurethane, transetherifying and nucleophilic addition) with the corresponding ionic stabilized systems shows the extraordinary quality of the new tones of emulsifiers.     

High reactive CH-acidic enamines: a novel approach to two-component waterborne systems

A new CH-acidic enamine crosslinking system is described. These crosslinking resins are prepared by the reaction of acetoacetate polymers with amines to increase the CH acidity; thus it is possible to cure ,β-unsaturated resins via Michael addition at room temperature, even without strong base catalysis. Furthermore, the high reactivity of the crosslinkers allows curing in water as the solvent. Extensive curing studies via IR spectroscopy are described to investigate shelflife, and the dependence the enamine/ketimine equilibrium on curing speed, which is influenced by the polarity of the solvents. Although the enamine function can be hydrolyzed in acidic media, the crosslinked films are resistant to a multitude of both organic and inorganic compounds.     

Potentiodynamic and potentiostatic deposition of polyaniline on stainless steel: Electrochemical and structural studies for a potential application to corrosion control

Polyaniline (PAn) films were electrodeposited on stainless steel 304 (SS) from 0.5 M H₂SO₄ solution containing 0.1 M aniline (An) by using potentiodynamic and potentiostatic techniques. In particular, PAn films were prepared as follows: (i) by cyclic potential sweep (CPS) deposition upon varying the upper potential limit (E_l) of the polymerization potential region between 0.8 and 1.1 V, while the lower potential limit was equal to −0.2 V; (ii) by potentiostatic deposition upon varying the applied potential (E_appl) between 0.8 and 1.1 V. The potential sweep rate (dE/dt) was also varied for the An polymerization during the CPS deposition. Variation of the E_l, dE/dt and E_appl affects the PAn growth leading to films of different electrochemical and structural properties. The electrochemical properties of the PAn were examined by using cyclic voltammetry. Scanning electron microscopy was used to reveal the structure and morphology of the PAn films. Monitoring the open circuit potential (E_OC) of the PAn-coated SS electrode in 0.5 M H₂SO₄ shows that the SS remains in the passive state. PAn films can also provide protection to SS in chloride-containing 0.5 M H₂SO₄ for the studied period of time, although pits were detected during prolonged immersion. The protection efficiency seems to be related with the parameters E_l, dE/dt and E_appl varied during polymerization. The mechanism of the SS protection provided by the PAn coatings is discussed in terms of the active role of PAn in corrosive environments.