The influence of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) additive concentration and stretch orientation on electronic transport in AMPSA-modified polyaniline films prepared from an acid solvent mixture

We examine the effects of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)-additive concentration, molecular weight, and specimen elongation on the temperature-dependent electronic transport properties of polyaniline films prepared with AMPSA in the presence of a great excess of a formic and dichloroacetic acid (DCAA) solvent mixture. The AMPSA-additive dependent resistivity and thermopower are reported for free-standing PANI:AMPSA_x (M_w=200,000 g mol⁻¹) films (x=0.1–0.5) in the temperature range from 2 to 325 K. The low-temperature data indicate that these samples are just on the insulating side of a disorder-induced metal–insulator (M–I) transition (dρ/dT<0), and that thermal motion at elevated temperatures is sufficient to produce a metallic state (dρ/dT>0) at room temperature. Transport occurs via variable-range hopping (VRH) for temperatures below 200 K, with hopping parameters that are a strong function of x; increased AMPSA concentration decreases the resistivity and moves the samples towards the M–I phase boundary. There is a minimum in the resistivity for all samples at a temperature T_min that is also doping dependent. Stretch orientation of PANI:AMPSA_0.5 films, prepared with higher molecular weight PANI (M_w=300,000 g mol⁻¹), along the resistivity measurement direction decreases the room-temperature resistivity at the expense of a more insulating low-temperature state. The T_min values of both stretched and unstretched PANI:AMPSA_0.5 films are pushed below 200 K, which reflects reduced disorder in film processed with higher molecular weight polyaniline. These results reflect an evolution in the underlying inhomogeneous mesoscopic disorder present in doped conducting polymers.     

Investigation of interaction among polyaniline,organic acid,and water

In this work, gel permeation chromatography (GPC) and UV–vis spectroscopy are used to investigate interaction between organic acid and polyaniline (PANI) in emeraldine base (EB) form at a molecular level. Dichloroacetic acid (DCAA) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA) are chosen to study the changes in the GPC chromatograms and the UV–vis spectra of the diluted EB/N-methyl-2-pyrrolidinone (NMP) solutions when the acid was added in the solutions. The studies reveal that the organic acids form H-bonds with EB in an anhydrous solution. DCAA tends to form H-bonds with EB through intra-chain interactions whereas AMPSA tends to form H-bonds with EB through inter-chains. The inter-chain interaction among EB and AMPSA molecules results in the formation of clusters, which occupy a larger hydrodynamic volume and give much higher molecular weights than un-clustered EB molecules. Due to a strong affinity of AMPSA, water molecules are localized inside the clusters when water is present in the solution. Therefore, a small amount of water can rapidly initiate EB protonation (H₂O/AMPSA molar ratio > 5.0) at ambient conditions.     

Spectroscopic investigation of the interactions between emeraldine base polyaniline and Eu(III) ions

The interactions of emeraldine base form of polyaniline (EB-PANI) and Eu(III) ions in 1-methyl-2-pyrrolidinone (NMP) solution and in films have been investigated by UV–vis–NIR, resonance Raman, luminescence and electron paramagnetic resonance (EPR) spectroscopies. These spectroscopic techniques allowed to characterize quinone and semiquinone segments in the polymeric chains, and the oxidation state of europium ions in Eu-PANI samples. For high values of Eu(III)/N molar ratio (24/1) the presence of a weak polaronic absorption band at 980 nm in UV–vis–NIR spectrum and the observation of bands at 1330 and 1378 (ν_C–N+) cm^?1 due to emeraldine salt in the Raman spectrum at 1064 nm indicate a low doping degree. Oxidation of EB-PANI to pernigraniline base (PB-PANI) occurs in diluted solutions. The experimental data showed that the solvent plays an important role on the nature of formed species. The narrow EPR signal at g = 2.006 (line width 8G) confirms the presence of PANI radical cations in Eu-PANI film. The absence of broad signal characteristic of Eu(II) in EPR spectrum suggested that europium ions are primarily at Eu(III) oxidation state. The luminescence spectra of Eu-PANI film presented emission bands at 405 and 418 nm assigned to PANI moieties and bands at 594, 615 and 701 nm assigned to ⁵D₀ → ⁷F_J (J = 1, 2 and 4, respectively) transitions of Eu(III). EPR and photoluminescence data confirm that europium ions are mainly in Eu(III) oxidation state in Eu(III)/PANI films.     

Electrical,structural and magnetic properties of polyaniline/pTSA-TiO2 nanocomposites

Polyaniline (PANI)/para-toluene sulfonic acid (pTSA) and PANI/pTSA-TiO₂ composites were prepared using chemical method and characterized by infrared spectroscopy (IR), powder X-ray diffraction (XRD), scanning electron microscopy (SEM). The electrical conductivity and magnetic properties were also measured. In corroboration with XRD, the micrographs of SEM indicated the homogeneous dispersion of TiO₂ nanoparticles in bulk PANI/pTSA matrix. Conductivity of the PANI/pTSA-TiO₂ was higher than the PANI/pTSA, and the maximum conductivity obtained was 9.48 (S/cm) at 5 wt% of TiO₂. Using SQUID magnetometer, it was found that PANI/pTSA was either paramagnetic or weakly ferromagnetic from 300 K down to 5 K with H_C ≈ 30 Oe and M_r ≈ 0.015 emu/g. On the other hand, PANI/pTSA-TiO₂ was diamagnetic from 300 K down to about 50 K and below which it was weakly ferromagnetic. Furthermore, a nearly temperature-independent magnetization was observed in both the cases down to 50 K and below which the magnetization increased rapidly (a Curie like susceptibility was observed). The Pauli susceptibility (χ_pauli) was calculated to be about 4.8 × 10^?5 and 1.6 × 10^?5 emu g^?1 Oe^?1 K for PANI/pTSA and PANI/pTSA-TiO₂, respectively. The details of these investigations are presented and discussed in this paper.     

Electrosynthesis of polyaniline films on titanium by pulse potentiostatic method

Polyaniline (PANI) was synthesized on titanium electrode from aqueous solution containing 0.3 mol L⁻¹ aniline and 1 mol L⁻¹ HNO₃ by pulse potentiostatic method. The chronoamperogram during polymerization process of aniline was recorded. The effects of the synthesis parameters, such as anodic pulse duration (t_a), cathodic pulse duration (t_c), lower limit potential (E_c) and upper limit potential (E_a), on the morphology and electroactivity of the PANI films were investigated by scanning electron microscopy (SEM) and cyclic voltammetry (CV). SEM results present that flake, mica-like, quasi-fibrous and nano-fibrous PANI film could be synthesized with various polymerization parameters. Under the following conditions, t_a = 0.8 s, t_c = 0.1 s, E_c = 0 V and E_a = 1.0 V, high quality nano-fibrous PANI film with the best electroactivity was obtained. The CV results show that the PANI films with different morphologies, which were prepared under the same anodic polymerization charge, have obvious different characteristics. This means that the PANI films with different morphologies have different electrochemical activity.     

NH3 and HCl sensing characteristics of polyaniline nanofibers deposited on commercial ceramic substrates using interfacial polymerization

This paper reports the use of the interfacial polymerization method in a simple route for fabricating low-cost, highly sensitive NH₃ and HCl gas sensors made of polyaniline (PANI) nanofiber coatings on commercially available ceramic substrates. The PANI coatings consisted of uniform nanofibers and formed emeraldine salt. NH₃ gas-sensing properties of as-synthesized PANI nanofibers were also investigated in detail. The influence of PANI nanofiber acidification treatment at different HCl solutions (pH = 0, 1, 2, and 3) on NH₃-sensing properties was discussed as well. As-synthesized PANI nanofibers exhibited very low detection limit (1 ppm) and high sensing response (response S) was above 2 when the sensor was exposed to 50 ppm NH₃ gas, though a limited drift of the response appeared in the reproducibility test. For acid-treated PANI sensors, the response time increased and response S decreased with increasing pH value of HCl solutions. Response S, especially after acid-treatment, increased as testing proceeded. This is possibly due to the creation of reaction sites on the surface and/or the bulk of the sensors. When PANI was used to detect gaseous HCl, an irreversible process occurred and response S became saturated when the concentration of gaseous HCl reached 200 ppm.     

Rheological characterization of 2-acrylamido-2-methyl-1-propanesulfonic acid-doped polyaniline solution

The rheological properties of 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPSA)-doped polyaniline (PAni) using dichloroacetic acid (DCA) as solvent were systematically studied using parallel-plate rotational rheometer. The influence of PAni/AMPSA concentration, PAni molecular weight, shear rate, temperature and time on the apparent viscosity was measured and analyzed. At certain shear rate (about 0.03–1 s^?1, in the second region), PAni/AMPSA solution presents typical shear-thinning behavior, and PAni/AMPSA concentration and PAni molecular weight obviously affected the rheological behaviors of PAni/AMPSA solution. By temperature sweeps, it was found that the apparent viscosity of PAni/AMPSA solution decreased with the increase of temperature, and the solution became gel after 80–90 °C. More importantly, a predominant transition temperature at about 55 °C was observed in the PAni/AMPSA solutions, suggesting a structural transition at this temperature. The results of the rheological stability of PAni/AMPSA solution at different concentration and molecular weight by monitoring the viscosity change with the time at 30 and 60 °C verified that the higher temperature might be responsible for the quick gelation of the PAni solution. In addition, the non-Newtonian exponent and the apparent viscous flow activation energies of PAni/AMPSA solution has been calculated and discussed as well.     

Viscoelastic and conductivity properties of thermoreversible polyaniline–DNNSA gel in m-cresol

The rheological behavior of polyaniline (PANI)–dinonylnaphthalene sulfonic acid (DNNSA) in m-cresol is studied for different weight percent (w/v) of PANI–DNNSA_0.5. From rheological viewpoint the sample behaves like viscous fluid at low concentration (2 wt%) and gel at the concentration ≥8 wt%. The 4 wt% PANI–DNNSA_0.5 in m-cresol is at typical viscoelastic percolation region which is sol in the absence of shear but show invariant storage modulus with frequency at 30 °C. SEM picture indicates fibrillar network structure in the gel and the doped polyaniline remain as nanofiber at ≤2 wt% concentrations. The complete doping of PANI in all the systems is confirmed from UV–vis spectra. The dc conductivity of the gel increases with increasing the concentration of PANI–DNNSA_0.5 in m-cresol showing a jump at ～4% concentration (percolation threshold). ac-Conductivity increases with increase in PANI–DNNSA_0.5 concentration studied here for each frequency. At lower frequency (<10⁵ Hz) ac-conductivity increase slowly with frequency but at higher frequency (>10⁵ Hz) the increase is large having a curve like behavior. The gel state shows an increase of module by ～5 orders and also an increase of ～3 orders in ac-conductivity at the same frequency. The impedance spectroscopy results suggest the formation of combined resistance and capacitance (R–C) circuits in the gel and the increase of PANI–DNNSA_0.5 in the gel increases the capacitive feature more dominantly though the path becomes less resistive. The process also signifies the preparation of DNNSA doped PANI nanofiber in the gel medium.     

Conducting and magnetic behaviors of polyaniline coated multi-walled carbon nanotube composites containing monodispersed magnetite nanoparticles

High conductivity and supermagnetism of polyaniline (PANI)-coated multi-walled carbon nanotube (MWCNT) composites containing monodispersed 6 nm iron oxide (Fe₃O₄) nanoparticles has been successfully synthesized by in situ chemical oxidative polymerization using anionic surfactant dodecylbenzenesulfonic acid sodium salt. Hydrophilic 6 nm spherical Fe₃O₄ nanoparticles fabricated by the thermal decomposition process were chemically modified using 11-aminoundecanoic acid tetramethylammonium salt. The modified nanoparticles were further mixed with carboxylic acid containing multi-walled carbon nanotubes (c-MWCNTs) in an aqueous solution to form one-dimensional Fe₃O₄ coated c-MWCNT template and PANI/c-MWCNT nanocomposite were then synthesized via in situ chemical oxidative polymerization in HCl solution. Structural and morphological analysis using FESEM, HRTEM and XRD showed that the fabricated Fe₃O₄ coated c-MWCNT/PANI nanocomposites are one-dimensional core (Fe₃O₄ coated c-MWCNT)–shell (PANI) structures. The electrical conductivity of 1 wt% Fe₃O₄ coated c-MWCNT/PANI nanocomposites at room temperature is 37.7 S/cm, which is decreased to 28.6 S/cm with the loading of 5 wt% Fe₃O₄ nanoparticles. The magnetic properties of Fe₃O₄ coated c-MWCNT/PANI nanocomposites exhibit supermagnetism with saturation magnetization in the range of 0.04–0.15 emu/g, which increases as the amount of Fe₃O₄ nanoparticles increases.     

Composite films of nanostructured polyaniline with poly(vinyl alcohol)

The uniform composite films of nanostructured polyaniline (PANI) (e.g. nanotubes or nanorods with 60–80 nm in diameter) were successfully fabricated by blending with water-soluble poly(vinyl alcohol) (PVA) as a matrix. The PANI nanostructures were synthesized by a template-free method in the presence of β-naphthalene sulfonic acid (β-NSA) as a dopant. The molecular structures of PANI–β-NSA and the related composite films were characterized by UV–Vis absorption spectrum, FTIR spectrum and X-ray diffraction. It was found that the electrical, thermal and mechanical properties of the composite films were affected by the content of nanostructured PANI–β-NSA in the PVA matrix. The composite film with 16% PANI–β-NSA showed the following physical properties: room-temperature conductivity is in the range 10⁻² S/cm, tensile strength ∼603 kg/cm², tensile modulus ∼4.36×10⁵ kg/cm² and ultimate elongation ∼80%.     

Functional electrospun nanofibres of poly(lactic acid) blends with polyaniline or poly(aniline-co-benzoic acid)

Functionalised nanofibres of a controlled fibre diameter were electrospun from solutions of polyaniline (PANI) or poly(aniline-co-m-aminobenzoic acid) (P(ANI-co-m-ABA)) with poly(lactic acid) (PLA). Soluble copolymers of aniline (ANI) and m-aminobenzoic acid (m-ABA) were prepared and the average molecular weight of the copolymers, as determined by gel permeation chromatography, was found to decrease from 13,800 g mol^?1 to 1640 g mol^?1 with an increase of m-ABA content in the copolymer. By contrast, FT-MS results revealed that homopolymerisation of m-ABA formed oligomers rather than polymeric chains due to low reactivity of m-ABA monomer. ATR FTIR, Raman spectroscopy, and conductivity measurements confirmed incorporation of the conducting (co)polymers within the PLA based nanofibres. The conductivity of the nanofibres increased significantly with increased proportion of PANI or P(ANI-co-m-ABA) to 2.0 × 10^?5 mS cm^?1 for PLA/PANI (3.27% of PANI) and 8.3 × 10^?6 mS cm^?1 for PLA/P(ANI-co-m-ABA) (5.80% of the copolymer in the blend). The nanofibre diameter decreased from 640 ± 195 nm for pure PLA fibres to 141 ± 68 nm for PLA/PANI, and to 124 ± 31 nm for PLA/P(ANI-co-m-ABA). These fibres have potential for a range of applications, such as electroactive scaffold tissue engineering and sensing.     

Preparation of organo-soluble polyanilines in ionic liquid

A method for preparation of organo-soluble polyaniline (PANI) is described. Oxidative coupling polymerization of anilium chloride with ammonium persulfate in a new ionic liquid, 2-hydroxyethyl ammonium formate (HAF), gives organo-soluble polyaniline with appreciable molecular weights (M_w = 86,400). Interestingly polyaniline (PANI) prepared by this method is highly soluble in many organic solvents such as acetone, tetrahydrofurane, dioxane, dimethyformamide and N-methyl, 2-pyrrolidinone. Thin films of PANI prepared at 0 °C (by solvent casting) show reasonable conductivities (up to 37.0 S cm⁻¹) when doped with p-toluene sulfonic acid.     

Preparation and characterization of polyaniline film on stainless steel by electrochemical polymerization as a counter electrode of DSSC

Polyaniline (PANI) films were electrodeposited on stainless steel 304 (SS) from 0.5 M H₂SO₄ solution containing 0.3 M aniline by potentiostatic techniques to prepare a low cost and non-fragile counter electrode in dye-sensitized solar cell (DSSC). The compact layer, micro-particles, nanorods and fibrils were observed on the top of PANI films with different applied potentials (E_appl) by SEM. Then the conductivity and electrochemical test illuminated that a polyaniline film with the highest conductivity and best electrocatalytic activity for I₃^?/I^? reaction was electrodeposited at 1.0 V E_appl. Finally, the photoelectric measurement showed that the energy conversion efficiency of DSSC with the PANI electrode was increased with the E_appl decreasing. And the efficiency of DSSC with PANI counter electrode at 1.0 V was higher than that with Pt electrode, owing to the loosely porous structure, high conductivity and excellent catalytic activity of PANI electrode.     

Magnetic properties of hydrophilic iron oxide/polyaniline nanocomposites synthesized by in situ chemical oxidative polymerization

This work describes the preparation and characterization of polyaniline (PANI)/hydrophilic iron oxide nanocomposites synthesized from monodispersed 13 nm iron oxide (Fe₃O₄) nanoparticles and aniline monomer in HCl solution by in situ chemical oxidative polymerization. Hydrophilic 13 nm spherical Fe₃O₄ nanoparticles fabricated using the thermal decomposition process were modified using 11-aminoundecanoic acid tetramethylammonium salt. The modified Fe₃O₄ nanoparticles that served as cores were dispersed in an aqueous solution with anionic surfactant dodecylbenzenesulfonic acid sodium salt to form spherical templates and the PANI/Fe₃O₄ nanocomposites were then synthesized via in situ chemical oxidative polymerization on the surface of spherical templates. Structural and morphological analysis using X-ray diffraction and high-resolution transmission electron microscopy showed that the fabricated PANI/Fe₃O₄ nanocomposites are core (Fe₃O₄)-shell (PANI) structures. The magnetic properties of PANI/Fe₃O₄ nanocomposites exhibit supermagnetism with saturation magnetization in the range of 0.23–0.91 emu/g, depending on the amount of 13 nm Fe₃O₄ nanoparticles.     

The role of solvent on the doping of polyaniline with Fe(III) ions

The products formed from the reaction of emeraldine base polyaniline (EB-PANI) with Fe(III) ions in N-methyl-pyrrolidone (NMP), dimethylacetamide (DMA), dimethylformamide (DMF) and m-cresol media have been investigated using UV–VIS–NIR and resonance Raman (λ₀ = 632.8 and 1064 nm) spectroscopies. Through these results it was verified that the different PANI forms in solution can be formed by the suitable choice of the solvent. The behavior of Fe(III)/EB-PANI in different solvents was rationalized in terms of the interactions among Fe(III) ions, EB-PANI and solvent. In basic NMP, DMA and DMF media, the reaction of Fe(III) with EB-PANI yields EB-PANI doping giving ES-PANI and/or the EB-PANI oxidation to PB-PANI. The formation of ES-PANI is favored in DMF while PB-PANI is formed in a greater extension in NMP and DMA. In acidic m-cresol, only ES-PANI is produced in Fe(III)/EB-PANI solutions indicating the important role played by the solvent in the nature of the product.     

Large magnetoresistance observed in facing-target sputtered Ni-doped CNx amorphous composite films

A series of amorphous Ni-doped CN_x films with ∼23 at.% Ni were fabricated using facing-target sputtering at different nitrogen partial pressures (P_N). The films were composed of ∼1–4 nm Ni-rich particles embedded in a CN_x matrix and turn from ferromagnetic at low temperatures to superparamagnetic at room temperature. The largest negative magnetoresistance (MR = [R(H) − R(0)]/R(0)) reaches −59% at a P_N of 4% and a temperature of 3 K. With a decrease of P_N from 4% to 0%, the electrical transport mechanism changes from tunneling to variable-range hopping and the maximum MR drops from ∼59% to ∼3.8%. The MR–H curves show a weak saturation trend in a high-field regime and the MR–T curves follow the relation of log|MR| ∝ −T below 20 K for all the films, despite the difference in transport mechanism. The origin of the large MR (−59%) can be ascribed to a spin-related high-order tunneling process.     

Fabrication and characterization of polyaniline/porous silicon heterojunction

Heterojunction between polyaniline (PANI) and porous silicon (PS) was fabricated by making a layer of PANI on PS, using spin coating method. PS was fabricated by electrochemical etching process. PS was characterized by photoluminescence (PL), scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) while the PANI was characterized by FTIR and absorption (UV–VIS) spectroscopy. Current–voltage and capacitance–voltage measurements were done to determine the electrical properties of the heterojunction structure. The ideality factor of the heterojunction was found to be 4.2, which was considered high due to large defect density at the interface. Built-in potential was measured by both I–V and C–V and was found to be Φ_b(I–V) = 0.41 V and Φ_b(C–V) = 0.28 V respectively. The discrepancy in the values of the built-in potential was discussed. Band discontinuity in conduction band and valence band were found to be 0.65 and 1.27 eV respectively. Solar response of the heterojunction was also observed at AM (air mass) 1.0 and it showed a promising behavior as a photovoltaic device.     

Deformation behavior of a two-phase Mo–Si–B alloy

Mo–Si–B alloys are being considered as possible candidates for high-temperature applications beyond the capabilities of Ni-based superalloys. In this paper, the high-temperature (1000–1400 °C) compression response over a range of quasi-static strain rates, as well as the monotonic and cyclic crack growth behaviors (as a function of temperature from 20 °C to 1400 °C) of a two-phase Mo–Si–B alloy containing a Mo solid solution matrix (Mo(Si,B)) with ∼38 vol% of the T2 phase (Mo₅SiB₂) is discussed. Analysis of the compression results confirmed that deformation in the temperature–strain-rate space evaluated is matrix-dominated, yielding an activation energy of ∼415–445 kJ/mol. Fracture toughness of the Mo–Si–B alloy varies from ∼8 MPa√m at room temperature to ∼25 MPa√m at 1400 °C, the increase in toughness with temperature being steepest between 1200 °C and 1400 °C. S–N response at room temperature is shallow whereas at 1200 °C, a definitive fatigue response is observed. Fatigue crack growth studies using R = 0.1 confirm the Paris slope for the two alloys to be high at room temperature (∼20–30) but decreases with increasing temperature to ∼3 at 1400 °C. The crack growth rate (da/dN) for a fixed value of ΔK in the Paris regime in the 900–1400 °C range, increases with increasing temperature.     

Effect of solute segregation on the strength of nanocrystalline alloys: Inverse Hall–Petch relation

We have used a high-energy ball mill to prepare single-phased nanocrystalline Fe, Fe₉₀Ni₁₀, Fe₈₅Al₄Si₁₁, Ni₉₉Fe₁ and Ni₉₀Fe₁₀ powders. We then increased their grain sizes by annealing. We found that a low-temperature anneal (T < 0.4 T_m) softens the elemental nanocrystalline Fe but hardens both the body-centered cubic iron- and face-centered cubic nickel-based solid solutions, leading in these alloys to an inverse Hall–Petch relationship. We explain this abnormal Hall–Petch effect in terms of solute segregation to the grain boundaries of the nanocrystalline alloys. Our analysis can also explain the inverse Hall–Petch relationship found in previous studies during the thermal anneal of ball-milled nanocrystalline Fe (containing ∼1.5 at.% impurities) and electrodeposited nanocrystalline Ni (containing ∼1.0 at.% impurities).     

I–V characteristics of the p–n junction between vertically aligned ZnO nanorods and polyaniline thin film

The characteristics of the p–n junction between vertically aligned ZnO nanorods and polyaniline (PANI) thin film were investigated. The rectifying behavior of the I–V curve of ZnO/PANI diode was verified with assembled ZnO/PANI structures. The cut-in voltage of the p–n junction was found to be around 0.5 V and the reverse breakdown voltage was about ?27 V. In addition, the effects of UV illumination and NH₃ exposure on the I–V characteristics of ZnO/PANI configuration were also investigated.