Structural investigation of lignosulfonate doped polyaniline

Lignosulfonate doped polyaniline (LGS-PANI) was prepared in the presence of sulfamic acid as a novel conducting filler. The room temperature conductivity of LGS-PANI increases more than two-fold with LGS at a mass fraction of 11.4 wt% and these conductivities (0.73–5.00 S/cm) exceed the highest reported for polymer acid-doped PANI systems. The conductivity stability and thermal stability are clearly improved at a certain content of LGS in LGS-PANI. These trends are accompanied by significant structural changes as evidenced by X-ray diffraction studies. The material characterization was also carried out by Fourier transform IR spectroscopy, thermogravimetric analysis and scanning electron microscopy.     

Characterization of polyaniline doped with diphenyl phosphate

UV–Vis spectroscopy and conductivity of the polyaniline (PANI) doped with diphenyl phosphate (DPHP), in comparison with that of HCl-doped polyaniline, show that the decrease in polaron delocalization and structural order results from the steric hindrance imparted by the longer chain counter ion. PANI protonated with DPHP is soluble in common organic solvents such as toluene, chloroform, dimethyl sulfoxide, etc. The conductivity of PANI/DPHP pressed pellet (at 25°C, 1.66 S cm⁻¹) increases with temperature from −40°C (1.18 S cm⁻¹) to +140°C (3.07 S cm⁻¹) due to thermal activation, and decreases with temperature from 140 to 180°C (0.25 S cm⁻¹) due to thermal undoping accompanied by the loss of some polarons. The temperature dependence of spin density is consistent with those of conductivity. After the heating scan, the conductivity (0.52 S cm⁻¹) at room temperature reduces to nearly one-third of the original value.     

Anticorrosion pigments with a shell of doped polyaniline

It has been determined that a dopant acid affects the dispersion composition of the prepared coreshell pigments. Anticorrosion properties of the pigments with the polyaniline (PAN) shell have been investigated. Pigments with a PAN shell doped by phosphoric acid possess the highest anticorrosion properties. The dependence of the electrical conductivity on the substrate-to-PAN ratio has been determined. Anticorrosion properties of polymer coatings containing the pigments with PAN shell have been studied.     

Magnetic properties of polyaniline doped with FeCl3

Magnetic properties of polyaniline (PANI) doped with FeCl₃ were investigated as a function of temperature and magnetic field. The temperature dependence of the magnetic susceptibility (χ) of PANI doped with FeCl₃ exhibits dominant paramagnetic component (well described by Curie–Weiss law with a negative Curie–Weiss temperature Θ) accompanied by a small temperature-independent paramagnetic contribution. Magnetization measured as the function of magnetic field shows smaller saturation effect than expected for non-interacting iron ions. These two observations suggest weak antiferromagnetic (AF) interactions between Fe ions.     

Magnetic behavior of polyaniline doped with oxidized ferrocenesulfonic acid

Ferrocenesulfonic acid (FSA) was oxidized by iodine (I₂) and then used as dopant for polyaniline emeraldine base. The resulted polyaniline showed an electrical conductivity of 4.50 × 10⁻² S/cm and a ferromagnetic interaction with a positive Weiss constant of 15 K, the magnetic behavior is attributed to the ferromagnetic coupling between ferrocenium cations in the counter-ions along the polyaniline chain.     

Electrochemical performance of mechanochemically prepared polyaniline doped with lithium salt

Oxides and phosphates of transition metals are now predominant cathode materials of lithium-ion batteries. Organic redox active materials, conducting polymers in particular, could be a more environmentally friendly alternative. But their electrochemical characteristics were of insufficient level as to the charge capacity, rate capability and cyclability. Here, electrochemical performance of lithium salt doped polyaniline samples prepared by mechanochemical and chemical methods is comparatively analyzed as an active component of cathode masses of lithium batteries. It is shown that mechanochemically prepared polyaniline possesses specific capacity close to the theoretical limit as well as high rate capability and cyclability during prolonged charge–discharge.     

Synthesis and characterization of organo-soluble conducting polyaniline doped with oleic acid

An emulsion polymerization process has been developed for the direct synthesis of the organo-soluble polyaniline (PANI) with oleic acid (OA) as the surfactant and dopant. The polyaniline doped with oleic acid (PANI/OA) powders, prepared by the proposed method, are highly soluble in many organic solvents such as dimethyl sulfoxide (DMSO), dimethyformamide (DMF) and N-methyl,2-pyrrolidinone (NMP). The PANI/OA powders were characterized by elemental analysis (EA), FTIR, UV–vis, TGA and SEM. The conductivities of the PANI/OA powders decreased with the increasing of the amounts of water in the emulsion polymerization.     

Preparation,degradation of polyaniline doped with organic phosphorus acids and corrosion essays of polyaniline–acrylic blends

Preparation and characterization of polyaniline (PANI) doped with anions containing phosphorus was investigated with the help of various technique. The chemical polymerization of aniline was carried out in acid media containing different anions of organic phosphorus acid with the use of ammonium peroxidisulfate as oxidant agent. The highest yield was observed in the case of styrilphosphonic acid. The conductivity increased in the following order: phenylphosphinic acid < 2chloroethylphosphonic acid < styrilphosphonic acid. The solubility tests carried out in DMF, DMSO and NMP showed that the presence of voluminous anions improves the solubility of doped PANI. The synthesized PANI was characterized by density, intrinsic viscosity, solubility, FTIR, UV–vis, NMR, conductivity and TGA measurements. The hardness, elasticity, resistance and protective behavior of acrylic films were determined. The acrylic dispersion based on PANI doped with anions containing phosphorus provides improved corrosion protection of carbon steel.     

Transmembrane redox reactions through polyaniline membrane doped with fullerene C60

Polyaniline (PANI)-C₆₀ membranes were chemically synthesized with fullerene C₆₀ content of 0.2, 0.5, 1, 2 and 3 mol% (relative to aniline fragment) respectively, and then systematically characterized with FTIR, field emission scanning electron microscopy (FESEM), XPS and electrochemical impedance spectroscopy (EIS). It is demonstrated that electron/ion coupled transport across PANI-C₆₀ membrane is possible in the presence of oxidizing agent at one side of the membrane and reducing agent at the other side. If 0.05 M acidic solution of FeCl₃ was used as the oxidizing agent and 0.3 M ascorbic acid as the reducing agent, a typical value of transmembrane transport rate of redox equivalents was 3.1 × 10⁻⁸ mol s⁻¹ cm⁻² with the membrane containing 0.5% C₆₀. This value was one order higher than that for HCl doped PANI membrane at identical conditions, which can be explained by superimposed C₆₀ doping and acid doping. The 0.5% content of C₆₀ is optimal and at higher content the rates of transmembrane redox transport decrease.     

The study of electrical and magnetic properties of LiPF6 doped polyaniline

The results of temperature dependent dc conductivity, EPR magnetic susceptibility, and X-ray photoelectron spectroscopy experiments (XPS) are reported for polyaniline (PAN) doped with lithium hexafluorophosphate (LiPF₆), PAN-LiPF₆. DC conductivity (σ_dc) and its temperature dependence of PAN-LiPF₆ samples vary with the average molecular weight (Mw) of polyaniline used and the composition of doping solution. The EPR linewidth and Pauli susceptibility (χ^P) depend on the Mw of PAN used. The σ_dc and the χ^P of the intermediate Mw PAN-LiPF₆ samples are higher than those of the low Mw PAN samples, indicating more highly conducting state of the intermediate Mw PAN samples. Based on the results of XPS and EPR experiments, some portions of quinoid rings in emeraldine base form of PAN are transformed into benzenoid rings through LiPF₆ doping process, indicating the formation of polarons. However, the existence of some portions of quinoid rings in PAN-LiPF₆ samples after doping suggests an inhomogeneous doping or a pseudo doping.     

Water-borne conductive polyaniline doped by acidic phosphate ester containing polysilsesquioxane precursor

Acidic phosphate ester (APES) bearing polysilsesquioxane precursor was prepared employing the ring-opening reaction of (3-glycidoxypropyl)trimethoxysilane (GPTMS) with acidic phosphate monoester carrying long hydrophilic tail. Doped with APES, polyaniline emeraldine base (PANI) was successfully dissolved or dispersed in water, and a free-standing film with electrical conductivity as high as 0.05 S/cm was available. The obtained film showed water-resistance due to the confinement from inorganic networks of amorphous polysilsesquioxane characterized by ²⁹Si-MAS NMR spectrum. When the conductive film was soaked in water for 14 days, its electrical conductivity showed a little decline at the first stage of 6 days, and a considerably long platform existed at the following stage. However, for the film without polysilsesquioxane network, the electrical conductivity showed a sharp decline, and the film was broken into pieces for only 1 day soaking. Covalently linked with inorganic network of polysilsesquioxane by POC bond, thermal stability of the conductive polyaniline was also improved compared with that of the conductive hybrid film from physical blending.     

EPR study of charge transfer in polyaniline highly doped by p-toluenesulfonic acid

Magnetic, relaxation and electronic dynamic parameters of paramagnetic centers in crystalline domains of polyaniline highly doped by p-toluenesulfonic acid (PANI-PTSA) as well as PANI-PTSA dispersed in poly(methyl methacrylate) were studied by the 3 cm (9.7 GHz) and 2 mm (140 GHz) wavebands EPR. These centers demonstrate the Lorentzian single line with the Dysonian contribution at both wavebands indicating intrinsic conductivity of metal-like domains near 1500–4000 S/cm at room temperature. Effective conductivity of the polymer is defined by Q3D delocalization of charge carriers within such domains and their Mott variable range hopping between the domains dominating its micro- and macroscopic conductivity. It was shown that the interaction of the charge carriers with the lattice phonons governs intradomain charge transfer at high temperatures. Reversible dipolare interaction of paramagnetic centers with oxygen was revealed. This interaction depends on electron precession frequency and/or on the PANI-PTSA dispersion in an insulating matrix. Charge transfer in PANI-PTSA was analyzed to be non-correlated with spin relaxation and dynamics that evidences the formation of Q3D metal-like domains contrary to the “single conducting chain” model.     

Structure and properties of selenious acid doped polyaniline with varied dopant content

In this study, the effects of dopant content on the structure, especially crystalline structure, and properties of selenious acid doped polyaniline (PAni) were investigated. The structure and properties of PAni were characterized by X-ray diffraction, FTIR spectroscopy, UV–vis spectroscopy, DSC, and TGA. By varying the dopant/monomer molar ratio (D/M), the morphology as well as the crystalline structure of PAni was significantly changed. The presence of water in the crystalline structure of PAni prepared with a low D/M ratio caused a change in the d-spacing of the PAni crystalline structure. The oxidation level and doping degree of PAni were also changed by varying the D/M ratio. The electrical conductivity of PAni increased with increasing D/M ratio, and the thermal stability of PAni in the doped state was about 200 °C for different D/M ratios.     

Electrochemical behavior of mild steel coated by polyaniline doped with organic sulfonic acids

A comparison of electrochemical behavior was made of coatings of pure undoped PANI cast from solution and this coating after doping as a film on the substrate. These were also compared to coatings of pure PANI/sulfonic acids adducts formed from the outset in the doped state through casting from xylene or chloroform solutions. The results obtained allowed to assume that the formation of protective iron oxide layers occurs mainly during the coating of pure undoped PANI (emeraldine base). During the doping stage a modification of these layers obviously proceeds leading to a change of the corrosion currents of the whole coating system. As a consequence, the formation of pure doped PANI coatings by casting doped PANI from solutions cannot give as good of results as does the two stage process.     

Preparation and electrical–magnetic properties of polyaniline doped with ionic ferrocenesulfonic acid

Conducting polyaniline with electrical conductivity of 2.34 × 10⁻¹ S cm⁻¹ was obtained using ferrocenesulfonic acid as dopant. After the ferrocenesulfonic acid was oxidized with FeCl₃, though the electrical conductivity of the doped polyaniline decreased by 1–2 orders of magnitude, the magnetic susceptibility (χ) increased with the increase of the oxidation degree of ferrocenesulfonic acid. EPR spectra showed not only a signal with a g value of around 2, but also a so-called half-field signal with a g value of about 4 even at room temperature. Coexistence of ferromagnetic intrachain interactions and antiferromagnetic interchain interactions in the materials has been suggested.     

Comparison of electronic transport properties of soluble polypyrrole and soluble polyaniline doped with dodecylbenzene-sulfonic acid

The temperature dependences of the conductivity of soluble polypyrrole (PPy) and soluble polyaniline (PANI) films doped with dodecylbenzene-sulfonic acid (DBSA) have been studied. The room temperature conductivities of samples were 1–8 and 95–100 S/cm, with resistivity ratio ρ_r=ρ(20 K)/ρ(300 K)∼10⁴ and ρ_r=ρ(1.4 K)/ρ(300 K)∼32 for PPy-DBSA and PANI-DBSA, respectively. At low temperatures, the temperature dependence follows the σ(T)=σ₀exp[−(T₀/T)^m] law, which has been explained within the framework of granular metals model (m=0.5) for PPy-DBSA and Mott's variable range hopping model (m=0.25) for PANI-DBSA. The magnetoresistance of PANI-DBSA is positive and follows H² and H^1/3 dependencies at low and high magnetic fields, respectively; the magnitude of the magnetoresistance is strongly temperature dependent.     

Corrosion inhibition of aluminum alloy in chloride mediums by undoped and doped forms of polyaniline

Corrosion inhibition of Al 3003 alloy by pure undoped PANI (emeraldine base) and PANI doped with p-toluene-sulfonic, camphorsulfonic and dodecylbenzenesulfonic acids was investigated. Corrosion resisting properties of PANI coatings with an artificially created hole defect were evaluated by electrochemical impedance spectroscopy (EIS) in aqueous 3.5% NaCl and 0.1 N HCl solutions. The highest corrosion inhibition factor was obtained for undoped PANI being equal to 12 and 4.4 in neutral and acidic media, respectively. The results indicated that corrosion protection of the bare aluminum alloy surface resulting from a defect of the PANI coating is in line with an increase of the thickness of the oxide layer protecting the aluminum alloy surface. The efficiency of corrosion protection of mild steel and aluminum alloy by polyaniline coatings was compared.     

Sensing behavior of the polypyrrole and polyaniline sensor for several volatile organic compounds

The sensing characteristics of conducting polymers to several volatile organic compounds were investigated with a UV-Vis-NIR spectrophotometer, dynamic contact angles measurement and scanning probe microscopy (SPM). When gases were absorbed, the polypyrrole (PPy) and polyaniline (PANi) exhibited positive and negative sensitivity, respectively. The PPy-based sensor demonstrated decreasing conductivity while the PANi sensor exhibited increasing conductivity when the polarity of the molecules absorbed increased. PPy film has an hydrophilic property while the PANi film a hydrophobic one. These changes in polymer conductivity, it is speculated, are due to the interruption of free carrier movement or the generation of polarons by the absorbed molecules.     

Environmental responses of polyaniline inverse opals: Application to gas sensing

Much attention has been directed toward the fabrication of nanostructured polyaniline and its applications. In this study, we examined the potential of polyaniline inverse opals as sensors. The inverse opals were chemically synthesized via templating polystyrene colloidal crystals and then subjected to four response tests: dry gas flow, ethanol vapor, hydrogen chloride, and ammonia. The three-dimensionally ordered macroporous polyaniline was of good quality as observed by scanning electron microscopy. The samples demonstrated high sensitivity and fast response to different conditions, which may be due to the porosity facilitating diffusion and large surface area interacting with substances. Moreover, the effect of the structural order on the responses is discussed.