Preparation,FTIR spectroscopic characterization and isothermal stability of differently doped fibrous conducting polymers based on polyaniline and nylon-6,6

The fibrous conducting polymers based on polyaniline and nylon-6,6 are obtained by stirring with magnetic bar. The increase in the ratio of conducting polymer volume in case of such fibers make them attractive materials for potential applications. As it is difficult directly to form fibers of conducting polymers, stirring process is attempted to form fibers of conducting polyaniline and nylon-6,6. In the present paper, the fibrous polyaniline:nylon-6,6 (PANI:Ny-6,6) with different weight percentages (5–20%, w/w) are prepared by stirring process. The fibers obtained are characterized using Fourier-transform infrared spectra (FTIR) and scanning electron microscopy (SEM), the variation of electrical conductivity with different type doping agents 0.1 M (HCl, H₂SO₄ and HClO₄) and the stability in terms of DC electrical conductivity retention was studied in an oxidative environment by isothermal characteristics.     

Self-assembled polyaniline nanotubes and nanoribbons/titanium dioxide nanocomposites

Self-assembled polyaniline (PANI) nanotubes, accompanied with nanoribbons, were synthesized by the oxidative polymerization of aniline with ammonium peroxydisulfate in an aqueous medium, in the presence of colloidal titanium dioxide (TiO₂) nanoparticles of 4.5 nm size, without added acid. The morphology, structure, and physicochemical properties of the PANI/TiO₂ nanocomposites, prepared at various initial aniline/TiO₂ mole ratios, were studied by scanning (SEM) and transmission (TEM) electron microscopies, FTIR, Raman and inductively coupled plasma optical emission (ICP-OES) spectroscopies, elemental analysis, X-ray powder diffraction (XRPD), conductivity measurements, and thermogravimetric analysis (TGA). The electrical conductivity of PANI/TiO₂ nanocomposites increases in the range 3.8 × 10^?4 to 1.1 × 10^?3 S cm^?1 by increasing aniline/TiO₂ mole ratio from 1 to 10. The morphology of PANI/TiO₂ nanocomposites significantly depends on the initial aniline/TiO₂ mole ratio. In the morphology of the nanocomposite synthesized using aniline/TiO₂ mole ratio 10, nanotubes accompanied with nanosheets prevail. The nanocomposite synthesized at aniline/TiO₂ mole ratio 5 consists of the network of nanotubes (an outer diameter 30–40 nm, an inner diameter 4–7 nm) and nanorods (diameter 50–90 nm), accompanied with nanoribbons (a thickness, width, and length in the range of 50–70 nm, 160–350 nm, and ～1–3 μm, respectively). The PANI/TiO₂ nanocomposite synthesized at aniline/TiO₂ mole ratio 2 contains polyhedral submicrometre particles accompanied with nanotubes, while the nanocomposite prepared at aniline/TiO₂ mole ratio 1 consists of agglomerated nanofibers, submicrometre and nanoparticles. The presence of emeraldine salt form of PANI, linear and branched PANI chains, and phenazine units in PANI/TiO₂ nanocomposites was proved by FTIR and Raman spectroscopies. The improved thermal stability of PANI matrix in all PANI/TiO₂ nanocomposites was observed.     

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.     

Electrical and magnetic properties of the Fe3O4–polyaniline nanocomposite pellets containing DBSA-doped polyaniline and HCl-doped polyaniline with Fe3O4 nanoparticles

DBSA-doped polyaniline (DBSA–PANI) powder and HCl-doped polyaniline with Fe₃O₄ nanoparticles (HCl–PANI–Fe₃O₄) powder were mechanically mixed to obtain the Fe₃O₄–polyaniline nanocomposites. Powders of the nanocomposites were pressed to the pellets. Micromorphology, electrical and magnetic properties of the nanocomposite pellets were studied by using scanning electron microscopy and by measuring the conductivity in 100–300 K and the magnetization curve at room temperature. The DBSA–PANI pellets consist of long fibrils while the HCl–PANI–Fe₃O₄ pellets consist of granular particles. Thus the Fe₃O₄–polyaniline nanocomposites pellets consist of long fibrils and granular particles. The conductivity of the nanocomposite pellets linearly decreases from 0.19 ± 0.06 to 0.05 ± 0.01 S/cm when the HCl–PANI–Fe₃O₄ content increases from 0 to 100 wt.%. The variation of conductivity with temperature reveals that the charge transport mechanism can be considered to be one-dimensional variable-range-hopping (1D-VRH). All the Fe₃O₄–polyaniline nanocomposites show the magnetization curves. The saturation magnetization monotonously increases with increasing HCl–PANI–Fe₃O₄ content while the coercivity is estimated to be about zero independent of the HCl–PANI–Fe₃O₄ content. The saturation magnetization of the HCl–PANI–Fe₃O₄ is 11 emu/g.     

Synthesis of polyaniline nanotubes using Mn2O3 nanofibers as oxidant and their ammonia sensing properties

In this work, a new method for the synthesis of polyaniline (PANI) nanotubes was presented. Experimentally, Mn₂O₃ nanofibers prepared by electrospinning technique were used as the oxidant template to initiate the polymerization of aniline in acid solution. After reaction, polyaniline shells were formed on the Mn₂O₃ nanofiber surface, and the Mn₂O₃ nanofibers were spontaneously removed. As a result, PANI nanotubes were obtained. As-prepared PANI nanotubes show an average diameter of 80 nm and inner diameter of 38 nm. The final PANI nanotubes were characterized by SEM, EDX, TEM, FTIR and XRD. The gas sensing of as-obtained PANI nanotubes was also investigated. It was found that the PANI nanotube sensing device could detect as low as 25 ppb NH₃ in air at room temperature with good reversibility.     

A three-in-one improvement in thermoelectric properties of polyaniline brought by nanostructures

β-Naphthalene sulfonic acid doped polyaniline nanotubes (PANI NT) was synthesized, a sample without specific nanostructure was prepared as a reference. Seebeck coefficient, electrical and thermal conductivity of both samples were studied. For a PANI NT prepared with an aniline/NSA ratio of 4:1, the Seebeck coefficient had a value of 212.4 μV/K at 300 K, which was 7 times higher than that of the reference sample. Meanwhile, electrical conductivity almost doubled, changed from 0.0045 to 0.0077 S/cm, while the thermal conductivity reduced by 27.5%, dropped from 0.29 to 0.21 W/m K. Finally, thermoelectric performance was evaluated by calculating the thermoelectric power factor and figure of merit, and there was a two orders of magnitude's increase for the tube-like PANI. A series of PANI NTs prepared under different aniline/NSA ratio were also investigated for searching an optimized performance. Tubular nanostructure was proved to be effective for enhancing the thermoelectric performance. This idea might be applicable to other organic thermoelectric materials as well.     

Synthesis and properties of high performance nanostructured polyaniline: Effect of initiator dosage and molecular oxygen

The effects of ammonium persulfate (APS)/aniline feed molar ratio or O₂ bubbling on the polymerization of polyaniline (PANI) in self-stabilized dispersion polymerization (SSDP) were examined. As the APS/aniline feed molar ratio was increased from 0.25/1.00 to 1.50/2.00, the polymerization yield was enhanced from 20% to 80%. However the molecular weight reduction with increased feed ratio, that is normally observed when PANI was polymerized in aqueous medium, was little. The O₂ bubbling during polymerization made the nanostructure of PANI to be finer, and this improved the solubility of PANI in solvent. The FT-IR spectra showed that the PANI prepared by SSDP, which have high conductivity in the range of 600–800 S/cm, contained less amount of the structures by ortho-coupling or Michael reductive addition of aniline compared to that synthesized by the standard method in an aqueous medium.     

Polyaniline nanofibers synthesized in compressed CO2

Polyaniline (PANI) nanofibers were synthesized in compressed liquid carbon dioxide without any template or surfactant. The polymerization of aniline took place at the interface between CO₂ and aqueous solution in a high-pressure stirred reactor. The prepared PANI nanofibers were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM), electrical conductivity (EC), Fourier-transform infrared (FT-IR), thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and X-ray diffraction (XRD) analyses. The yield of polymerization was high enough to reach 63.04% while maintaining small diameters of the PANI nanofibers. This result is very important for the preparation of the PANI nanofibers because no other previous investigations have achieved both high yield and small diameter of fibers at the same time. Through SEM and TEM analyses, we observed that the PANI nanofibers had diameter range of 30–70 nm and a length range of 0.3–1 μm, which caused them to disperse well in various solvents such as water, ethanol, 2-propanol, m-cresol and toluene. The electrical conductivity of the PANI nanofibers was 4.34 S/cm at 20 °C. The XRD diffraction pattern showed that the PANI nanofibers had crystalline one-dimensional structures, which gave high thermal stabilities as confirmed by TGA.     

Stable polyaniline dispersions prepared in nonaqueous medium: synthesis and characterization

Peroxodisulfate-induced polymerization of aniline at 10°C in acidic (HCl) nonaqueous medium using dimethyl sulfoxide (DMSO) as the solvent, readily produced polyaniline (PANI) in a stable dispersion form. The stability of the dispersion of PANI in the nonaqueous (DMSO) medium is much enhanced when the same is synthesized in the presence of a support polymer, poly(vinyl alcohol) (PVA) dissolved in the solvent. Results of studies on HCl-doped PANI prepared in DMSO medium by UV–VIS and FTIR spectroscopy support that the doped PANI so obtained is structurally similar to that of doped PANI prepared likewise in acidic aqueous medium. PANI and PANI–PVA composite as prepared in DMSO medium and the relevant isolated dry products were further characterized thermally, employing differential scanning calorimetry (DSC) and thermogravimetry (TG) and morphologically, employing transmission electron microscopy (TEM). HCl-doped PANI prepared separately in DMSO and aqueous media shows electrical conductivity values of 1.07 and 12.0 S cm⁻¹, respectively, the polymer prepared in nonaqueous medium (DMSO) being measurably poorer in electrical conductivity,     

Preparation and characterization of polyaniline nanoparticles synthesized from DBSA micellar solution

Chemical oxidative polymerization of aniline was performed in a micellar solution of dodecylbenzene sulfonic acid (DBSA, anionic surfactant) to obtain conductive nanoparticles with enhanced thermal stability and processability. DBSA was used to play both the roles of surfactant and dopant. The polymerization kinetics and optimum polymerization conditions were determined by UV–VIS spectra. The optimum molar ratio of oxidant to aniline was 0.5 and DBSA content was the most important factor in the formation of polyaniline (PANI) salt. The polymerization rate was increased with increasing DBSA concentration. The reaction model was proposed on the basis of the roles of DBSA. The electrical conductivity varied with the molar ratio of DBSA to aniline and the highest conductivity of particles was 24 S/cm. The layered structure due to PANI backbone separated by long alkyl chains of DBSA was observed and it seems to facilitate the electrical conduction. The doping level of particle was fairly high and was dependent on the preparative conditions. The average size of the PANI particles determined by Guinier plot of small-angle X-ray scattering (SAXS) measurement was 20–30 nm, which was well coincidence with scanning electron microscopy (SEM) results     

One-step reverse micelle polymerization of organic dispersible polyaniline nanoparticles

Organic solvent dispersible dodecylbenzenesulfonic acid (DBSA)-doped polyaniline (PANI) was prepared from DBSA micelles with ammonium persulfate (APS) as an oxidant in hexane by one-step polymerization. Morphology observation showed PANI–DBSA powder polymerized with 0.0375 mol DBSA consisting of spherical particles having diameters of 40–60 nm that formed irregular aggregates with about 1 μm diameter. Polymerization was carried out in the hydrophilic aqueous microdomains of micelle dissolved reactants. The experimental conditions were optimized for direct synthesis of DBSA-doped PANI with high electrical conductivity by adjusting various reaction conditions. This research showed the importance of adjusting reaction conditions such as DBSA, aniline, ammonium persulfate, and acidity for polymerization. It was also found that a portion of an electrically neutral anilinium–DBSA complex could be assembled into reverse micelles together with DBSA molecules, where DBSA and anilinium–DBSA acted as both surfactants and doping agents to achieve nano-scaled DBSA-doped PANI with high conductivity. The doping level of DBSA in PANI particles was studied by UV–vis spectroscopy and X-ray diffraction (XRD). From TG/DTA/mass spectrometry, it was found that the PANI–DBSA was doped with both free and bound DBSA.     

Enhanced electrical conductivity of polyaniline film by a low magnetic field

We report the enhanced electrical conductivity of polyaniline (PANI) films produced in a low magnetic field using polyaniline that was synthesized by a self-stabilized dispersion polymerization (SSDP). The sample PANI film prepared with a low magnetic field of 1.4 T showed a 1.85-fold increase in electrical conductivity. Moreover, the film using the polyaniline prepared using the SSDP method showed greater conductivity enhancement than the conventionally prepared sample. In addition, the PANI films exhibited considerable anisotropy of the electrical conductivity depending on the direction of the applied magnetic field. This was attributed to the non-negligible contribution of the orientation of the polyaniline backbone segment and the face-to-face π–π stacking of the main-chains by the magnetic field.     

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.     

The growth of PANI films at 450 MPa

A series of polyaniline (PANI) films were prepared on quartz substrates by in situ polymerization with different reaction time under 450 MPa of hydrostatic high pressure. For investigating the effect of high pressure on the growth of the films, two additional series of samples with comparable conditions under ambient pressure were synthesize. The aniline cation radicals nucleated within 2 min and the polyaniline films grew within 10 min at 450 MPa of pressure. This compared with about 10 min for nucleation and 60 min for growth of polyaniline films under comparable ambient conditions. The process of PANI film growth under high pressure was obviously different from that in ambient pressure case. The high pressure used in polymerization affected directly the electrical property, the morphology, and growth of the films. A formation model of polyaniline film growth in high pressure case was proposed.     

Conductive surface via graft polymerization of aniline on a modified glass surface

A functionalization with an aniline monolayer of a modified glass surface, followed by the surface grafting of polyaniline (PANI) was used to prepare a conductive surface. A bromopropylsilane monolayer was first generated by reacting a hydroxylated surface with 3-bromopropyltrichlorosilane under an inert atmosphere. This layer was functionalized by its reaction with aniline, which substituted the bromide atoms of the silane chain. Further, the tethered aniline molecules were used as active sites for the graft polymerization of PANI on the surface. The composition and microstructure of the PANI-grafted glass surfaces were examined by X-ray photoelectron spectroscopy (XPS), and ultra-violet (UV) spectroscopy, as well as by contact angle measurements. The surface conductivity of the modified glass surface-grafted with PANI was of the order of 10 S/cm, hence, larger than the usual value (∼1 S/cm) of the bulk PANI.     

Synthesis and characterization of novel conducting composites of polyaniline prepared in the presence of sodium dodecylsulfonate and several water soluble polymers

Various conductive composites were prepared by in situ chemical polymerization of aniline in the presence of several water soluble polymers [alginic acid (2a, AA), poly(acrylic acid) (2b, PAA), and poly(vinyl alchol) (2c, PVA)] and/or anionic surfactants [dodecylbenzenesulfonic acid (1a, DBSA) and sodium dodecylsulfate (1b, SDS)] under various polymerization conditions. As a result, the corresponding composites having good film forming property were readily obtained even in the cases with SDS, although PANI prepared in the presence of SDS (PANI/SDS) generally shows extremely poor film forming property due to its low solubility/miscibility and processability in the similar manner as PANI doped with HCl (PANI/HCl). Among the resulting composites, the conductivities of the composites synthesized with SDS tended to be higher than those of the similar composites prepared with DBSA or without anionic surfactants. In particular, the composite prepared by using PVA bearing high molecule weight (PVA-H) and 20 mmol of SDS to aniline monomer was found to show the highest conductivity among the present investigations (32 S/cm), although the conductivity of typical conductive polyaniline doped with HCl, which was synthesized under the similar polymerization conditions, was ca. 3 S/cm at the best. The present PANI composites were characterized by spectroscopic and thermal analysis. Formation of oxidation states of PANIs in these composites was confirmed by the spectroscopic (UV–vis and FT-IR) analysis. The thermal stability of the resulting composite was somewhat lower than those of PANI/SDS itself and PANI/HCl.     

Synthesis of PANI nanostructures with various morphologies from fibers to micromats to disks doped with salicylic acid

Shape-controllable polyaniline (PANI) nanostructures varying from fibers to micromats and disks were synthesized via a self-assembly process with salicylic acid (SA) as dopant. It has been achieved just by tuning the concentration of aniline, the mole ratio of SA to aniline, and the mole ratio of APS to aniline in the same reaction. The diameters of the fibers could be controlled from 30 to 400 nm by adjusting the concentration of aniline. Micromats of fibers would be formed by changing the mole ratio of SA to aniline. Disk-like PANI nanostructures were synthesized when decreasing the mole ratio of APS to aniline. Scanning electron microscopy and transmission electron microscopy were applied to investigate various kinds of morphologies. The mechanism of forming these morphologies was proposed to be adjusted by the pH value during polymerization. Ultraviolet–visible (UV–vis) absorption spectra and Raman spectra suggested that these as-prepared PANI were in conductive emeraldine state and featured obviously different molecular structures, which aroused from different reaction conditions.     

Nanostructured polyaniline synthesized using interface polymerization and its redox activity in a wide pH range

Purely nanostructured polyaniline with the conductivity of 7.2 S cm^?1 was synthesized via the quick addition of the oxidant of the solid ammonium peroxydisulfate into a cooled solution containing aniline and hydrochloric acid without any templates. The morphology of polyaniline is constructed of interwoven fibers with an average diameter of about 50 nm with lengths varying from 250 nm to 370 nm. In general, the conventional polyaniline completely lost its electric activity including conductivity and redox activity at pH 6; however, the polyaniline reported here shows two pairs of redox peaks on its cyclic voltammogram in 1.0 M NaCl solution with pH 7.0, which is similar to that of the conventional polyaniline in the more acidic solutions; and it still holds the redox activity until pH 9.0. The pH dependence of conductivity of polyaniline is also improved compared to that of the conventional polyaniline. The ESR measurements show that the deprotonated polyaniline still holds rather high unpaired spin densities. The ¹H NMR spectra of polyaniline synthesized using interface polymerization are different those of the conventional polyaniline. The electrochemical behavior and spectra of polyaniline synthesized via the quick addition of an oxidant solution into a solution of aniline were reported and discussed.     

X-ray irradiation: A non-conventional route for the synthesis of conducting polymers

A non-conventional methodology for polyaniline (PANI) synthesis using X-ray irradiation is presented in this article, and shows the oxidants normally used in the (chemical or electrochemical) conventional synthesis of PANI are not necessary. The method uses only high energy photons to interact with nitrate ions (NO₃^?) and aniline monomer in an aqueous solution. The polymerization mechanism has also been investigated using radical scavenger (DMSO), and the results suggest that the hydroxyl radical (OH) generated in situ during exposure to X-ray could be the main agent responsible for oxidation and subsequent polymerization of the aniline monomer. Characterization of the morphology of the polymer by scanning electron microscopy (SEM) reveals that the PANI obtained by X-ray presents a predominantly fibrillar morphology with an average fiber diameter of 90 nm. Additionally, thermogravimetric analysis (TGA), elemental analysis, gel permeation chromatography (GPC), conductivity measurements, and spectroscopic characterization in the UV–vis and IR regions, showed that the polymer obtained is the polyemeraldine salt (the conducting form of the polymer).     

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.