Polyaniline Solution Research Articles

Self-assembled multilayer films based on a Keggin-type polyoxometalate and polyaniline

Multilayer ultrathin films were fabricated from partially doped polyaniline (PAN) and a Keggin-type polyoxometalate [ α-SiW 12O 40] 4− ( α-SiW 12) in aqueous solution via the layer-by-layer self-assembly technique and characterized by UV–vis, FTIR, and X-ray photoelectron spectra (XPS), ellipsometry, scanning electron microscopy (SEM), and atomic force microscopy (AFM). UV–vis spectroscopy shows that the absorbance values at characteristic wavelengths of the multilayer films increase almost linearly with the number of PAN/ α-SiW 12 bilayers, suggesting that the deposition process is regular and highly reproducible from layer to layer. FTIR and XPS spectra confirm the incorporation of α-SiW 12 and PAN into the films. Ellipsometric measurements show that the PAN/ α-SiW 12 bilayer thickness increases with the increasing PAN solution concentration. SEM and AFM images indicate that the film surface is relatively uniform and smooth. In addition, the electrical conductivities of the multilayer films doped with hydrochloric acid were also measured.

Studies on solution and solution-cast film of polyaniline colloids prepared in the absence and presence of ultrasonic irradiation

Spectroscopic and voltammetric features for the solution and solution-cast film of polyaniline (PANI) colloids prepared in the absence and presence of ultrasonic irradiation were examined. Significant differences in the color and absorption spectra between the solution of colloids prepared in the absence and presence of irradiation were observed. Effects of ambient atmosphere on the solution of colloids were also studied. A gradual decay in the absorption at ≈365 nm was occurred upon ageing the solution in air for the colloid prepared under ultrasonic irradiation. PANI film, cast from its colloidal solution, exhibited excellent electroactivity. The films thus cast were applied to electrode modification to control electrochemical reaction. Clear voltammetric response was observed on the electrode modified with the colloid prepared in the presence of ultrasonic irradiation.

Confinement of polyaniline chains in capillary layers: an ordering effect of the uniaxially aligned surfaces

An ordering effect of uniaxially aligned poly(tetrafluoroethylene) (PTFE) substrates prepared by rubbing on polyaniline (PANI) molecules at the interfaces of PTFE/PANI film and PTFE/PANI solution has been investigated using electronic absorption spectroscopy. It was observed slight dichroism in electronic spectra from only very thin (thickness ∼20 nm and less) PANI films as well as from PANI solutions of capillary thickness (10 to 30 μm) confined by oriented PTFE surfaces. The ordering effect is discussed in terms of a hydrodynamic flow arising upon sample formation and steric factors at the PTFE surface, which cause uniaxial deformation of the polymer coil on the rubbed PTFE surface.

Induced Optical Activity in Polyaniline: Solvent and Acid Dependence

The circular dichroism (CD) spectra are reported for N-methylpyrrolidinone and dimethylformamide solutions of polyaniline (PANI) containing a series of chiral acids. Several chiral phosphoric acids protonate/dope PANI and yield CD spectra from the polymer that are nearly identical to that observed with camphorsulfonic acid. The phosphoric acids do not have a remote hydrogen bonding acceptor site indicating that the hydrogen bonding between the acid and PANI is not necessary for the polymer to adopt an optically active form Several carboxylic acids of varying sizes have been investigated and all give approximately the same CD spectrum for the polymer.

Optically Anisotropic Films and Fibres from Conductive Polyaniline Solution

Polyaniline (PANi) anisotropic thin films and fibres were produced from 15 %w/w PANi in concentrated sulphuric acid (con. H 2 SO 4 ). The UV-VIS spectroscopy shows some degree of physical ordering of polymer chains. The cross-polarised microscopy also shows a large region of coloured birefringence in these thin films and fibres.

Conducting polyaniline nanofiber networks prepared by the doping induction of camphor sulfonic acid

AbstractBranched nanofibers of conducting polyaniline (PANI) buried in the crystals of camphor sulfonic acid (CSA) were prepared from an m‐cresol solution of PANI and excessive CSA. After the excessive CSA was dissolved through ultrasonication in deionized water, networks of PANI nanofibers with spherical nodes, nanoparticles, leaf‐vein‐shaped nanofibers, and so forth were obtained according to the strength of the ultrasonic treatment. The X‐ray diffraction patterns of the CSA‐doped PANI showed high crystallinity. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1537–1540, 2003

Ultrafast Dephasing of Photoexcited Polarons in Primary Doped Polyaniline

Ultrashort pulse pump−probe and transient anisotropy methods are used to study polaron dynamics of primary doped conductive polyaniline in solution. The degenerate frequency pulses are resonant with the polaron absorption of the emeraldine salt form of polyaniline. Pronounced oscillatory components with frequencies of 160 and 210 cm-1 are observed, in good agreement with recent Raman and infrared spectral studies, and are likely to represent ground states modes. However, the close agreement with the excited state lifetime suggests that they may have partial excited state character. Photoexcited carrier dynamics have been identified on two distinct time scales. The very fast component, with a 34 fs exponential decay and 90% of the total amplitude, is attributed to the relaxation of the initially delocalized excitations within the polymer chain. This is supported by the transient anisotropy signal exhibiting a 30 fs Gaussian decay. In analogy with exciton dynamics in photosynthetic light harvesting assembli...

Shear-Induced Delocalization of Polarons in Polyaniline−Surfactant Complexes

A transition for a random coil to an extended chain conformation in dilute polyaniline solutions has been shown to induce delocalization of polarons and to increase the conductivity in the solid state by MacDiarmid et al. We have investigated a similar chain extension during a transition from isotropic to a liquid crystalline phase of polyaniline (PANi). We now report the use of an extra additive, the zinc salt of the dopant, to improve the viscoelastic behavior of the doped PANi complex by applying external force, shearing for the possibility of chain alignment. PANi was initially doped with dinonylnaphthalenesulfonic acid (DNNSAH), and then controlled amounts of the zinc salt of DNNSAH were added to this doped PANi complex in the solution state. The addition of zinc salt improved the viscoelastic behavior, and we were able to apply manual shear to the solid samples at elevated temperatures. The shearing was shown to induce chain alignment as seen by strong birefringence under the optical microscope and ...

C 60–polymer nanocomposites: evidence for interface interaction

Polyaniline–fullerene (PA–C 60) composites have been studied by Surface Enhanced Raman scattering (SERS) spectroscopy and X-ray diffraction. They were obtained by mixing solutions of polyaniline–emeraldine base (PA–EB) and C 60, as well as by chemical synthesis from aniline, sulfuric acid and potassium dichromate, with addition of C 60. The Raman bands peaking at 1330–1370 cm −1, associated with a protonated structure were used as indicative for changes of the PA–EB phonon spectrum resulting from C 60 doping. The two types of compounds show different SERS spectra, also dependent on the metallic support used (Au or Ag). Variation of the SERS spectra with the type of metallic support is related to a chemical interface interaction between composite and metal. In mixture samples, a doped polymeric chain (with ionically attached C 60 −) was evidenced by an increased fraction of quinoid rings. The SERS spectra of the chemically synthesized PA–C 60 reveals the existence of two polymeric structures: a doped PA (doped with C 60 − ions) and an undoped one, the latter with a structure of ‘pendant chain’ type. Structural (XRD) data reveal the presence of C 60 nano-zones, with a lattice parameter increase of 0.3–0.6%, attributed to slight oxidation. Detailed analysis of the fcc(111) line asymmetry suggests, in mixture samples, a boundary zone with an ‘expanded’ lattice, induced by ionic interface effects.

Nonlinear Optical Properties of Polyaniline Liquid Solutions

Nonlinear optical properties of polyaniline solutions were measured for different concentrations with the single beam Z-scan technique. Results obtained with pulse trains consisting of several 70-ps-duration pulses at 532 nm indicate that the nonlinearity initially presents a fast electronic contribution, followed by a cumulative thermal lensing associated to the pulses' arrival.

2-Ethyl-9,10-anthraquinone hydrogenation over Pd/polymers: Effect of polymers–Pd(II) chlorocomplexes interactions

Two polymers, namely poly(4-vinylpyridine) (PVP) and polyaniline (PANI), were used as the supports for palladium catalysts acting in 2-ethyl-9,10-anthraquinone (EAQ) hydrogenation, a key step in the industrial production of H 2O 2. The nature of PVP and PANI interactions with various chlorocomplexes of Pd(II) coexisting in PdCl 2–H 2O–HCl solutions was studied using IR (mid-IR, far-IR), UV–Vis and XPS spectroscopies. It was found that the type of interactions involving nitrogen atoms of the polymers depended mainly on the acidity of PdCl 2 solution. Protonation of polymers (via acid–base reactions) as well as coordination of Pd 2+ ions by nitrogen atoms of the polymers took place in highly acidic PdCl 2 solution (2 M HCl) containing predominantly anionic [PdCl 4] 2−, [PdCl 3(H 2O)] − complexes (series A of experiments). In the weakly acidic PdCl 2 solutions (0.66×10 −3 M HCl ) (series B of experiments) containing predominantly electrically neutral [PdCl 2(H 2O) 2] complexes, hydrolysis of the complex proceeded as the main process resulting in precipitation of palladium oxide on PVP. In the case of PANI in solution B, the redox mechanism was involved resulting in the reduction of some Pd 2+ to Pd 0 accompanied by partial oxidation of the polymer chain. As a consequence of various mechanisms of polymers reactions with Pd 2+ ions, surface morphology of the final catalysts, characterized by XRD and SEM methods, was different. It was found that dispersion of palladium in Pd/PVP and Pd/PANI catalysts (1–10 wt.% Pd) influenced the course of EAQ hydrogenation. The presence of large palladium particles promoted reactions leading to the formation of the so-termed “degradation products” not capable of hydrogen peroxide formation. Pd/PVP catalysts (series B) exhibited higher activity. Selectivity of EAQ hydrogenation in their presence was better than that seen for Pd/PANI catalysts.

Electrical resistance and diffusion permeability of microporous polyethylene membranes modified with polypyrrole and polyaniline in solutions of electrolytes

Composite systems based on a microporous polyethylene (PE) membrane modified with conducting polymers such as polypyrrole (PPy) and polyaniline (PANI) have been elaborated. Conducting polymers were deposited onto PE membranes in situ during the oxidative polymerization of pyrrole from gas phase or by the polymerization of aniline in aqueous medium. Composite membranes have a low resistance in electrolyte solutions owing to the coating with conducting polymers inside the pores. The dependence of electrical resistance of modified membranes on concentration of hydrochloric acid or sodium hydroxide solutions, in which the conducting polymers are in protonated or non-protonated states, respectively, was studied using alternating and direct electric currents. Diffusion permeability of composite membranes to acid, salt and alkali solutions has been also studied.

Characterization of highly conducting lithium salt doped polyaniline films prepared from polymer solution

We have developed a new method for preparing conducting polyaniline (Pani) films and investigated their chemical and physical properties by means of UV–Vis, FT-IR, EPR, XPS, and dc conductivity measurements. Conducting polyaniline films are prepared by casting from the solution of polyaniline with lithium salt. The free-standing films have relatively high dc conductivity without further treatment with HCl. The effects of lithium salts, such as LiBF 4, LiPF 6, and LiClO 4, and their concentrations on dc conductivity are studied. The dc conductivity of Pani–LiBF 4 film has been found to be better than those of Pani–LiPF 6 and Pani–LiClO 4 films. The dc conductivity of the systems increases with increasing lithium salt concentration in the range from 0.025 to 0.1 M, and exhibits a maximum value of ∼10 −1 S/cm when 0.1 M LiBF 4 is doped.

Interactions between polyaniline and viologens

The interactions between polyaniline (PANi) and viologen solutions were investigated. The changes in the structure of PANi were monitored using X-ray photoelectron spectroscopy (XPS) and UV–VIS absorption spectroscopy. The results indicated that electron transfer from PANi to viologen occurs readily, resulting in the formation of positively charged nitrogen species in the PANi. This is accompanied by an increase in conductivity of the PANi, together with a transfer of halogen anions from the viologen to PANi. Dissolved oxygen appears to play an important role in these interactions.

Third-order nonlinear optical properties of undoped polyaniline solutions and films probed at 532 nm

The third-order nonlinear optical properties of polyaniline (PANI) solutions and films were investigated at 532 nm by use of Z-scan, power limiting, and optical Kerr gate techniques. The polymers studied were the undoped partially oxidized (emeraldine base) and fully reduced (leucoemeraldine base) forms of PANI. Our results demonstrate that the leucoemeraldine base is more suitable for use in devices such as all-optical switches and optical power limiters operating at 532 nm. The worse performance of the emeraldine base is due to the presence of defects inside the bandgap of the polymer.

Preparation of Nanosized Metallic Particles in Polyaniline

The preparation of nanosized gold and palladium particles in polyaniline has been carried out via the reduction of AuCl3 or Pd(NO3)2 by polyaniline in either aqueous media or N-methylpyrrolidinone (NMP). When the reduction of AuCl3 was carried out in NMP solutions of polyaniline, the Au particles were on the order of 20 nm. The reduction of AuCl3 or Pd(NO3)2 by polyaniline in the powder form in aqueous media resulted in the accumulation of the elemental Au or Pd on the surface of the polyaniline particles. Subsequent dissolution of the polyaniline in NMP resulted in metal particles of about 50 to 200 nm being dispersed in the NMP solution of polyaniline. The rate of metal salt reduction and the size of the metal particles were found to be strongly dependent on the medium used, the initial ratio of metal ions to polyaniline, and the reaction time. The polyaniline–metal particle systems were characterized using X-ray photoelectron spectroscopy, UV-visible absorption spectroscopy, and FTIR spectroscopy. Scanning and transmission electron microscopy and laser light scattering were used to determine the size of the metal particles in polyaniline.

Confinement of Polyaniline Chains in Thin Layers of the Polymer Solution

Electronic absorption spectra of polyaniline (PANI) solutions in a transparent cell were observed to change as the cell gap was reduced to ∼10 μm. Although the cell gap size was wide enough, at least two orders of magnitude larger than the polymer coils in the solution, the observed changes were explained by self-confinement of polymer molecules at the liquid/solid interface as a result of their intense adsorption and depletion of the relatively small solution volume, respectively. It was shown that the cell material affects electronic spectra of confined polymer solutions.

Inorganic salts effect on the properties of polyaniline

Conducting polymers have been widely investigated for over two decades. Polyaniline, one of the most stable and processible conducting polymers, was synthesized by adding inorganic salt technique. A high molecular weight with lower polydispersity (Mw 200,000 and PD < 2.0) polyaniline was made and characterized by elemental analysis, GPC, FTIR, UV/Vis, and solution NMR. It was found that the polyaniline powder morphology such as, particle size and surface areas, can be controlled by the crystal shapes of inorganic salts and their concentrations. A pseudo protonic doping mechanism is proposed when adding a high concentration inorganic salts. Certain amount (0.5∼3 wt.%) inorganic salts act as gel-inhibitors to extend the gelation time of polyaniline solution and the surface morphologies of polyaniline film and blends. A high conductivity of the film was obtained and discussed in the paper.

A new approach to prepare highly conducting polyaniline films

We have developed a new method for preparing conducting polyaniline films and investigated their chemical and physical properties by means of UV-Vis., FT-IR, and dc conductivity measurements. Conducting polyaniline films are prepared by casting directly a lithium salt containing non-conducting polyaniline solution. The dried films show high dc conductivity even without further treatment with HCl. Effects of lithium salts, such as LiBF 4 , LiPF 6 , and LiClO 4 , and their concentrations on dc conductivity are examined. The dc conductivity of Pani-LiBF 4 film is found to be better than those of Pani-LiPF 6 and Pani-LiClO 4 films. The dc conductivity increases with lithium salt concentration ranging from 0.1M to 0.025M, and exhibits maximum value of ∼10 -1 S/cm when 0.1M LiBF 4 is doped.

Synthesis and Properties of Composite Polyaniline–Nafion Films on Platinum

Information on the synthesis of a polyaniline film on platinum covered with a Nafion film is obtained. The effect of electrochemical conditions on the synthesis is studied. The relationship between these conditions and properties of obtained composite polyaniline–Nafion films is revealed. It is established that on platinum covered with a Nafion film in certain electrochemical conditions in a polyaniline solution there occurs the formation of a composite polyaniline–Nafion film. The polyaniline in the film mainly retains its individual properties. It is demonstrated that the mechanism of the synthesis of polyaniline in the composite film substantially differs from that in the case of the formation of a film on platinum.