Formation Of Polyaniline Films Research Articles

Elucidating molecular mechanisms of two-dimensional chemical reactions

Elucidating molecular mechanisms of two-dimensional chemical reactions

Real-time study of on-water chemistry: Surfactant monolayer-assisted growth of a crystalline quasi-2D polymer

<h2>Summary</h2> Unlike in the bulk, the hydrogen bond network of water is interrupted at water interfaces, and thus chemical reaction occurs at the water interface in a different manner than in the bulk, owning to, e.g., the possibility of templating molecules. On-water chemistry has generated highly crystalline, functional 2D materials through surfactant-monolayer-assisted interfacial synthesis (SMAIS). Yet, the details of the on-water reaction mechanism have remained unresolved. Here, by tracking the quasi-2D polyaniline film generation process using <i>in situ</i> surface-specific vibrational technique, we clarify how the polymerization reaction occurs at the water surfaces during SMAIS. We identify an aniline derivative with a positively charged terminal =NH₂ group as a key reaction intermediate species for highly crystalline film formation. A comparison of differently designed water interfaces reveals that intermediate species can be accumulated and ordered at the interface by the negatively charged surfactant headgroups, prompting highly crystalline, conductive polyaniline film formation. These results demonstrate the importance of interfacial electric fields and electrostatic interactions for controlled on-water chemistry.

Sensitive pH Monitoring Using a Polyaniline-Functionalized Fiber Optic-Surface Plasmon Resonance Detector.

In this work, we report results on the fabrication and characterization of a surface plasmon resonance (SPR) pH sensor using platinum (Pt) and polyaniline (PANI) layers successively coated over an unclad core of an optical fiber (FO). The plasmonic thin Pt layer was deposited using a magnetron sputtering technique, while the pH-sensitive PANI layer was synthesized using an electroless polymerization method. Moreover, the formation of PANI film was confirmed by X-ray photoelectron spectroscopy (XPS) technique and its surface morphology was investigated using scanning electron microscopy (SEM). It was found that the PANI/Pt-coated FO-SPR pH sensor exhibits a fast and linear response in either acid or alkali solutions (pH operational range: 1 to 14). The proposed FO-SPR sensor could be used for biomedical applications, environmental monitoring or any remote, real-time on-site measurements.

The First Stages of Chemical and Electrochemical Aniline Oxidation—Spectroscopic Comparative Study

There are several types of aniline oligomers that can be formed in the early stages of aniline oxidation: linear oligomers with repeating units joined in para positions, and various branched and polycyclic oligomers, being the two most important groups. The fraction of these different oligomeric groups depends upon the reaction conditions of aniline oxidation. The aim of this study was to analyze the first products of the chemical and electrochemical oxidation of aniline at the (starting) pH 1 and 7, in order to specify the conditions of the formation of phenazine-like oligomers, and to test the theory that they have an important role in polyaniline film formation. We have confirmed that phenazine-like oligomers do not form at pH 1, neither in the chemical nor the electrochemical oxidation of aniline; however, they form in both chemical and electrochemical oxidation of aniline at pH 7. Phenazine-like oligomers are thus definitely not necessary intermediates for PANI film formation, not even in the chemical polymerization of aniline. Finally, the redox behavior of phenazine-like oligomers was demonstrated in a medium at pH 1.

Effect of Space Stabilizer on In-Situ Deposition of Polyaniline on Carbonyl Iron Powder

Carbonyl iron powder/polyaniline (CIP/PANI) composites were prepared by in-situ polymerization. High molecular weight PVP-K90, low molecular weight PVP-K30 and small molecular surfactant Twain-20 were used as space stabilizers for dispersion polymerization. The effects of different kinds of space stabilizers and the concentration of PVP-K90 on the in-situ deposition of PANI on the surface of carbonyl iron powder were investigated. The effect of film formation is briefly discussed and its stability mechanism is discussed. The results showed that CIP/PANI core-shell structure composites with good morphology could be prepared by dispersion polymerization with high molecular weight PVP-K90 as space stabilizer, and polyaniline film formation could not be well stabilized by low molecular weight PVP and small molecular surfactant. The conductivity of the CIP/PANI composites changed little with the concentration and type of space stabilizers, about 10 −2 S· cm−1.

Comparison of polyaniline electrodeposition on carbon steel from oxalic acid and salicylate medium

Abstract Polyaniline (PANI) coatings on carbon steel (CS) substrate were electrodeposited from two different mediums such as oxalic acid (H 2 C 2 O 4 ) and sodium salicylate (C 7 H 5 NaO 3 ). In oxalic acid, the importance of the passivation of the carbon steel surface prior to PANI electrodeposition was investigated by linear potentiodynamic test. It showed below 0.3 M oxalic acid concentration PANI film formation was not complete. The extent of passivation of the carbon steel was found to depend on the strength of the oxalic acid, which determined the formation and the nature of the PANI film. Whereas, deposition from the sodium salicylate solution did not show any passivation peak, but resulted in the formation of a transparent, uniform, compact and adherent PANI coating. The formation, morphology and characteristics of the coatings were compared by cyclic voltammetry, scanning electron microscopy (SEM) and Raman spectroscopy.

Spectroscopic study of the highly homogeneous polyaniline film formation on gold support

The oxidation of aniline with ammonium peroxydisulfate in the aqueous solution of acetic acid has two subsequent phases: the oxidation of the neutral aniline molecules at low acidity, which was followed by the oxidation of the anilinium cations after the acidity became higher. The final polyaniline film deposited on immersed surfaces is usually contaminated with semi-crystalline oligomers which precipitated during induction period from the reaction medium. To obtain a homogeneous film, which is important in the fabrication of many molecular electronic devices, we have studied the course of aniline oxidation in a view of new experimental evidence. In the unique series of experiments, the silicon or gold supports have been immersed in the reaction mixture at crucial stages of oxidation reaction, and the deposits at the end of the reaction were analyzed. The growth of a highly homogenous film on the gold-coated glass substrate immersed in the reaction mixture at the end of the polymerization period has been observed. The molecular structure of the products was monitored with UV–visible, infrared, and Raman spectroscopies. The possible mechanism of the film formation and the molecular mechanism of the surface interaction of chemisorbed aniline oligomers with gold support are proposed.

Mechanisms of polyaniline film formation via solution casting: Intra-chain contraction versus inter-chain association

Two different mechanisms of formation of solution-cast films of emeraldine base (EB) of polyaniline are shown. The first mechanism was found in films drop-cast from the concentrated solution of EB. This mechanism is suggested to be due to entanglement of different polymer chains when the film is formed. It results in the relatively loose film morphology with fractal dimensionality of 1.68 and blue color. This film has a relatively good ability to absorb analyte vapors from the environment and a better ability to be protonated from the acidic medium as compared to films formed by the second mechanism. It is suggested that the polymer has an extended coil conformation in such a film, similar to that in a good solution. The second mechanism takes place when the film is drop-cast from a solution of low concentration and it is controlled by intramolecular processes which play the major role before the molecules aggregate into the film. This mechanism is suggested to be due to prevailing intramolecular tendency to compact-coil conformation. It results in formation of films of the grained morphology with fractal dimensionality of 1.56 and violet color. These films have a poor ability for absorption of analyte vapors and protonation as well. Various factors that affect the above mechanisms are discussed. The different properties of the films resulted from the different formation mechanisms allow us to specify them as different polymer phases, where either inter- or intra-chain processes play a crucial role, respectively.

Studies on morphology of polyaniline films formed at liquid–liquid and solid–liquid interfaces at 25 and 5 °C, respectively, and effect of doping

It is well accepted that the morphology of the nanomaterials has great effect on the properties and hence their applications. Therefore, morphology of materials has become a focus of research in the scientific world. The present study shows that interfacial polymerization and subsequent self-assembly provides a control over the morphology, nanorod/nanosheet, of polyaniline (PANI) films synthesized by liquid–liquid interface reaction technique and solid–liquid interface reaction technique. The synthesized PANI films and its particulate structure are characterized by using various spectroscopic techniques such as UV–visible, ATR-IR, Raman and XPS. The study confirmed the formation, the structure, the size and shape of particles and morphology of PANI by using analytical techniques namely, SAED, SEM and TEM. An important observation is that doping with HCl significantly improves the nanorod formation at the interface. The doped PANI electrode exhibits a higher area with rectangular shape in CV cycle and better cycle stability when compared with the performance of undoped PANI films. We believe that the results of these studies can give valuable leads to manoeuvre formation of PANI films with desired morphology for various applications.

Kinetic Study of Polyaniline Film Formation Using Ferric Chloride/Ammonium Persulfate as Composite Oxidant

Polyaniline (PANI) was synthesized by in situ emulsion polymerization. The kinetics of the PANI film formation was investigated by the quartz crystal microbalance technique (QCM). PANI film doped with dodecylbenzenesulfonic acid (DBSA) was synthesized by emulsion polymerization using ferric chloride/ammonium persulfate (FeCl3/APS) as composite oxidant in the presence of a constant (0.4 T) magnetic field (MF). The results showed that the peak current and conductivity of PANI synthesized by composite oxidant was higher than that synthesized by APS in the presence of an MF and it was also suggested that the PANI/FeCl3 composite has higher conductivity than pure PANI. The reaction exhibited first order with respect to composite oxidant, half-order to aniline, and half-order to DBSA, and the activation energy calculated from the temperature dependence of the growth rate was 40.23 kJ/mol. The polymerization conditions of aniline were optimized tentatively by cyclic voltammetry testing, which was studied by using carbon paper–loaded PANI as a working electrode for the first time. The experimental results indicated that the peak currents and conductivity of PANI were the largest under the following conditions: MF intensity of 0.4 T, composite oxidant concentration of 0.18 mol/L, and concentrations of aniline and DBSA of 0.08 mol/L and 0.05 mol/L, respectively.

In situpolyaniline film formation using ferric chloride as an oxidant

AbstractIn situpolyaniline (PANI) films were grown from an aqueous hydrochloric acid solution on glass substrates via the chemical oxidation of aniline using hydrated ferric chloride, FeCl3.6H2O (FC). The effect of initial molar ratios of FC/aniline on the yield of PANI films was monitored using the quartz crystal microbalance technique. The morphology of the resultant polymer film and powder was examined using scanning electron microscopy. It was found that the film possesses a porous character; however, the polymer powder consists of small particles with interconnected nanofibers. The polymer powder formed in the bulk was characterized using the energy dispersive analysis of X‐ray, the X‐ray diffraction, and the thermal gravimetric analysis. A comparison between the PANI produced from FC and ammonium peroxydisulfate was considered and discussed. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Study the effect of phenylenediamine compounds on the chemical polymerization of aniline

The polyaniline (PANI) film deposition during the oxidative polymerization of aniline was studied using the quartz crystal microbalance (QCM) technique. PANI was prepared in the presence and absence of PDAs ( p-phenylenediamine (PPDA), o-phenylenediamine (OPDA) and m-phenylenediamine (MPDA)). The effect of PDAs concentrations on the PANI films formation were monitored using QCM technique. It was found that PPDA has an acceleration effect, OPDA has no or little effect and MPDA has retardation effect and work as inhibitor for the PANI film formation. The G r and m′ increases by increasing PPDA concentrations in the same time induction period and reaction time decreases, in the opposite direction MPDA The G r and m′ decreases by increasing MPDA concentrations and the induction period and reaction time increases, in the case of OPDA there is no measurable effect on the induction period, G r , m′ and reaction time. UV–vis absorption spectra for the bulk and PANI films deposited onto glass supports were used for justification the data obtained from QCM. The presences of PDAs have no effect on the chemical structure and crystallinity of PANI and were confirmed using FTIR and X-ray.

Investigation on cell biocompatible behaviors of polyaniline film fabricated via electroless surface polymerization

Considering for the potential application in tissue engineering, polyaniline (PANi) film was fabricated via a two-step route: a self-assembled monolayer of C 6H 5NHC 3H 6Si(OMe) 3 was firstly formed on the single-crystal Si substrate; the conducting PANi film was then prepared through electroless surface polymerization of the aniline molecules on the aniline monolayer-bearing silane surface in an acidic aqueous solution. The formation of PANi film on Si surface was confirmed by characterizations of X-ray photoelectron spectroscope (XPS) and specular reflectance Fourier transform infrared (SR-FTIR) spectrum, etc. At last, the proliferation behaviors of PC-12 cells on the PANi film surface were studied by the [3-(4,5-dimethyldiazol-2-yl)-2,5-diphenyl tetrazolium bromide] (MTT) colorimetric assays, acridine orange fluorometric staining, and scanning electron microscope (SEM) observation, etc. The results demonstrate that the as-prepared PANi film provides high ability for cell proliferation, exhibiting promising potentials as surface coating to cultivate neuronal cells for applications in the tissue engineering.

The Kinetics of DBSA-Doped Polyaniline Film Formation in a Constant Magnetic Field (0.6 T)

Polyaniline (PANI) doped with dodecylbenzene sulfonic acid (DBSA) was synthesized by emulsion polymerization using ammonium persulfate (APS) as oxidant in the presence of a constant magnetic field (0.6 T). The kinetics of the PANI film formation was investigated by the quartz crystal microbalance (QCM) technique. The reaction exhibited first order with respect to aniline and half-order to APS and DBSA. The effects of temperature and different magnetic field intensity on the film growth rate were investigated. The activation energy calculated from the temperature dependence of the growth rate was 40.4 KJ/mol. It was observed from the plot of the PANI film growth rate versus the magnetic field intensity that the growth rate increased with the increasing magnetic intensity. The UV-visible spectra of the PANI polymerization was measured and compared to the polymerization process of the PANI using the QCM technique. The result showed that the absorption intensity of the PANI polymerized in the presence of a magnetic field was greater than that of the PANI polymerized in the absence of a magnetic field at the same time.

Morphological characterization and kinetics study of polyaniline film formation by emulsion polymerization

The kinetics and morphology of polyaniline film prepared by using ammonium persulfate (APS) as oxidant and dodecylbenzoyl sulfonic acid (DBSA) as both emulsifier and dopant were studied in this paper. The kinetics of the formation of polyaniline film was determined by using the quartz crystal microbalance (QCM), and the film morphology was characterized by scanning electron microscopy (SEM). The reaction exhibited half-order kinetics with respect to APS concentration and first-order kinetics with respect to aniline concentration. The activation energy is 41.15 kJ/mol, and the growth rate of PANI film increased with increasing temperature and decreased with increasing concentration of DBSA.

Application of QCM technique in the kinetic study of polyaniline film formation in the presence of a constant (0.4 T) magnetic field

The kinetics of PANI film formation was investigated in the presence of a constant (0.4 T) magnetic field (MF) by the quartz crystal microbalance (QCM) technique. The reaction exhibited half-order with respect to APS and first-order to aniline. The effects of temperature and different MF intensity on the film growth rate were investigated. The activation energy calculated from the temperature dependence of the growth rate was 38.36 kJ/mol. The growth rate increased with increasing magnetic intensity. The UV–visible spectra of the PANI polymerization was measured; the results showed that the reaction rate in the presence of a MF is higher than that of PANI polymerized in the absence of a MF at the same reaction time. It was suggested that the QCM technique can provide an efficient method for the kinetic study of polyaniline film formation in the presence of a MF.

Reaction monitoring of polyaniline film formation on carbon nanotubes with TOF-SIMS

A polyaniline (PANI) film was successfully prepared on multiwall carbon nanotubes (CNTs) by modifying the CNTs with aromatic amine group (CNTs-(NC 6H 6) n ) followed by aniline polymerization. TOF-SIMS was used to monitor C 6H 6N −, C 2H 3Cl 2 −, C 8H − and C 10 − to reveal the interfacial change at PANI film/CNTs-(NC 6H 6) n . The functionalized group of CNTs modified with aniline was determined to be C 6H 6N −, which showed positive effect on polymerization of aniline as shown by the TOF-SIMS ion image.

The optimum HCl concentration for the in situ polyaniline film formation

The chemical oxidation of aniline with ammonium persulphate (APS) in aqueous hydrochloric acid solutions to form polyaniline (PANI) films has been studied using the quartz crystal microbalance (QCM) technique. The effect of hydrochloric acid concentration on PANI film deposition was studied. The acid has an effect on the yield and the growth rate of the polymer film deposition. The yield has an optimum value when hydrochloric acid equals ∼0.1 M HCl. This was justified by measuring the UV-Vis absorption for the formed films on glass supports immersed into solutions have the same experimental condition like that used in QCM experiments. Degradation for the formed PANI films during the polymerization was observed at high concentrations of HCl. The degradation quantity depends on the concentration of the acid and the temperature of polymerization.

Role of a chelating agent in the formation of polyaniline films on aluminum

AbstractA chelating agent, alizarin, was used to pretreat an aluminum surface before the electrochemical synthesis of polyaniline. Alizarin had two main effects on the process: (1) it suppressed the hydrogen evolution reaction and increased the current efficiency and (2) it stabilized the open‐circuit potential in a corroding environment, such as in 0.1M NaCl. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 819–823, 2003

The kinetics and spectral studies of the in situ polyaniline film formation

The chemical oxidation of aniline with ammonium persulfate (APS) in an aqueous acidic solution to form polyaniline (PANI) films has been studied using the quartz crystal microbalance (QCM) technique. The kinetics of the film formation was investigated. The reaction exhibited half-order with respect to APS and first-order to aniline. The effect of temperature on the growth rate of PANI films was studied. The activation energy is 39.79 kJ/mol. This is in agreement with the corresponding one determined for the chemical polymerization of PANI in the bulk. The UV–visible spectra of the PANI films grown onto a glass support immersed into the bulk solution were measured. The absorption of the PANI film with time was also studied and compared to the growth of the PANI film thickness using the QCM technique.