Polyaniline film deposition from the oxidative polymerization of aniline using K2Cr2O7

The deposition of the polyaniline (PANI) films was monitored using the quartz crystal microbalance (QCM) technique. The films were grown from an aqueous dilute hydrochloric acid solution by the chemical oxidation of aniline using potassium dichromate (KDC). The effect of the initial molar ratio of the KDC/aniline on the yield and the growth rate of the PANI films were studied. There is no optimum initial molar ratio of KDC/aniline of PANI film deposition. Also there was a small depletion period and no degradation to the deposited PANI films. The order of the polymerization kinetics was studied with respect to KDC. 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 the time of polymerization was compared to the growth of the PANI film thickness with time determined from the QCM technique. The characteristics of the PANI film deposition were compared to the corresponding ones that were observed during the oxidative polymerization of aniline with ammonium persulphate (APS).     

Preparation and characterization of composite polyaniline materials for catalytic purposes

Composite film electrodes were prepared by open-circuit Pt deposition on polymeric PANI films that were electrosynthesized from aniline acid solutions with suspended carbon particles (CPs). Gold, nickel, and a Ni-based alloy, Nichrome, were used as substrates, and carbon particles, carbon nanotubes (CNT), and Vulcan XC-72R carbon black, suspended in the monomer acid solution, were incorporated into the film. Pt particles were dispersed on films grown on Ni-based substrates by deposition from a Pt(IV) acid solution at open circuit (OC). CNT trapped into the PANI films have a favorable influence on Pt dispersion. The novel composite electrodes showed significant catalytic activity for methanol oxidation.     

Influence of the magnitude and direction of electric field on the transport and growth property of deposited polyaniline films

Polyaniline (PANI) films were deposited by electrochemical polymerization of aniline monomer on a fluorine-doped glass substrate at room temperature under different electric field directions. The as-synthesized PANI films obtained at different growth cycles were characterized by AC impedance spectroscopy and scanning electron microscopy (SEM). The results revealed that the film morphology, transport kinetics, and electrical properties are strongly dependent on the electric field direction and magnitude of the applied field during electropolymerization. The SEM morphology and AC impedance (modulus spectroscopy) indicate that a more homogeneous, high-porous, and conducting PANI film is induced by horizontal electric field direction (HEFD) electrodeposition, whereas the modulus spectroscopy of the PANI film deposited by vertical electric field direction (VEFD) reveals that VEFD deposition favours two-dimensional growth of PANI. The obtained polymer is more of dielectric in nature due to preferable dendritic growth which is supported by SEM analysis.     

Biocatalytic synthesis of polypyrrole powder, colloids, and films using horseradish peroxidase

Polypyrrole was synthesized in high yield by a biocatalytic method in mild aqueous media using hydrogen peroxide as oxidizer. A redox mediator, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) diammonium salt, was used to oxidize the pyrrole. ABTS is a very effective peroxidase substrate, which was enzymatically oxidized to generate a radical cation that in turn was able to chemically oxidize pyrrole. This indirect biocatalytic method was implemented because pyrrole is not a substrate of horseradish peroxidase, however, the polymerization process was successfully optimized and later adapted to prepare also polypyrrole thin films and water dispersible polypyrrole colloids. The polypyrrole powder and colloids were characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, electrical conductivity, and thermogravimetric analysis. In addition, the deposition of the polypyrrole thin film was monitored using a quartz-crystal microbalance and its morphology studied by optical and scanning electron microscopy. The biocatalytic polymerization of pyrrole results in a polymer spectroscopically very similar to chemically synthesized polypyrrole.     

乳液聚合中聚苯胺膜形成的动力学研究

以(NH4)2S2O8(APS)为氧化剂,十二烷基苯磺酸(DBSA)同时为乳化剂和掺杂剂,采用乳液聚合方法制备聚苯胺膜(PANIfilm),用石英晶体微天平(QCM)实时监测聚苯胺膜的形成过程,并对其动力学过程进行研究.结果表明,聚苯胺成膜反应对APS是0.5级,对苯胺是1级,聚苯胺膜增长速率随温度的升高而增加,而聚苯胺膜的最终沉积量却减小,表观活化能Ea=41.15kJ/mol,与均相溶液聚合成膜法的结果相近;随着DBSA浓度的增加,聚苯胺膜增长速率减小,而最终的沉积量增大.     

Oligomer orientation in vapor-molecular-layer-deposited alkyl-aromatic polyamide films

The surface-limited molecular-layer deposition of alkyl-aromatic polyamide films using sequential doses of 1,4-butane diamine (BDA) and terephthaloyl dichloride (TDC) is characterized using in situ quartz crystal microbalance and ex situ spectroscopy analysis. For the first time, near-edge X-ray absorption fine structure (NEXAFS) spectroscopy is used to offer insight into molecular orientation in films deposited via molecular-layer deposition (MLD). The results show that the oligomer units are lying nearly parallel to the surface, which differs from the linear vertical growth mode often used to illustrate film growth.     

PANI膜电聚合过程及电控分离苯酚的EQCM研究

通过电沉积方法在镀铂石英晶片上制备了导电聚苯胺(PANI)膜,采用电化学石英晶体微天平(EQCM)技术探讨了苯胺聚合机制及在苯酚溶液中的氧化还原特性.在0.5 mol/L硫酸溶液中结合循环伏安法考察了PANI膜在完全还原态(L)-半氧化态(E)-完全氧化态(P)之间的电活性和稳定性;在不同浓度的苯酚溶液中结合恒电压阶跃...     

Solid-state electropolymerization and doping of triphenylamine as a route for electroactive thin films

Solid-state electropolymerization could be a way to produce organic semiconductors with potential application as Hole Transporting Materials (HTMs) in hybrid organic-inorganic devices. Thereby, thin solid films of triphenylamine (TPA) deposited by spin coating on conducting glass substrates have been electrochemically treated by performing multiple voltammetric cycles between -0.4 V and 1.0 V vs. Ag/AgCl in a 0.5 M sodium perchlorate aqueous electrolyte. Subsequent characterization by means of in situ UV-Vis spectroscopy, in situ Electrochemical Quartz Crystal Microbalance, Atomic Force Microscopy, Contact Angle analysis, and Open Circuit Potential measurements reveals cross-linking of the monomeric units in the thin film. Such polymerized films are characterized by a high electroactivity linked to doping/undoping, a reversible electrochromic behavior under potentiodynamic conditions and fast changes of the open circuit potential upon illumination, indicating efficient charge transport throughout the film. While extensive polymerization has been demonstrated for TPA, this process is negligible in the case of tri-p-tolylamine, which is linked to the para substitution of the phenyl rings. In more general vein, the feasibility of solid-state electropolymerization is illustrated as well as the potential advantages of this methodology for the preparation of hybrid inorganic/organic materials based on nanoporous oxide matrices.     

基底材料对脉冲电流法制备的聚苯胺膜性能的影响

本文采用脉冲电流法(PGM)在不同的基底材料表面沉积PANI, 通过平均电位\|时间曲线及扫描电子显微镜(SEM)等方法研究了基底材料对PGM法制备PANI的影响; 并采用循环伏安(CV)和电化学阻抗谱(EIS)研究了不同电极材料表面PANI的电化学性能.     

Polyaniline-coated carbon particles and their electrode behavior in organic carbonate electrolyte

In an attempt to increase the interface stability of carbon used in Li-ion batteries, a thin conducting polyaniline (PANI) film was fabricated on the surface of carbon by in situ chemical polymerization. The chemical and electrochemical properties of the composite material were characterized using X-ray diffraction, Raman spectroscopy, scanning electron microscope, cyclic voltammetry, and electrochemical impedance spectroscopy. It was confirmed that the PANI film has an obvious effect on the morphology and the electrochemical performance of carbon. The results could be attributed to the electronic and electrochemical activity of the conducting PANI films.     

Production of Polyacrylic Acid Homo- and Copolymer Films by Electrochemically Induced Free-Radical Polymerization: Preparation and Swelling Behavior

Films of polyacrylic acid hydrogels were produced on a conducting substrate by means of electrochemically initiated polymerization (EIP). An electro-chemical quartz crystal microbalance was used to monitor film growth in situ. Homopolymer and copolymer films of polyacrylic acid and poly-N-isopropylacrylamide were characterized by FTIR spectroscopy. The degree of swelling of these films could be tuned via the pH.     

The effect of HCl on the polymerization of aniline with ferric chloride

The chemical oxidation of aniline with ferric chloride, FeCl₃ · 6H₂O in the HCl aqueous solutions to form polyaniline (PANI) powder and films has been investigated. The effect of acid concentration on the deposition of PANI film in situ was studied. The presence of an acid affects both the yield of the polymer and the growth rate of the film. This effect was corroborated by the UV-visible absorption studies of the films deposited on glass supports during the polymerization. The influence of the acid on the yield of the PANI powder formed in the bulk solution was also examined. We have found that the yield of the polymer formed either on the surface or in the bulk solution decreased with the increasing concentration of HCl. The effect of HCl concentration on the in situ UV-visible absorption at the early stages of aniline polymerization is also discussed. The text was submitted by the authors in English.     

Characterization and electrochemical deposition of natural melanin thin films

Melanin is an important class of biological pigments because of its distinct chemical and physical properties. The electrochemical deposition of natural melanin thin films was studied using two different techniques; constant potential and cyclic voltammetry along with a deposition time of five hours. The thin films deposited electrochemically on a fluorine-doped tin oxide conductive glass substrate using the constant potential method, exhibited faster growth rate and better adhesion to the fluorine-doped tin oxide working electrodes than those deposited using the cyclic voltammetry method. The thin films deposited on the fluorine-doped tin oxide conductor glass using the constant potential method were also more homogeneous than those deposited via the cyclic voltammetry technique. The increase of film thickness is related to the increase of electrochemical deposition time. Interestingly, the electrochemical deposition using the constant potential method had the advantage of consuming less electric charge. The physical and chemical structures of the melanin thin films were characterized using ultraviolet–visible absorption spectroscopy, Fourier-transform infrared spectroscopy, and X-ray diffraction analysis. The ultraviolet–visible absorption spectra showed the correlation between the variation of deposition rates of melanin and the type of electrochemical technique employed as well as the thickness of the film. The average thickness of the film is 500 nm which absorb 40% of light in both type of films. The atomic force microscopy images illustrated the homogeneous deposition of the melanin molecules on the fluorine-doped tin oxide conductive glass substrate, indicating that the thickness of the thin films can be controlled. We estimated an average grain size of 14.093 Å. The ease of preparing such thin films of organic materials can open new avenues towards the use of soft conductors, in contrast to the complex preparation of industrial semiconductors.     

Study of the growth process of in situ polyaniline deposited films

Polyaniline (PAni) thin films were deposited onto BK7 glass substrates using the in situ deposition technique. The control of the time and the aniline concentration in the PAni polymerization reaction on the film deposition allowed us to prepare films with different thickness, down to approximately 25 nm. The film growth process was monitored by measuring the UV-vis spectra and the AFM height profiles of the film surface. The curves of adsorption kinetics were analyzed with the Avrami's model, yielding an exponent n=3, thus indicating nucleation of spheroids at the initial stages of polymerization that grow through a diffusion process. AFM images of the surface height profiles corroborate this hypothesis, with spheroids growing with no preferred orientation during the in situ deposition.     

聚苯胺/二氧化钛复合薄膜的制备及其气敏性能

室温条件下, 运用静电力自组装和原位化学氧化聚合相结合的方法制备了聚苯胺/纳米二氧化钛(PANI/TiO2)复合薄膜和聚苯胺(PANI)薄膜, 并通过XPS和SEM对薄膜进行了分析表征. 采用平面叉指电极式器件制备了PANI/TiO2复合薄膜和PANI薄膜气体传感器, 研究了其在常温下对有毒气体NH3和CO 的敏感性能. 结果表明, PANI/TiO2复合薄膜较PANI薄膜具有更优的灵敏度和响应恢复特性.     

Nanoscale measurements of conducting domains and current-voltage characteristics of chemically deposited polyaniline films

Spatial variations in electric conductivity and evolutions of band structures of polyaniline (PANI) films have been studied by use of a so-called current-sensing atomic force microscope (CS-AFM) or atomic force microscope current image tunneling spectroscopy (AFM-CITS). PANI films were deposited chemically onto indium-tin oxide- (ITO-) glass substrates, and their thickness and doping levels were controlled by polymerization and acid-doping conditions. The conducting uniformity of the PANI films depends on their doping level and thickness. Conducting domains were observed in fully doped PANI film, even when the bias voltage was reduced to as small as 30 mV. High current flowing regions gradually disappeared when conducting PANI films were partially dedoped. The point-contact current-voltage (I-V) characteristics of conducting tip-polymer/ITO systems were investigated on PANI films with different thickness and degree of doping. Various types of I-V curves representing metallic, semiconducting, and insulating states were obtained depending on the aggregation of polymer chains and doping level of the polymer film. The band gap energies (estimated from the I-V or dI/dV-V curves) of emeraldine base (EB) (undoped polyaniline) films are all higher than 3.8 eV, and a wide distribution of the band gap energies (0-1.1 eV and 0.75-1.8 eV for fully and partially doped PANI thin films, respectively) was found in a single polymer film.     

Cobaltocenium-functionalized poly(propylene imine) dendrimers: redox and electromicrogravimetric studies and AFM imaging

The first four generations of cobaltocenium-functionalized, diaminobutane-based poly(propylene imine) dendrimers DAB-dend-Cb,(PFb)x (x = 4, 8, 16, and 32; Cb=[Co(eta5-C5H4CONH)(eta5-C5H5)] (1-4) have been synthesized and characterized. The redox activity of the cobaltocenium centers in 1-4 has been characterized by using cyclic voltammetry and the electrochemical quartz-crystal microbalance (EQCM). All of the dendrimers exhibit reversible redox chemistry associated with the cobaltocenium/cobaltocene redox couple. Upon reduction. the dendrimers exhibit a tendency to electrodeposit onto the electrode surface, which is more pronounced for the higher generations. Pt and glassy carbon electrodes could be modified with films derived from 1-4,exhibiting a well-defined and persistent electrochemical response. EQCM measurements show that the dendrimers adsorb, at open circuit, onto platinum surfaces at monolayer or submonolayer coverage. Cathodic potential scanning past -0.75 V at which the cobaltocenium sites are reduced, gave rise to the electrodeposition of multilayer equivalents of the dendrimers. The additional material gradually desorbs upon re-oxidation so that only a monolayer equivalent remains on the electrode surface. Changes in film morphology as a function of dendrimer generation and surface coverage were studied by using admittance measurements of the quartz-crystal resonator on the basis of its electrical equivalent circuit, especially in terms of its resistance parameter. In general, we find that films of the lower dendrimer generation 1 behave rigidly, whereas those of the higher generation 4 exhibit viscoelastic behavior with an intermediate behavior being exhibited by 2 and 3. Using tapping-mode atomic force microscopy (AFM). we have been able to obtain molecularly resolved images of dendrimer 4 adsorbed on a Pt(111) electrode.     

纳米纤维聚苯胺膜在不锈钢电极表面的生长过程

研究了脉冲电流法(PGM)聚合苯胺时, 纳米纤维聚苯胺(PANI)膜在不锈钢(SS)电极表面的生长过程. 用计时电位法和扫描电子显微镜(SEM)表征了聚苯胺生长过程的电化学特征和微观形貌; 并通过循环伏安(CV)法研究了苯胺的聚合速率. 结果表明, 聚苯胺的生长经历了两个阶段, 首先是在裸不锈钢电极表面上形成颗粒状聚苯胺, 此时聚合电位约为1.10 V, 经历了30 s后, 电极表面被一层颗粒状聚苯胺膜所覆盖; 在此基础上, 聚苯胺以纳米纤维状结构继续生长, 当颗粒状聚苯胺被纳米纤维状聚苯胺膜完全覆盖时, 聚合电位降至0.75 V左右并保持稳定.     

Voltammetric and conductometric behavior of nanocomposites of polyaniline and gold nanoparticles prepared by layer-by-layer technique

Multilayer nanocomposites from polyaniline (PANI) and gold nanoparticles (AuNPs) were formed by layer-by-layer deposition. The formation of PANI–AuNPs multilayer structures was monitored by UV-vis absorption spectroscopy and cyclic voltammetry. Each deposited bilayer of PANI–AuNPs led to a monotonous and almost linear increase in both optical absorbance and the first current peak of PANI oxidation. The prepared multilayer nanocomposites were characterized by in situ conductivity measurements at different pH and potential and by transmission electron microscopy. Finally, chemosensitive properties of the new material based on the intrinsic affinity of gold nanoparticles were studied. Changes in the film resistance on exposure to vapors of mercury and sulfur-containing compounds were observed.     

A comparative study on the viscoelasticity and morphology of polyaniline films galvanostatically grown on bare and 4-aminothiophenol-modified gold electrodes using an electrochemical quartz crystal impedance system and SEM.

The equivalent-circuit parameters of the 9-MHz piezoelectric quartz crystal (PQC) resonance were measured in situ during the galvanostatic polymerization of aniline on 4-aminothiophenol(4-ATP)-modified and bare Au electrodes for ca. 2000 s, respectively. Two polymerization media, 0.100 mol L-1 aniline in 1.0 mol L-1 H2SO4 and in 2.0 mol L-1 HClO4 aqueous solutions, and two values of the current density, 12 and 36 microA cm-2, were used. At identical levels of the resonant frequency shifts in the solutions, obviously greater increases in the motional resistance (R1) were found after aniline polymerization on bare Au electrodes, though the absolute values of delta f0/delta R1 were all large; also, the resonant frequency shifts in air (delta f0g) were considerably smaller for PANI films grown on bare Au electrodes. It is thus concluded that, under identical polymerization conditions, (1) the PANI film grown on a bare gold electrode is rougher, less compact, and can entrap solution more notably; (2) the deposition efficiency of PANI is higher on a 4-ATP-modified Au electrode, owing to a significantly greater observed "dry" frequency shift, and thus a greater "net" mass value of the polyaniline backbone. SEM observations have confirmed that PANI films on 4-ATP-modified Au electrodes were smoother and more compact than those grown on bare Au ones under identical polymerization conditions. In addition, a technique of simultaneous measurements of the electroacoustic admittance of the PQC resonance and the electrochemical impedance was used to monitor the adsorption of 4-ATP onto a PQC gold electrode.