Raman spectroelectrochemical study of polyaniline and sulfonated polyaniline in solutions of different pH

Raman spectroelectrochemical study has been done with electrochemically prepared films of polyaniline and a copolymer of polyaniline and metanilic acid using a green laser excitation (532 nm). The experimental variables included solutions of different pH between 0.5 and 9.0, and varying electrode potential between 0.0 and 0.8 V versus Ag/AgCl. Raman bands within the wavenumber limits of 500–1700 cm⁻¹ have been analysed, and their changes, proceeding with varying of electrode potential and solution pH, have been interpreted. It has been stressed that the spectral changes of polymer films proceed continuously rather than stepwise by changing the electrode potential. Considering leucoemeraldine and pernigraniline forms of polyaniline as fully reduced and oxidised structures, respectively, it could be concluded that many different redox forms can exist between these two limiting forms, rather than the only possible emeraldine form.     

The spectroelectrochemical behavior of films of polyaniline interpolymer complexes in the near infrared spectral region

In this work, we carry out spectroelectrochemical studies of films of interpolymer complexes of polyaniline (PANI) prepared via the chemical and electrochemical template polymerization of aniline in the presence of polyamide sulfonic acids with different structures. It is shown that their spectroelectrochemical behavior in the near infrared region depends on the rigidity of the chain of the polymer sulfonic acid matrix. Electrodeposited films of PANI complexes with a rigid-chain polyacid exhibit a more intense absorption in the near infrared region (1000–2200 nm) and a less intense absorption in the absorption region of localized polarons (around 750 nm) in comparison with complexes with a flexible-chain polyacid. The comparison of the dependence of absorption in the near infrared region on potential with the cyclic voltammetry curves suggests that the chromophores responsible for this absorption are radical cations in nature. In the spectra of the films of chemically synthesized PANI complexes with a flexible-chain polyacid, during a long-term cycling in the region of potentials of the first redox stage of PANI, the absorption in the near infrared region which corresponds to delocalized polarons is also formed. This is apparently attributed to the intensification of the intermolecular interactions under the conformational fluctuations that accompany the change in the degree of oxidation of the film during cyclic voltammetry.     

Spectroelectrochemistry of conducting polypyrrole and poly(pyrrole–cyclodextrin) prepared in aqueous and nonaqueous solvents

Conducting polypyrrole (PPy) and poly(pyrrole-2,6-dimethyl-β-cyclodextrin) [poly(Py-β-DMCD)] films were prepared by electrode potential cycling on a gold electrode in aqueous and nonaqueous (acetonitrile) electrolyte solutions containing lithium perchlorate. The resulting products were characterized with cyclic voltammetry, in situ UV–Vis spectroscopy, and in situ conductivity measurements. For the electrosynthesis of poly(Py-β-DMCD), a (1:1) (mole–mole) (Py-β-DMCD) supramolecular cyclodextrin complex of pyrrole previously characterized with proton NMR spectroscopy was used as starting material. A different cyclic voltammetric behavior was observed for pyrrole and the poly(Py-β-DMCD) complex in aqueous and nonaqueous solutions during electrosynthesis. The results show that in both solutions in the presence of cyclodextrin, the oxidation potential of pyrrole monomers increases. However, the difference of oxidation potentials for films prepared in aqueous solution is larger than for the films prepared in nonaqueous solution. In situ conductivity measurements of the films show that films prepared in acetonitrile solution are more conductive than those synthesized in aqueous solutions. Maximum conductivity can be observed for PPy and poly(Py-β-DMCD) films prepared in nonaqueous solution in the range of 0.10 < E _Ag/AgCl < 0.90 V and 0.30 < E _Ag/AgCl < 0.90 V, respectively. In situ UV–Vis spectroelectrochemical data for both films prepared potentiodynamically by cycling the potentials from −0.40 < E _Ag/AgCl < 0.90 V in nonaqueous solutions are reported. This paper is dedicated to Prof. Alan Bond on the occasion of his 65th birthday in recognition of his numerous contributions toward electrochemistry.     

掺杂态聚苯胺的性能及其防腐应用研究进展

聚苯胺具有良好的导电性和独特的掺杂-解掺杂特性,成为近年来备受关注的导电高分子材料,其特有的抗划伤、抗点蚀和钝化性能使其在金属防腐领域拥有巨大的应用前景。聚苯胺结构中苯环的存在,使得其分子链具有较大刚性,而分子间氢键又导致其难溶、难熔、可加工性能较差,严重制约了聚苯胺的应用。掺杂过程能有效改善聚苯胺的某些性能,或赋予其新的功能,扩展聚苯胺的应用。本文综述了聚苯胺的掺杂方式、掺杂机理、聚苯胺防腐材料的制备方法,以及其在金属防腐领域的应用,展望了聚苯胺的研究和应用前景。     

聚苯胺基LB膜的制备及气敏特性的研究

以聚苯胺 (PAN)为原料 ,利用LB(Langmuir Blodgett)超薄分子膜技术 ,制备了不同层数的纯聚苯胺LB膜及聚苯胺与乙酸 (AA)混合 (PAN AA)LB膜 ,对其进行了紫外 可见光光谱分析研究 ,并对不同层数的聚苯胺基LB膜的二氧化氮 (NO2 )气敏特性进行了研究 ,发现PANLB膜较PAN AALB膜具有更好的敏感性、响应性和可逆性 ,3层和 15层PANLB膜对相对百分比为 2 0× 10 -6NO2 的响应时间分别为 10s和 30s,15层PANLB膜的恢复时间约为 4min     

In situ vibrational spectroscopy of conducting polymer electrodes

The application of in situ Fourier transform infrared spectroscopy for the study of electrochemical redox reactions of conducting polymers is described. The experimental setup of two different methods, external reflection absorption spectroscopy and attenuated total reflection spectroscopy, is shown. The results of spectroelectrochemical investigations of the reactions of polyaniline in different electrolyte solutions are discussed.     

Electrochemical formation of conducting polymer coating on porous p‐ and n‐silicon substrates

Electrochemical synthesis of polyaniline was carried out in aqueous sulfuric acid solutions of aniline on porous p‐ and n‐silicon under galvanostatic, potentiostatic and potential pulse regimes. It is shown that the introduction of catalytic quantities of oxidants, potassium hexachloroiridate, potassium dichromate, potassium permanganate and chloranilic acid, in electrolytes accelerates the formation of polymer films and lowers the overvoltage of electrosynthesis. The resulting polymer coatings are characterized by cyclic voltammetry and IR spectroscopy. It is shown that polyaniline coatings on porous p‐ and n‐silicon electrodes are electroactive and conducting in anodic and cathodic ranges. Copyright © 2000 John Wiley & Sons, Ltd.     

导电聚合物的电化学制备和电化学性质研究——中国科学院有机固体重点实验室导电聚合物电化学研究工作简介(I)

简要介绍本研究组自上世纪80年代以来在导电聚合物的电化学制备和电化学性质研究中取得的一些主要成果,包括吡咯电化学聚合条件的影响、电化学聚合反应机理及其反应动力学、导电聚吡咯的两种掺杂结构及其两步电化学氧化还原过程和电化学过氧化的机理、导电聚苯胺的电化学性质、导电聚合物稳定性的电化学解释等等.     

In situ Raman spectroscopic studies on potential-induced structural changes in polyaniline thin films synthesized via surface-initiated electropolymerization on covalently modified gold surface

The work describes the in situ Raman spectroelectrochemical studies on polyaniline (PANi) thin films covalently bound to the modified gold surface. The PANi thin films were synthesized via surface-initiated electrochemical polymerization on gold substrates initially modified by the formation of self-assembled monolayer of 4-aminothiophenol, or comparatively by the electrografting of 4-nitrobenzenediazonium salt followed by the electrochemical reduction of aromatic nitro-groups to form aniline-containing monolayer. Due to the defined surface-chain bonding and the ordered polymer structure, the obtained thin PANi films exhibit a narrow peak separation of the polymer redox transitions and negatively shifted potential of its full oxidation, as revealed by the PANi Raman spectra recorded at controlled potentials and cyclic voltammetry measurements.     

Effects of solvent and electrolyte on the electrochromic behavior and degradation of chemically prepared polyaniline-poly(vinyl alcohol) composite films

Effects of solvent and electrolyte on the electrochromic behavior and degradation of polyaniline in nonaqueous aprotic media, as well as its electrochemical redox and degradation mechanisms, were investigated with chemically prepared polyaniline-poly (vinyl alcohol) composite films and polyaniline homogeneous films. Visible and FT-IR absorption spectra of the polyaniline films, oxidized electrochemically at various polarization potentials, showed that the mechanisms in aprotic media involved two successive oxidation processes. In contrast to aqueous systems, the higher oxidation process involved further anion insertion without deprotonation, and the degradation was due to partial formation of the electrochemically inactive quinonediimine structure at excessive polarization potentials. From investigations of solvent and electrolyte effects, it is suggested that the electrochromic behavior and degradation of polyaniline are influenced by the electron-donating and accepting ability of solvents, acceptor strength of electrolyte cations, and the nucleophilic character of electrolyte anions. It was also suggested that some anions like as well as protons, are constrained in the PVA matrix by specific electrostatic interactions and steric effects to improve the stability of polyaniline in the highly oxidized state. © 1994 John Wiley & Sons, Inc.     

Raman study of PANI thin film during long time period in dependence on storage conditions

Conducting polymer polyaniline which is nowadays in forefront of the interest was in our study prepared in a form of thin films from anilinium sulfate by its chemical oxidation using ammonium peroxydisulfate. During the oxidation process, the polyaniline was deposited on glass slides and immersed into reaction mixture. Two sets of polyaniline thin films were prepared with different oxidation times (10, 20, 30, and 40 min). The first set was kept dry in desiccator and the second one was freely exposed to air moisture. Raman spectroscopy, nondestructive technique which is very sensitive to changes in structure of polymers, was used for the characterization of the protonation state of prepared polyaniline thin films. It was found that storage conditions affect the protonation state which in case of samples kept in desiccator is maintained without significant changes for longer time. Raman spectroscopy also revealed the dependence of protonation state on the oxidation time and 10 min proved as not sufficient for the creation of the protonation form of polyaniline.     

高导电聚苯胺薄膜的制备及其电磁屏蔽性能的研究

随着电器制品、电子器件的商用、军事用和科学应用的迅速增长 ,产生了亟待解决的电磁干扰 (也称作电磁环境污染 )问题 ,电磁干扰屏蔽日益受到关注 .本文从聚苯胺掺杂工艺角度出发 ,通过改变掺杂剂用量和溶剂种类 ,制备出高导电的聚苯胺薄膜 ,并对其电磁屏蔽特性进行了初步的测试与理论分析 ,将屏蔽效能的实测结果与理论计算值进行了比较     

循环伏安法的电扫描方式对苯胺聚合产物形貌影响的观察

在含有0.2 mol.L-1苯胺的0.5 mol.L-1H2SO4溶液中,以扫描速度50 mV.s-1,扫描电位为-0.1~0.9 V,采用循环伏安法(CV),在金属Ti基体上,通过控制扫描方式分别得到了颗粒状、纤维状及管-片状的苯胺聚合产物,分析了形成不同形貌聚苯胺的原因,并通过扫描电子显微镜(SEM)、循环伏安法和电化学阻抗谱(EIS)对不同形貌聚苯胺的结构和性能进行了表征.结果表明,不同形貌聚苯胺的形成是由于聚苯胺的成核及生长模式不同,而无论何种形貌的聚苯胺膜都具有很大的比表面积和良好的导电性能,其中,管-片状聚苯胺的膜层阻抗最小,导电性能最好.     

In situ Raman spectroelectrochemical study of electrocatalytic processes at polyaniline modified electrodes: Redox vs. metal-like catalysis

Two processes of electrocatalytic oxidation of solution species at conducting polymer modified electrodes have been studied for the first time with in situ Resonance Raman spectroelectrochemical technique at a red laser excitation (λ = 632.8 nm), namely electrooxidation of hydroquinone at a sulfonated polyaniline modified electrode in an acidic solution and electrooxidation of ascorbic acid at polyaniline modified electrode in a pH-neutral solution. In both cases, characteristic Raman features have been identified for different redox forms of conducting polymers and changes in the net redox state of a polymer layer during electrooxidation of solution species have been studied. It has been shown that an increase in the concentration of oxidizable species causes an increase of the net content of a reduced form of polyaniline in the modifying layer. From this, the redox (vs. metal-like) mechanism of electrocatalysis at conducting polymer modified electrodes has been deduced.     

Isolation of individual components in the electronic absorption spectra of polyaniline from the spectroelectrochemical data

The absorption spectra of polyaniline (PAN) films obtained by electrochemical polymerization on transparent SnO₂-glass electrodes are analyzed. The spectra are recorded at steady-state potentials of 0.0 to 0.8 V (Ag/AgCl) in an aqueous HC1 solution. Individual absorption bands, isolated by the Alentsev-Fok method, include both earlier known bands and some new absorption bands. The former correspond to π-π* transitions in the benzenoid rings (300-320 nm), radical cations (∼435 nm), localized polarons (∼755 nm), and quinoid structures (∼655 nm). By comparing these results with the spectroelectrochemical data obtained earlier for electrochemically synthesized PAN in solutions of various acids and for vacuum-deposited PAN, the newly found bands are assigned to different intermolecular interactions, specifically, a donor-acceptor coupling of the quinoid moieties with counter anions (at 570 nm) and an electron exchange between highly conducting domains of the film (∼900 nm)     

Saccharide imprinting of poly(aniline boronic acid) in the presence of fluoride

A new approach for the electrosynthesis of saccharide-imprinted poly(aniline boronic acid) is described. The method involves the formation of a saccharide-aminophenylboronic acid complex in the presence of fluoride to allow the electropolymerization of a self-doped, molecularly imprinted polyaniline. The formation of the anionic monomer complex enables electrochemical polymerization at near neutral pH (5-7) ensuring the incorporation of saccharide in the resulting, self-doped polymer. In this work, films were imprinted with D-fructose where saccharide-aminophenylboronic acid complexation occurred in the presence of one equivalent of fluoride. The selectivity toward D-fructose relative to D-glucose showed an increase of over 25% as a result of imprinting. In addition to the enhanced selectivity, to the best of our knowledge this is the first example of the electropolymerization of a self-doped polyaniline homopolymer under neutral pH conditions.     

Spectroscopy of thin polyaniline films deposited during chemical oxidation of aniline

Any surface immersed in the aqueous reaction mixture used for the preparation of polyaniline becomes coated with a polyaniline film of submicrometre thickness. In this way, various materials can be modified by an overlayer of conducting polymer. The present review illustrates the role of infrared, Raman, and UV-VIS spectroscopies in the studies of polyaniline film growth. Spectroscopic methods are crucial in the evaluation of the performance of polyaniline films alone or in combination with nanoparticles of noble metals. The assessment of film ageing and stability can be followed conveniently by these methods. Carbonization of polyaniline films to nitrogen-containing carbon analogues is also discussed.     

Polyaniline thin film optical waveguides for integrated optics and VLSI prepared by vacuum evaporation technique

Polyaniline is emerging as an important polymer material which offers challenging opportunities for both fundamental research and new technological applications in waveguides. Metal doped polyaniline has been prepared initially in the form of powder by a solution growth technique. The emeraldine salt with doped metal was also prepared by solution growth technique. This powder was used for vacuum evaporation on optically flat glass substrate. The dark green doped (Fe, Al) polyaniline thin films were prepared by vacuum evaporation technique (10^?4 torr). Deposited waveguide thin films have been characterized structurally, using X‐ray diffraction (XRD), optically etc. Effective refractive index of the thin film waveguide was also calculated theoretically and experimentally. Waveguide parameters, namely refractive index, propagation loss and depth of vacuum deposited polyaniline thin films optical waveguide have been determined. The optical spectra and structure and waveguide parameters of vacuum deposited polyaniline thin films are strongly affected by the type of doping. It is possible to reduce the losses by addition of Fe to the vacuum deposited polyanine thin film and modify the effective refractive index (O_eff) according to particular requirements. Results are compared with the results in the literature. Copyright © 2002 John Wiley & Sons, Ltd.     

Hydrogen Peroxide Electrosynthesis on Nonplatinum Materials

A combination of electrochemical and physicochemical methods is used to investigate electrocatalytic and corrosion properties of nonplatinum materials in a direct hydrogen peroxide electrosynthesis by the oxygen ionization. A modifying action of ozone and hydroquinone added in solution is established. Surface properties of the electrocatalysts are studied. Presumably, the electrosynthesis occurs via a mixed path, which includes direct oxygen electroreduction catalyzed by redox processes involving surface groups and chemical oxidation processes.     

Synthesis and electrochromic properties of polybismaleimides containing triphenylamine units

The bismaleimide (BMI) monomer containing triphenylamine was prepared firstly. Then BMI was reacted with different diamines by Michael addition to obtain prepolymers, respectively. Finally, polyimides (PIs) were obtained through melting procedure. The effects of the structure of BMI moiety and thermal curing condition on thermal stability of PIs were studied by thermogravimetric analysis. PIs have excellent processing properties for film casting. Cyclic voltammetry of PI films was carried out on an indium-doped tin oxide-coated glass substrate. Results which exhibit two reversible oxidations at 0.71–0.78 and 1.06–1.16 V vs Ag/AgCl. The electrochromic performance was investigated by spectroelectrochemical methods. These anodically coloring polymer films not only showed good electrochromic properties but also exhibited high optical contrast ratio of transmittance with a color changing from yellow to green. After 100 cyclic switches, the polymer films still retained excellent redox and electrochromic activity.