Polyaniline and polypyrrole: A comparative study of the preparation

Aniline and pyrrole have been oxidized with ammonium peroxydisulfate in aqueous solutions, in the presence of equimolar quantities of hydrochloric acid. The oxidation of pyrrole was faster; the induction period typical of aniline oxidation was absent in the case of pyrrole. As the proportion of oxidant-to-monomer molar concentration increased up to 1.5, the yield increased in both cases. Similarities between the two oxidations are illustrated and discussed. The oxidant-to-monomer molar ratio 1.25 is proposed to be the optimum stoichiometry, in the accordance with the data published in the literature. The conductivities of the polymers prepared were only slightly dependent on the oxidant-to-monomer ratio in the range 0.3-1.5, and were of the order of 10⁰ S cm⁻¹ for polyaniline and ∼10⁻²-10⁻¹ S cm⁻¹ for polypyrrole. Outside this interval, the conductivity of both polymers was reduced. Polyaniline having conductivity ∼10 S cm⁻¹ was produced in solutions of phosphoric acid of various concentrations. On the contrary, the conductivity of polypyrrole was reduced as the concentration of phosphoric acid became higher. The type of protonation is discussed with the help of FTIR spectra by analyzing the ammonium salts obtained after deprotonation. Sulfate or hydrogen sulfate anions produced from peroxydisulfate always constitute a part of the counter-ions.     

A novel chemical route to SiO2 nanowires

A white substance was got by directly heating TiSi powder on Ti foil, under Ar+O ₂ atmosphere. ED, EDX, SEM and HRTEM studies reveal that the white substance consists of amorphous SiO ₂ nanowires of smooth surface and uniform diameter (40-90 nm). X-ray-induced luminescent emission experiment shows that two broad peaks are at 430 and 570 nm. A one-dimensional growth mechanism, on the basis of the one-dimensional thermal flow during nanowire formation, is discussed.     

Synthesis and characterization of aniline and aniline-o-sulfonic acid copolymers

The copolymer of aniline (An) and aniline-o-sulfonic acid (AS) is synthesized by chemical oxidation polymerization. The effects of mole ratio of copolymerized monomers on chain structure, thermostability, conductivity, redox properties of copolymer are discussed. It is indicated that if more AS monomers in polymerization system the corresponding structure units will increase, but their relation isn’t linear. When An:AS = 1:1, the ratio of structure unit in copolymer is 9:1, and it is only 1:2 for copolymer with An:AS = 1:6. The measurements of conductivity and redox activity also prove that the properties of An-co-AS(1:1), (1:3), and (1:4) are similar to polyaniline due to more An units than AS. When An:AS is higher than 1:6, it shows out the properties of copolymer is similar to those of poly(aniline-o-sulfonic acid), and their redox route is different. They will transform to follow the route of LH ↔ EH ↔ P. The results of thermo-analysis indicate that the decomposition temperature of AS units is lower than An units because of the electron-withdrawing group substitution. The decomposition temperature of polymer is related to dopant and doping degree. Electron-withdrawing group, -SO₃H, substitution and HCl doping will decrease polymer chain decomposition temperature. The mechanism of copolymerization of An and AS is different from homopolymerization. The monomer with low oxidation potential forms free radical cation firstly, which transfers to monomer with higher oxidation potential and initiates its polymerization.     

聚苯胺纳米点阵列的制备和库仑台阶现象

本文制备了PANI纳米点阵列, 利用导电原子力显微镜(C-AFM)表征了其形貌和导电性能, 在室温下观察到PANI纳米点的库仑台阶(Coulomb staircase)现象, 并利用库仑阻塞效应的理论进行了初步的分析.     

ZnO纳米线的电化学制备研究

High-quality ZnO nanowires have been synthesized at relatively low temperature via one-step electrochemical anodization technique. In this method, Zn sheet acted as the anode and Pb sheet served as the counter electrode, and the complex solution of HF-C₂H₅OH-H₂O was used as electrolyte. ZnO nanowires were characterized by Field Emission Scanning Electron Microscopy (FE-SEM), Transmission Electron Microscopy (TEM) and Selected Area Electron Diffraction (SAED) and X-ray Diffraction (XRD). The results show that the nanowires were wurtzite crystalline ZnO, and the ZnO nanowires with the diameters of 70 nm and 30～40 nm were obtained by adjusting preparation conditions, respectively.     

Macrocyclic cobalt(III) complexes as precursors for metal-polythiophene hybrid materials

A thiophene-functionalised macrocyclic ligand trans-6,13-dimethyl-6-((thiophen-3-ylmethyl)amino)-1,4,8,11-tetraazacyclotetradecane-13-amine (L¹) has been prepared and complexed with Co^III. The ligand L¹ binds as a pentadentate in the crystallographically characterised complexes [CoL¹(OAc)](ClO₄)₂ and [CoL¹Cl]Cl₂. Electro-copolymerisation of [CoL¹Cl]Cl₂ with 3,4-ethylenedioxythiophene (EDOT) in a 1:2 ratio on a preformed poly-3,4-ethylenedioxythiophene (PEDOT) film resulted in metal–polymer hybrid films of high quality, consistency and uniformity in appearance. The copolymerised films were characterised by XPS indicating a 1:11 ratio of incorporation of complex to EDOT. Electrochemistry of the Co-PEDOT film (cast on an indium-doped tin oxide working electrode) in water revealed a Co^III/II redox couple at a potential ca. −600 mV (vs Ag/AgCl) which is similar to that seen in solution for the monomeric aqua complex [CoL¹(OH₂)]³⁺.     

Planar potentiometric sensors based on Au and Ag microelectrodes and conducting polymers for flow-cell analysis

Back-side contact Au and Ag microelectrodes were used as transducers to construct planar all-solid-state electrodes suitable for flow-through analysis. The microsensors were based on plasticized PVC potassium-selective membranes containing ion-electron conducting polymer—polypyrrole doped with di(2-ethylhexyl) sulfosuccinate. The proposed technique allowed simple construction of microsensors in one step, by membrane solution casting directly on the surface of the planar metallic transducers. The performance of the microsensors based on Au and Ag transducers were determined and compared with planar sensors based on internal electrolyte immobilized in polyHEMA. The addition of the polypyrrole to the membrane composition did not influence on the selectivity, reproducibility and long-term stability of the microsensors but improved their standard potential stability in time in comparison with coated-wire type sensors. Moreover, all-solid-state microsensors based on Au transducers exhibited better signal stability than Ag based sensors.     

Electrochemical synthesis, characterization and some properties of a polymer derived from thioflavin S

Polymeric films derived from thioflavin S were electrosynthesized on mild steel and silver electrodes in sulfuric acid and lithium perchlorate-containing aqueous solutions. The introduction of thioflavin S in an acidic solution protected the surface of steel from corrosion. The electrochemical behavior of the steel coated with a layer of poly(thioflavin) was examined by electrochemical impedance spectroscopy. The films exhibited a capacitive behavior and were semi-conductive in nature. Infra red reflectance measurements of the polymer films at the steel surface showed that the polymer structure retained the aromatic structure of the benzene and thiazole rings with the distinction of a nitrogen quinone vibrational band. Surface morphology of the polymer film was examined with scanning electron microscopy. The films are yellow, compact and dense when electrochemically formed onto steel surfaces when compared to a blue rather porous when formed onto silver electrode. The mechanism of electropolymerization of thioflavin is given and found similar to that of aniline with the possibility of metal chelation with the sulfur and/or nitrogen in the thiazole ring.     

Probing buried carbon nanotubes within polymer-nanotube composite matrices by atomic force microscopy

Multi-walled carbon nanotubes (MW-CNT) inside a polyamide-6 (PA6)-MW-CNT composite were visualized by atomic force microscopy (i) in a field-assisted intermittent contact and (ii) in the tunneling (TUNA) mode. Individual buried MW-CNTs were clearly discerned within the PA6 matrix. An average diameter of 33 ± 5 nm of the MW-CNTs was determined based on field-assisted intermittent contact mode AFM images, which is consistent with the expected size of PA6-coated MW-CNTs. Single well dispersed MW-CNTs that are located in the sub-surface region of the composite were also observed in the TUNA mode. These new AFM approaches circumvent the tedious sample preparation based on ultramicrotoming required for high resolution electron microscopy studies to obtain “in-depth” morphological information and hence are expected to facilitate the analysis of CNT-based and other nanocomposites in the future.     

Polyaniline-coated silica gel

Silica gel microspheres 7 and 15 μm in diameter were coated with an overlayer of polyaniline camphorsulfonate or hydrochloride during the oxidative polymerization of aniline. Coated silica gel and polyaniline precipitate were separated using a difference in sedimentation rate. In an alternative approach, the microspheres were modified with polyaniline in the presence of 35 nm colloidal silica. This technique prevented the macroscopic precipitation of polyaniline. Coatings of neat, 3-aminopropyl- and octadecyl-modified silica gel with polyaniline hydrochloride were compared. The surface composition of coated microspheres was characterized by X-ray photoelectron spectroscopy. Potential applications of particles in electrorheology, organic catalysis, and in modeling of conductivity behavior in composites are demonstrated.