Electrochemical impedance spectroscopy of poly(N-methyl pyrrole) on carbon fiber microelectrodes and morphology

This work reports the supercapacitive properties of electrochemically grown homopolymer films on carbon fiber microelectrode (CFME) via poly(N-methyl pyrrole) (P(NMPy)) which is characterized by cyclic voltammetry (CV), Fourier transform infrared reflectance (attenuated total reflection) spectroscopy (FTIR-ATR), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrochemical impedance spectroscopy (EIS). Microporosity of P(NMPy) electrocoated carbon fiber microelectrodes facilitated improved capacitance and redox behaviours by applying different DC potentials in electrochemical impedance spectroscopic measurements. The capacitance values of P(NMPy)/CFME is obtained (0.059 F) which is in the range of manufactured values.     

A theoretical study on the interaction between N-methylpyrrole and 3,4-ethylenedioxythiophene units in copolymer molecules

Quantum mechanical calculations at the density functional theory level have been used to examine the interaction between 3,4-ethylenedioxythiophene and N-methylpyrrole units when they are directly linked in copolymer chains. Specifically, in this study, which was motivated by experimental observations of electrochemically synthesized copolymers, the conformation and electronic properties of co-oligomers formed by two, three and four units have been examined in both neutral and radical cation states. Results reveal significant differences, especially in the radical cation state, between the co-oligomers and the corresponding individual homo-oligomers, which have also been explored considering the same theoretical method. Furthermore, electronic properties of oligomers have been used to estimate those of poly(3,4-ethylenedioxythiophene), poly(N-methylpyrrole) and the copolymer with alternated structure, which have been compared among them. The overall results allowed to understand the anomalous features detected in copolymers prepared by electrochemical techniques from 3,4-ethylenedioxythiophene and N-methylpyrrole mixtures, which were initially attributed to some type of unfavourable interaction between the two types of monomeric units.     

Poly(N-methylpyrrole) electrodeposited on copper: Corrosion protection properties

Electrochemical synthesis of poly(N-methylpyrrole) films on copper electrodes from an aqueous oxalic acid has been achieved. A potential higher than 2 V (SCE) was needed to generate the polymer, for this reason, the polymer was in the overoxidized state. The inhibiting corrosion properties of this coating on copper were investigated for the first time in aqueous 0.1 M sodium chloride solution using potentiodynamic polarization, Tafel analyses, open-circuit potential and electrochemical impedance spectroscopy. Corrosion protection properties comparable to those of polypyrrole (PPy) films were observed for these films. A physical barrier effect is the most likely protection mechanism.     

Electrochemical impedance spectroscopy of poly[carbazole-co-N-p-tolylsulfonyl pyrrole] on carbon fiber microelectrodes,equivalent circuits for modelling

Polycarbazole (PCz) and copolymerization of carbazole (Cz) and N-p-tolylsulfonyl pyrrole (pTsp), P(Cz-co-pTsp), thin films have been cyclovoltammetrically coated onto carbon fiber electrodes as an active functionalized microelectrode in sodium perchlorate (NaClO₄)/acetonitrile (ACN) medium. The resulting thin films of homopolymer and copolymer were characterised by using Fourier transform infrared reflectance spectroscopy (ATR-FTIR), energy dispersive X-ray (EDX) point analysis, scanning electron microscopy (SEM) and atomic force microscopy (AFM). An electrical impedance study on the prepared electrodes is reported in the present paper under different feed ratios of [pTsp]₀/[Cz]₀ during electrochemical impedance spectroscopic (EIS) measurements. Specific capacitance (C_sp) were calculated, P(Cz-co-pTsp) in feed ratio of [pTsp]₀/[Cz]₀ = 200 has preserved more capacitive behavior especially at lower frequency (C_sp = ∼156 mF g⁻¹) than polycarbazole (C_sp = ∼2.1 mF g⁻¹. The electrochemical impedance data fitted to three different equivalent models were used to find out numerical values of the proposed components.     

Effect of electrochemical anodization and growth time on continuous growth of carbon nanotubes on carbon fiber surface

Carbon nanotubes (CNTs)/carbon fiber (CF) reinforcements were prepared by chemical vapor deposition after electrochemical anodization and catalyst impregnation. The results showed that after the electrochemical anodization, the CFs were oxidatively etched and the surface roughness increased, which is helpful to form a uniform catalyst coating on the surface of CF. Under the current of 0.4 A and 0.6 A, CNTs can grow evenly on the surface of CF. Within a certain range, with the increase of growth time, the density and length of CNTs are improved. The CNTs/CF reinforcement prepared at the current intensity of 0.4 A and the growth time of 8 min has the best comprehensive performances compared with other as-fabricated samples. The tensile strength of the sample can reach a high value of 4.56 GPa, and the wettability of resin has an effective improvement.     

Morphological and impedance studies on electropolymerized 3,4-(2,2-dibenzylpropylenedioxy)thiophene nanostructures on micron sized single carbon fiber

Micron sized single carbon fibers were cyclovoltammetrically coated with poly[3,4-(2,2-dibenzylpropylenedioxy)thiophene] resulting in a nanofiber network at the surface. The method provides conjugated polymer nanostructures covalently and uniformly bound to micron sized substrates. When the electropolymerization is carried out with different electrolytes in acetonitrile the dopant influences the structure of the coating layer what is proved by electrochemical impedance spectroscopy and electron microscopy. Electrodes based on poly[3,4-(2,2-dibenzylpropylenedioxy)thiophene] on single carbon fiber microelectrodes (SCFMEs) prepared in Bu₄NPF₆/ACN show the best capacitance performance due to their higher surface area. The improvement is attributed to the formed nanofiber network structure which results in a more efficient charge transport and collection.     

Characterization by electrochemical impedance spectroscopy of magnetite nanoparticles supported on carbon paste electrode

Magnetite nanoparticles were supported on carbon paste electrode and characterized by low scan rate voltammetry and electrochemical impedance spectroscopy (EIS) to obtain mechanistic information related to its oxidation and reduction in acid media.The voltammograms showed only one reduction and one oxidation peak for the supported magnetite, which were attributed to formation of ferrous ion and ferric oxide, respectively. Both peaks are fairly wide, indicating complex mechanisms.Using EIS, a mechanism showing up to three time constants, capacitive all of them, was evidenced, both in anodic and cathodic domain. These were attributed to charge transfer at the highest frequencies, adsorption of generated species at intermediate frequencies, and proton adsorption at low frequencies. Discussion about the nature of the adsorbed species and the concerned mechanism for each domain is developed.     

Review study of electrochemical impedance spectroscopy and equivalent electrical circuits of conducting polymers on carbon surfaces

Electrochemical impedance spectroscopy (EIS) is an experimental method for characterizing electrochemical systems. This method measures the impedance of the concerned electrochemical system over a range of frequencies, and therefore the frequency response of the system is determined, including the energy storage and dissipation properties. The aim of this article is to review articles focusing on electrochemical impedance spectroscopic studies and equivalent electrical circuits of conducting polymers, such as polypyrrole, polycarbazole, polyaniline, polythiophene and their derivatives, on carbon surfaces. First, the conducting polymers are introduced. Second, the electrochemical impedance spectroscopic method is explained. Third, the results of EIS applications using equivalent electrical circuits for conducting polymers taken from the literature are reviewed.     

Influence of the acidity level on the electropolymerization of N-vinylcarbazole: Electrochemical study and characterization of poly(3,6-N-vinylcarbazole)

Poly(3,6-N-vinylcarbazole) films were prepared by electrochemical oxidation of N-vinylcarbazole on a Pt electrode using acetonitrile as solvent and tetraethylammonium tetrafluoroborate as electrolyte. The electrosynthesis was carried out by electrical potential cycling in the presence of two different bases: tetraethylammonium benzoate (Bz⁻) and tetraethylammonium phthalate (Ph⁻). These salts were expected to modify the acidity level of the electrolyte since they can act as scavengers for the protons released during the polymerization, when the reaction takes place in the carbazole unit.Products were characterized by cyclic voltammetry, scanning electron microscopy, FTIR spectroscopy, thermogravimetric analysis, differential scanning calorimetry, absorption spectroscopy and four-probe electrical conductivity measurements. Both bases influenced significantly the chemical structure and morphology of the deposited materials. The presence of Ph⁻ in the electrolyte decreases the cross-linking of the electrodeposited polymer, leading to a poly(3,6-N-vinylcarbazole) bearing a more uniform morphology, higher thermal stability and electrical conductivity compared to those of the polymers obtained in the presence of Bz⁻ and without acidity control.     

Electropolymerization of poly(N-ethyl aniline) on mild steel: Synthesis, characterization and corrosion protection

Poly(N-ethylaniline) (PNEA) coatings on the mild steel electrode were synthesized by electrochemical oxidation of N-ethylaniline using aqueous oxalic acid solutions as reaction medium. Electrodeposition was carried out by potentiodynamic, potentiostatic and galvanostatic synthesis techniques. Smooth, adhesive and thick PNEA coatings on mild steel could be electrosynthesized during sequential scanning of the potential region between −0.5 and 1.4 V versus SCE, with scan rate of 20 mV s⁻¹. The electrodeposited coatings were characterized by cyclic voltammetry, FT-IR and UV-vis techniques. Corrosion behavior of PNEA coated steels was investigated by linear anodic potentiodynamic polarization technique and Tafel test. Anodic potentiodynamic polarization results showed that electrodissolution current value of PNEA coated steel decreased about 90% compared to that of the uncoated steel in 0.5 M H₂SO₄ aqueous solution. Tafel plots showed also strong decrease of corrosion current for the PNEA coated electrode compared to the uncoated steel electrode in 3% NaCl as corrosive medium.     

Kinetic characterization of p-tert-butylcalix[4,8,12]arene functionalized gold electrode by electrochemical impedance spectroscopy

Kinetic characterizations of impedimetric sensors having as transducers gold electrodes and as recognizing elements p-tert-butylcalix[4,8,12]arene were accomplished. Calixarene membranes were first studied using contact angle measurements. These revealed that all membranes exhibited hydrophobic and rough behaviours. Besides, based on the Van Oss model, surface energy components were determined and the main difference for the basic energy component was related to the calixarene conformation where hydroxyl groups were pointing towards gold surface.Electrochemical impedance spectroscopy results were modeled by appropriate equivalent circuits for the aim of elucidating electrical properties of calixarene functionalized gold electrodes. As results, a fast ionic transfer took place for p-tert-butylcalix[4] based impedimetric sensor, and a slow ionic transfer occurred for both p-tert-butylcalix[8,12] based impedimetric sensors. These behaviours were well accommodated with potentiometric outcomes that were previously encountered.     

Thermally responsive poly(N-isopropylacrylamide) monolayer on gold: synthesis, surface characterization, and protein interaction/adsorption studies

This report describes a novel method for preparing a thermally responsive poly(N-isopropylacrylamide) (PNiPAM) monolayer on a gold surface, and demonstrates the function of this monolayer in aqueous media. Thiol (-SH) terminated PNiPAM was synthesized by UV polymerization followed by hydrolysis, and a monolayer of this polymer (2.84±0.2 nm) was prepared on a gold substrate by simply dipping a precleaned gold plate into an aqueous solution of the PNiPAM. Cyclic voltametry and atomic force microscopy studies showed that the gold surface was well covered by the PNiPAM chains, and X-ray photoelectron spectroscopic data showed that this monolayer was chemisorbed on the gold surface. Studies of the water contact angle, protein interaction, and protein adsorption on the PNiPAM monolayer demonstrated that this monolayer shows a temperature dependence of the interfacial properties in aqueous media.     

表面处理对玻纤/碳纤增强橡胶基密封复合材料性能的影响

采用压延成张工艺制备碳纤维和玻璃纤维混杂增强非石棉橡胶基密封复合材料(NAFC),以横向抗拉强度作为表征混杂增强橡胶基密封材料中纤维与橡胶界面粘结性能的指标.通过扫描电镜(SEM)对材料横向拉伸试样断口进行形貌分析,及对材料的耐油、耐酸、耐碱性能进行测试,探讨了不同表面处理工艺对纤维与基体界面粘结效果的影响.研究结果表明,对玻璃纤维采用偶联剂KH-550浸渍后涂覆环氧树脂涂层,对碳纤维在空气氧化后涂覆环氧树脂涂层,可有效增强纤维、基体的界面粘结,所制得的混杂纤维增强复合材料具有较好的机械性能和耐介质性能.     

The bulk polymerisation of N-vinylcarbazole in the presence of both multi- and single-walled carbon nanotubes: A comparative study

The bulk polymerisation of N-vinylcarbazole (NVC) at an elevated temperature in the presence of both multi- and single-walled carbon nanotubes (CNTs) leads to the formation of two different types of composite materials, the morphology and properties of which were characterised by a field emission scanning electron microscopy (FE-SEM), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, and electrical property measurements. The efficiency of CNTs to initiate the NVC polymerisation was investigated using both multi-walled CNTs (MWCNTs) and single-walled CNTs (SWCNTs). The focus was on three major aspects: the degree of polymerisation, the morphology and the properties of the resulting nanocomposite materials. Results showed that SWCNTs were more efficient in initiating NVC polymerisation than MWCNTs, and the morphology of resultant nanocomposites revealed wrapping and grafting of some poly(N-vinylcarbazole) (PNVC) chains on the SWCNT surfaces. The morphology of the PNVC/MWCNT nanocomposites showed only homogeneous wrapping of the outer surfaces of MWCNTs by PNVC chains. The direct current (dc) electrical conductivity of pure PNVC improved dramatically in the presence of both MWCNTs and SWCNTs, however, the extent of improvement is higher in the case of PNVC/MWCNT nanocomposites.     

酸碱不同电解质对碳纤维阳极氧化表面处理的研究

以碳酸氢铵和硫酸为电解质,采用阳极氧化表面处理法对聚丙烯腈(PAN)基碳纤维进行表面处理,对表面处理时间进行了对比研究,获取了S-酸和S-碱2个系列样品,经研究发现,碳纤维在碳酸氢铵电解质中处理时间80s时,同在硫酸电解质中处理时间为5s所取得到的拉伸强度、层间剪切强度基本相当。通过对样品的微观表面、表面官能团的分析,发现2种电解质在PAN基碳纤维表面发生的氧化反应不同,S-酸系列样品表面官能团多生成羟基和醚基,S-碱系列样品表面团多生成羰基。     

Synthesis and photovoltaic properties of low-bandgap polymers based on N-arylcarbazole

Low-bandgap poly(2,7-carbazole) derivatives with variable N-substituent of ethyl (PEtCzBT), phenyl (PPhCzBT) and 4-diphenylaminophenyl (PTPACzBT) on the carbazoles, were synthesized through Suzuki coupling reaction. The polymers show excellent solubility in organic solvents (readily soluble in chloroform, THF and toluene etc.), good thermal stability (5% weight loss temperature of more than 417 °C), and electrochemical properties (reversible redox process with narrow bandgap), and deep HOMO energy levels (∼5.1 eV), allowing them promising candidates in the solar cell fabrication. Bulk-heterojunction solar cells with these polymers as electron donor and (6,6)-phenyl-C₇₁-butyric acid methyl ester (PC₇₁BM) as electron acceptor exhibit high V_oc (0.91-0.95 V) and good power conversion efficiency (PCE) of 1.69% for PEtCzTB, 2.01% for PPhCzTB, and 2.42% for PTPACzTB.     

Effect of the alkyl group on the synthesis and the electrochemical properties of N-alkyl-N-methyl-pyrrolidinium bis(trifluoromethanesulfonyl)imide ionic liquids

The effect of the alkyl side group on the synthesis and the electrochemical properties of N-alkyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR_1ATFSI) ionic liquids (ILs) is reported. The investigation was focused on the PYR_1ATFSI ionic liquid family because of the interesting electrochemical properties of the members with propyl and butyl side chains. Side alkyl groups (A = C_nH_2n+1 with n ranging from 1 to 10) of different length and structure were used for the synthesis of PYR_1ATFSI materials. NMR and DSC have shown that the ionic liquids were correctly synthesized with the exception of the compounds with tertiary side chains. Most of the materials exhibited a conductivity higher than 10⁻³ S cm⁻¹ already at 12 °C. In the molten state a moderate conductivity decrease was observed with increasing the length and the branching of the side chain (C₂H_2n+1) group according with the change of viscosity of the ionic liquids. Most of the PYR_1ATFSI samples exhibited an electrochemical stability window exceeding 5 V.     

Characterization of surface fouling of Ti/IrO2 electrodes in 4-chlorophenol aqueous solutions by electrochemical impedance spectroscopy

Electrochemical impedance spectroscopy (EIS) was used as the main technique coupled with cycling voltammetry (CV) to characterize the surface fouling of a conventional Ti/IrO₂ in 4-CP aqueous solutions caused by the electropolymerization of chlorinated phenol. Capacitive information of polymeric films formed was successfully derived from both the on-line and off-line impedance measurements and was used to characterize the surface fouling of IrO₂ electrodes. Results showed that the fouling extent at IrO₂ electrode decreased when its heating temperature was increased. With increasing the anodic potential, the surface fouling was enhanced firstly and then weakened, reaching the highest extent at 0.9 V. More positive potentials were believed to further oxidize the formed films and thereby to reactivate the deactivated electrode surface. With the increase of positive potential, the regeneration was enhanced, but no entire recovering could be achieved after the reactivation even at very high potentials.     

Interface improvement of carbon fiber/methylphenylsilicone resin composites by fiber surface coating of polyhedral oligomeric silsesquioxanes

To enhance interfacial properties of carbon fibers (CFs)-reinforced methylphenylsilicone resin (MPSR) composites, we introduced an appropriate interface reinforced by trisilanolphenyl-polyhedral oligomeric silsesquioxanes (trisilanolphenyl-POSS) between CFs and MPSR with a liquid phase deposition strategy. Chemical bonds among silanol groups of trisilanolphenyl-POSS, hydroxyl-functionalized CF (CF–OH), and silanol end groups of MPSR in the coating were expected to be formed through condensation reaction during the prepared process. CFs with and without sizing treatment-reinforced MPSR composites were prepared by a compression molding method. X-ray photoelectron spectroscopy revealed that trisilanolphenyl-POSS particles enhanced the contents of fiber surface oxygen-containing groups and silicon-containing functional groups. Scanning electron microscopy and atomic force microscopy images showed that trisilanolphenyl-POSS nanoparticles have been introduced onto the fiber surface obviously and the surface roughness increased sharply. Dynamic contact angle analysis indicated that trisilanolphenyl-POSS-modified sizing agent could improve the fiber wettability and surface energy significantly. Short-beam bending test and impact toughness test results showed that the interlaminar shear strength and impact resistance of the sized CFs composites were enhanced greatly with increasing amplitudes of more than 35 and 27% in comparison with those of untreated CF composites, respectively. Cryo-fractured surface topographies of composites confirmed that interfacial adhesion between CFs and MPSR has been improved after sizing treatment. Meanwhile, the sizing treatment does not decrease single fiber tensile strength.     

Hydrolytic processes and condensation reactions in the cellulose solvent system N,N-dimethylacetamide/lithium chloride. Part 2: degradation of cellulose

Certain cellulose samples, especially those of higher molecular weight, are initially insoluble in N,N-dimethylacetamide (DMAc, 1)/lithium chloride, which is a very common solvent system for cellulosic materials. According to a common protocol, heating or refluxing these samples in DMAc, or in DMAc containing dissolved LiCl, represents one of several so-called ‘activation’ procedures, which are aimed at facilitating subsequent dissolution. In the present work, it is shown that the improved solubility achieved by this method is not only caused by a better activation or improved accessibility of the pulp, but also by a progressing degradation of the cellulosic material (DP loss).The degradation of cellulose in DMAc or DMAc/LiCl is due to two separate chemical processes. The first one, involving N,N-dimethylacetoacetamide (2) which is the primary condensation product of DMAc, causes a slow degradation by thermal endwise peeling. The glucose units peeled off the reducing end are released as furan structures (3). The mechanism appears to be a thermal cleavage of the glycosidic bond, which becomes quite selective towards the proximal anhydroglucose unit by a neighbor group-assisted effect according to quantum-chemical calculations. Due to its stepwise and thus slow mechanism, this pathway contributes only insignificantly to the overall cellulose degradation.The second degradation mechanism causes random chain cleavage and thus pronounced and rather fast changes in the molecular weight distribution. It involves N,N-dimethylketeniminium ions (5), whose presence in DMAc/LiCl at temperatures above 80 °C—the coalescence temperature of DMAc as determined by dynamic NMR—was unambiguously demonstrated by specific trapping in a thermal [2+2]-cycloaddition with lipophilic olefins. The keteniminium ion is an extremely reactive electrophile, which is able to directly cleave glycosidic bonds. The detrimental effect of this intermediate on the integrity of cellulosic pulps was confirmed by addition of an external degrading agent of the keteniminium type. Also the precursor compound, a ketene aminal, was confirmed to be present in heated DMAc or DMAc/LiCl by trapping with allyl alcohol in a spontaneous Claisen-type rearrangement.