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.     

Voltammetry in viscous poly(ethylene glycol) solutions at microelectrodes

Voltammetric currents of the ferrocenyl derivative in highly viscous poly(ethylene glycol) solution (PEG) at microelectrodes were independent of their viscosity, contrary to the prediction from the diffusion-controlled current combined with the Stokes–Einstein equation. The usage of microelectrodes generally prevents deformation of voltammograms by poor conductivity. However, the voltammograms even at the disk electrode 10 μm in diameter and slow scan rates exhibited hysteresis, because the diffusion coefficient in PEG was smaller than in water owing to high viscosity of the solution. The diffusion coefficients evaluated from the peak current through the diffusion equation at microelectrode were of the order of 10⁻⁷ cm² s⁻¹ for the viscosity ranging from 0.1 to 160 Pa s. They are at most by 1000 times larger than the values calculated from the viscosities by the Stokes–Einstein equation. A practical significance of this result is to suggest a possibility of using highly viscous PEG as solid-like solvents without large restriction of mass transport. A possible diffusion model is that the redox species diffuses through lowly viscous local domains, avoiding collision with the backbone of the polymer network.     

Chemical modification of poly(N-vinylcarbazole)

Investigation of the phosphorylation reaction of poly(vinylcarbazole) was carried out using different phosphorylating reagents and in the presence of various catalysts. PCl₃, PBr₃, P₂S₅, and H₃PO₄ + P₂O₅ were examined, and it was noticed that PCl₃ and PBr₃ were the most effective phosphorylating reagents. The best results for the phosphorylation process of poly(vinylcarbazole) were obtained at 76°C when PCl₃ was used and at 140°C when PBr₃ was used. It was confirmed that the percentage of phosphorus which was introduced into the polymer can be expressed by the following formula: The optimal value of the reaction time for both these phosphorylating reagents PCl₃ and PBr₃ amounts to 6 hr. The phosphorylated poly(vinylcarbazole) obtained under these conditions shows ion exchange behavior—the value of ion-exchange capacity amounts 3.2 mval/g. The pH-metric titration curve indicates two stages of dissociation. The DTA curve shows that there is no decomposition of the phosphorylated poly(vinylcarbazole) up to a temperature of 300°C; at 550°C, there is 37.5% loss of weight. Spectrophotometric IR studies of phosphorylated poly(vinylcarbazole) indicate that the maximal quantity of phosphorus in the polymer is 11.3% P, that means one phosphone group in each monomer unit.     

Photocurrent in and miscibility of poly(N-vinylcarbazole)/poly(methyl methacrylate) blends

Summary Steady-state photocurrent in poly(N-vinylcarbazole)(PVCz) (26,48 wt%)/poly(methyl methacrylate)(PMMA) blends is for the first time measured. The PVCz(26,48 wt%)/PMMA blends showed almost the same carrier-generation efficiencies at electric fields higher than 1 × 10⁵ V · cm⁻¹. The results are explained by high miscibility of the PVCz(26,48 wt%)/PMMA blends, suggesting the existence of PVCz chains in continous PMMA-rich phase in the phase-separated structure. The miscibility is also evaluated by means of excimer fluorescence of PVCz in these blends and fluorescence microscopy. Received: 26 December 2000/Revised version: 16 January 2001/Accepted: 19 January 2001     

Benzene and anthraquinone sulfone derivatives of poly(N-vinylcarbazole)

Summary Benzene and anthraquinonesulfonyl chlorides were reacted with poly-N-vinylcarbazole in presence of Friedel-Crafts catalyst to form the corresponding sulfonyl derivatives. The sulfonated poly-N-vinylcarbazoles were characterized by elemental analyses, IR spectroscopy, thermogravimetric analysis and evaluation of permittivity and loss-tangent behaviour with varying applied frequencies.     

Photoelectronic properties of iodine-incorporated poly(N-vinylcarbazole) films

Iodine was incorporated into poly(N-vinylcarbazole) (PVK) films by exposing the films to saturated iodine vapor at 100°C for 10 h. The content of iodine in the films was 2.3% by weight. The films were stable at room temperature. The infrared spectra indicate that no chemical reaction has taken place during the incorporation process. The dark conductivity of these films is about two orders of magnitude greater than that of pure PVK films. Carriers can be photogenerated in the films by light illumination from the UV region to the entire visible region. The most significant feature of these films is that the photoconductivity has a peak at the photon energy of 1.8eV. This is attributed to the charge transfer from the carbazole to I₂. The results of thermally stimulated currents (TSC) indicate that there are deep traps in pure PVK films, but after iodine incorporation, these deep traps disappear or are replaced by a large quantity of shallow traps.     

Small-angle light scattering studies of poly(N-vinylcarbazole)

Morphology of PVK samples cast from various solvents (cyclohexanone, tetrahydrofuran, benzene) and crystallized on a glass surface, was studied by means of SALS. Results show existence of rod-like elements forming a morphology with nonrandom correlations of orientations. This morphology is practically independent of crystallization conditions.     

The anodic oxidation of poly(N-vinylcarbazole) films

The electrochemical oxidation of thin coats of poly(N-vinylcarbazole) on platinum electrodes has been studied. The oxidation is shown to involve initially the cross-linking of the polymer chains through the oxidation of up to 50% of the carbazole moieties in the coat and the dimerization of the resulting pendant carbazole cation radicals. The resulting dimeric carbazole unit is more easily oxidized than the monomer and undergoes a further (reversible) two-electron oxidation. Theory is presented describing the shape of the current-voltage curves obtained, and this together with current transients obtained from potential-step experiments is used to confirm the mechanism and obtain a rate constant of 6×10^–3M^–1s^–1 for the dimerization of the carbazole cation radicals within the coat.     

Crystallization of poly(etheretherketone) (PEEK) in carbon fiber composites

The tendency of carbon fiber to nucleate the zation of poly(etherettterlcetone) (PEEK) has been evaluated by DSC and other techniques. As the carbon fiber content was increased, the supercooling necessary for PEEK crystallization decreased. The repeated melting (at 396°C) of the same PEEK sample results in a decrease of the number of nuclei for crystallization. At equivalent thermal histories, PEEK with carbon fiber was found to have a higher nucleation density than PEEK itself. The surface of carbon fibers and nuclei in the PEEK matrix compete for crystallization growth. As the holding time in melt was increased, the number of matrix spherulites formed on cooling decreased, hence a more pronounced transcrystalline region was developed. Correspondingly, the composites preheated in the melt for 100 min showed about two times the transverse tensile strength and strain-to-failure of those preheated for only 30 min. Corresponding fracture surface produced in tension showed that the former samples had a greater matrix adhesion to the carbon fiber than the latter. A strong interfacial bond is thus developed by crystallization on carbon fiber surface. Destroying nuclei in the PEEK matrix by long preheating enhances crystallization on the carbon fiber.     

Isothermal crystallization and melting behavior of short carbon fiber reinforced poly(ether ether ketone) composites

Films of short carbon fiber reinforced poly(ether ether ketone) (PEEK) composite were formed by compression molding pellets for 10 min at 380 °C under air. A heating stage was used to prepare isothermally treated PEEK composites before DSC scan. The dependence of degree of crystallinity on the heating rate (10–80 °C/min) was investigated for specimens crystallized at different temperatures. The results indicated that 50 °C/min was an optimum heating rate to suppress the reorganization and to avoid the superheating of high crystallinity specimens with the sample weight of 10 mg. The upper peak temperature of double-melting peaks continued to increase with crystallization temperature. This peak temperature was related to the transition from regime II to III. The phenomenon of lower crystallinity and higher melting temperature supports the interpretation that the upper melting peak corresponded to crystals growing during the earlier stage of isothermal crystallization.     

Fluorescence from poly(N-vinylcarbazole) in uniaxially stretched polymer films

Steady-state and time-resolved fluorescence properties of poly(N-vinylcarbazole) (PVCz) dispersed in a polystyrene (PS) cast film were studied under tensile loadings at room temperature. The excited monomer emission of PVCz located around 350 nm decreased with increasing applied tensile strain from 0 to 0.8%. The strain enhanced the emission which was ascribed to the partial-overlap excimer of PVCz in a 360–430 nm region. The emission due to the full-overlap excimer of PVCz between 430 and 500 nm was unchanged by the action of the tensile loadings. The ratio of fluorescence intensities at 375 nm and 345 nm I₃₇₅/I₃₄₅ was proportional to the applied strain. The time-resolved fluorescence study indicated that the lifetimes of the excited monomer and of the partial-overlap excimer were not affected by the strain. The obtained results mean that the strain applied to the PS matrix increases the partial-overlap conformation of two adjacent carbazolyl chromophores in a PVCz chain and suggest that PVCz is a useful probe for detecting residual strains in polymer matrices. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1569–1573, 1997     

Study of crystallization behavior of neat poly(vinylidene fluoride) and transcrystallization in carbon fiber/poly(vinylidene fluoride) composite under a temperature gradient

The crystallization behavior of poly(vinylidene fluoride) (PVDF) and transcrystallization in carbon fiber (CF)/PVDF composite were investigated under a temperature gradient. The crystallization temperature (T_c) was controlled in the range of 110–180 °C. For neat PVDF, the results showed that exclusive γ phase formed at T_c above 164 °C, but coexisted with α phase at T_c ranging from 137 to 160 °C. The promotion of γ phase to nucleation of α phase at low T_c was observed for the first time. For CF/PVDF composite, a cylindrical transcrystalline (TC) layer formed on the surface of CF when T_c was between 137 and 172 °C. The TC layer was exclusively composed of γ phase at T_c above 164 °C. The hybrid nucleation was dominated by γ phase though some α phase nuclei emerged on the surface of CF when T_c was in the range of 144–160 °C. As T_c decreased, competition between the hybrid nucleation of α and γ phase became more intense. The γ phase nuclei was soon circumscribed by the rapidly developed α phase when T_c was below 144 °C. Furthermore, some α phase nuclei were induced at the surface of the γ phase TC layer, and developed into α phase TC layer when T_c was in the range of 146–156 °C, which resulted in a doubled TC layer of α and γ phase at the interface of the composite. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43605.     

Vinyl polymerization by carbon black,VI. Physico-chemical characteristics of poly(N-vinylcarbazole) prepared by modified and unmodified carbon black

The polymerization initiating activity of carbon black N220, unmodified as well as modified by pretreatment with various protonic and aprotonic acids has been examined in regards to N-vinylcarbazole polymerization. The physico-chemical characteristics of the polymer obtained by these catalyst systems have been investigated by I.R., X-ray, ¹H-NMR, ¹³C-NMR, gel permeation chromatography and thermal analysis measurements. Under certain conditions the resultant polymer shows some partial insolubility in methylethylketone. Contrary to the usual belief, this is not due to any stereochemical difference between the polymeric entities as observed by ¹³C-NMR spectrum analysis of the methylethylketone insoluble fraction of the polymer.     

First electrochemical intercalation of lithium into fullerenated poly(N-vinylcarbazole)

Lithium batteries are attractive for energy storage because of their high theoretical energy densities. A mechanism of an electrochemical intercalation reaction is suggested for the discharge of the first Li-fullerenated poly(N-vinylcarbazole) battery on the basis of experimental data obtained from cyclic voltammetry, FTIR, XRD, and ESR. The above battery has a higher open-circuit voltage (ca. 3.2 V), and its discharge may be ascribed to the electrochemical interacalation process of lithium in fullerenated poly(N-vinylcarbazole) for positive electrode materials. The effect of the discharge of the electric cell on the structure and paramagnetic property of fullerenated poly(N-vinylcarbazole) is discussed. © 1996 John Wiley Sons, Inc.     

Development and application of a poly(2,2′-dithiodianiline) (PDTDA)-coated screen-printed carbon electrode in inorganic mercury determination

In this work, monomer solutions of aniline (ANI) and 2,2′-dithiodianiline (DTDA), an aniline derivative containing -S-S- links, were prepared and used in the electrochemical copolymerisation of ANI and DTDA by cyclic voltammetry on a screen-printed electrode (SPE) in 1 M HCl. Electropolymerisation of aniline on the surface of the screen-printed working electrode was performed by sweeping the potential between −500 and + 1100 mV (vs. Ag/AgCl) at a sweep rate of 100 mV/s. Electrocopolymerisation was performed with a mixture of ANI and DTDA by sweeping the potential between −200 and + 1100 mV (vs. Ag/AgCl) at a sweep rate of 100 mV/s [J.L. Hobman, J.R. Wilson, N.L. Brown, in: D.R. Lovley (Ed.), Environmental Microbe Metal Interactions, ASM Press, Herndon, Va, 2000, p. 177]. The cyclic voltammogram (CV) for each of the electrochemically deposited polyaniline (PANI) and the mixture of ANI and DTDA for the co-polymer polymerisation on SPCE were recorded for electrochemical analysis of the peak potential data for the mono and copolymer. Anodic stripping voltammetry (ASV) was used to evaluate a solution composed of (1 × 10⁻⁶ M HgCl₂, 0.1 M H₂SO₄, 0.5 M HCl), in the presence of the co-polymer sensor electrode. The Hg²⁺ ions were determined as follows: (i) pre-concentration and reduction on the modified electrode surface and (ii) subsequent stripping from the electrode surface during the positive potential sweep. The experimental conditions optimised for Hg²⁺ determination included the supporting electrolyte concentration and the accumulation time. The results of the study have shown the use of a conducting polymer modified SPCE as an alternative transducer for the voltammetric stripping and analysis of inorganic Hg²⁺ ions.     

Investigation of phase behavior and water binding in poly(alkylene oxide) solutions

The aqueous solution properties of alkylene oxide polymers and copolymers are related to their interaction with water. In an attempt to better understand this behavior, differential scanning calorimetry has been employed to measure phase changes and water binding in solutions of polyethylene glycol (PEG), polypropylene glycol (PPG), and a 50/50 random copolymer of ethylene oxide and propylene oxide. PEG (M _n = 3510) forms a crystalline eutectic with water at 0.48 weight fraction of polymer. The liquidus curve for water can be fit accurately using the Flory–Huggins expression for solute activity with an interaction parameter of 0.05. PPG and the random copolymer do not crystallize and thus do not form a crystalline eutectic. Based on decreases in the heat of fusion of free water with added polymer, PEG binds more water than the copolymer which binds more water than PPG. The estimated hydration numbers per polymer segment are 1.5 for PPG, 2.3 for the copolymer, and 2.7 for PEG.     

A review on medical applications of poly(N-vinylcarbazole) and its derivatives

Poly(N-vinylcarbazole) (PVK) based materials are still exciting for researchers because new aspects and properties in the field have been revealed. In this regard, polymeric derivatives of carbazole with biomedical applications have been developed in time. This article reviews the latest applications of PVK based materials as medical materials: biosensors, cellular markers, radioprotectors, and antibacterial coatings.