Potentiometric sensors based on poly(3,4-ethylenedioxythiophene) (PEDOT) doped with sulfonated calix[4]arene and calix[4]resorcarenes

Potentiometric ion sensors have been prepared by galvanostatic electrosynthesis of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) doped with p-sulfonated calix[4]arene (C[4]S) and p-methylsulfonated calix[4]resorcarenes (R_n[4]S) with alkyl substituents of different chain length (R₁=CH₃; R₂=C₂H₅; R₃=C₆H₁₃). The bowl-shape of these doping ions makes them suitable as ionic recognition sites, and their bulky character is expected to prevent them from leaching out of the conducting polymer membrane. For comparison, sensors based on PEDOT doped with poly(styrene sulfonate) (PSS) and poly(vinyl sulfonate) (PVS) were also constructed. The resulting GC/PEDOT electrodes were conditioned in 0.01 mol L^–1 AgNO₃ and their performance as Ag⁺ ion-selective electrodes (ISEs) studied. Results reveal that selectivity and lifetime of the electrodes is affected by the doping anion structure, although all electrodes show selectivity towards Ag⁺ ions. Interaction of Ag⁺ with sulfur atoms present in the conducting polymer backbone is considered to be the main reason for this behavior. A second set of electrodes was constructed and conditioned in 0.1 mol L^–1 KCl. These electrodes were tested in chloride solutions of quaternary ammonium cations, showing that C[4]S and R₂[4]S exhibit significant sensitivity towards pyridinium.Dedicated to Professor György Horányi on the occasion of his 70th birthday in recognition of his outstanding contributions to electrochemistry     

Electrochemical Impedance Spectra of Poly(3-octylthiophene) Films

Charge transfer in poly(3-octylthiophene) films in 0.05–0.5 M LiClO₄ solutions in acetonitrile is studied by an electrochemical impedance method. The resistance to charge transfer R _ct and the capacitance of the electrical double layer C _dl are calculated from the high-frequency semicircle and referred to the film/electrolyte interface. The low-frequency capacitance C _lf and effective diffusion coefficient D _ef are determined by analyzing the region of medium and low frequencies. The discrepancies between potential dependences of C _lf and D _ef derived experimentally and calculated within a simple model for a redox film are analyzed. The assumption is made that additional factors, such as a macroporous character of the films and the change in their properties during oxidation, which results from the film swelling, the change in the film volume and the solvation character, should be taken into account.     

Electrochemical determination of iodide by poly(3-aminophenylboronic acid) film electrode at moderately low pH ranges

A new potentiometric sensor for the determination of iodide based on poly(3-aminophenylboronic acid) (PAPBA) film electrode was constructed. Poly(3-Aminophenylboronic acid) films were synthesized electrochemically on platinum electrode by cyclic voltammetry. The effect of film thickness, pH, and preconditioning parameters on the electrode performance were examined. The analytical performance was evaluated and linear calibration graphs were obtained in the concentration range of 10⁻⁶ to 10⁻¹ M iodide ion. The limit of detection was found to be 8 × 10⁻⁷ M. The response time of the sensor was 5 s and its lifetime is about one week. To check the selectivity of the PAPBA film for iodide ion, potential interferences such as Cl⁻, Br⁻, F⁻, CN⁻, IO₃⁻, Ca²⁺, and Mg²⁺ were tested. The PAPBA electrode was also employed as a sensing platform for the determination of iodide ions in commercial table salt.     

Layered self-organized structures on poly(3-octylthiophene) thin films studied by scanning probe microscopy

The morphology and mechanical properties of poly-(3-octylthiophene) P3OT films thin has been studied by scanning force microscopy techniques. On these films we find self-assembled layered structures that appear regardless of the preparation conditions, that is, spin-coating or drop-casting, of the solvent concentration or of the type of substrate. Using the drop-casting method for sample preparation these layered structures are hardly visible due to the high surface roughness, while using spin-coating these structures are the main topographic feature on the surface. These structures have typically one or two layers, even though occasionally up to four layers have been observed. Each layer has a height of 4-5 nm, which is associated to crystalline P3OT domains and lay on the polymer film. The size of these structures increases with increasing concentration of the P3OT in the solvent. We find well differentiated morphological, electrostatic as well as mechanical properties for the self-assembled structures as compared to the rest of the polymer film. Finally, the growth rate of these structures has been studied.     

Properties of nanometric and submicrometric multilayered films of poly(3,4-ethylenedioxythiophene) and poly(N-methylpyrrole)

Multilayered films formed by 3, 5 and 7 alternated layers of poly(3,4-ethylenedioxythiophene) and poly(N-methylpyrrole) have been prepared by chronoamperometry under a constant potential of 1.4 V using a layer-by-layer electrodeposition technique. In order to examine influence of the interface:bulk dimensional ratio, the thickness of the yielded films was reduced from the submicrometric to the nanometric scale by decreasing the polymerization time of each layer from 100 s to 10 s. The electroactivity, electrochemical characteristics and morphologies of the resulting multilayered films have been compared with those obtained for both single-component poly(3,4-ethylenedioxythiophene) films prepared using identical experimental conditions and previously reported multilayered films with thickness within the micrometric scale [Estrany F, Aradilla D, Oliver R, Alemán C. Eur Polym J 2007;43:1876].     

Gel processing of electrically conductive blends of poly(3-octylthiophene) and ultrahigh molecular weight polyethylene

The mechanical and electrical properties of solution-processed [or gel-spun] blends of poly(3-octylthiophene) and ultrahigh molecular weight polyethylene are discussed. Tensile drawing at elevated temperatures of the phase-separated blends resulted in significant improvements of the mechanical properties, in comparison with those of the neat conducting polymer, with values of the Young's modulus reaching > 40 GPa and tensile strengths in excess of 2 GPa. Doping of the undrawn polyblend fibers with iodine vapor or FeCl₃ resulted in materials of useful levels of electrical conductivity covering the full range of 10^?15 to 10 S/cm. A distinct percolation threshold for electrical conductivity was not observed, even at poly(3-octylthiophene) concentrations as low as 0.5 w/w %; the electrical conductivity of the latter blend, after doping with iodine vapor, was 8 × 10^?8 S/cm.     

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.     

Voltammetric and waveguide spectroelectrochemical characterization of ultrathin poly(aniline)/poly(acrylic acid) films self-assembled on indium-tin oxide

We report on the spectroelectrochemical characterization of conducting polymer (CP) films, composed of alternating layers of poly(aniline) (PANI) and poly(acrylic acid) (PAA), deposited on ITO-coated, planar glass substrates using layer-by-layer self-assembly. Absorbance changes associated with voltammetrically induced redox changes in ultrathin films composed of only two bilayers (ITO/PANI/PAA/PANI/PAA) were monitored in real time using a unique multiple reflection, broadband attenuated total reflection (ATR) spectrometer. CP films in contact with pH 7 buffer undergo a single oxidation/reduction process, with ca. 12.5% of the aniline centers in the film being oxidized and reduced. The ATR spectra indicate that during an anodic sweep, the leucoemeraldine form of PANI in these films is oxidized to generate both the emeraldine and pernigraniline forms simultaneously. A comparison of the behavior observed during anodic and cathodic sweeps suggests that the rate of oxidation is limited by structural changes in the polymer film originating in electrostatic repulsion between positively charged PANI chains.     

Electrochemical preparation and <Emphasis Type="Italic">in situ</Emphasis> characterization of poly(3-methylpyrrole) and poly(3-methylpyrrole-cyclodextrin) films on gold electrodes

A Electrosynthesis of conducting poly(3-methylpyrrole) (P3MPy) and poly(3-methylpyrrole-2,6-dimethyl-β-cyclodextrin) (poly(3MPy-β-DMCD)) films on a gold electrode in acetonitrile electrolyte solution containing lithium perchlorate has been carried out by potential cycling. Products were characterized with cyclic voltammetry CV, in situ UV-Vis spectroscopy, and in situ resistance measurements. Electrosynthesis of poly(3MPy-β-DMCD) started with a (1:1) (3MPy-β-DMCD) supramolecular cyclodextrin CD complex of 3-methylpyrrole characterized with proton NMR spectroscopy. The oxidation peak of poly(3MPy-β-DMCD) in CVs is shifted to more positive values than P3MPy. In situ resistance measurements show that the resistance of poly(3MPy-β-DMCD) is higher than of P3MPy by approximately an order of magnitude. Minimum resistance can be observed for P3MPy and poly(3MPy-β-DMCD) at 0.40 < E _Ag/AgCl < 1.10 V and 0.60 < E _Ag/AgCl < 1.10 V, respectively. The higher resistance of P3MPy compared with polypyrrole may result from the presence of the methyl group substituent resulting in a decreased conjugation length. When CD is present during synthesis, resistance is even higher. In situ UV-Vis spectroelectrochemical data for both films prepared potentiodynamically by cycling the potential in the range −0.20 < E _Ag/AgCl < 1.10 V in acetonitrile electrolyte show major effects of CD presence during electrosynthesis.      

聚3-辛基噻吩/MWNTs复合材料的导电性能研究

采用在氯仿溶液中超声共混, 制备聚3-辛基噻吩(P3OT)和多壁碳纳米管(MWNTs)复合材料. 当MWNTs掺杂量为3%时复合材料的电导率为1.43 S&#8226;m－1, 达到纯MWNTs的电导率水平. 用FTIR光谱, TG, UV-Vis光谱, XPS和FESEM进行研究分析, 认为MWNTs的离域电子与P3OT主链上的π电子之间形成π-π共轭, 增加了P3OT主链的有效共轭度, 被掺杂的P3OT具有很高的电导率, 提高了复合材料的导电性能. MWNTs与被掺杂的P3OT组成相对独立的导体单元, 对复合材料的导电网络形成起着主要作用.     

Characterization of a Silver Modified PVCAc Electrode and Its Application as a Ag(I)‐Selective Potentiometric Sensor

An all solid‐state Ag(I) ion‐selective electrode has been prepared by simply immersing a glassy carbon rod coated with PVCAc, which contained plasticizer and additive but no ionophore, into the AgNO₃ solution. The response of the electrode was linear with a Nernstian slope of 60.25 mV/decade within the concentration range from 1×10^?1 to 1×10^?5 M and with a detection limit of 4.25×10^?6 M. The stability as an effect of various cations was defined. The electrode is suitable for use in high acidic solutions (pH<1 to 7) and has successfully been applied for the determination of silver(I) concentrations in different samples.     

Transport of ionic charge and solvent in poly(3-octylthiophene) films: An electrochemical quartz crystal microbalance study

The results of a study of poly(3-octylthiophene) films with the aid of an electrochemical quartz microbalance are presented. The effect of the nature of the electrolyte anion on the determined weights of mobile species that are transported through the film/electrolyte interface is discussed. The obtained results point to a substantial role played by the solvent transport in the course of the electrode reaction. The results concerning the influence exerted by the electrode material on the observed regularities are presented.     

Potentiometric Ag+ Sensors Based on Conducting Polymers: A Comparison between Poly(3,4‐ethylenedioxythiophene) and Polypyrrole Doped with Sulfonated Calixarenes

Potentiometric Ag⁺ sensors were prepared by galvanostatic electropolymerization of 3,4‐ethylenedioxythiophene (EDOT) and pyrrole (Py) on glassy carbon electrodes by using sulfonated calixarenes as doping ions. Poly(3,4‐ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy) doped with p‐sulfonic calix[4]arene (C4S), p‐sulfonic calix[6]arene (C6S) and p‐sulfonic calix[8]arene (C8S) were compared. PEDOT and PPy doped with poly(styrene sulfonate) (PSS) were also included for comparison. The analytical performance of the conducting polymer‐based Ag⁺ sensors was studied by potentiometric measurements. All conducting polymer and dopant combinations showed sensitivity and selectivity to Ag⁺ compared to several alkali, alkaline‐earth, and transition‐metal cations. The type of the conducting polymer used for the fabrication of the electrodes was found to have a more significant effect on the selectivity of the electrodes to Ag⁺ than the ring size of the sulfonated calixarenes used as dopants. Selected conducting polymer‐based sensors were studied by cyclic voltammetry (CV) and energy dispersive analysis of X‐rays (EDAX) measurements. Results from the EDAX measurements show that both PEDOT‐ and PPy‐based membranes accumulate silver.     

Conducting poly(3,4-ethylenedioxythiophene)-montmorillonite exfoliated nanocomposites

Exfoliated nanocomposites formed by poly(3,4-ethylenedioxythiophene) and different concentrations of non-modified montmorillonite (bentonite), which range from 1% to 10% w/w, have been prepared by anodic electropolymerization in aqueous solution. Analyses of the electrochemical and electrical properties reveal that the electroactivity of the nanocomposites is higher than that of the individual homopolymer, while the electrical conductivity of the two systems is practically identical. On the other hand, the exfoliated distribution of the clay in the polymeric matrix and the morphology of the prepared materials have been characterized using transmission electron microscopy, X-ray diffraction and atomic force microscopy. The overall of the results represents a significant improvement with respect to other nanocomposites constituted by conducting polymers and clays, including those involving poly(3,4-ethylenedioxythiophene), and evidences the reliability of the preparation procedure employed in this work.     

Effect of poly(vinyl acetate) (PVAc) on thermal behavior and mechanical properties of poly(3-hydroxybutyrate)/poly(propylene carbonate) (PHB/PPC) blends

To assess the compatibility of blends of synthetic poly(propylene carbonate) (PPC), with a natural bacterial poly(3-hydroxybutyrate) (PHB), a simple casting procedure of blend was used. poly(3-hydroxybutyrate)/poly(propylene carbonate) blends are found to be incompatible according to DSC and DMA analysis. In order to improve the compatibility and mechanical properties of PHB/PPC blends, poly(vinyl acetate) (PVAc) was added as a compatibilizer. The effects of PVAc on the thermal behavior, morphology, and mechanical properties of 70PHB/30PPC blend were investigated. The results show that the melting point and the crystallization temperature of PHB in blends decrease with the increase of PVAc content in blends, the loss factor changes from two separate peaks of 70PHB/30PPC blend to one peak of 70PHB/30PPC/12PVAc blend. It is also found that adding PVAc into 70PHB/30PPC blend can decrease the size of dispersed phase from morphology analysis. The result of tensile properties shows that PVAc can increase the tensile strength and Young’s modulus of 70PHB/30PPC blend, and both the elongation at break and the tensile toughness increase significantly with PVAc added into 70PHB/30PPC.     

Small-volume radial flow cell for all-solid-state ion-selective electrodes

A flow cell with a radial distribution of four all-solid-state ion selective electrodes (ISEs), or alternatively three ISEs and one reference electrode, was designed and optimized for mass production. The radial distribution of the electrodes reduces the cell volume and is expected to minimize cross-contamination between different electrodes. Two different cell prototypes were developed and tested for all-solid-state K⁺-ISEs based on a solvent polymeric ion-selective membrane (ISM) and a conducting polymer, poly(3,4-ethylenedioxythiophene), as solid internal contact. In the first prototype, PEDOT was electropolymerized from an aqueous solution of the monomer and the doping ion salt, sodium polystyrenesulfonate (NaPSS). The second prototype employed an aqueous dispersion of PEDOT(PSS) that is commercially available (Baytron P, Bayer AG). Compared to electrochemical synthesis, solution casting of the polymer dispersion was found to be a more advantageous method to deposit the conducting polymer layer aiming at mass production. The resulting prototypes of the flow cell had a small volume (ca. 17-37 μl), which makes them suitable for application in clinical analysis.     

Miscibility and crystallinity of poly(3-hydroxybutyrate)/poly(3-hydroxybutyrate-co-3-hydroxyvalerate) blends

With the objective of developing new biodegradable materials, the miscibility and the crystallinity of blends of poly(3-hydroxybutyrate), P(3HB), and poly(3-hydroxybutyrate-co-3-hydroxyvalerate), P(3HB-co-3HV), have been studied. P(3HB) (300 kg mol⁻¹)/P(3HB-co-3HV)–10% 3HV (340 kg mol⁻¹) blends were prepared by casting in a wide range of proportions, and characterized by differential scanning calorimetry (DSC) and Fourier transform infrared spectroscopy (FT-IR). The experimental values for the glass transition temperatures (T_g) are in good agreement with the values provided by the Fox equation, showing that the blends are miscible. It was observed that the T_g and the melting temperature (T_m) decreases with the increase in the P(3HB-co-3HV)–10% 3HV content, while the crystallization temperature (T_c) increases. FT-IR analyses confirmed the decrease on the crystallinity of P(3HB)/P(3HB-co-3HV)–10% 3HV blends with higher copolymer contents. Bands related to the crystallinity were changed, due to the copolymer content that produced miscible and less crystalline blends.     

Comparative study of Ag(I) selective poly(vinyl chloride) membrane sensors based on newly developed Schiff-base lariat ethers derived from 4,13-diaza-18-crown-6

The six Schiff-base lariat ether chelates based on 4,13-diaza-18-crown ether, have been synthesized and explored as a neutral ionophores for preparing poly(vinyl chloride) based membrane sensors selective to silver(I). The addition of potassium tetrakis(4-chlorophenyl) borate and various plasticizers, viz., o-NPOE, DBP, DBBP, DOP and CN has been found to substantially improve the performance of the sensors. The best performance was obtained with the sensor no. 5 having membrane of chelate (A₆) with composition (w/w) chelate (2.8%):PVC (45.7%):o-NPOE (48.6%):KTpClPB (2.8%). This sensor exhibits Nernstian response with slope 59.3 mV/decade of activity in the concentration range 5.6 × 10⁻⁸-1.0 × 10⁻¹ M Ag(I), performs satisfactorily over wide pH range of (3.0-8.0) with a fast response time (12 s). The sensor was also found to work satisfactorily in partially non-aqueous media up to 25% (v/v) content of acetonitrile, methanol or ethanol and can tolerate the concentration 1.0 × 10⁻² M of ionic (SDS, TBC) and nonionic (Triton X-100) surfactants. The proposed sensor can be used over a period of 4 months without significant drift in potentials. The response of the sensor was highly selective to Ag⁺ over a large number of cations and it could therefore be used for Ag⁺ estimation in blood of occupationally exposed persons.     

Improved mechanical property and biocompatibility of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) for blood vessel tissue engineering by blending with poly(propylene carbonate)

Poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (PHBHHx) and poly(propylene carbonate) (PPC) were blended by solvent casting method into films at various weight ratios in order to obtain materials with properties more suitable for blood vessel tissue engineering than pure PHBHHx alone. FTIR and XRD analysis indicated the crystal structure of PHBHHx was not altered but the crystallinity was reduced by the interfusion of PPC. Mechanical properties of the films were improved significantly by blending with PPC. A lower elastic modulus and a higher elongation at break were obtained with the increase of PPC content. Wettability, fibronectin adsorption and adhesion of rabbit aorta smooth muscle cells (RaSMCs) on blend films were similar to or better than that on PHBHHx film. All these results showed promises of PHBHHx/PPC blended materials as scaffold material for blood vessel tissue engineering.