A. Sezai Sarac

Conducting Polymers and their Applications

This review article focuses on conducting polymers and their applications. Conducting polymers (CPs) are an exciting new class of electronic materials, which have attracted an increasing interest since their discovery in 1977. They have many advantages, as compared to the non-conducting polymers, which is primarily due to their electronic and optic properties. Also, they have been used in artificial muscles, fabrication of electronic device, solar energy conversion, rechargeable batteries, and sensors. This study comprises two main parts of investigation. The first focuses conducting polymers (polythiophene, polyparaphenylene vinylene, polycarbazole, polyaniline, and polypyrrole). The second regards their applications, such as Supercapacitors, Light emitting diodes (LEDs), Solar cells, Field effect transistor (FET), and Biosensors. Both parts have been concluded and summarized with recent reviewed 233 references.

Characterization of Micrometer-Sized Thin Films of Electrocoated Carbazole with p-Tolylsulfonyl Pyrrole on Carbon Fiber Microelectrodes

Carbazole (Cz) monomers with p-tolylsulfonyl pyrrole (pTsp) (used as self-dopant) were electrochemically coated onto micrometer-sized carbon fiber by potentiodynamic method. The resulting micrometer-sized thin films of homopolymer and copolymers were characterized by using electrochemical methods (i.e., cyclic voltammetry), solid-state conductivity measurements (four-point probe), spectrophotometric methods (in situ spectroelectrochemistry), Fourier transform infrared reflectance spectroscopy, and scanning electron microscopy. Cyclic voltammetric results indicate that an increase of pTsp concentration in copolymer formation (while the Cz concentration was kept constant) current density increases randomly. The maximum anodic current density was obtained as 0.49 μA cm -2 by the initial feed ratio of [pTsp] 0 /[Cz] 0 = 5. This is three times higher than the anodic current density of polycarbazole (PCz) (0.15 μA cm -2 ). The electrocoated copolymer corresponding to an initial feed ratio of [pTsp] 0 /[Cz] 0 = 5 was observed as polaron and bipolaron on indium tin oxide (ITO) by UV-vis spectrophotometry. The solid-state conductivity was measured with a four-point probe apparatus. Results show that a tenfold increase in Cz concentration leads to an increase in conductivity from 0.08 to 6.36 mS cm -1 , and also raises yields from 13.69% to 97.72%. In contrast, a 10 times increase in pTsp concentration leads to a decrease in conductivity from 0.39 to 0.02 mS cm -1 , and also decreases yields from 21.72% to 2.82% which is due to the polymers bulky structure. The efficiency of the electropolymerization process on the carbon fiber surfaces by cyclic voltammetry, depending on the experimental conditions, was evaluated to ascertain the effects of copolymer thickness, dopant, optical bandgap (Eg), and the redox parameters (anodic and cathodic potentials, E a ,E c ), oxidation peak potentials, E ox, and stability test of electrodes.

Electrografting of poly(carbazole-co-acrylamide) onto several carbon fibers: Electrokinetic and surface properties

Electrografting onto untreated high modulus (HM) and high strength (HS) carbon fibers as well as on electrochemically oxidized HM carbon fibers was carried out under preparative constant current electrolysis conditions by electrocopolymerizing carbazole-acrylamide. The surface morphology of the electrografted carbon fibers was determined by scanning electron microscopy (SEM). In order to obtain at least some information about the relative surface composition of the electrografted fibers energy dispersive X-ray microanalysis (EDX) was applied. For the characterization of chemical composition FTIR reflectance measurements were performed as well. The electrografted copolymer exhibited good thermal stability, which was determined by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The efficiency of the electrocopolymerization on carbon fiber surfaces under preparative constant current electrolysis conditions was also supported by electrokinetic measurements.

The polymerization of acrylamide initiated with CE(IV) and KMNO4 redox systems in the presence of glycine

Glycine-Ce(IV) salts and -KMnO 4 initiator systems were used for the polymerization of acrylamide, resulting in water-soluble polyacrylamide, which contains amino acid end groups. The dependence of polymerization yields and molecular weights of polymers on the mole ratio of acrylamide monomer to glycine, the polymerization time, the temperature, and the concentration of sulfuric acid were investigated. The decrease in the mole ratio of acrylamide to glycine resulted in a decrease in the molecular weight, and an increase in the yield of acrylamide polymer, which contains a glycine end group. With increasing acid concentration of the polymeric solution, the polymerization yield and the molecular weight of polymer decrease. Ce(IV) and Mn(IV) reduced to Ce(III) and Mn(II) in the polymerization reaction. The amounts of Ce(III) and Mn(II) bound to polymer were determined. The composition of the polymerization product was investigated and a bimodal character of the molecular weight distribution was observed. The mechanism of this phenomena is discussed.

Incorporation of growth factor loaded microspheres into polymeric electrospun nanofibers for tissue engineering applications.

Nanofibrous double-layer matrices were prepared by electrospinning technique with the bottom layer formed from PCL (poly-ε-caprolactone)/PLLA (poly-l-lactic acid) nanofibers and the upper layer from PCL/Gelatin nanofibers. Bottom layer was designed to give mechanical strength to the system, whereas upper layer containing gelatin was optimized to improve the cell adhesion. Gelatin microspheres were incorporated in the middle of two layers for controlled growth factor delivery. Successful fabrication of the blend nanofibers were shown by spectroscopy. Scanning electron microscopy results demonstrated that bead-free nanofibers with uniform morphology could be obtained by 10% w/v concentrations of PCL/PLLA and PCL/Gelatin solutions. Microspheres prepared by 15% gelatin concentration and cross-linked with 7.5% glutaraldehyde solution were chosen after in vitro release studies for the incorporation to the double-layer matrices. The optimized conditions were used to prepare fibroblast growth factor-2 (FGF-2) loaded microspheres. Preliminary cell culture studies showed that the FGF-2 could be actively loaded into the microspheres and enhanced the cell attachment and proliferation. The complete system had a slow degradation rate in saline (18% weight loss in 2 months) and it could meanwhile preserve its integrity. This sandwich system prevented microsphere leakage from the scaffold, and the hydrophilic and bioactive nature of the fibers at the upper layer promoted cell attachment to the surface. PLLA/PCL layer, on the other hand, improved the mechanical properties of the system and enabled better handling.

Poly(carbazole-co-acrylamide) electrocoated carbon fibers and their adhesion behavior to an epoxy resin matrix

The surface properties of original high strength and preoxidized high modulus carbon fibers were altered by electrocopolymerizing acryl amide and carbazole and therefore depositing a copolymer coating onto the fibers. Scanning electron microscopy and zeta-potential measurements confirmed the presence of a rough but dense and continuous electrocoating with a basic surface character. Therefore, ‘good’ adhesion behavior between the electrocoated carbon fibers and an epoxy resin matrix should be expected. The interfacial adhesion was measured using the single fiber pull-out and single fiber indentation test. It was shown that only ‘intermediate’ adhesion was present between the carbon fibers and the electrocoating, but superior adhesion between the coating and epoxy resin exists. The single fiber model composites always failed at the fiber/electrocoating interface. However, as shown by using the indentation test, the interfacial adhesion between fibers and electrocoating can be significantly improved if preoxidized fibers are used as substrate for electropolymerization. A very high tensile strength for the electrocoating can be expected as derived from the single fiber pull-out tests.

A review: effect of conductive polymers on the conductivities of electrospun mats

The effects of conductive polymers on conductivities and morphologies of electrospun fabrics are analyzed. The factors that affect the conductivities and morphologies are discussed. Some applications of these conductive nanofibers are reported. The introduction of conductive polymers into nanofiber mats has the potential to provide sufficient conductivity for many applications. An improved conductivity can be achieved by maximizing the content of conjugated polymers. The selection of conductive and carrier polymers, solvents, doping agents, oxidizing agents and ratios of them are also important to obtain sufficient properties. Carbon fiber, carbon black and carbon nanotubes are not covered in this review.

Description of the turbidity measurements near the phase transition temperature of poly(N-isopropyl acrylamide) copolymers: the effect of pH, concentration, hydrophilic and hydrophobic content on the turbidity

Abstract Absorbance values between 300 and 800 nm of aqueous solutions of poly(N-isopropyl acrylamide-co-itaconic acid-9.80), poly(N-isopropyl acrylamide-co-itaconic acid-52.05) and poly(N-isopropyl acrylamide)s containing Tegomer H–Si 2111 end groups and/or blocks were measured using a Shimadzu 160-A UV–visible spectrometer. Turbidities obtained from these absorbance values were used to interpret the macromolecular phase transition from a hydrophilic to a hydrophobic structure of the polymers. The effects of comonomer type and content, concentration of the solutions, pH and temperature on the coil–globule transition were discussed in terms of turbidity form factor, β related to size and shapes of particles and calculated by using the simplified form of Debye equation. The results presented in this work show that the presence of Tegomer H–Si 2111 (Si containing end groups and/or blocks) or high amount of itaconic acid (IA) in the chains prevent a collapse transition from hydrated extended coils to hydrophobic globules, which aggregate and form a separate phase (β 2). This stage of the transition corresponds to macroscopic phase separation after an intramolecular process.

Comparative Study of Chemical and Electrochemical Copolymerization of N-Methylpyrrole with N-Ethylcarbazole Spectroscopic and Cyclic Voltammetric Analysis

ABSTRACT The copolymerization of N-Methylpyrrole (N-MPy) and N-ethylcarbazole (ECz) by chemical and electrochemical methods is investigated in detail. Random copolymers of poly[N-Methylpyrrole-N-ethylcarbazole], P[N-MPy-co-ECz], were synthesized in the presence of ceric ammonium nitrate (CAN) in acetonitrile. Electrocopolymerization of N-MPy, and ECz was carried out in various solvents on platinum electrode. Propylene carbonate (PC) was found to be the most suitable solvent for film formation. The effects of sweep rate, supporting electrolyte type, mole ratio, and temperature on the electropolymerization were discussed. The electrochemical properties of Poly(N-ethylcarbazole), (PECz) were improved on copolymerizing it with N-MPy. A copolymerization mechanism has been suggested. The resulting copolymer was characterized by UV-Vis and FT-IR spectroscopic methods, as well as cyclic voltammetric measurements.

ELECTROCHEMICAL COPOLYMERIZATION OF N-METHYL PYRROLE WITH CARBAZOLE

Electrocopolymerization of N-methylpyrrole (NMePy) and Carbazole (Cz) was conducted in acetonitrile. Oxidative chemical random copolymerization of NMePy and Cz was also realized by Cerium (IV) ammonium nitrate (CAN) for comparison. The properties of the resulting copolymers were investigated by spectroscopic methods (UV-VIS, FT-IR), cyclic voltammetry and four point probe conductometer, to understand the oligomeric pyrrole ring interaction with carbazole ring where the reactive nitrogen of pyrrole ring was capped (substituted) by methyl group.