Browsing by Author "Toppare, L."

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Open Access
Bioactive surface design based on functional composite electrospun nanofibers for biomolecule immobilization and biosensor applications
(American Chemical Society, 2014-03-24) Uzun, S. D.; Kayaci, F.; Uyar, T.; Timur, S.; Toppare, L.
The combination of nanomaterials and conducting polymers attracted remarkable attention for development of new immobilization matrices for enzymes. Hereby, an efficient surface design was investigated by modifying the graphite rod electrode surfaces with one-step electrospun nylon 6,6 nanofibers or 4% (w/w) multiwalled carbon nanotubes (MWCNTs) incorporating nylon 6,6 nanofibers (nylon 6,6/4MWCNT). High-resolution transmission electron microscopy study confirmed the successful incorporation of the MWCNTs into the nanofiber matrix for nylon 6,6/4MWCNT sample. Then, these nanofibrous surfaces were coated with a conducting polymer, (poly-4-(4,7-di(thiophen-2-yl)-1H-benzo[d]imidazol-2-yl) benzaldehyde) (PBIBA) to obtain a high electroactive surface area as new functional immobilization matrices. Due to the free aldehyde groups of the polymeric structures, a model enzyme, glucose oxidase was efficiently immobilized to the modified surfaces via covalent binding. Scanning electron microscope images confirmed that the nanofibrous structures were protected after the electrodeposition step of PBIBA and a high amount of protein attachment was successfully achieved by the help of high surface to volume ratio of electroactive nanofiber matrices. The biosensors were characterized in terms of their operational and storage stabilities and kinetic parameters (K mapp and Imax). The resulting novel glucose biosensors revealed good stability and promising Imax values (10.03 and 16.67 μA for nylon 6,6/PBIBA and nylon 6,6/4MWCNT/PBIBA modified biosensors, respectively) and long shelf life (32 and 44 days for nylon 6,6/PBIBA and nylon 6,6/4MWCNT/PBIBA modified biosensors, respectively). Finally, the biosensor was tested on beverages for glucose detection. © 2014 American Chemical Society.
Open Access
A conducting composite of polypyrrole I. synthesis and characterization
(Elsevier, 1994-02) Selampinar, F.; Akbulut, U.; Yalçin, T.; Süzer, Ş.; Toppare, L.
A conducting composite of polypyrrole was prepared via electrochemical methods. A polyamide was used as the insulating matrix polymer. The characterization of the composite was done by FT-IR, SEM, TGA, DSC and pyrolysis studies. Conductivity and solubility studies together with spectroscopic methods reveal that H bonding exists between the two polymers and a possible grafting to a certain extent.
Open Access
A conducting composite of polypyrrole II. As a gas sensor
(Elsevier, 1995) Selampinar, F.; Toppare, L.; Akbulut, U.; Yalçin, T.; Süzer, Ş.
Pure polypyrrole (PPy) and polypyrrole-polyamide (PPy-PA) composite films were synthesized electrochemically. The gas-sensing ability was investigated for both pure PPy and PPy-PA films. The composite films' response to several gases are better defined and reproducible compared to pristine conducting polymer. Electrochemical behaviour of PPy and PPy-PA electrodes in the presence of pyrrole and pyrrole-free medium is investigated via cyclic voltammetry. Mass spectrometry studies strictly reveal that the composite is completely different to a mechanical mixture. This phenomenon is discussed in comparison to polyaniline-polycarbonate composite. © 1995.
Open Access
A conducting composite of polythiophene: synthesis and characterization
(John Wiley & Sons Ltd., 1996) Vatansever, F.; Hacaloglu, J.; Toppare, L.
Conducting polymer composites of polythiophene, using a polyamide as the insulating matrix, were prepared via electrochemical methods. The characterization of the composite was done by scanning electron microscopy, differential scanning calorimetry, thermogravimetric analysis, Fourier transform infrared and pyrolysis studies. The conductivities were measured by a four-probe technique. The cited methods revealed that the composites have properties different from those of simple mechanical mixtures of the two polymers.
Open Access
Conducting composites of polypyrrole with polytetramethylbisphenol A carbonate
(John Wiley & Sons, Inc., 1996) Kalaycioglu, E.; Akbulut, U.; Toppare, L.
A new conducting composite of polypyrrole (PPy) has been prepared electrochemically where polytetramethylbisphenol A carbonate is used as the insulating matrix polymer. Characterization of the freestanding films of the composites were based on scanning electron microscopy, differential scanning calorimetry, and Fourier transform infrared studies as well as electrical conductivity measurements and solubility. Electrical conductivities were measured by a four-probe technique. Spectroscopic methods, together with conductivity and solubility studies, indicate that the synthesized composite is a homogeneous blend of the two polymers. No evidence of hydrogen bonding in the composite or grafting of the two polymers has been found, contrary to the PPy-polybisphenol A carbonate case. 0 1996 John Wiley & Sons, Inc.
Open Access
Conducting polymer composites of polypyrrole and polyimide
(Elsevier, 1997) Selampinar, F.; Akbulut, U.; Toppare, L.
A conducting composite of polypyrrole with a polyimide as the insulating matrix polymer was prepared via electrochemical methods. The characterization of the composite was done by FTIR, SEM and TGA studies, Conductivity and solubility studies together with spectroscopic methods reveal that a chemical interaction between the two polymers exists.
Open Access
Conducting polymer composites of polypyrrole and polyindene
(Elsevier, 1996) Bozkurt, A.; Akbulut, U.; Toppare, L.
Polypyrrole-polyindene composites were prepared via electrochemical methods. Two different approaches were utilized. In the first, the electro-initiated polymerization of indene on a platinum electrode was achieved at 2.0 V versus Ag/Ag+ in acetonitrile. Then the polyindene-coated electrode was used for the electrochemical polymerization of pyrrole at 1.0 V versus Ag/Ag+. In the second case, electrochemical coating of platinum electrode with polypyrrole at 1.0 V versus Ag/Ag+ was carried out and indene was polymerized on the conducting polymer at 2.0 V versus Ag/Ag+ in acetonitrile medium. The characterizations of these composites were done by FT-IR, scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA). Electrical conductivities were evaluated by two-probe and four-probe methods.
Open Access
Conducting polymer composites of polythiophene with natural and synthetic rubbers
(Elsevier, 1996) Yigit, S.; Hacaloglu, J.; Akbulut, U.; Toppare, L.
Electrochemical synthesis of conducting polymer composites of polythiophene was achieved. Synthetic and natural rubbers were used as the insulating polymer matrices. FT-IR, differential scanning calorimetry (DSC), scanning electron microscopy (SEM) and mass spectrometry (MS) were utilized to characterize the composite blends. The conductivity measurements were done by using a standard four-probe technique. The above-mentioned methods show that the resultant composites have different properties compared to polythiophene due to interaction of the rubbers with electrochemical polymerization of thiophene, whereas the same argument is not valid for the polypyrrole synthesis via the same procedure.
Open Access
Conducting polymer composites: polypyrrole and poly (vinyl chloride-vinyl acetate) copolymer
(John Wiley & Sons, Inc., 1997) Balci, N.; Bayramli, E.; Toppare, L.
Composites of a polypyrrole (PPy) and poly (vinyl chloride-vinyl acetate) copolymer (PVC-PVA) were prepared both chemically and electrochemically. An insulating polymer was retained in the blend and the thermal stability of the polymer was enhanced by polymerizing pyrrole into the host matrix in both cases. The composites prepared electrochemically gave the best results in terms of conductivity and air stability. © 1997 John Wiley * Sons, Inc.
Open Access
Cyclodextrin functionalized poly(methyl methacrylate) (PMMA) electrospun nanofibers for organic vapors waste treatment
(Elsevier BV, 2010) Uyar, Tamer; Havelund, R.; Nur, Y.; Balan, A.; Hacaloglu, J.; Toppare, L.; Besenbacher, F.; Kingshott, P.
Poly(methyl methacrylate) (PMMA) nanofibers containing the inclusion complex forming betacyclodextrin (_-CD) were successfully produced by means of electrospinning in order to develop functional nanofibrous webs for organic vapor waste treatment. Electrospinning of uniform PMMA nanofibers containing different loadings of _-CD (10%, 25% and 50% (w/w)) was achieved. The surface sensitive spectroscopic techniques; X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectrometry (ToF-SIMS) showed that some of the _-CD molecules are present on the surface of the PMMA nanofibers, which is essential for the trapping of organic vapors by inclusion complexation. Direct pyrolysis mass spectrometry (DP-MS) studies showed that PMMA nanowebs containing _-CD can entrap organic vapors such as aniline, styrene and toluene from the surroundings due to inclusion complexation with _-CD that is present on the fiber surface. Our study showed that electrospun nanowebs functionalized with cyclodextrinsmayhave the potential to be used as molecular filters and/or nanofilters for the treatment of organic vapor waste and air filtration purposes.
Open Access
Electronic properties of polypyrrole/polyindene composite/metal junctions
(Elsevier, 1997) Bozkurt, A.; Ercelebi, C.; Toppare, L.
Junction properties between conducting polymer composites of polypyrrole/polyindene (PPy/PIn) with different conductivities and metals like Pt, Au, Al and In have been investigated. Rectifying junctions were observed for low work function metals, In and Al; however, high work function metals, Pt and Au, were observed to form ohmic contacts to PPy/PIn composite in the sandwich geometry. The rectifying behavior of the metal/composite/Pt junctions improved when the conductivity of the composite was decreased from 1 to 0.01 S/cm. Using the ideal Schottky theory various junction parameters have been determined. All planar junctions were ohmic regardless of the conductivities of the samples.
Open Access
Graphene oxide-doped PEDOT:PSS as hole transport layer in inverted bulk heterojunction solar cell
(Springer, 2020) Özcan, Şefika; Erer, M. C.; Vempati, S.; Uyar, Tamer; Toppare, L.; Çırpan, A.
Transparent poly (3,4-ethylenedioxythiophene): poly (styrenesulfonate) (PEDOT:PSS) is widely used hole conducting material in optoelectronic devices. Secondary doping of PEDOT:PSS enables the tunability of its electronic properties. In this work, graphene oxide (GO) was used as a secondary dopant for PEDOT:PSS and the doped materials (composites) were tested for their efficiency as hole transport material in inverted bulk heterojunction (BHJ) solar cell. The composites were studied to unveil the effects of Coulombic interaction between GO and PEDOT:PSS where we note some segregation of PEDOT phase. We found that the GO majorly interacts with PSS through oxygeneous functional groups which promote the detachment of PEDOT from PSS and segregation of PEDOT. Electrochemical properties with and without illumination revealed some photo-induced changes to surface of the samples. Device performances showed about 2.2% efficiency enhancement when GO doping level was 0.25 (v:v) when compared to that of pristine PEDOT:PSS.
Open Access
Immobilization of invertase in conducting polymer matrices
(Elsevier, 1997-10) Selampinar, F.; Akbulut, U.; Özden, M. Y.; Toppare, L.
This paper reports a novel approach in the electrode immobilization of an enzyme, invertase, by electrochemical polymerization of pyrrole in the presence of enzyme. The polypyrrolelinvertase and polyamide/polypyrrole/invertase electrodes were constructed by the entrapment of enzyme in conducting matrices during electrochemical polymerization of pyrrole. This study involves the preparation and characterization of polypyrrole/invertase and polyamidelpolypyrrolelinvertase electrodes under conditions compatible with the enzyme. It demonstrates the effects of pH and temperature on the properties of enzyme electrode. Enzyme leakage tests were carried out during reuse number studies. The preparation of enzyme electrodes was done in two different electrolyte/ solvent systems. The enzyme serves as a sucrose electrode and retains its activity for several months. (c) 1997 Elsevier Science Limited. All rights reserved
Open Access
On the possibility of grafting conducting polymers into insulating ones
(Elsevier, 1996) Bahçeci, S.; Toppare, L.; Yurtsever, E.
The possibility of grafting between conducting polymers, like polypyrrole (PPy) and polyaniline (PAn), and insulating polymers, such as polybisphenol A carbonate (PC) and polyamide (PA), is studied via semi-empirical methods using the AM1 parametrization. Several experimental studies on the issue have previously revealed that a chemical interaction exists between the couples (PAn-PC, PPy-PC and PPy-PA) during the electrochemical synthesis of PAn and PPy in the insulating host matrices. Here we present additional theoretical evidence indicating that such grafting is possible, at least for small oligomers.
Open Access
A photoelectron spectroscopic investigation of conducting polypyrolle-polyamide composite film
(Elsevier, 1995-04) Süzer, Şefik; Toppare, L.; Allen, G. C.; Hallam, K. R.
X-ray photoelectron spectrum of the electrochemically prepared polypyrrole and polypyrrole-polyamide composite films exhibit an additional strong high binding energy peak at 402.0 eV corresponding to N+ moieties. Intensity of this peak is significantly reduced upon electrochemical reduction. Atomic concentrations derived from the observed N+ and F (stemming from the dopant BF4-) peaks reveal a slightly higher cation/anion ratio for this composite and suggest that the composite has a different chemical composition than the corresponding polymers. © 1995 Elsevier Science B.V.
Open Access
Polypyrrole grafts with poly[(methyl methacrylate)-CO-(2-(N-pyrrolyl)ethyl methacrylate)]
(Elsevier, 1997-10) Balcı, N.; Akbulut, U.; Toppare, L.; Stanke, D.; Hallensleben, M. L.
Conducting polymer grafts of pyrrole and poly[(methyl methacrylate)-co-(2- (N-pyrrolyl) ethyl methacrylate)] containing 0.7% PEMA units were prepared by potentiostatic anodic polymerization of pyrrole in different electrolytic media. Grafting between copolymer and pyrrole was achieved in media where tetrabutylammonium fluoroborate and sodium perchlorate were used as the supporting electrolytes. Characterizations were made by using IT-IR, DSC, TGA, SEM, CV, and elemental analysis. The conductivities of the resultant polymers seemed to be in the order of pure polypyrrole prepared under the same conditions. Copyright o 1997 Elsevier Science
Open Access
A pyrolysis mass spectrometry study of polythiophene-natural rubber and polythiophene-synthetic rubber conducting polymer composites
(Elsevier, 1997) Yigit, S.; Hacaloglu, J.; Akbulut, U.; Toppare, L.
The thermal behaviors and degradation products of conducting polymer composites prepared by electrooxidation of thiophene using natural rubber or synthetic rubber as the insulating matrix were studied by direct and indirect mass spectrometry techniques. The pyrolysis mass data revealed that a chemical interaction formed between the components of the composites during polymerization. Thermal characteristics of rubbers totally disappeared in the composites indicating presence of some chain scissions leading to degradation of rubbers during electrooxidative polymerization. The multiscan cyclic voltammetry runs showed that polythiophene is also electroactive on the rubber coated metal electrodes, with a small shift in the redox peaks compared to the one on the bare electrode.
Open Access
Synthesis of a hexafluoropropylidene-bis(phthalic anhydride)-based polyimide and its conducting polymer composites with polypyrrole
(John Wiley & Sons, Inc., 1997) Selampinar, F.; Akbulut, U.; Yilmaz, T.; Gungor, A.; Toppare, L.
A new electrically conducting composite film from polypyrrole and 4,4′(hexafluoroisopropylidene)-bis(phthalic anhydride)-based polyimide was prepared. Pyrrole and the dopant ion can easily penetrate through the polyimide substrate and electropolymerize on the platinum (Pt) electrode due to the swelling of the polyimide on the metal electrode. The electrochemical properties of polypyrrole-polyimide (PPy/PI ) composite films have been investigated by using cyclic voltammetry. The PPy/PI composite film is suitable for use as the electroactive material owing to its stable and controllable electrochemical properties. The electrical conductivity of composites falls in the range 0.0035-15 S/cm. Scanning electron micrograph, FTIR, and thermal studies indicate that PPy and PI form a homogeneous material rather than a simple mixture. © 1997 John Wiley & Sons, Inc.
Open Access
Synthesis of a novel poly(arylene ether ketone) and its conducting composites with polypyrrole
(Elsevier, 1997) Selampinar, F.; Akbulut, U.; Yildiz, E.; Güngör, A.; Toppare, L.
The synthesis of a 1,3-bis(4-fluorobenzoyl)-5-tert-butyl benzene and hexafluoro bisphenol A based poly(arylene ether ketone) (PEK) was described. The electrically conductive composites of polypyrrole (PPy) and PEK were formed by electropolymerization of pyrrole on a PEK coated platinum electrode in a medium containing water andp-toluenesulfonic acid as the solvent and the electrolyte, respectively. The electrical conductivity of the composites was found to be between 1 and 4 S/cm. The polypyrrole/poly (ether ketone) composites were characterized by scanning electron microscopy, FT-IR and thermal analyses (TGA, DSC). © 1997 Elsevier Science S.A.
Open Access
X-ray photoelectron spectroscopic investigation of conducting polymer blends
(Springer, 1996) Süzer, Ş.; Toppare, L.; Hallam, K. R.; Allen, G. C.
Electrochemically prepared films of conducting polymers of polypyrrole and polythiophene and their blends with polyamide have been investigated by X-ray photoelectron spectroscopy. In the N1s region of the spectra of films containing polypyrrole the peak corresponding to N+ at 402.0 eV is separated from that of neutral N. The intensity of the N+ peak can be correlated with the electrical conductivity of the films and the spectroscopically derived ratio of F/N+ is close to 4 indicating that one BF4 - dopant ion is incorporated for every oxidized nitrogen center. In the spectra of films of polythiophene and its blends peaks corresponding to S and S+ can not be resolved but again the F/C ratio correlates with the electrical conductivity. © Springer-Verlag 1996.