Browsing by Author "Güven, O."
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Item Open Access Composition of γ-ray induced triethoxyvinylsilane-methyl methacrylate copolymers determined by XPS(Elsevier, 1998) Çaykara, T.; Güven, O.; Süzer, Ş.Methyl methacrylate (MMA) was copolymerized with triethoxyvinylsilane (TEVS) using 60Co-γ radiation at varying masses of the liquid monomers in the feed. Their homopolymers PMMA and PTEVS were also prepared by the same method. Thin copolymer and homopolymer blend films were prepared by dissolving the polymers in tetrahydrofuran and casting on clean Teflon or glass substrates. Analysis of the surface composition of these films using XPS indicated that the surfaces of the blend films were completely covered by PTEVS after 10% composition by weight. Similar analysis on the copolymer films, however, revealed that the surfaces of the copolymers contain comparable amounts of PMMA and PTEVS in agreement with the bulk analysis using infrared spectrometry. Hence, use of PMMA/PTEVS copolymers for stone preservation seems feasible by radiation induced polymerization. © 1998 Elsevier Science Ltd. All rights reserved.Item Open Access Doping of 2-Cl-PANI/PVC films by exposure to UV, γ-rays and e-beams(Elsevier Sequoia SA, Lausanne, Switzerland, 2000) Sevil, U. A.; Güven, O.; Birer, Ö.; Süzer, Ş.2-Chloro-polyaniline (2-Cl-PANI) is chemically prepared in its non-conducting (Emeraldine Base, EB) form and dissolved together with polyvinylchloride (PVC) in THF for casting into thin (10-50 μm) composite films. The electrical conductivity of these films increases by more than four orders of magnitude (from 10-6 to 10-2 S/cm) when they are exposed to UV, γ-rays and e-beams. This is attributed to the dehydrochlorination (loss of HCl) of PVC by exposure to energetic particles and subsequent doping of the 2-Cl-PANI (i.e., conversion to Emeraldine Salt, ES) by the in-situ-created HCl. The doped films can also be returned to their undoped form by further exposure to NH3 vapours. The UV (or other particles)-induced doping/NH3 undoping cycles can be repeated several times until almost total dehydrochlorination of the PVC matrix. UV-Vis-NIR, Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopic (XPS) techniques are employed to follow the changes in the composite films upon doping by exposure to these energetic particles.Item Open Access Effect of brush length of stabilizing grafted matrix on size and catalytic activity of metal nanoparticles(Elsevier, 2020-06-01) Barsbay, Murat; Özgür, T. Ç.; Sütekin, S. D.; Güven, O.The rationale of this work is to investigate the effect of chain length of stabilizing polymer brushes attached to silica surface on the formation and catalytic activity of metallic palladium nanoparticles (Pd NPs). Poly(vinyl pyrrolidone) (PVP) brushes forming a very thin shell were grafted on silica microparticles (PVP@SiO2) via RAFT mediated graft polymerization, thus controlling the molecular weights and structures of PVP grafts. Pd nanoparticles were formed in PVP stabilizing matrix by gamma-induced reduction of polymer-bound Pd(II) ions to yield Pd(0) decorated core-shell particles (PVP-PdNP@SiO2). SEC and TGA results indicated the formation of PVP brushes with different molecular weights on silica substrate. DLS and TEM measurements revealed that particle growth was sterically blocked by the increase in PVP brush length, thereby forming a greater number of small Pd nanoparticles rather than larger ones. PVP-PdNP@SiO2 samples with different PVP chain lengths and Pd sizes were evaluated for their catalytic activity and reusability in the reduction of 4-nitrophenol to 4-aminophenol. Although the nanoparticles formed in the presence of longer grafted chains are smaller, their leakage into the solution has been found to be more effectively prevented by these long grafts. Thus, PVP-PdNP@SiO2 samples with longer PVP grafts showed more stable catalytic activity in repeated reaction cycles. These findings are particularly important for heterogeneous catalysis systems in that they show the effect of the size of surface-bound polymeric stabilizers on metal NP formation and catalytic activity.Item Open Access Poly(vinyl amine) microparticles derived from N-Vinylformamide and their versatile use(Springer, 2021-09-03) Demirci, S.; Sütekin, S.Duygu; Kurt, S.B.; Güven, O.; Sahiner, N.Cationic polymers with primary amine groups that can easily be functionalized or coupled with substrates by complexation or hydrogen bonding are especially advantageous in preparing particles for biomedical applications. Poly(vinyl amine) (PVAm) is a cationic polyelectrolyte containing the highest number of primary amine groups among any other polymers. Here, we introduce a general method in synthesizing PVAm microparticles via a surfactant-free water-in-oil emulsion technique using cyclohexane as the oil phase and aqueous PVAm solution as the dispersed phase. PVAm particles were prepared to employ two different bifunctional chemical crosslinkers, divinyl sulfone (DVS) and poly(ethylene glycol) diglycidyl ether (PEGGE). The prepared particles were further treated with HCl to protonate the amine groups of PVAm within particles. The effect of crosslinker types and pH on the hydrolytic degradation of PVAm particles were also investigated at three different solution pHs, 5.4, 7.4, and 9, to simulate the skin, blood, and intestinal pH environments, respectively. The blood compatibility of the PVAm particles was evaluated by in vitro hemolysis and blood clotting assays. Furthermore, antifungal and antibacterial efficacy of PVAm-based particles and their protonated forms were tested against C. albicans yeast and E. coli, S. aureus, B. subtilis, and P. aeruginosa bacterial strains. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.Item Open Access A smartphone-based colorimetric PET sensor platform with molecular recognition via thermally initiated RAFT-mediated graft copolymerization(Elsevier, 2019) Kuşçuoğlu, C.; Güner, Hasan; Söylemez, M.; Güven, O.; Barsbay, MuratIn this work, we report a low-cost and easy-to-use molecularly-imprinted colorimetric sensor platform that can sense target analyte with high sensitivity and good selectivity. The platform has been examined for colorimetric detection and quantitation of a model textile dye, basic red 9 (BR9), by employing methacrylic acid (MAA), ethylene glycol dimethacrylate (EGDMA) and cumyl dithiobenzoate (CDB) as functional monomer, crosslinker and RAFT agent, respectively. Benzophenone (BP), a photoinitiator, was covalently immobilized on the surface of poly(ethylene terephthalate) (PET) and then thermally activated by homolytic cleavage to form radicals on the surface that initiate RAFT-mediated grafting of a thin recognition layer. The molecularly imprinted polymer (MIP) layer of about 100 nm showed excellent removal of 76.7% target dye in 10 min and high selectivity compared to other similar dyes with an imprinting factor of 10.31 in the competitive environment. The resulting MIP grafted PET substrate was efficiently used as recognition unit in a smartphone-based colorimetric detection method using a color adaptation algorithm for point-of-care applications. Based on the obtained performance, it is promising to use the method for the detection and quantification of various analytes with chromophores.Item Open Access Spectroscopic investigation of onset and enhancement of electrical conductivity in PVC/PANI composites and blends by γ-ray or UV irradiation(American Chemical Society, 1998) Sevil, U. A.; Güven, O.; Süzer, S.Electrical conductivity of blends and composites of poly(vinyl chloride) (PVC) with nonconducting polyaniline (PANI) increases when they are subjected to γ-rays or UV radiation. This is attributed to a radiation-induced dehydrochlorination (loss of HCl) of PVC, which in turn oxidizes (dopes) PANI within the PVC matrix causing the increase in electrical conductivity of these films. XPS, UV - vis - NIR and FTIR spectroscopic methods are used to characterize and verify this novel process. After the films are subjected to γ-rays (or UV radiation) the intensities in the XPS spectra of both -N+- and Cl- peaks increase, confirming the increase in charged species within the PVC matrix. Similar observations attributable to radiation-induced electrical conductivity are also observed in both the UV - vis - NIR and FTIR spectra. This radiation-induced conductivity can also be reversed to some extent by further exposing the films to NH3 vapors, where the oxidized centers are partially reduced (undoped). Several UV/NH3/UV cycles can be performed without much loss in conductivity- and/or conductivity-related spectroscopic features. The onset of the photoinduced conductivity both in PVC-only and PVC/PANI composite films is determined to be 300 nm (4.1 eV), which coincides with the first UV absorption band of PVC.Item Open Access XPS investigations on conducting polymers(TÜBİTAK, 1998) Süzer, Şefik; Birer, Özgür; Sevil, U. A.; Güven, O.X-ray photoelectron spectroscopy, XPS, was used for the characterization of electrically conducting polymeric materials. In the spectrum of polypyrrole, PPy, the Nls region exhibits two peaks, at 402.0 and 399.8 eV, corresponding to -N+ - and -N-moieties, respectively. The intensity of the N+ peak decreases as the material loses its conductivity, hence the ratio of the experimentally derived N+/C atomic ratio correlates exponentially with the measured conductivity. A similar observation also exists between the F-/C atomic ratio both in polypyrrole and polythiophene. In the XPS spectrum of the composite material prepared using polyaniline, PAN and Polyvinylchloride, PVC, two different kinds of C12p spin-orbit doublets are present after irradiation by 60Co γ-rays. One of the C12p doublets can be assigned to the C-Cl in PVC and the other one is assigned to Cl- ions appearing after radiation. Since no Cl- peak is observed in PVC even after radiation, the presence in the composite must be related to dehydrochlorination of PVC and subsequent capture of the H-Cl by the neighboring PAN moieties. The measured Auger parameter of the Nals level of NaBr deposited on an oxidized form of the conducting polymer is between the values of NaBr deposited on Au (metal) and on Si (semiconductor). However, when NaBr is deposited on a reduced form of conducting polymer, the corresponding value approaches to that deposited on quartz (insulator).