Browsing by Author "Sevil, U. A."
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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 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 UV-Vis, IR, and XPS analysis of UV induced changes in PVC composites(Elsevier, 1999-05-25) Birer, O.; Süzer, Şefik; Sevil, U. A.; Guven, O.PVC undergoes a high degree of dehydrochlorination when exposed to energetic photons. The released HCl (acid), however, can be trapped if a suitable trapping material (base) is also enclosed within the solid matrix as a result of formation an acid-base adduct. Color changes or electrical conductivity changes can easily be obtained if suitable acid-base indicators or conducting polymers in their basic (nonconducting) form are enclosed in the matrix as trapping materials. We used bromcresol green and polyaniline for inducing color and electrical conductivity changes, respectively, within the PVC matrix as a result of exposure to UV light at 254 nm. Both changes can to some extent be reversed by further exposure of the films to NH3 vapour. The color and electrical conductivity changes and their reversibility were followed by using UV–Vis, IR and XPS spectroscopic techniques. qItem 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).