Browsing by Author "Birer, O."
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Item Open Access Photosensitization of PVC dehydrochlorination by hydroquinone for improved optical and electrical properties(Elsevier, 2004) Balci, S.; Birer, O.; Süzer, ŞefikHydroquinone (HQ) is incorporated into the PVC films containing methyl violet or polyaniline (emeraldine base) for sensitizing the UV induced optical or electrical changes, respectively. It is observed that introduction of a small amount (less than 10% by weight) of HQ not only brings the dehydrochlorination onset down to 310 nm but also sensitizes the process by more than one order of magnitude as well as leading to strong polyene formation. UV-Vis-NIR spectroscopy is used to characterize the changes and investigate the mechanism. Accordingly, it is postulated that this HQ assisted photo-dehydrochlorination involves predominantly the formation of an excited triplet via an efficient intersystem crossing in HQ followed by abstraction of hydrogen from the poly(vinyl chloride) to initiate a zipping reaction in the PVC matrix. © 2004 Elsevier Ltd. All rights reserved.Item Open Access UV-induced electrical and optical changes in PVC blends(Springer, 2001) Süzer, Şefik; Birer, O.; Sevil, A. U.; Guven, O.2-Chloro-polyaniline (2-Cl-PANI) in its non-conducting (emeraldine base, EB) form, prepared by a chemical route, was dissolved together with poly-(vinylchloride) (PVC) in THF for casting into thin (10-50 μm) films. Upon exposure to UV radiation, the electrical conductivity of these films increased by more than 4 orders of magnitude (from 10-6 to 10-2 S/cm). This is attributed to the dehydrochlorination of PVC by exposure to energetic photons and subsequent doping of 2-Cl-PANI (i.e. conversion to emeraldine salt, ES) by in situ created HCl. The doped films could be returned to their undoped form by exposure to NH3 vapours. The UV-induced doping/NH3 undoping cycles could be repeated several times. Various spectroscopic techniques were employed to follow the changes in the films upon exposure to UV radiation. The same photo-dehydrochlorination process has also been utilized for optical and/or lithographic purposes by preparing PVC blends containing methyl violet, and acid-base indicator dye. The photo-dehydrochlorination can be effectively sensitized by incorporating hydroquinone into the PVC blends containing methyl violet.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 investigation of thin SiOx and SiOxNy overlayers(Elsevier, 1999-05-04) Birer, O.; Sayan, S.; Süzer, Şefik; Aydınlı, AtillaAngle-resolved XPS is used to determine the thickness and the uniformity of the chemical composition with respect to oxygen and nitrogen of the very thin silicon oxide and oxynitride overlayers grown on silicon. (C) 1999 Elsevier Science B.V. All rights reserved.