Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 23Citation - Scopus: 23Use of Polyethylene Glycol Coatings for Optical Fibre Humidity Sensing(Springer Verlag, 2008) Açıkgöz, Sabriye; Bilen, Bukem; Demir, Mustafa Muammer; Menceloğlu, Yusuf Z.; Skarlatos, Yani; Aktaş, Gülen; İnci, Mehmet N.Humidity induced change in the refractive index and thickness of the polyethylene glycol (PEG) coatings are in situ investigated for a range from 10 to 95%, using an optical waveguide spectroscopic technique. It is experimentally demonstrated that, upon humidity change, the optical and swelling characteristics of the PEG coatings can be employed to build a plastic fibre optic humidity sensor. The sensing mechanism is based on the humidity induced change in the refractive index of the PEG film, which is directly coated onto a polished segment of a plastic optical fibre with dip-coating method. It is observed that PEG, which is a highly hydrophilic material, shows no monotonic linear response to humidity but gives different characteristics for various ranges of humidity levels both in index of refraction and in thickness. It undergoes a physical phase change from a semi-crystalline structure to a gel one at around 80% relative humidity. At this phase change point, a drastic decrease occurs in the index of refraction as well as a drastic increase in the swelling of the PEG film. In addition, PEG coatings are hydrogenated in a vacuum chamber. It is observed that the hydrogen has a preventing effect on the humidity induced phase change in PEG coatings. Finally, the possibility of using PEG coatings in construction of a real plastic fibre optic humidity sensor is discussed.Article Citation - WoS: 36Citation - Scopus: 38Investigation on Glassy Skin Formation of Porous Polystyrene Fibers Electrospun From Dmf(BME-PT, 2010) Demir, Mustafa MuammerMicrometer and submicrometer diameter of polystyrene (PS) fibers were electrospun from various dimethyl formamide (DMF) solutions at different weight fractions under 35% relative humidity. Increasing polymer fraction in the solution results in a gradual morphological transition from beads-with-incipient to bead-free fibers and also increases the diameter. The formation of uniform glassy skin presumably due to radial capillary flow within the liquid jet was confirmed by scanning electron microscope. The thickness of the skin varies with the weight fraction of PS; therefore, it was normalized with respect to average fiber diameter (AFD). The skin gets thinner as the weight fraction of PS increases. In addition, the fibers exhibit highly porous internal structure and smooth surface along with slight porosity. The development of porosity is attributed to liquid-liquid phase separation of water molecules in atmospheric moisture and DMF.Article Citation - WoS: 74Humidity Sensing Properties of Zno-Based Fibers by Electrospinning(Elsevier Ltd., 2011) Horzum Polat, Nesrin; Taşçıoğlu, Didem; Okur, Salih; Demir, Mustafa MuammerZinc oxide (ZnO) based fibers with a diameter of 80-100 nm were prepared by electrospinning. Polyvinyl alcohol (PVA) and zinc acetate dihydrate were dissolved in water and the polymer/salt solution was electrospun at 2.5 kV cm-1. The resulting electrospun fibers were subjected to calcination at 500 °C for 2 h to obtain ZnO-based fibers. Humidity sensing properties of the fiber mats were investigated by quartz crystal microbalance (QCM) method and electrical measurements. The adsorption kinetics under constant relative humidity (RH) between 10% and 90% were explained using Langmuir adsorption model. Results of the measurements showed that ZnO-based fibers were found to be promising candidate for humidity sensing applications at room temperature.