Publications

  • Mf Can, L Avdan, A.Bedeloglu
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    ABSTRACT: In this study, poly(vinyl alcohol) (PVA) nanocomposite fiber mats with sepiolite were prepared via electrospinning technique. The measurements of fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), contact angle, scanning electron microscopy (SEM), and atomic force microscopy (AFM) were used for the characterization. The effect of polymer/sepiolite ratio and heat treatment on the properties of samples was investigated. The heat treatment which decreased the solubility of nanofibers and the addition of sepiolite resulted in a decrease in nanofiber diameter, contact angle with water, and water drop spreading rate on the material, and also resulted in an increase in water drop spreading rate inside the material. POLYM. COMPOS., 2014. © 2014 Society of Plastics Engineers
    Polymer Composites 12/2014; · 1.48 Impact Factor
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    ABSTRACT: Controlling the wettability of nano textured surface structures is essential for understanding of its role particularly in biomedical applications. The main objective of this study is to explore the wetting mechanism of a water drop on a nano textured Si surface. Si nano-columns with 4-, 3- and 2-fold in-plane symmetries were grown on p-type (100) Si wafer by oblique angle deposition (OAD). The surface morphology was characterized by scanning electron microscopy (SEM). The contact angle technique was used to reveal the wetting characteristics of these textured surfaces. Experimental results were compared with the theoretical contact angle calculations derived from the Young, Wenzel and Cassie-Baxter equations in order to identify the conditions for the minimum free energy of the drop. Water droplets on all plenary symmetries water droplets showed good agreement with the Cassie-Baxter model of Sunny side up. These findings were used to simulate the extent of the hydrophilicity on the fabricated textures by taking the contact angle hysteresis (CAH) into account.
    Materialwissenschaft und Werkstofftechnik 05/2012; 43(5). · 0.51 Impact Factor
  • Materialwissenschaft und Werkstofftechnik 01/2012; 43(5):366-372. · 0.51 Impact Factor
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    ABSTRACT: We prepared biocomposite gel dispersions involving sodium alginate (Na-Alg) and calcium bentonite (Ca-B) with various solid concentrations and characterized their rheological, electrokinetic, and morphological properties. The flow properties, such as the apparent and plastic viscosities, shear stress, and yield value point, changed with increasing clay dosage. The viscosities of the homogeneous dispersions were represented by the Herschel–Bulkley model. The ζ-potential results were examined in the light of different characterization methods (X-ray diffraction, Fourier transform infrared spectroscopy, and atomic force microscopy) to understand the interactions between the Na and Ca ions of the alginate biopolymer and bentonite clay. A plausible structural model for the alginate–bentonite composite gel, known as the egg-box model, is proposed. The presence of Ca ions in the Ca-B partially crosslinked Na-Alg may be regarded as an excellent example of a self-assembling process. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.
    Journal of Applied Polymer Science 10/2011; 122(1). · 1.40 Impact Factor
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    ABSTRACT: Sepiolite is a natural clay mineral characterized by a nanofiber structure, unique crystal morphology and composition, and high surface area. It is capable of producing stable suspensions of high viscosity at lower solid concentrations. Dispersion of sepiolite fibers in water can increase the inner and outer surface areas of fibers in the form of a network which enables adsorption of water molecules within the inter particles resulting in a significant increase on the viscosity of the suspension. The viscosity of 3% (w/w) sepiolite suspension prepared at 21,000 rpm remarkably increased with increasing the stirring time from 1 to 3 min. Sepiolite particles are expected to disperse in water to nanosizes. Towards this aim, an Atomic Force Microscopy (AFM) study was undertaken to determine the dimensions of the fibers against the stirring time. The sepiolite suspensions stirred for 1 min showed that the fibers remained in the form of bundles. An increase in the stirring time to 3 min caused the fibers to break into pieces on all dimensions but less effective on the length. However, in the case of 5 min of stirring time, those broken fiber pieces could not organize themselves in a randomly establishing network and thus led to a significant viscosity reduction. The AFM study revealed that the average fiber dimensions at the highest viscosity were determined as 249 × 1127 × 29 nm (width × length × height). The size distribution of fibers is elaborated in order to define an optimum strategy for fiber disintegration.
    Applied Clay Science 01/2010; · 2.34 Impact Factor
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    ABSTRACT: Effects of different acids (HCl, H2SO4 and citric acid) on rheological properties of brown sepiolite from the Eskisehir region of Turkey have been determined. The optimum apparent viscosity value was obtained at the natural pH of the suspension. Below the natural pH, partial collapse of the structure due to the release of Mg ions causes a significant decrease in viscosity values. However, below pH 1, there is a substantial increase in viscosity values owing to gel formation. On the other hand, above the natural pH of suspension, increased amounts of OH ions lead to a decrease in viscosity values and inhibit gel formation. The reversible nature of sepiolite was tested by changing the pH of acid and alkaline treated sepiolite suspensions back to its natural pH by washing with water and acid, respectively. In summary, from a practical point of view, there is no favorable effect of acid treatment of sepiolite on its rheological properties. On the contrary, reducing the pH to natural pH after grinding in a basic environment led to an improvement in rheological properties.
    Applied Clay Science 01/2009; 42:422-426. · 2.34 Impact Factor
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    ABSTRACT: In this work, chemically modified sodium montmorillonite and epoxy monomer were used to prepare nanocomposites in two consecutive stages. In the first stage, dodecylamine, octadecylamine, hexadecylamine, and hexadecyltrimethyl ammonium bromide were used to prepare various organophilic clays. In the second stage, the bisphenol-A based epoxy monomer and predetermined amounts of organoclay were mixed together and then cured by an aliphatic polyamine for 20 min under microwave at 400 W. Furthermore, -ω diacrylate poly(dimethylsiloxane) was added to the mixture before the curing process to modify the toughness of the samples. The mixture was poured into the poly(tetrafluoroethylene) mold; the epoxy resin/curing agent ratio was maintained as 2/1. The clear films formed after microwave irradiation were removed from the mold, cooled, and then stored in a cool and dry medium until characterization. The samples were analyzed by wide angle X-ray diffraction, differential scanning calorimetry, and mechanical tests. Surfaces of the cold fractured samples were also observed under the scanning electron microscope. The results revealed that microwave curing of the samples of 5% organoclay and 5% siloxane showed improvement in mechanical properties. POLYM. ENG. SCI. 46:1104–1110, 2006. © 2006 Society of Plastics Engineers
    Polymer Engineering and Science 07/2006; 46(8):1104 - 1110. · 1.24 Impact Factor
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    ABSTRACT: Application of the thin-layer wicking (TLW) technique on powdered minerals is useful for characterizing their surfaces. Albite (Na-feldspar) and orthoclase (K-feldspar) are feldspar minerals which are frequently found in the same matrix. Despite similarities in their physicochemical properties, separation of these minerals from each other by flotation is generally possible in the presence of monovalent salts such as NaCl. Both albite and orthoclase exhibit the same microflotation properties and rather close electrokinetic profiles in the absence of salt. In this study, contact angles of albite and orthoclase determined by the TLW technique yielded close values in the absence and presence of amine collector. While the calculated surface energies and their components determined using contact angle data reveal that the energy terms remain farther apart in the absence of the collector, the differences narrow down at collector concentrations where full flotation recoveries are obtained. However, the effect of addition of NaCl on contact angles and surface free energy components at constant amine concentration indicates that albite is significantly affected by salt addition, whereas orthoclase remains marginally affected. This interesting finding is explained on the basis of ion-exchange properties, the stability of the interface, flotation data, and zeta potential data in the presence of NaCl.
    Journal of Colloid and Interface Science 06/2005; 285(1):192-200. · 3.55 Impact Factor
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    ABSTRACT: Modification of zeolite (clinoptilolite) surface with a quaternary amine, hexadecyl trimethyl ammonium bromide (HTAB), to improve the removal efficiency of reactive azo dyes in a zeolite fixed bed was investigated. A series of adsorption tests were conducted to find out the uptake of three types of reactive dyes, i.e. CI Reactive Black 5, Red 239 and Yellow 176. Each run consisted of modifying zeolite with HTAB in the column followed by removal of color from the modified zeolite bed. The breakthrough curves for modification process were constructed under different conditions by plotting the normalized effluent concentration (C/C(0)) versus time or bed volumes (BV). Optimization studies show that 3g/l of HTAB dosage at a flowrate of 0.025l/min showed the best performance. Examination of the dye removal under the optimum modification conditions reveals that the black dye gives the highest breakthrough point among the three dyes tested. This is ascribed to the hydrophobic/hydrophilic match of the zeolite surface with the dye molecule, which depends upon the way zeolite is modified with HTAB. Calculations of the HTAB coverage on zeolite surface indicate that a bilayer formation is the most viable packing that enables maximum removal of the dye.
    Water Research 01/2005; 39(2-3):487-93. · 4.66 Impact Factor

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