Pekcan, Mehmet Önder

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https://hdl.handle.net/20.500.12469/6171
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Mehmet Onder Pekcan
Mehmet Onder, Pekcan
Mehmet Önder Pekcan
Pekcan ö.
P., Mehmet Önder
Pekcan, MEHMET ÖNDER
Pekcan,Mehmet Onder
Pekcan, M. Ö.
Mehmet Önder PEKCAN
P., Mehmet Onder
PEKCAN, Mehmet Önder
Pekcan, Mehmet Onder
Pekcan,M.Ö.
M. Ö. Pekcan
MEHMET ÖNDER PEKCAN
M. Pekcan
Pekcan, M.
PEKCAN, MEHMET ÖNDER
PEKCAN Ö.
Pekcan N.
Pekcan Ö.
Pekcan, Mehmet Önder
Pekcan O.
P.,Mehmet Onder
Pekcan,M.O.
Pekcan, Önder
Pekcan, Onder
Pekcan, Oonder
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Prof. Dr.
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[email protected]
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Molecular Biology and Genetics
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Former Staff
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ORCID ID
0000-0002-0082-8209
Scopus Author ID
35479982700
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WoS Researcher ID
Y-3158-2018

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Journal of Macromolecular Science, Part B10
Phase Transitions8
Polymer Composites8
Polymer Bulletin7
Progress in Organic Coatings6
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  • Thumbnail Image
    Article
    Citation - WoS: 4
    Citation - Scopus: 3
    Polymer/Carbon Nanotube Composite Film Formation: a Fluorescence Study
    (Wiley-Blackwell, 2014) Yargı, Önder; Uğur, Saziye; Pekcan, Önder
    In this study the effect of multi-walled Carbon nanotube (MWNT) on film formation behavior of Polystrene (PS) latex film was investigated by using steady state fluorescence technique. Films were prepared by mixing of pyrene (P)-labeled PS latex with different amounts of MWNTs varying in the range between 0 and 20 wt%. After drying MWNT containing films were separately annealed above glass transition temperature (T-g) of PS ranging from 100 to 270 degrees C for 10 min. In order to monitor film formation behavior of PS/MWNT composites Scattered light (I-s) and fluorescence intensities (I-P) from P were measured after each annealing step to monitor the stages of film formation. At 0-20 wt% range of MWNT content films minimum film formation (T-o) void closure (T-v) and healing (T-h) temperatures were determined. Void closure and interdiffusion stages were modeled and related activation energies were determined. It was observed that while void closure activation energies increased backbone activation energies decreased as the percent of MWNT is increased in the composite films. POLYM. COMPOS. 35:817-826 2014. (c) 2013 Society of Plastics Engineers
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    Article
    Citation - WoS: 6
    Citation - Scopus: 6
    Slow Release of Trapped Homopolymers From a Swelling Polymeric Gel: a Fluorescence Study
    (Taylor & Francis Inc, 2008) Erdoğan, Matem; Yağcı, Yusuf; Pekcan, Önder
    In-situ steady-state fluorescence experiments were performed for studying slow release of pyrene-labeled polystyrene chains from polystyrene gels formed by free-radical crosslinking copolymerization. Atom transfer radical polymerization was used to produce the pyrene end-capped polystyrene chains. In order to load the pyrene end-capped polystyrene chains into the gel disc-shaped gels were left in toluene solutions of pyrene end-capped polystyrene chains of various molecular weights. These swollen gels were redried in air and then immersed in pure toluene solution for monitoring slow release from the gel. These reswelling experiments were performed at room temperature in real time by monitoring the pyrene emission intensity using steady-state fluorescence measurements. Slow-release diffusion coefficients were measured and found to decrease as the crosslink density of the gels increased. It was observed that higher molecular weight pyrene end-capped polystyrene chains released much faster than low molecular ones during the slow-release process.
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    Article
    Citation - WoS: 4
    Citation - Scopus: 4
    Diffusion Energies of Oxygen Diffusing Into Polystyrene (ps)/Poly (n-Isopropylacrylamide) Composites
    (Wiley-Blackwell, 2012) Yargı, Önder; Ugur, Saziye; Pekcan, Önder
    Diffusion coefficient of oxygen penetrating into polystyrene (PS) latex/poly (N-isopropylacrylamide) (PNIPAM) microgel composite films were measured using Fluorescence technique. Three different (5 15 and 40wt%) PS content films were prepared from PS/PNIPAM mixtures. Diffusivity of PS/PNIPAM composite films were studied by diffusion measurements which were performed over the temperature range of 24-70 degrees C. Pyrene was used as the fluorescent probe. The diffusion coefficients (D) of oxygen were determined using the SternVolmer fluorescence quenching method combined with Fickian transport and were computed as a function of temperature for each PS content film. The results showed that D values were strongly dependent on both temperature and PS content in the film. Diffusion energies were measured and found to be dependent on the composition of the composite films. Copyright (C) 2011 John Wiley & Sons Ltd.
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    Article
    Drying process in vapor swollen heterogels
    (Springer, 2010) Erdogan, Matem; Pekcan, Önder
    Disk-shaped heterogels were prepared by combining methyl methacrylate (MMA) and styrene (S) with ethylene glycol dimethacrylate (EGDM) as a crosslinker agent in the presence of 22'-azobisisobutyronitrile (AIBN). Swelling experiments were performed under chloroform vapor and the swollen gels are then allowed to dry under room temperature. Gravimetric technique was used to study drying processes. It is observed that two different regimes are present in the drying processes of these heterogels. Fickian diffusion model was used to determine desorption coefficients for each drying step in both regimes. Desorption coefficients D (d) of heterogels were found to be strongly correlated with the mixture composition of polymeric materials in the heterogel system for both regimes. Heterogels with high S content dry much slower than the heterogels with low S content.
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    Article
    Citation - WoS: 3
    Citation - Scopus: 3
    The Effect of Film Thickness and Tio2 Content on Film Formation From Ps/Tio2 Nanocomposites Prepared by Dip-Coating Method
    (Hindawi Publishing Corporation, 2012) Sunay, M. Selin; Pekcan, Önder; Ugur, Saziye
    Steady-state fluorescence (SSF) technique in conjunction with UV-visible (UVV) technique and atomic force microscope (AFM) was used for studying film formation from TiO2 covered nanosized polystyrene (PS) latex particles (320 nm). The effects of film thickness and TiO2 content on the film formation and structure properties of PS/TiO2 composites were studied. For this purpose two different sets of PS films with thicknesses of 5 and 20 mu m were prepared from pyrene-(P-) labeled PS particles and covered with various layers of TiO2 using dip-coating method. These films were then annealed at elevated temperatures above glass transition temperature (T-g) of PS in the range of 100-280 degrees C. Fluorescence emission intensity I-p from P and transmitted light intensity I-tr were measured after each annealing step to monitor the stages of film formation. The results showed that film formation from PS latexes occurs on the top surface of PS/TiO2 composites and thus developed independent of TiO2 content for both film sets. But the surface morphology of the films was found to vary with both TiO2 content and film thickness. After removal of PS thin films provide a quite ordered porous structure while thick films showed nonporous structure.
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    Review
    Citation - WoS: 21
    Citation - Scopus: 24
    Conductivity Percolation of Carbon Nanotubes (cnt) in Polystyrene (ps) Latex Film
    (Canadian Science Publishing Nrc Research Press, 2010) Uğur, Şaziye; Yargı, Önder; Pekcan, Önder
    In this study the effect of multiwalled carbon nanotubes (MWNT) on film formation behaviour and electrical conductivity properties of polystrene (PS) latex film was investigated by using the photon transmission technique and electrical conductivity measurements. Films were prepared by mixing PS latex with different amounts of MWNTs varying in the range between 0 and 20 wt%. After drying MWNT content films were separately annealed above the glass transition temperature (T-g) of PS ranging from 100 to 270 degrees C for 10 min. To monitor film formation behavior of PS-MWNT composites transmitted light intensity I-tr was measured after each annealing step. The surface conductivity of annealed films at 170 degrees C was measured and found to increase dramatically above a certain fraction of MWNT (4 wt%) following the percolation theory. This fraction was defined as the percolation threshold of conductivity R-c. The conductivity scales with the mass fraction of MWNT as a power law with exponent 2.27 which is extremely close to the value of 2.0 predicted by percolation theory. In addition the increase in I-tr during annealing was explained by void closure and interdiffusion processes. Film formation stages were modeled and the corresponding activation energies were measured.
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    Article
    Citation - WoS: 2
    Citation - Scopus: 3
    Tailoring the Electrical and Optical Properties of Carbon Nanotube Reinforced Transparent Tio 2 Composites by Varying Nanotube Concentrations
    (World Scientific Publ Co Pte Ltd, 2019) Uysal, Bengü Özuğur; Akkaya Arier, Ümit Özlem; Pekcan, Önder
    In the present work multi-walled carbon nanotube (MWCNT)-doped TiO 2 nanocomposite films were synthesized by sol-gel method. The influence of nanotube concentration on the structural electrical and optical properties of the films was investigated. The beneficial effects of the addition of carbon nanotubes into a TiO 2 film and titania-coated MWCNTs have much in common. On the other hand this work contributes to the previous studies in terms of the optical and electrical properties of MWCNT. For this reason MWCNT/rare brookite-phased TiO 2 matrix as simple sol-gel deposited composite films were investigated in our study. The XRD studies showed that the composite film has a brookite crystal structure at the annealing temperature of 450C. According to the surface morphology investigations SEM image of nanocomposite film shows that composite film has a granular and rod-like structure. The absorbance measurements of the films were carried out by the UV-Vis spectrophotometer to investigate transparency and to calculate the bandgap energy of composite films. The surface resistivity of the MWCNT-doped TiO 2 composites decreased from 2.50×1010 to 2.20×109 ohm/sq with increase in MWCNT content. © 2019 World Scientific Publishing Company.
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    Article
    Citation - WoS: 4
    Citation - Scopus: 3
    Drying of Polyacrylamide-Multiwalled Carbon Nanotube (mwnt) Composites With Various Mwnts Contents: a Fluorescence Study
    (Walter De Gruyter Gmbh, 2013) Evingür, Gülşen Akin; Pekcan, Önder
    We studied the drying of polyacrylamide (PAAm)-multiwalled carbon nanotube (MWNT) composites prepared by free radical crosslinking copolymerization in water with a steady state fluorescence technique. Composite gels were prepared at room temperature with pyranine (Py) doped as a fluorescence probe. Drying experiments were performed in air at various MWNT contents by real time monitoring of the Py fluorescence intensity (I) which increased as the drying proceeded. The Stern-Volmer equation combined with the moving boundary diffusion model was used to explain the behavior of I during drying. It was observed that the desorption coefficient (D) increased as the temperature increased. Drying energies (Delta E) were measured for the drying processes for each MWNT content gel by using fluorescence gravimetrical and volumetric methods. It is understood that Delta E values decrease by increasing MWNT content until 1 wt % MWNT and then increase above the level of this threshold value. The energy of drying is strongly correlated with the MWNT content in the composite. Delta E drops to its lowest value at which conducting cluster starts to appear.
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    Book Part
    Graphene Oxide-Polyacrylamide Composites: Optical and Mechanical Characterizations
    (Wiley Blackwell, 2019) Evingür, G.A.; Pekcan, Önder
    Graphene oxide (GO) is a two-dimensional carbon material with similar one-atom thickness, and is a light material having extremely high strength and thermal stability [1]. Thus, GO is an efficient filler for the enhancement of the electrical, mechanical, and thermal properties of composite materials [2]. We focused on GO as a nanofiller in polyacrylamide hydrogels and GO-PAAm composites to investigate the optical and mechanical properties of the composites in this chapter. Gelation, fractal analysis, and optical energy band gap measurements of the composites were performed by UV-Vis and fluorescence spectroscopy techniques. The sol-gel phase transition and its universality were monitored and tested as a function of GO contents. The geometrical distribution of GO during gelation was presented by the fractal analysis. The fractal dimension of the composite gels was estimated based on the power law exponent values using scaling models. UV-Vis spectroscopy was used to investigate the behavior of optical band gap of GO-PAAm composites. On the other hand, mechanical measurements were employed to determine toughness and compressive modulus of the polymer composites before and after swelling. The behavior of compressive modulus was explained by the theory of rubber elasticity. © 2019 John Wiley & Sons, Inc. All rights reserved.
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    Article
    Citation - WoS: 17
    Citation - Scopus: 16
    Cation Effect on Slow Release From Alginate Beads: a Fluorescence Study
    (Springer/Plenum Publishers, 2014) Kaygusuz, Hakan; Erim, F. Bedia; Pekcan, Önder; Evingür, Gülşen Akin
    In this study spherical alginate beads containing pyranine (P-y) as a fluorescence probe were prepared by ionotropic gelation of a sodium alginate solution. The steady state fluorescence technique was used to study pyranine release from the alginate beads crosslinked with calcium barium and aluminum ions respectively. The slow release of P-y was observed with the time drive mode of the spectrophotometer at 512 nm. Fluorescence emission intensity (I-p) from P-y was monitored during the release process and the encapsulation efficiency (EE) of pyranine from the alginate beads was calculated. The Fickian Diffusion model was used to measure the release coefficients D-sl. It was seen that the slow release coefficients of pyranine from the alginate beads crosslinked with Ca2+ Ba2+ and Al3+ ions increased in the following order: D-sl (Al3+)> D-sl (Ca2+)> D-sl (Ba2+). In contrast the initial amount of pyranine and EE into the beads showed the reverse behavior.