Mehmet Önder Pekcan

This item is non-discoverable

Pekcan, Mehmet Önder

Name Variants

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

Job Title

Prof. Dr.

Email Address

pekcan@khas.edu.tr

ORCID ID

0000-0002-0082-8209

Scopus Author ID

35479982700

Full item page

Scholarly Output

116

Articles

98

Citation Count

0

Supervised Theses

0 Scholarly Output Search Results

Now showing 1 - 10 of 116

Citation Count: 1
Group Behaviour in Physical Chemical and Biological Systems
(Indıan Acad Scıences, 2014) Saçlıoğlu, Cihan; Pekcan, Önder; Nanjundiah, Vidyanand
Groups exhibit properties that either are not perceived to exist or perhaps cannot exist at the individual level. Such 'emergent' properties depend on how individuals interact both among themselves and with their surroundings. The world of everyday objects consists of material entities. These are ultimately groups of elementary particles that organize themselves into atoms and molecules occupy space and so on. It turns out that an explanation of even the most commonplace features of this world requires relativistic quantum field theory and the fact that Planck's constant is discrete not zero. Groups of molecules in solution in particular polymers ('sols') can form viscous clusters that behave like elastic solids ('gels'). Sol-gel transitions are examples of cooperative phenomena. Their occurrence is explained by modelling the statistics of inter-unit interactions: the likelihood of either state varies sharply as a critical parameter crosses a threshold value. Group behaviour among cells or organisms is often heritable and therefore can evolve. This permits an additional typically biological explanation for it in terms of reproductive advantage whether of the individual or of the group. There is no general agreement on the appropriate explanatory framework for understanding group-level phenomena in biology.
Citation Count: 3
Kinetic Models for the Dynamical Behavior of Polyacrylamide (paam)-Kappa (kappa C) Composite Gels
(Springer, 2015) Evingür, Gülşen Akın; Pekcan, Önder
A fluorescence method was employed for studying the drying and swelling of PAAm-kappa C composite gels which were formed from acrylamide (AAm) and N N'- methylenebisacrylamide (BIS) with various kappa-carrageenan (kappa C) contents by free radical crosslinking copolymerization in water. Composite gels were prepared at 80 A degrees C with pyranine (Py) as a fluorescence probe. Scattered light I (sc) and fluorescence emission intensities I (em) were monitored during drying and swelling of these gels. The fluorescence intensity of pyranine increased and decreased as drying and swelling time are increased respectively for all gel samples. The Stern-Volmer equation combined with moving boundary and Li-Tanaka models were used to explain the behavior of I (em) during drying and swelling processes respectively. It is found that the desorption coefficient D (d) decreased as kappa C contents were increased for a given temperature during drying. However the cooperative diffusion coefficient D (s) presented exactly the opposite case. Conventional gravimetrical and volumetric experiments were also carried out during drying and swelling of PAAm-kappa C composite gels. It was observed that D (d) and D (s) values measured with the fluorescence method were found to be much larger than they were measured with the conventional methods.
Citation Count: 3
Temperature Effect on the Elasticity of Acrylamide-N Copolymers
(Taylor & Francis Inc, 2018) Evingür, Gülşen Akin; Pekcan, Önder
Acrylamide (AAm) - N-isopropylacrylamide (NIPA) copolymers were prepared via free radical crosslinking copolymerization with various weight percentages (wt%) of AAm and NIPA. The temperature dependence of the compressive elastic modulus G and toughness U-TU- of the PAAm- NIPA copolymers due to a volume phase transition was found using a compressive testing technique. It was observed that the compressive elastic modulus increased comprehensively when the temperature was increased between 30 degrees C and 60 degrees C. The PAAm- NIPA copolymers presented higher values of the compressive elastic modulus than pure NIPA above the lower critical solution temperature (LCST) (NIPA exhibits a volume phase transition from hydrophilic to hydrophobic in water at 31 degrees C) and their compressive elastic modulus and toughness had a strong temperature dependence.
Citation Count: 1
Evaluation of the Fractal Dimension of Polyacrylamide During Gelation and Swelling
(Elsevier, 2021) Arda, Ertan; Kara, Selim; Pekcan, Önder; Gülşen, Akın-Evingür
[Abstract Not Available]
Citation Count: 3
Oxygen Diffusion Into Polymer-Clay Composite Films as a Function of Clay Content and Temperature
(Wiley-VCH Verlag GmbH, 2009) Uğur, Şaziye; Yargı, Önder; Elaissari, Abdelhamid; Pekcan, Önder
A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene-clay composite films as a function of clay content and temperature. The composite films were prepared from a mixture of surfactant-free pyrene-labeled polystyrene latexes and modified Na-montmorillonite clay of various compositions at room temperature. Diffusion measurements were performed with films at room temperature for seven different clay contents (0 5 10 20 30 50 and 60 wt.%). The diffusion coefficients of oxygen increased from 7.4 x 10(-10) to 26.9 x 10(-10) cm(2)s(-1) with increasing clay content. On the other hand diffusion measurements were performed over a temperature range Of 25-70 degrees C for 0 5 and 20 wt.% clay content films. The calculated diffusion activation energies decreased from 2.44 to 0.44 kcal/mol with increasing clay content. No clay content and temperature effects were observed on quenching rate constant and mutual diffusion coefficient values. The results showed that the diffusion coefficients are strongly dependent on both the temperature and clay content in the film.
Citation Count: 0
Fluorescence Study of Film Formation From Ps Latex-Tio2 Composites: Effects of Tio2 Content Film Thickness and Particle Size
(Amer Scientific Publishers, 2015) Ugur, Saziye; Sunay, M. Selin; Pekcan, Önder
Steady-state fluorescence (SSF) technique in conjunction with UV-visible (UVV) technique atomic force microscope (AFM) and scanning electron microscope (SEM) is used for studying film formation from TiO2 covered polystyrene (PS) latex particles. The effects of TiO2 content film thickness and PS particle size on film formation and structure properties of PS/TiO2 composites are studied. For this purpose in the first part two different sets of PS films with thicknesses of 5 and 20 mu m were prepared from pyrene-(P-) labeled PS particles (320 nm) and covered with various layers of TiO2 with the use of 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 show that film formation from PS latexes occurs on the top surface of PS/TiO2 composites and thus develop independent from TiO2 content for both film sets. However 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 show nonporous structure. In the second Part two film series were prepared from PS particles with diameters of 203 nm (SmPS) and 382 nm (LgPS) covered with different layers of TiO2 and annealed at elevated temperatures. Results reveal that SmPS/TiO2 films undergo complete film formation independent of the TiO2 content. However no film formation occurs above a certain TiO2 content in LgPS/TiO2 films. SEM images demonstrate that SmPS/TiO2 films have highly well-ordered microporous structures with increasing TiO2 content after extraction of PS polymer whereas LgPS/TiO2 composites show no porous structure for high TiO2 content. Our experiments also show that porous TiO2 films with different sizes could successfully be prepared with this technique.
Citation Count: 6
Effect of Calcium Ion Concentration on Small Molecule Desorption From Alginate Beads
(Taylor & Francis Inc, 2014) Evingür, Gülşen Akin; Kaygusuz, Hakan; Erim, F. Bedia; Pekcan, Önder
Spherical alginate beads were prepared by ionotropic gelation of sodium alginate through the use of calcium ions. Pyranine (Py) was added to the alginate solution as a small molecule probe for fluorescence studies. Desorption of Py in water from the alginate beads cross-linked with calcium ions was studied by using the steady state fluorescence technique. The fluorescence emission intensity (I) from Py was monitored during the desorption process at 512 nm using the time drive mode of the spectrofluorometer. The increase in I was attributed to Py release from the beads. The Fickian diffusion model was used to calculate the desorption coefficients D which were found to be increased up to 3% (w/v) CaCl2 concentration in the beads and then decreased with a further increase of CaCl2 content. On the other hand the encapsulation efficiency of Py in the calcium alginate beads presented the reverse behavior compared to D. It was observed that when the content of CaCl2 was increased the incubation time t(0) for the start of desorption increased.
Citation Count: 1
Gelation Electrical Conductivity and Elasticity of Pam- Mwnt
(Cambridge Univ Press, 2011) Evingür, Gülşen Akin; Pekcan, Önder
Polyacrylamide- Multiwalled carbonnanotube (PAM- MWNT) composites were prepared via free radical crosslinking copolymerization with different amounts of MWNT varying in the range between 0.1 and 15 wt. %. PAM- MWNT composite gels were characterized by fluorescence dielectric spectroscopy and the tensile testing technique. A small content of doped nanotubes dramatically changed gelation time conductivity and young modulus respectively. The gel fraction exponent ? of PAM- MWNT composite gels were measured for various monomer and MWNT concentrations and observed that the gel fraction exponent ? agrees best with the percolation theory for various amounts of PAM- MWNT. These polymer systems which are initially of an isolator character are doped with carbon nanotubes of nano dimensions and when the amount of this addition exceeds a critical value (0.3 wt. % MWNT) known as the percolation threshold then composite gel systems with carbon nanotubes become electrically conducting structures with a critical exponent around r=2 which is close to the theoretical prediction of this value in 3D percolated system as known random resistor network. The observed elasticities are decreased above 3 wt. %MWNT with critical exponent around y=0.72 which is indicative of a transition from liquid-like to solid-like viscoelastic behavior. © 2011 Materials Research Society.
Citation Count: 6
The Ws(2)dependence on the Elasticity and Optical Band Gap Energies of Swollen Paam Composites
(Sage Publications, 2020) Evingür, Gülsen Akın; Sağlam, Nafia Alara; Çimen, Büşra; Uysal, Bengü Özuğur; Pekcan, Önder
New generation nano-filler polymer composites have many applications including biomedical, electronic and maritime related applications because of their mechanical, electronic and optical properties. The properties of composites were investigated as a function of nano-filler content. Among these, tungsten disulfide (WS2) has the potential to be used as a component in electronic devices owing to its high electron mobility and easily tunable optical band gap energy. Tungsten disulfide (WS2)- Polyacrylamide (PAAm) composite was prepared using free radical co-polymerization and wet laboratory methods with WS(2)content. Composites were characterized for mechanical and optical properties using an Elasticity Instrument and UV-vis Spectrophotometer, respectively. Elastic modulus was modeled by a statistical thermodynamics model. Tauc's and Urbach's Tail model for direct transition were used to model for the optical band gap. In this study, the swelling and WS(2)effect on the optical band gap and elasticity of WS2- PAAm composites were investigated. It was observed that the elasticity presented a reversed behavior of optical band gap energies with respect to WS(2)content. For the applications of nano-filler doped polymer composites in flexible electronic devices, WS(2)content strongly influences the mechanical and optical properties.
Citation Count: 81
Electrical and Optical Percolations of Polystyrene Latex-Multiwalled Carbon Nanotube Composites
(Academic Press Inc Elsevier Science, 2010) Kara, Selim; Arda, Ertan; Dolastir, Fahrettin; Pekcan, Önder
Electrical conductivity and optical transmittance properties of polystyrene (PS)-multiwalled carbon nanotube (MWCNT) composite films were investigated. Composite films were prepared by mixing of various mass fractions of MWCNT in PS-water dispersions. After water evaporates powder composite films were annealed at 175 degrees C above the glass transition of PS for 20 min. Photon transmission and two point probe resistivity techniques were employed to determine the variations of the optical and the electrical properties of composites. Transmitted light intensity I(tr) and surface resistivity R(s) were monitored as a function of MWCNT mass fraction (M). It was observed that both the surface resistivity and the optical transparency were decreased by increasing the amount of MWCNT added to the polymeric system. Conductivity and optical results were interpreted according to the classical and site percolation theory respectively. The electrical (sigma) and the optical (op) percolation threshold values and critical exponents were calculated as M(sigma) = 1.8 wt.% M(op) = 0-0.13 wt.% and beta(sigma) = 2.25 beta(op) = 0.32 respectively. (C) 2010 Elsevier Inc. All rights reserved.