Browsing by Author "Uğur, Şaziye"

Now showing 1 - 14 of 14

Citation Count: 21
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.
Citation Count: 9
Film Formation of Nano-Sized Hard Latex (PS) in Soft Polymer Matrix (PBA): An Excimer Study
(John Wiley & Sons Inc, 2010) Uğur, Şaziye; Sunay, Selin; Pekcan, Önder
This work reports steady state fluorescence (SSF) technique for studying film formation from pyrene (P)labeled nano-sized polystyrene (PS) and poly(n-butyl acrylate) (PBA) hard/soft latex blends. Blend films were prepared from mixtures of PS and PBA in dispersion. Eight different blend films were prepared in various hard/soft latex compositions at room temperature and annealed at elevated temperatures above glass transition temperature (T(g)) of polystyerene. Monomer (I(P)) and excimer (I(E)) intensities from P was measured after each annealing step to monitor the stages of film formation. The evolution of transparency of latex films was monitored using photon transmission intensity I(tr). Film morphologies were examined by atomic force microscopy (AFM). The results showed that as the amount of hard component (PS) in the blend is decreased a significant change occurred in both I(E)/I(P) and I(tr) curves at a certain critical weight fraction (50 wt%) of PS hard latex. Two distinct film formation stages which are named as void closure and interdiffusion were seen in (I(E)/I(P)) data above this fraction. However below 50 wt% PS no film formation was observed. AFM pictures also confirmed these findings. Void closure and interdiffusion stages for (50-100) wt% range of PS were modeled and related activation energies were determined. There was no observable change in activation energies confirming that film formation behavior is not affected by varying the blend composition in this range. POLYM. COMPOS. 31:16111619 2010. (C) 2009 Society of Plastics Engineers
Citation Count: 2
Film Formation of Poly (methyl methacrylate) Latex With Pyrene Functional Poly (divinylbenzene) Microspheres Prepared by Click Chemistry
(Wiley-Blackwell, 2011) Uğur, Şaziye; Yargı, Önder; Durmaz, Yasemin Yuksel; Karagöz, Bünyamin; Bıçak, Niyazi; Yağci, Yusuf; Pekcan, Önder; Pekcan, Önder
This work reports on the application of steady state fluorescence (SSF) technique for studying film formation from poly(methyl methacrylate) (PMMA) latex and poly(divinylbenzene) (PDVB) microsphere composites. Pyrene (P) functionalized PDVB cross-linked spherical microspheres with diameters of 2.5 mu m were synthesized by using precipitation polymerization technique followed by click coupling reaction. The diameter of the PMMA particles prepared by emulsion polymerization were in the range of 0.5-0.7 mu m. PMMA/PDVB composite films were then prepared by physically blending of PMMA latex with PDVB microspheres at various composition (0 1 3 5 10 20 40 and 60 wt%). After drying films were annealed at elevated temperatures above T(g) of PMMA ranging from 100 to 270 degrees C for 10 min time intervals. Evolution of transparency of the composite films was monitored by using photon transmission intensity I(tr). Monomer (I(P)) and excimer (I(E)) fluorescence intensities from P were measured after each annealing step. The possibility of using the excimer-to-monomer intensity ratio (I(E)/I(P)) from PDVB microparticles as a measure of PMMA latex coalescence was demonstrated. Diffusion of the PMMA chains across the particle-particle interfaces dilutes the dyes increasing their separation. The film formation stages of PMMA latexes were modeled by monitoring the I(E)/I(P) ratios and related activation energies were determined. There was no observable change in activation energies confirming that film formation behavior is not affected by varying the PDVB composition in the studied range. SEM images of PMMA/PDVB composites confirmed that the PMMA particles undergo complete coalescence forming a continuous phase in where PDVB microspheres are dispersed. POLYM. COMPOS. 32: 869-881 2011. (C) 2011 Society of Plastics Engineers
Citation Count: 4
Fluorescence quenching method for monitoring oxygen diffusion into PS/CNT composite films
(Elsevier Science SA, 2013) Yargı, Önder; Uğur, Şaziye; Pekcan, Önder
Oxygen permeabilities of nanocomposite films consisting of multi wall carbon nanotubes (MWNT) and polystyrene (PS) were determined to investigate the oxygen diffusion depending on MWNT and temperature. A method which is based on quenching of an excited phosphorescent by oxygen was applied for the measurements. The composite films were prepared from mixtures of (MWNT) and surfactant-free pyrene (P)-labeled (PS) latexes of various compositions at room temperature. These films were then annealed at 170 degrees C which is well above the glass transition (T-g) temperature of polystyrene for 10 min. Diffusion experiments were performed for eight films with different MWNT content (0 1.5 3 5 10 15 25 and 40 wt%) to evaluate the effect of MWNT content on oxygen diffusion. Diffusion coefficients were found to increase from 1.1 x 10(-12) to 41 x 10(-12) cm(2) s(-1) with increasing MWNT content. On the other hand to examine the effect of temperature on oxygen diffusion diffusion measurements were performed over a temperature range of 24-70 degrees C for three different MWNT contents (3 15 and 40 wt%) within the films. The results indicated that the values of the diffusion coefficient D are strongly dependent on both temperature and MWNT content in the film. It was also observed that the diffusion coefficients obey Arrhenius behavior from which diffusion energies were determined which increased with increase of MWNT content and temperature. (C) 2013 Elsevier B.V. All rights reserved.
Citation Count: 0
Fluorescence study of effect of particle size in PS latex/Al2O3 nanocomposite films
(MANEY PUBLISHING, 2015) Uğur, Şaziye; Sunay, M. Selin; Pekcan, Önder
Steady state fluorescence and BioUV-Visible techniques were used to study film formation of polystyrene (PS) latex and Al2O3 composites depending on PS particles size and Al2O3 content. Two film series (SmPS/Al2O3 and LgPS/Al2O3) were prepared covering PS sphere (SmPS: 203 nm
Citation Count: 1
Fluorescence study of film formation from PS/Al2O3 nanocomposites
(Elsevier Science, 2014) Pekcan, Önder; Uğur, Şaziye; Sunay, M. Selin
Steady state fluorescence (SSF) and UV-vis (UVV) techniques were used to study the film formation behavior of pyrene (P) labeled polystyrene (PS) latex and Al2O3 (PS/Al2O3) composites depending on PS particles size and Al2O3 content. The close-packed arrays of PS spheres (SmPS: 203 nm ; LgPS: 382 nm) templates on clean glass substrates were covered with various layers of Al2O3 by dip-coating method. Two different film series (SmPS/Al2O3 and LgPS/Al2O3) were prepared in various Al2O3 layer content. The film formation behavior of these composites were studied by annealing them at a temperature range of 100-250 degrees C and monitoring the scattered light intensity (I-sc) fluorescence intensity (I-p) from P and transmitted light intensity (I-tr) through the films after each annealing step. Optical results indicate that classical latex film formation was occurred for all Al2O3 content films and film formation process was unaffected by the Al2O3 content for both film series. Extraction of PS template produced highly ordered porous structures for high Al2O3 content in both film series. SEM images showed that the pore size and porosity could be easily tailored by varying the PS particle size and the Al2O3 content. (C) 2014 Elsevier B.V. All rights reserved.
Citation Count: 0
Measurement of oxygen diffusion in PS/PNIPAM films using fluorescence quenching
(Taylor & Francis Ltd, 2015) Yargı, Önder; Pekcan, Önder; Uğur, Şaziye
The diffusion of oxygen into pyrene labelled polystyrene (PS) latex/poly(N-isopropylacrylamide) (PNIPAM) composite films (PS/PNIPAM) was studied based on PS content with the use of fluorescence quenching method. Fluorescence experiments were carried out on composite films containing pyrene as a sensor dye. The Stern-Volmer equation for fluorescence quenching is combined with Fick's law for diffusion to derive mathematical expressions. Diffusion coefficients (D) were produced and found to be decreased with increasing PS content. This decrease was explained with the formation of a tortuous path for diffusing gas molecules which extends the diffusion path of oxygen in the films. In addition at high PS content two different D values were obtained which were attributed to the existence of two different areas in the composite films.
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: 10
Oxygen diffusion into polystyrene-bentonite films
(Elsevier, 2009) Uğur, Şaziye; Yargı, Önder; Pekcan, Önder
A simple fluorescence technique is proposed for the measurement of the diffusion coefficient of oxygen into polystyrene-clay composite films. The composite films were prepared from the mixture of surfactant-free pyrene (P)-labeled polystyrene latexes (PS) and modified bentonite (MNaLB) at various compositions at room temperature. These films were annealed at 200 degrees C above the glass transition (T-g) temperature of polystyrene for 10 min. Oxygen diffusion into the films was monitored with steady state fluorescence (SSF) measurements. Measurements were performed at room temperature for different film compositions (0 510 2030 50 and 60 mass% modified bentonite) films to evaluate the effect of MNaLB content on oxygen diffusion. The diffusion coefficient D of oxygen was determined by the fluorescence quenching method by assuming Fickian transport and increased from 7.4 x 10(-10) to 26.9 x 10(-10) cm(2) s(-1) with increasing MNaLB content. This increase in D value was explained by formation of microvoids in the film. These voids are large enough to contribute to the penetration of oxygen molecules through the films. The montmorillonite content did not affect the quenching rate constant k(q) and mutual diffusion coefficient D-m values. (C) 2008 Elsevier B.V. All rights reserved
Citation Count: 5
Particle Size Effect on the Film-Forming Process of PS/PBA Composite Latexes
(John Wiley & Sons Inc, 2010) Uğur, Şaziye; Sunay, M. Selin; Elaissari, Abdelhamid; Pekcan, Önder
In this work the effect of hard particle size and blend ratio on the film formation behavior of hard polystyrene (PS) and soft poly(n-butyl acrylate) (PBA) latex blends was studied by means of steady-state fluorescence and UV-visible techniques in conjunction with atomic force microscopy. Three different sets of latexes were synthesized: PBA latex (diameter 97 nm) pyrene (P)-labeled large PS (LgPS
Citation Count: 6
Percolation and Film Formation Behaviors of MWNT/PS Nanocomposites
(Elsevier Science Bv, 2011) Uğur, Şaziye; Yargı, Önder; Pekcan, Önder
This study involves the investigation of film formation and electrical conductivity properties of polystrene (PS) latex/multi-walled Carbon nanotube (MWNT) composites. Films prepared from PS/MWNT mixtures with different MWNT content were separately annealed above glass transition temperature of PS. Film formation stages of PS/MWNT composites were followed by monitoring the change in transmitted light intensity I-tr. The surface conductivity of films was found to increase dramatically above 4 wt% MWNT following the percolation theory. The conductivity scales with the mass fraction of MWNT as a power law with exponent 2.27 extremely close to the value of 2.0 predicted by percolation theory. (C) 2011 Published by Elsevier Ltd. Selection and peer-review under responsibility of ICM11
Citation Count: 0
Polymer-Ceramic Nanocomposites
(Spie-Int Soc Optical Engineering, 2009) Pekcan, Önder; Uğur, Şaziye
Steady state fluorescence (SSF) and photon transmission (PT) techniques were used for studying film formation from TiO2 and Al2O3 covered polystyrene (PS) latex particles. These films were annealed at elevated temperatures in 10 min time intervals above glass transition (T-g) temperature of polystyrene. Fluorescence emission I-P and transmitted photon I-tr intensities were measured after each annealing step to monitor the stages of film formation. Films present dramatic increase in both I-tr and I-P above the certain onset temperature called minimum film forming temperature T-0. Dissolution of annealed PS film with high TiO2 content presented a nice ordered nano-sized ceramic structure which may predict the construction of nano-layer photonic crystals. It was observed that latex particles are encapsulated above a critical Al2O3 content of 33 wt% which corresponds to the critical occupation probability of p(c)=0.33 at which the film obey the site-percolation model with a critical exponent of 0.45.
Citation Count: 5
Temperature Dependence of Oxygen Diffusion into Clay-Doped PS Films
(John Wiley & Sons Inc, 2010) Uğur, Şaziye; Yargı, Önder; Pekcan, Önder
Fluorescence technique was employed for the measurement of the diffusion coefficient of oxygen into polystyrene (PS) latex/modified Na-activated bentonite (MNaLB) clay composite films. Three different MNaLB content (0 5 and 20 wt%) composite films were prepared from PS/MNaLB mixtures by annealing them at 200 degrees C above the glass transition temperature of PS for 10 min. To determine the diffusivity of oxygen in PS/MNaLB composite films diffusion measurements were performed over the temperature range from 25 to 70 degrees C. Pyrene (P) was used as the fluorescent agent. The diffusion coefficients (D) of oxygen were determined by combining the fluorescence quenching method with Fickian transport model and were found as a function of temperature for each MNaLB content film. The results showed that D values are strongly dependent on both temperature and clay content in composite film. It was also observed that D coefficients obey Arrhenius behavior from where diffusion activation energies were measured. POLYM. COMPOS. 31:77-82 2010. (C) 2009 Society of Plastics Engineers
Citation Count: 4
Temperature dependence of oxygen diffusion into polymer/carbon nanotube composite films
(Wiley-Blackwell, 2012) Yargı, Önder; Uğur, Şaziye; Pekcan, Önder
This study examines the transport properties of polystyrene (PS)/multiwalled carbon nanotube (MWNT) composite films taking into consideration both MWNT composition and temperature via fluorescence technique. Three different (3 15 and 40 wt%) MWNT content films were prepared from PS/MWNT mixtures by annealing them at 170 degrees C above the glass transition temperature of PS for 10 min. The diffusivity of the PS/MWNT composite was determined by performing oxygen (O2) diffusion measurements within a temperature range of 24 to 70 degrees C for each film and pyrene (P) was used as the fluorescent probe. The diffusion coefficients (D) of oxygen were determined by the fluorescence quenching method assuming Fickian transport. Results indicated that D values are strongly dependent on both temperature and the MWNT content in the film and it was also observed that D coefficients obey Arrhenius behavior from which diffusion energies were produced and increased along with increases of MWNT content. POLYM. ENG. SCI. 2012. (C) 2011 Society of Plastics Engineers