Browsing by Author "Pekcan, Önder"
Now showing items 1-20 of 101
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A Fluorescence Study on Swelling of Hydrogels (PAAm) at Various Cross-Linker Contents
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Publisher and Date:(Wiley, 2009)Disk-shaped acrylamide (AAm) gels were prepared from AAm with various NN'-methylenebisacrylamide (Bis) contents as cross-linker in the presence of ammonium persulfate as an initiator by free-radical cross-linking copolymerization in water. Polyacrylamide (PAAm) gels were dried before using for swelling experiments. Steady-state fluorescence spectrometer was employed during the swelling of PAAm hydrogels in water. Pyranine was introduced as a fluorescence probe. Fluorescence intensity of pyranine ...
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Application of epidemic models to phase transitions
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Publisher and Date:(Taylor & Francis Ltd, 2012)The Susceptible-Infected-Recovered (SIR) and Susceptible-Exposed-Infected-Recovered (SEIR) models describe the spread of epidemics in a society. In the typical case, the ratio of the susceptible individuals fall from a value S-0 close to 1 to a final value S-f, while the ratio of recovered individuals rise from 0 to R-f = 1 - S-f. The sharp passage from the level zero to the level R-f allows also the modeling of phase transitions by the number of "recovered" individuals R(t) of the SIR or SEIR ...
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Cation Effect on Slow Release from Alginate Beads: A Fluorescence Study
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Publisher and Date:(Springer/Plenum Publishers, 2014)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 ...
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Comparison of cation effects on phase transitions of kappa and iota carrageenan
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Publisher and Date:(European Polymer Federation, 2010)Phase transitions of kappa and iota carrageenan in KCl NaCl and CaCl2 solutions were separately studied during heating and cooling processes by using fluorescence technique. Scattered light I-SC and fluorescence intensity I was monitored against temperature to determine the critical transition temperatures and exponents. Kappa and iota carrageenans with monovalent (KCl NaCl) salt system presented only coil to double helix (c-h) and double helix to coil (h-c) transitions upon cooling and heating ...
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Conductivity percolation of carbon nanotubes (CNT) in polystyrene (PS) latex film
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Publisher and Date:(Canadian Science Publishing Nrc Research Press, 2010)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 ...
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Conductivity Percolation of Carbon Nanotubes in Polyacrylamide Gels
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Publisher and Date:(Intech Europe, 2011)
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Critical Exponents of Gelation and Conductivity in Polyacrylamide Gels Doped by Multiwalled Carbon Nanotubes
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Publisher and Date:(Taylor & Francis Ltd, 2010)Polyacrylamide (PAM) doped by multiwalled carbon nanotube (MWNT) gels were prepared with different amounts of MWNTs varying in the range between 0.1 and 15 wt%. The PAM-MWNT composite gels were characterized by the steady state fluorescence technique (SSF). The alternative electrical conductivity (AC) of PAM-MWNT composite gels was measured by the dielectric spectroscopy technique. Observations around the gel point t(gel) for PAM-MWNTs composite gels showed that the gel fraction exponent beta ...
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Critical Exponents of Kappa Carrageenan in the Coil-Helix and Helix-Coil Hysteresis Loops
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Publisher and Date:(Taylor & Francis Inc, 2009)The steady-state fluorescence technique was used to study coil-helix (sol-gel) and helix-coil (gel-sol) transitions of the kappa carrageenan-water system with various carrageenan contents. Fluorescence (I) and scattered light (I-sc) intensities were measured against temperature to determine critical phase transition temperatures and exponents. It was observed that the coil-helix transition temperatures T-ch were much lower than the helix-coil (T-hc) transition temperatures due to the hysteresis ...
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Critical Exponents of Photoinitiated Gelation at Different Light Intensities
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Publisher and Date:(Taylor & Francis Inc, 2009)A photo-differential scanning calorimetric (Photo-DSC) technique was used to study the photoinitiated radical polymerization of a 75% epoxy diacrylate (EA) and 25% tripropyleneglycoldiacrylate (TPGDA) mixture with 2-mercaptothioxanthone (TX-SH) as photoinitiator by using different light intensities. Photopolymerization reactions were carried out under identical conditions of temperature and initiator concentration. It was observed that all conversion curves during gelation at various Might intensities ...
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Critical Exponents of Thermal Phase Transitions of kappa-Carrageenan in Various Salt Solutions
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Publisher and Date:(Wiley-VCH Verlag GmbH, 2009)The steady state fluorescence (SSF) technique was employed to study the phase transitions Of kappa-carrageenan in NaCl and KCl solutions. Pyranine was used as a fluorescence probe for monitoring these transitions. Scattered light I(sc) and fluorescence intensity 1 was monitored against temperature to determine transition temperatures and exponents. It was observed that transition temperatures are strongly correlated with the NaCl and KCl contents. The weight-average degree of polymerization DP(w) ...
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Critical phenomenon during photoinitiated gelation at different temperatures: A Photo-DSC study
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Publisher and Date:(Elsevier Science, 2011)The behaviour of photoinitiated radical polymerization of an 80 wt% epoxy diacrylate (EA) and 20 wt% tripropyleneglycoldiacrylate (TPGDA) mixture with 2-mercaptothioxanthone (TX-SH) photoinitiator was studied at different temperatures by using photo-differential scanning calorimetric (Photo-DSC) technique. All photopolymerization reactions were carried out under the same conditions. It was observed that all conversion curves during gelation at different temperatures present nice sigmoidal behaviour ...
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Diffusion energies of oxygen diffusing into polystyrene (PS)/poly (N-isopropylacrylamide) composites
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Publisher and Date:(Wiley-Blackwell, 2012)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 ...
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Drying of Polyacrylamide Composite Gels Formed with Various Kappa- Carrageenan Content
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Publisher and Date:(Springer/Plenum Publishers, 2011)Drying of polyacrylamide (PAAm)-kappa-carrageenan (kappa C) composite gels were monitored by using steady-state fluorescence technique. Disc shaped gels were formed from acrylamide (AAm) and N N'- methylenebisacrylamide(Bis) with various kappa- carrageenan (kappa C) contents by free radical crosslinking copolymerization in water. Pyranine (P) was doped as a fluorescence probe and scattered light I (sc) and fluorescence intensities I were monitored during drying of these gels. It is observed that ...
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Drying of polyacrylamide-multiwalled carbon nanotube (MWNT) composites with various MWNTs contents: a fluorescence study
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Publisher and Date:(Walter De Gruyter Gmbh, 2013)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 ...
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Drying process in vapor swollen heterogels
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Publisher and Date:(Springer, 2010)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 ...
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Effect of Calcium Ion Concentration on Small Molecule Desorption from Alginate Beads
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Publisher and Date:(Taylor & Francis Inc, 2014)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 ...
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EFFECT OF CONTENT AND TEMPERATURE ON THE PHASE TRANSITIONS OF POLYMER COMPOSITES DOPED BY KAPPA CARRAGEENAN AND ALGINATE
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Publisher and Date:(Elsevier Academic Press Inc, 2016)
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Effect of LCST on the swelling of PAAm-NIPA copolymers: a fluorescence study
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Publisher and Date:(Springer, 2012)Temperature sensitive copolymers were prepared by free radical crosslinking copolymerization in aqueous solution with different molar percentage of N-isopropylacrylamide (NIPA) and acrylamide (AAm) monomers. NN'-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as a crosslinker and an initiator respectively. The steady-state fluorescence (SSF) technique was used to determine the low critical phase transition temperature (LCST) for PAAm-NIPA copolymers. Swelling experiments ...
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Effect of multiwalled carbon nanotube (MWNT) on the behavior of swelling of polyacrylamide-MWNT composites
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Publisher and Date:(Sage Publications Ltd, 2014)The purpose of this paper is to discuss the role of multiwalled carbon nanotube in the swelling of polyacrylamide-multiwalled carbon nanotube composites. Swelling experiments were performed in water at various temperatures by real-time monitoring of the decrease in pyranine (Py) and emission light intensity (I-em). The Stern-Volmer equation is modified for low-quenching efficiencies to interpret the behavior of pyranine intensity during the swelling of polyacrylamide-multiwalled carbon nanotube ...
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Effect of temperature and graphene oxide on the swelling of PAAm-GO composite gels
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Publisher and Date:(Avestia Publishing, 2019)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 PAAm-GO composites to investigate the effect of temperature and graphene oxide on the swelling. Polyacrylamide (PAAm) hydrogels have ...
