Browsing by Author "Kara, Selim"
Now showing items 1-14 of 14
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A comparison of fluorescence and UV-visible spectrometry techniques for thermal phase transitions of agarose gels
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Publisher and Date:(Springer, 2015)In this study thermoreversible phase transitions of high (HMP) and low (LMP) melting point agarose gels were investigated by using the UV-vis and fluorescence spectroscopy techniques. Pyranine was added to the aqueous solution of agarose as a fluorescence-probe. Transmitted light (I (tr)) and fluorescence emission (I (fl)) intensities from the gel samples with different agarose concentrations were monitored during the heating (gel-sol) and cooling (sol-gel) processes. For the both techniques gel-sol ...
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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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Effects of GNP addition on optical properties and band gap energies of PMMA films
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Publisher and Date:(Wiley, 2019)In this study the effects of graphene nanoplatelet (GNP) doping on the optical parameters (absorption coefficient alpha and extinction coefficient k) and the optical transition energies (optical band gap and Urbach energies) of poly(methyl methacrylate)/graphene nanoplatelet (PMMA/GNP) composite films were studied. PMMA/GNP composite films with various GNP mass fractions were prepared by spin coating technique. The absorbance (A) changes of the prepared composites were measured by using UV-Vis ...
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Electrical and optical percolations of polystyrene latex-multiwalled carbon nanotube composites
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Publisher and Date:(Academic Press Inc Elsevier Science, 2010)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 ...
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Electrical optical and fluorescence percolations in P(VAc-co-BuA)/MWCNT composite films
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Publisher and Date:(Taylor & Francis Ltd, 2013)Effects of multiwall carbon nanotube (MWCNT) addition on the electrical conductivities optical transparencies and fluorescence emissions of poly(vinyl acetate-co-butyl acrylate) (P(VAc-co-BuA))/MWCNT composite films were studied. Optical transmission fluorescence emission and two point probe resistivity techniques were used to determine the variations of the optical fluorescence and electrical properties of the composites respectively. Transmitted photon intensity (I-tr) fluorescence emission ...
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Epidemic models for phase transitions: application to a physical gel
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Publisher and Date:(Taylor & Francis Ltd, 2017)Carrageenan gels are characterized by reversible sol-gel and gel-sol transitions under cooling and heating processes and these transitions are approximated by generalized logistic growth curves. We express the transitions of carrageenan-water system as a representative of reversible physical gels in terms of a modified Susceptible-Infected-Susceptible epidemic model as opposed to the Susceptible-Infected-Removed model used to represent the (irreversible) chemical gel formation in the previous work. ...
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Evaluation of the fractal dimension of polyacrylamide during gelation and swelling
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Publisher and Date:(Elsevier, 2021)
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Fractal Dimensions of kappa-Carrageenan Gels during Gelation and Swelling
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Publisher and Date:(Taylor & Francis Inc, 2018)A photon scattering technique for research on the sol-gel and gel-sol transitions in kappa-carrageenan-water systems with various carrageenan contents (CC) was utilized for characterizing the fractal dimensions during gelation and swelling. It was observed that the scattered photon intensity I-sc increased at all temperatures with an increase in the CC when I-sc was monitored against temperature. Additionally the sol-gel transition temperatures were found to be much lower than the gel-sol transition ...
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GELATION MECHANISMS
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Publisher and Date:(World Scientific Publ Co Pte Ltd, 2012)In this paper, we survey the gelation mechanisms for various polymeric systems which are classified by the type and the strength of the cross-linkages. These are the "irreversible" gels that are cross-linked chemically by covalent bonds and the "reversible" gels that are cross-linked physically by hydrogen or ionic bonds and by the physical entanglement of polymer chains. Some of the natural polymer gels fall into the class of physical gels, among which the red algae that has attracted attention ...
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Mathematical Characterization of Thermo-reversible Phase Transitions of Agarose Gels
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Publisher and Date:(Taylor & Francis Inc, 2018)The thermal phase transition temperatures of high (HMP) and low melting point (LMP) agarose gels were investigated by using UV-vis spectroscopy techniques. Transmitted light intensities from the gel samples with different agarose concentrations were monitored during the heating (gel-sol) and cooling (sol-gel) processes. It was observed that the transition temperatures T-m defined as the location of the maximum of the first derivative of the sigmoidal transition paths obtained from the UV-vis ...
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Sorption and Desorption of PVA-Pyrene Chains in and out of Agarose Gel
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Publisher and Date:(Springer/Plenum Publishers, 2012)In situ steady-state fluorescence (SSF) measurement technique was applied to investigation of pyrene labeled Poly(vinyl alcohol) (PVA-Py) molecules diffusion in and out of agarose gels. Gel samples with four different concentration of agarose were prepared. PVA-Py was synthesized by "click" chemistry method and dissolved in water to use in diffusion experiments. The results were analyzed by using Fickian type diffusion model, and it was found that sorption and desorption processes of PVA-Py molecules ...
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Study of Thermal Phase Transitions in Iota Carrageenan Gels via Fluorescence Technique
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Publisher and Date:(Wiley-Blackwell, 2011)The effect of carrageenan concentration on thermal phase transitions of the iota carrageenan gels was investigated by using fluorescence technique. During heating and cooling processes scattered light I(sc) and fluorescence intensity I(p) were monitored against temperature to investigate phase transitions. Transition temperatures from the derivative of the transition paths were determined. Two regions were observed during the heating and cooling processes. At the first step of the heating dimers ...
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Thermal Phase Transitions of Agarose in Various Compositions: A Fluorescence Study
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Publisher and Date:(Springer/Plenum Publishers, 2011)The effect of agarose content on thermal phase transitions of the agarose gels was investigated by using Steady State Fluorescence (SSF) method. Scattered light I(sc) and fluorescence intensity I(fl) were monitored against temperature during heating and cooling processes to investigate phase transitions. Two regions were observed during the heating and cooling processes. At the high temperature region double helix to coil (h-c) transition took place. However during the cooling process coil to ...
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Thermal Phase Transitions of IOTA Carrageenan in CaCl2 Solutions: A Fluorescence Study
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Publisher and Date:(Taylor & Francis Inc, 2011)The fluorescence technique was employed to study thermal phase transitions of iota (-) carrageenan (IC) in CaCl2 solution. IC gels underwent coil to double helix (c-h) and double helix to dimer (h-d) transitions upon cooling. Upon heating IC gels presented dimer to double helix (d-h) and double helix to coil (h-c) transitions showing hysteresis types of transition paths. Scattered light Isc and fluorescence intensity I were monitored against temperature to determine phase transitions. Transition ...
