Person: TAV, CUMALİ
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TAV
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CUMALİ
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Publication Metadata only Viscous Behavior of PS, PP, and ABS in Terms of Temperature and Pressure-Dependent Hole Fraction(JOHN WILEY & SONS INC, 2010) TAV, CUMALİ; Akdeniz, Guelsuem; Yahsi, Ugur; Tav, CumaliWe have developed a zero-shear viscous model in terms of temperature- and pressure-dependent hole fraction computed from Simha-Somcynsky Hole Theory. This model successfully interprets the viscosity data of PS, PP, and ABS as a function of hole fraction for a broad range of temperature and pressure. We have also introduced and discussed a new term: Viscoholibility; the derivative of logarithm of viscosity with respect to hole fraction. When the hole fraction takes highest available value, the viscoholibility approaches asymptotically to a constant value by which the viscosity changes linearly with the hole fraction. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 117: 110-113,2010Publication Metadata only Linking the viscous and vacancy behavior of mixtures of high-molecular-weight hydrocarbons(SPRINGER/PLENUM PUBLISHERS, 2006) TAV, CUMALİ; Sahin, F.; Tav, C.; Yahsi, U.A zero-shear viscosity model has now been extended to mixtures of three-branch alkanes with and without cyclopentyl or cyclohexyl attachments. The model links the equilibrium theory of Simha-Somcynsky (SS) statistical thermodynamics of liquids and the Eyring significant structure (ESS) transport theory. The predicted quantity of the hole fraction as a measure of the free volume, computed from the SS equation of state, plays a primary role in the approach to combine both theories. Experimental PVT eta data from 310 to 408 K and 0.1 to 344.5 MPa have been used. The proportionality constant of the activation energy and the transmission coefficient have been calculated for each species separately, and they are in the expected trend with the fraction of mixtures. Satisfactory agreement in the prediction of viscosity from the hole fraction has been obtained. The volumetric and viscous data of physical mixtures are predicted from and compared with their chemical correspondence.Publication Metadata only Ionic conductivity of PVdF-co-HFP/LiClO4 in terms of free volume defects probed by positron annihilation lifetime spectroscopy(TAYLOR & FRANCIS LTD, 2019) TAV, CUMALİ; Yahsi, Ugur; Deligoz, Huseyin; Tav, Cumali; Ulutas, Kemal; Deger, Deniz; Yilmazturk, Serpil; Erdemci, Gonca; Coskun, Bilgehan; Yilmazoglu, Mesut; Yakut, SahinPolymers based on ionic conducting materials have important interest because of their potential applications in polymer electrolytes and membranes for fuel cell application. PVdF-co-HFP poly(viniliden-co-hexafluoropropylene) was chosen as a polymer matrix because of its high ionic conductivity and better mechanical properties. Polymer matrix composites were prepared with various amounts of LiClO4 salt by a solution casting method. The sample-ionic conductivity measurements were recorded by AC impedance analyzer at different frequencies from 0.1 Hz to 20 MHz and at different temperatures from 273 to 373 K. The changes of nanoscopic free volume and free volume fraction in these materials were investigated in terms of temperature from 273 to 373 K using Positron Annihilation Lifetime Spectroscopy (PALS) and Simha-Somcynsky (SS) Hole Theory. The free volume had a bump at about 3% in weight percentage of the salt and there is a slight increase after 10%. The effects of weight percentages of LiClO4 and temperature were investigated. The mechanism of the ac ionic conductivity was presented in terms of the free volume models, however thermo-occupancy function justifies the best accurate representation of the data.Publication Metadata only On the Ionic Conductivity of Polymer Electrolytes in Terms of Hole Fraction(JOHN WILEY & SONS INC, 2008) TAV, CUMALİ; Yahsi, Ugur; Ulutas, Kemal; Tav, Cumali; Deger, DenizA theoretical model to interpret the conductivity of ions through polymer electrolytes is established in terms of the temperature and pressure-dependent hole fraction computed from Simha-Somcynsky hole theory. The model successfully linearizes the logarithm of PPG and PEG conductivity data with NaCF3SO3 in a 20:1 ratio for a broad range of temperature and pressure. The conductivity parameter and transmission coefficient with an additive hole fraction constant are discussed and compared for both species. The derivative of the logarithm of conductivity with respect to the hole fraction decreases inversely with the hole fraction and saturates at about 0.08 and 0.12 hole fractions for PPG and PEG, respectively. (C) 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 46: 2249-2254, 2008Publication Open Access Effect of Free Volume on Curcumin Release from Various Polymer-Based Composite Films Analyzed Using Positron Annihilation Lifetime Spectroscopy(MDPI, 2021-09-29) TAV, CUMALİ; Rhim, Jong-Whan; Kuzeci, Saygin; Roy, Swarup; Akti, Necmettin; Tav, Cumali; Yahsi, UgurThis work reports the effects of free volume on curcumin release in various polymer-based composite films. Curcumin-reinforced biocomposite films were fabricated with natural biopolymers (carrageenan and chitosan) and bioplastics (poly(lactide) (PLA) and poly (butylene adipate-co-terephthalate) (PBAT)) via the solvent casting method. The curcumin release test was performed using an aqueous medium, and it was found that it was released the fastest in the carrageenan film, followed by the chitosan, PLA, and PBAT films, presumably owing to the dissimilarity of the polymer matrix. The free volume of the polymer films was determined using positron annihilation lifetime spectroscopy (PALS) to understand the release phenomena of curcumin. The free volume fraction was varied and reliant on the type of polymer, with the highest in the PBAT-based film followed by the PLA-, chitosan-, and carrageenan-based films. The free volume method helps analyze the release of bioactive compounds in a polymer matrix and may help to achieve a better understanding of the release of bioactive compounds.Publication Open Access Decoding Polymer Architecture Effect on Ion Clustering, Chain Dynamics, and Ionic Conductivity in Polymer Electrolytes(2023-01-01) YAHŞİ, UĞUR; TAV, CUMALİ; Bakar R., Darvishi S., Aydemir U., YAHŞİ U., TAV C., Menceloglu Y. Z., Senses E.Poly(ethylene oxide) (PEO)-based polymer electrolytes are a promising class of materials for use in lithium-ion batteries due to their high ionic conductivity and flexibility. In this study, the effects of polymer architecture including linear, star, and hyperbranched and salt (lithiumbis(trifluoromethanesulfonyl)imide (LiTFSI)) concentration on the glass transition (Tg), microstructure, phase diagram, free volume, and bulk viscosity, all of which play a significant role in determining the ionic conductivity of the electrolyte, have been systematically studied for PEO-based polymer electrolytes. The branching of PEO widens the liquid phase toward lower salt concentrations, suggesting decreased crystallization and improved ion coordination. At high salt loadings, ion clustering is common for all electrolytes, yet the cluster size and distribution appear to be strongly architecture-dependent. Also, the ionic conductivity is maximized at a salt concentration of [Li/EO ≈ 0.085] for all architectures, and the highly branched polymers displayed as much as three times higher ionic conductivity (with respect to the linear analogue) for the same total molar mass. The architecture-dependent ionic conductivity is attributed to the enhanced free volume measured by positron annihilation lifetime spectroscopy. Interestingly, despite the strong architecture dependence of ionic conductivity, the salt addition in the highly branched architectures results in accelerated yet similar monomeric friction coefficients for these polymers, offering significant potential toward decoupling of conductivity from segmental dynamics of polymer electrolytes, leading to outstanding battery performance.Publication Metadata only Structural and dielectrical properties of PMMA/TiO2 composites in terms of free volume defects probed by positron annihilation lifetime spectroscopy(SAGE PUBLICATIONS LTD, 2021) TAV, CUMALİ; Kaya, A. U.; Kosem, G.; Yener, M. Y.; Tav, C.; Yahsi, U.; Esmer, K.A suspension of ultrasonically agitated Titanium dioxide micrometer-sized powder has been introduced into a poly(methyl methacrylate) (PMMA) matrix by solvent (CHCl3) mixing under slow mechanical stirring, and the resulting suspension was used to cast free-standing PMMA/TiO2 composite films. Filler contents from 0 wt% to 7.5 wt% were selected, since TiO2 particles could not be previously suspended in chloroform at higher concentrations by ultrasonic agitation. Optical and dielectric properties of composites were determined by ultraviolet (UV)-visible and dielectric spectrometry. In the UV region, 450% improvement of UV absorption was achieved in the TiO2/PMMA composite compared with neat PMMA. The structural properties and hole-free volume of the composites were determined by X-ray diffractometry and positron annihilation lifetime spectroscopy, respectively. The particle size and homogeneous dispersion of the particles in the polymer matrix were related to the hole-free volume of the PMMA.