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Öğe Bilgisayar kontrollu ultrasonik ölçme sistemi(Trakya Üniversitesi, 1997) Kara, Selim; Oskay, TanerÖZET Bu çalışmada ultrasonik ses dalgalarının katı içindeki yayılma hızlarını tespit eden bir ölçüm sistemi gerçekleştirilmiştir. Sistem, ölçüm tekniği olarak, dört dönüştürücülü daldırma yöntemini kullanmaktadır. Bu sistemde ikisi referans ve diğer ikisi de ölçüm çifti olarak görev yapan dönüştürücüler kullanılmaktadır. Ölçümün esası, daldırma sıvısı (saf su) içinde yayılan ses dalgalarının alıcılara ulaşmaları arasındaki zaman farkının tespitine dayanır. İncelenen örnek 1.8° adımlı bir motor tarafından döndürülebilmekte ve açıya bağlı ölçümler alınabilmektedir. Açılı ölçümlerde belirli bir kritik değerden sonra yayılan dalganın enine bileşeni de ölçülebilmektedir. Motor ve sistemi çalıştıran elektronik devreler istendiğinde bilgisayar tarafından kontrol edilebilmekte ve bu şekilde kısa bir süre içinde çok sayıda ölçüm yapılarak, sonuçlar bilgisayara aktarılabilmektedir. Sistem tamamlandıktan sonra yapılan testlerde elde edilen sonuçlara göre; boyuna dalga için %1.21 ve enine dalga için %0.88 bağıl hata oranı belirlenmiştir. Bu rakamlar standart değerler ölçüsündedir. Ayrıca yapılan ölçüm ortalamaları değerlendirilerek, sistemin ölçüm doğruluğunun zaman içindeki değişiminin de çok küçük olduğu tespit edilmiştir.Öğe Cation effects on phase transition of kappa-iota-carrageenan hybrids(Vsp Bv, 2007) Pekcan, Onder; Kara, Selim; Arda, ErtanPhase transitions of kappa-iota-carrageenan hybrid in various types of salts were studied using photon transmission technique: NaCl, KCI, MgCl2, CaCl2 and KCl+CaCl2 were chosen as the salt solutions for the carrageenan hybrid. Coil-to-helix (c-h), helix-to-dimer (h-d) and back to helix-to-coil (h-c), dimer-to-helix (d-h) phase transitions of carrageenan hybrid in these mono- and bivalent cation solutions were studied upon cooling and heating, respectively. Photon transmission intensity, It, was monitored against temperature to determine the (c-h), (h-d) and (h-c), (d-h) transition temperatures (T-ch, T-hd and T-hc, T-dh) and activation energies (Delta E-ch, Delta E-hd and Delta E-hc, Delta E-dh) of carrageenan hybrids. Two distinct transition regions were observed both during heating and cooling of the carrageenan-bivalent salt systems. During the heating process, at first dimers decompose into helices by making a (d-h) transition. Then at the high temperature region, a (h-c) transition takes place. During cooling, back transitions repeat themselves. However, the carrageenan-monovalent salt system presented only (c-h) and (h-c) transitions during the cooling and heating processes, respectively. A hysteresis was observed between (h-c)-(c-h) and (d-h)-(h-d) transitions for the monovalent and bivalent cation systems respectively.Öğe A comparative study on the AC/DC conductivity, dielectric and optical properties of polystyrene/graphene nanoplatelets (PS/GNP) and multi-walled carbon nanotube (PS/MWCNT) nanocomposites(Elsevier Sci Ltd, 2020) Mergen, Omer Bahadir; Umut, Evrim; Arda, Ertan; Kara, SelimPolystyrene/graphene nanoplatelets (PS/GNP) and polystyrene/multi-walled carbon nanotube (PS/MWCNT) nanocomposites were prepared through solution mixing processing. The effect of carbon filler (CF) (GNP or MWCNT) doping on the DC/AC electrical conductivity, dielectric characteristics and optical parameters (absorption coefficient, alpha and band gap energy, E-g) of nanocomposites were investigated and compared for similar doping concentrations. The observed behavior of the DC surface conductivity for PS/CF nanocomposites was explained according to the classical percolation theory, where the percolation thresholds (phi(c)) for PS/GNP and PS/MWCNT nanocomposites were determined as 12.0 vol% and 3.81 vol% and the critical exponents (t) were calculated as 2.19 and 2.13, respectively. These results indicate that CFs create three dimensional CF network in PS matrix. The dielectric relaxation properties and the AC conductivity studied by means of Broadband Dielectric Spectroscopy (BDS) measurements, showed that the presence of carbon fillers significantly enhanced the capacitive/charge storage capabilities of the nanocomposites. The optical band gap energies (E-g) of PS/GNP and PS/MWCNT nanocomposites were obtained by using Tauc method. From applicative point of view, with their enhanced dielectric and AC conductivity properties of the PS/GNP and PS/MWCNT nanocomposites have the potential to be used in energy storage and electromagnetic interference (EMI) shielding applications.Öğe A comparison of fluorescence and UV-visible spectrometry techniques for thermal phase transitions of agarose gels(Springer, 2015) Arda, Ertan; Kara, Selim; Mergen, Omer Bahadir; Pekcan, OnderIn 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 (T (gs)) and sol-gel (T (sg)) transition temperatures were determined from the first derivatives of the sigmoidal transition paths. It was observed that the critical transition temperatures obtained from UV-vis and fluorescence data slightly increased depending on the agarose type and concentration, and those values were found to be in accord with each other. Transition activation energies were determined using the Arrhenius type equation and were found to be strongly correlated with the agarose content in the gel system. The produced gel-sol (Delta E (gs)) and sol-gel (Delta E (sg)) transition energies from the fluorescence data were found to be lower than that of the UV-vis data, which was attributed to the temperature-dependent fluorescence quenching effect.Öğe Critical Exponents of Kappa Carrageenan in the Coil-Helix and Helix-Coil Hysteresis Loops(Taylor & Francis Inc, 2009) Tari, Oezlem; Kara, Selim; Pekcan, OenderThe 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 of the phase transition loops. The gel fraction exponent (beta) was measured and found to be in accord with the classical Flory-Stockmayer model.Öğe Effect of annealing rate on film formation from poly(vinyl acetate) latex particles(Taylor & Francis Ltd, 2008) Arda, Ertan; Kara, Selim; Pekcan, OenderThe photon transmission technique was used to monitor the time and temperature evolution of film formation from poly(vinyl acetate) (PVAc) latex particles. The latex films were prepared below the glass transition temperature (T-g) of PVAc. These films were annealed at various annealing rates above the Tg of PVAc. It was observed that transmitted photon intensity (I-tr) from these films increased at all annealing rates as the annealing time and temperature are increased. The increase in the I-tr is attributed to the increase in crossing density at the junction surface. The healing points (tau(H), T-H) were determined for various annealing rates and the healing activation energy (Delta H) was measured and found to be 43.4 kcal/mol. The interdiffusion (backbone) activation energies (Delta E) and reptation frequencies (nu) of PVAc chains were measured. The averaged value of Delta E was found to be 226.6 kcal/mol. It is observed that Delta E is unchanged but nu is increased as increasing the annealing rates.Öğe Effects of GNP addition on optical properties and band gap energies of PMMA films(Wiley, 2019) Mergen, Omer Bahadir; Arda, Ertan; Kara, Selim; Pekcan, OnderIn 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 technique. The alpha and k values of the composites were obtained from UV-Vis data. The observed rapid increase in A values in UV-region were associated with the optical transitions of GNP electrons from valence to conduction band. The direct (E-d) and indirect (E-i) optical band gap energies of the composites were determined by using Tauc method. Both of the band gap energies were decreased when the GNP content in the PMMA matrix is increased. The decrease in the band gap energies was interpreted as evidence of increased conductivity of the composites. Additionally, energies of the band tails (Urbach energy) were calculated. It was seen that the Urbach energy levels were increased with GNP content. POLYM. COMPOS., 40:1862-1869, 2019. (c) 2018 Society of Plastics EngineersÖğe Electrical and optical percolations of polystyrene latex-multiwalled carbon nanotube composites(Academic Press Inc Elsevier Science, 2010) Kara, Selim; Arda, Ertan; Dolastir, Fahrettin; Pekcan, OenderElectrical 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.Öğe Electrical, optical and fluorescence percolations in P(VAc-co-BuA)/MWCNT composite films(Taylor & Francis Ltd, 2013) Arda, Ertan; Kara, Selim; Pekcan, OnderEffects 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 intensity (I-fl) and surface resistivity ((s)) of the composite films were monitored as a function of MWCNT mass fraction (M) at room temperature. All these measured quantities of the composites were decreased by increasing the content of MWCNT in the composite. The conductivity and the optical results were attributed to the classical and site percolation theories, respectively. The fluorescence results, however, possessed both the site and classical percolation theories at low and high MWCNT content regions, respectively.Öğe Evaluation of the fractal dimension of polyacrylamide during gelation and swelling(Elsevier, 2021) Arda, Ertan; Kara, Selim; Pekcan, Onder; Evingur, Gulsen AkinThe photon scattering method was performed to monitor the free radical crosslinking copolymerization (FCC) of acrylamide (AAm) applied with N,N'-methylenebis (acrylamide) (Bis) in time. FCC experiments were conducted using different Bis contents to create fractal-like network structures in polyacrylamide (PAAm) gels. Higher intensity values of the scattered photons, Isc were observed with increasing Bis content, BC, at a given time, which was attributed to fractal-like macrogel formation from interconnected microgels. The same gels were used in swelling experiments after drying, and increased Isc intensities from the PAAm gels were observed during the swelling process. Fractal dimensions, d during the gelation and swelling processes were measured and found to be increased as gelation and swelling times increased. According to the results obtained from the gelation measurements, it was seen that the fractal size, d, increased from very small values to 3.00. A similar increase in the range 1.00-1.66 was observed during swelling experiments.Öğe Film formation stages for poly(vinyl acetate) latex particles(Springer, 2006) Kara, Selim; Pekcan, Onder; Sarac, Ayfer; Arda, ErtanPhoton transmission technique was used to monitor the evolution of transparency during film formation from poly(vinyl acetate) (PVAc) latex particles. The latex films were prepared below the glass transition temperature (T-g) of PVAc. These films were annealed at elevated temperatures in various time intervals above the T-g of PVAc. It is observed that transmitted photon intensity (I-tr) from these films increased as the annealing temperature is increased. It is seen from I (tr) curves that there are two film formation stages. These successive stages are named void closure (viscous flow) and interdiffusion. The activation energies for viscous flow (Delta H) and backbone motion (Delta E (b)) were obtained by using well-defined models. The averaged values of the backbone (Delta E (b)) and the viscous flow activation energies (Delta H) were found to be 188.6 and 5.6 kcal/mol, respectively. The minimum film formation (tau (M),T (M)) and healing points (tau (H),T (H)) were determined. Minimum film formation (Delta E (M)) and healing activation energies (Delta E (H)) were measured using these time-temperature pairs. Delta E (M) and Delta E (H) were found to be 32.5 and 28.3 kcal/mol, respectively.Öğe Fractal dimensions of kappa-carrageenan gels during gelation and swelling(Taylor & Francıs Inc, 2018) Kara, Selim; Arda, Ertan; Pekcan, OnderA 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 temperatures, causing hysteresis of the phase transition loops. I-sc increased with an increase in CC at all test temperatures, which is attributed to the formation of a fractal-like carrageenan gel. After drying, the gels were used in swelling experiments where the gels were immersed in water at room temperature, reswelling to the original structure. It was observed that I-sc from the carrageenan gels increased as the CC was increased. The fractal dimension, d, during gelation was found to increase as the gelation temperature was increased. On the other hand, the d values during swelling decreased as the swelling time was increased.Öğe GELATION MECHANISMS(World Scientific Publ Co Pte Ltd, 2012) Pekcan, Onder; Kara, SelimIn 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 for various applications is discussed in detail. Various composite gels, formed from mixture of physical and chemical gels are also discussed in the last section of the article. Theoretical models describe the gelation as a process of random linking of subunits to larger and larger molecules by formation of an infinite network, where no matter what type of objects are linked, there is always a critical gel point at which the system behaves neither as a liquid nor as a solid on any length scale. The Flory-Stockmayer theory and percolation theory provide bases for modeling this sol-gel phase transition. The experimental techniques for measuring the critical exponents for sol-gel phase transitions in different polymeric systems are introduced and the validation of various theoretical predictions are surveyed.Öğe Mathematical Characterization of Thermo-reversible Phase Transitions of Agarose Gels(Taylor & Francis Inc, 2018) Ogrenci, Arif Selcuk; Pekcan, Onder; Kara, Selim; Bilge, Ayse HumeyraThe 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 technique, slightly increased by increasing the agarose concentration in both the HMP and LMP samples. Here, we express the phase transitions of the agar-water system, as a representative of reversible physical gels, in terms of a modified Susceptible-Infected-Susceptible epidemic model whose solutions are the well-known 5-point sigmoidal curves. The gel point is hard to determine experimentally and various computational techniques are used for its characterization. Based on previous work, we locate the gel point, T-0, of sol-gel and gel-sol transitions in terms of the horizontal shift in the sigmoidal transition curve. For the gel-sol transition (heating), T-0 is greater than T-m, i.e. later in time, and the difference between T-0 and T-m is reduced as the agarose content increases. For the sol-gel transition (cooling), T-0 is again greater than T-m, but it is earlier in time for all agarose contents and moves forward in time and gets closer to T-m as the agarose content increases.Öğe Monovalent and divalent cation effects on phase transitions of ?-carrageenan(Sage Publications Ltd, 2007) Kara, Selim; Arda, Ertan; Pekcan, OnderPhase transitions Of L-carrageenan in a variety of monovalent (Li, Na, K) and divalent (Mg, Ca, Sr) cation solutions were studied during heating and cooling by using photon transmission technique. Photon transmission intensity (I-tr) was monitored against temperature to determine the transition temperatures and activation energies during the heating and cooling processes in the monovalent and divalent systems. Three distinct transition regions were observed during the heating and cooling cycles for the carrageenan-divalent salt system. At the first step of the heating process, dimer groups were transformed into dimers that presented (g-d) transitions, then these dimers were directly converted into a double helix by undergoing a (d-h) transition. In the higher temperature region, a double helix-to-coil (h-c) transition took place. During the cooling process, these transitions are arranged in the order of (c-h), (h-d), and (d-g). The carrageenan-monovalent salt system presented only coil-to-rod-like helix (c-r) and rod-like helix-to-coil (r-c) transitions during the cooling and heating processes, respectively. A hysteresis was observed between (r-c)-(c-r) and (g-d)-(d-g) transitions for the monovalent and divalent cations, respectively.Öğe Phase transitions of ?-Carrageenan gels in various types of salts(John Wiley & Sons Inc, 2006) Kara, Selim; Arda, Ertan; Kavzak, Burhan; Pekcan, OnderSol-gel and gel-sol phase transitions of K-carrageenan in various types of salts were studied using photon transmission technique. Here, LiCl, NaCl, KCl, MgCl2, CaCl2, and SrCl2 were chosen as the proper salts for the K-carrageenan-water system. Photon transmission intensity, I-tr was monitored against temperature to determine the sol-gel and gel-sol temperatures (T-sg and T-gs) and activation energies (Delta E-sg and Delta E-gs). It was observed that T-gs temperatures were notably higher than T-sg due to the hysteresis on the phase transition loops. It was observed that stronger carrageenan gels are formed in the presence of KCl compared to the others. (c) 2006 Wiley Periodicals, Inc.Öğe A photon transmission study for film formation from poly(vinyl acetate) latex particles with different molecular weights(Wiley-Blackwell, 2007) Arda, Ertan; Kara, Selim; Pekcan, OenderThe photon transmission technique was used to monitor the temperature evolution of film formation from poly(vinyl acetate) (PVAc) latex particles with two different molecular weights. Two sets of latex films were prepared below the glass transition temperature (T-g) of PVAc, which are named as low (LM) and high molecular weight (HM) films. These films were annealed at elevated temperatures above the Tg of PVAc for various time intervals. It is observed that transmitted photon intensity (I-tr) from these films increased as the annealing temperature was increased. Onset temperatures (T-H) at given times (tau H) for starting the optical clarity of LM and HM films were measured and used to calculate the healing activation energies (Delta H) for the PVAc minor chains, and found to be as 28.1 kcal/mol and 27.7 kcal/mol, respectively. The increase in the transmitted photon intensity, Itr above TH was attributed to the increase in the number of disappeared interfaces between the deformed latex particles. Prager-Tirrell (PT) model was employed to interpret the increase in the crossing density of chains at the junction surfaces. The interdiffusion (backbone) activation energies (Delta E) were measured and found to be 177.5 kcal/mol and 210.7 kcal/mol for a diffusing PVAc chains across the junction surface of LM and HM latex films, respectively. (c) 2007 Wiley Periodicals, Inc.Öğe Polimer jellerin oluşum ve faz geçişi süreçlerinin foton geçirme tekniği ile incelenmesi(Trakya Üniversitesi, 2003) Kara, Selim; Sabaner, AkifPhD Thesis Trakya University, Graduate School of Natural and Applied Science Department of Physics SUMMARY In this work, gelation and volumetric and thermal phase transitions of chemically crosslinked polyacrylamide (PAAm), poly(N-isopropylacrylamide) (PNIPA) and physically bonded K-carrageenan gels were studied by using Photon Transmission Technique. A computer-controlled electronic temperature measurement system was designed for investigation of temperature effect on the gels to be able to work with high precision calibration. Temperature and transmitted photon intensity, 7fr values were recorded simultaneously during the measurements. For the measurements at various wavelengths, calculated Isc values were modeled using Rayleigh scattering equation. Concentrations and sizes of the particular microgels in the gel were approximately determined. Gelation activation enthalpies of PAAm gel samples were calculated by using Arrhenius type relations. Various cosslinker and polymer content disc-shaped and dried PAAm and K-carrageenan samples were swelled in water which used as a solvent. D0 cooperative diffusion coefficients were calculated from the T^-time and simultaneously measured weight and gel size data during the swelling process by using Li-Tanaka gel swelling model. Critical spinodal temperatures (Ts) of the PNIPA gel samples heated with a constant rate were obtained. The gel-sol and sol- gel transition temperatures and transition activation energies were determined. We found that Photon Transmission Technique with temperature measurements is an effective and useful method to study the physical structures of the gels, and values we obtained from the experiments are in agreement with similar works done with other experimental techniques. Year : 2003 Pages: 191 Keywords : Photon transmission technique, gelation, diffusion, light scattering, phase transition, swelling, acrylamide gel, NIP A gel, carrageenan gel.ONSOZ Bilim ve teknolojinin hızlı gelişimiyle birlikte bütün endüstri alanlarında uygulama alanı bulan polimer malzemeler üzerinde yapılan çalışmalar halen yoğun bir şekilde sürmektedir. Pek çok uygulamada vazgeçilmez oluşları ve sürekli yeni özelliklerde çeşitlerinin üretilmesi polimer bilimini son derece önemli bir ilgi odağı haline getirmektedir. Polimer j eller; tıp, kimya, gıda, kozmetik ve temizlik gibi pek çok sektörde kullamlmaktadır. Bu tez çalışmasında bazı kimyasal ve biyolojik polimer j ellerin, jel oluşum aşamaları ve hacimsel ve termal faz geçişlerini incelemek için deneysel yöntemler geliştirildi ve kullanıldı. Yoğun deneysel çalışmalarla dolu yıllar boyunca bana yol gösteren ve destek olan Tez Yöneticisi Hocam Yrd. Doç. Dr. M. Akif Sabaner 'e teşekkürlerimi sunarım. Birlikte pek çok ortak deneysel çalışma gerçekleştirdiğimiz değerli hocam Prof. Dr. Önder Pekcan'a, tecrübe ve bilgilerini benimle paylaştığı ve teze olan değerli katkılarından dolayı çok teşekkür ederim. Deneysel tekniklerin doğru uygulanmasında beni yönlendiren ve her konuda bilgi ve desteğini eksik etmeyen Yüksek Lisans Tez Yöneticisi Hocam Prof. Dr. Taner Oskay'a ve benzer katkılarından ötürü Prof. Dr. Yüksel Güney' e teşekkür ederim. Bazı analitik hesaplamalarda bana yol gösteren Yrd. Doç Dr. Mustafa Özcan'a, kimya konusunda yardım ve görüşlerinden yararlandığını Prof. Dr. Ömer Zaim'e, her konuda bana destek veren Yrd. Doç Dr. Ertan Arda'ya, arkadaşlarıma ve aileme çok teşekkür ederim. Haziran 2003 Selim Kara 111Öğe A Quartz Crystal Microbalance (QCM) Study on the Formation of Aqueous ?-Carrageenan-Chitosan Composite Bilayers with NaCl and Graphene Oxide(Taylor & Francis Inc, 2023) Kara, Selim; Arda, Ertan; Dolastir, Fahrettin; Pekcan, Onder; Evingur, Gulsen AkinBiomaterials and thin biofilms play a fundamental role in the medical, food and pharmaceutical industries. The Quartz crystal microbalance (QCM) measurement technique is one of the attractive techniques which have been used for monitoring the thin-film formation process. In the current work described here, kappa-carrageenan and chitosan solutions were used for the layer-by-layer (LBL) deposition of polyelectrolyte multilayers (PEMs) on the gold surface of a 5 MHz AT-cut (thickness-shear mode) quartz crystal in a flow module. A sensitive QCM system was designed to detect 0.1 Hz differences in the resonance frequency (Delta f) and 10(-7) changes in the energy dissipation (Delta D) values, which are the measures of the deposited mass and the film rigidity, respectively. Negatively charged carrageenan and positively charged chitosan biomolecules in the solutions were used to build up sequential and very thin bilayers on the modified gold surface. The effects of NaCl and graphene oxide (GO) addition on the mass of the deposited films were also investigated. Intermolecular interactions between the biopolymer chains, Na+ cations and GO sheets were explained by interactions between molecules, such as electrostatic forces and hydrogen bondings.Öğe Sorption and Desorption of PVA-Pyrene Chains in and out of Agarose Gel(Springer/Plenum Publishers, 2012) Kara, Selim; Gacal, Burcin; Tunc, Deniz; Yagci, Yusuf; Pekcan, OnderIn 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 in and out of agarose gel have two distinct regions for short and long diffusion times. Sorption and desorption coefficients were measured and it was seen that the diffusion rates were much larger at short times and at lower agarose concentrations.
