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Yayın Swelling of iota-carrageenan gels prepared with various CaCl2 content: A fluorescence study(European Polymer Federation, 2008-01-05) Tarı İlgin, Özlem; Pekcan, Mehmet ÖnderIota carrageenan gels prepared with various CaCl2 content were completely dried and then swelled in water vapor. Steady-state fluorescence ( SSF) technique was used to monitor the swelling process of each iota carrageenan gels at various temperatures. Pyranine was used as a fluorescence probe. Apparent fluorescence intensity, I increased as swelling time increased for all gel samples. The increase in I was modelled using Li-Tanaka equation from which the swelling time constants, tau(1) and cooperative diffusion coefficients, D-c were determined. It was observed that D-c increased as the swelling temperature was increased. On the other hand at each temperature, it was seen that D-c decreased as CaCl2 content was increased. Activation energies for swelling were obtained and found to be 60.5, 61.0, 61.5 and 62.8 kJmol(-1) for the gels prepared with increasing amount of CaCl2 content.Yayın Small molecule diffusion into swelling Iota-Carrageenan gels: A fluorescence study(Taylor & Francis Group, 2007-04) Ataman, Evren; Pekcan, Mehmet ÖnderSmall molecule diffusion into Iota-Carrageenan gel was studied by using steady-state fluorescence (SSF) technique. Pyranine, dissolved in water was used as fluorescence probe. Fluorescence emission intensity, I-p, and scattered light intensity, I-sc, were monitored to study diffusion and swelling processes at various temperatures respectively. Fickian and Li-Tanaka models were elaborated to produce diffusion, D, and collective diffusion, D-0, coefficients. Diffusion and swelling activation energies were also obtained and found to be 20.5 kj mol(-1) and 28.2 kj mol(-1). respectively.Yayın Swelling activation energy of kappa-carrageenan in its gel state: A fluorescence study(John Wiley & Sons Inc, 2007-12-15) Tarı İlgin, Özlem; Pekcan, Mehmet ÖnderA steady-state fluorescence technique was employed to study the swelling Of K-carrageenan gels at various temperatures. Pyranine was used as a fluorescence probe. The fluorescence intensity of pyranine was measured during the in situ swelling process of K-carrageenan gels. The fluorescence intensity increased exponentially as the swelling time increased. The increase in the fluorescence intensity was modeled with the Li-Tanaka equation, from which the swelling time constants and cooperative diffusion coefficients were determined. The swelling time constants decreased and the cooperative diffusion coefficients increased as the swelling temperature was increased. The swelling activation energies were measured to be 47.05 kJ/mol.Yayın Reordering of polystyrene gel due to multiple swelling in organic vapor fast transient fluorescence technique study(Elsevier Science SA, 2006-07-31) Erdoğan, Matem; Pekcan, Mehmet ÖnderReordering of disc-shaped polystyrene (PS) gels due to multiple swelling, under organic vapor was studied by using Fast Transient Fluorescence (FTRF) technique. Disc-sbaped polystyrene gels were prepared by free radical copolymerization (FRC) of styrene (S) with ethylene glycol dimethacrylate (EGDM) as a crosslinker. Pyrene (P) was introduced as a fluorescence probe during polymerization. Swelling experiments were performed by using P doped PS gels under chloroform vapor. After each swelling step, gels were left to dry in an oven at 30 degrees C for consecutive reswelling experiments. Decay curves of P were measured and pyrene lifetimes, tau, were determined. It was observed that tau values decreased as swelling recycles were repeated. It was observed that after the fifth swelling step, two different regimes appeared in the swelling processes in PS gels. Swelling time constant, tau(c), and cooperative diffusion coefficients, D-c were determined by using Li-Tanaka equation for each swelling step in both regimes. It was observed that D-c values decreased up to tenth swelling step and then remained unchanged in both regimes.Yayın Dissolution of Al2O3-polystyrene latex composites: A fluorescence study(Taylor & Francis Ltd, 2005) Uǧur, Şaziye; Tepehan, Fatma Zehra; Pekcan, Mehmet ÖnderThis work reports the use of the steady state fluorescence (SSF) technique to study dissolution of a composite film formed from a mixture of Al 2O3 and polystyrene (PS) latex particles. The composite films were cast from dispersion of pyrene (P)-labeled PS particles in Al 2 O3 solution at room temperature and annealed at 280°C temperature for 10 min. Eight different composite films were studied in various latex contents. Toluene was used as dissolution agent. Fluorescence intensities Ip from P were monitored during dissolution. Fickian diffusion was employed to model the dissolution processes. Dissolution coefficients, D d, were measured and found to be increased at high PS content in the composite films.Yayın Reconstruction of thermally quenched glow curves in quartz(Pergamon-Elsevier Science Ltd, 2012-04) Subedi, Bhagawan; Polymeris, George S.; Tsirliganis, Nestor C.; Pagonis, Vasilis; Kitis, GeorgeThe experimentally measured thermoluminescence (TL) glow curves of quartz samples are influenced by the presence of the thermal quenching effect, which involves a variation of the luminescence efficiency as a function of temperature. The real shape of the thermally unquenched TL glow curves is completely unknown. In the present work an attempt is made to reconstruct these unquenched glow curves from the quenched experimental data, and for two different types of quartz samples. The reconstruction is based on the values of the thermal quenching parameter W (activation energy) and C (a dimensionless constant), which are known from recent experimental work on these two samples. A computerized glow-curve deconvolution (CGCD) analysis was performed twice for both the reconstructed and the experimental TL glow curves. Special attention was paid to check for consistency between the results of these two independent CGCD analyses. The investigation showed that the reconstruction attempt was successful, and it is concluded that the analysis of reconstructed TL glow curves can provide improved values of the kinetic parameters E, s for the glow peaks of quartz. This also leads to a better evaluation of the half-lives of electron trapping levels used for dosimetry and luminescence dating.Yayın Temperature lags of luminescence measurements in a commercial luminescence reader(Elsevier Science Inc, 2015-09-15) Güneç Kıyak, Nafiye; Kitis, George; Polymeris, George S.The temperature recorded in thermoluminescence and optically stimulated luminescence equipments is not the temperature of the sample but that of the heating element on which the thermocouple is attached. Depending upon the rate of heating, a temperature difference appears between the samples and the heating element, termed as temperature lag, which could have serious effects on the curve shapes and trapping parameters. In the present work the temperature lag effect is studied in a newly developed luminescence equipment measuring both thermoluminescence and optically stimulated luminescence. It is found that the temperature lag could be large for heating rates above 2 K/s and it is strongly dependent upon the sample holder. A simple approximation method is proposed in order to both predict as well as correct for temperature lag effects in luminescence measurements.
