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Yayın Study on swelling of hydrogels (PAAm) at various temperatures by using fluorescence technique(Springer US, 2007-10) Kaya Aktaş, Demet; Akın Evingür, Gülşen; Pekcan, Mehmet ÖnderSteady-state fluorescence (SSF) technique was employed for studying swelling of polyacrylamide (PAAm) hydrogels. Disc-shaped gels were prepared by free-radical crosslinking copolymerization of acrylamide (AAm) with N, N'- methylenebis (acrylamide) (BIS) as crosslinker in the presence of ammonium persulfate (APS) as an initiator. Pyranine was introduced as a fluorescence probe. Fluorescence intensity of pyranine was measured during in situ swelling process at various temperatures and it was observed that fluorescence intensity values decreased as swelling is proceeded. Li-Tanaka equation was used to determine the swelling time constants, tau(c) and cooperative diffusion coefficients, D-c from intensity, weight and volume variations during the swelling processes. It is observed that swelling time constants, tau(c) decreased and diffusion coefficients, D-c increased as the swelling temperature is increased. The swelling activation energies, Delta E were measured from the intensity, weight and volume variations and found to be 10.7, 32.2 and 64.1 kJ mol(-1), respectively.Yayın Monitoring small molecule diffusion into hydrogels at various temperatures by fluorescence technique(Elsevier B.V., 2006-12-01) Evingür, Gülşen Akın; Karslı, Kadir; Pekcan, Mehmet Öndersteady state fluorescence technique was used to study small molecule diffusion into polyacrylamide (PAAm) gels at various temperatures. Pyranine (P-y), dissolved in water was introduced as a probe and fluorescence emission (I-p) from Py was monitored during diffusion. Scattered light intensities, I-sc from PAAm gel was also monitored to observe structural variations during diffusion process. Increase in I-P intensity was attributed to P-Y diffusion into PAAm get. On the other hand decrease in I-sc intensity was interpreted as the variation of the spatial heterogeneities in the system. Li-Tanaka and Fickian models were used to quantify the swelling and diffusion experiments and diffusion coefficients were produced in both cases. Related activation energies were also calculated from the corresponding physical processes.Yayın Study of drying of kappa-carrageenan gel at various temperatures using a fluorescence technique(Taylor & Francis Inc, 2008-01) Tarı İlgin, Özlem; Pekcan, Mehmet ÖnderThe steady-state fluorescence technique was used to study drying of kappa-carrageenan gel at various temperatures. Pyranine was doped as a fluorescence probe, and scattered light, I-sc, and fluorescence intensities, I, were monitored during drying of these gels. It was observed that I decreased linearly as drying time is increased. The moving boundary model based on Case II diffusion was applied to produce the packing constants, k(0), at higher temperatures. Activation energy for drying was found to be 53.9 kJ mol(-1). Supporting gravimetric and volumetric measurements were also carried out during drying of gels and the corresponding activation energies were determined to be 46.4 and 58.9 kJ mol(-1), respectively.
