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Yayın Monitoring diffusion of reptating polymer chains by a direct energy transfer method: A Monte Carlo simulation(Wiley-Blackwell, 2002-07-29) Tüzel, Erkan; Kısacıkoğlu, Kemal Batuhan; Pekcan, Mehmet ÖnderA kinetic Monte Carlo method was used to simulate the diffusion of reptating polymer chains across an interface. A time-resolved fluorescence technique in conjunction with a direct energy transfer method was used to measure the extent of diffusion of dye-labeled reptating polymer chains. The diffusion of donor- and acceptor-labeled polymer chains between adjacent compartments was randomly generated. The fluorescence decay profiles of donor molecules were simulated at several diffusion steps to produce mixing of the polymer chains. Mixing ratios of donor- and acceptor-labeled polymer chains in compartments were measured at various stages (snap-shots) of diffusion. It was observed that for a given molecular weight, the average interpenetration contour length was found to be proportional to the mixing ratio. Monte Carlo analysis showed that the curvilinear diffusion coefficient is inversely proportional to the weight of polymer chains during diffusion.Yayın Drying of PAAm hydrogels at various temperatures: A fluorescence study(Taylor & Francis Group, 2007-05) Aktaş, Demet Kaya; Evingür, Gülşen Akın; Pekcan, Mehmet ÖnderThe steady-state fluorescence (SSF) technique was employed for studying the drying of polyacrylamide (PAAm) hydrogels. Disc-shaped hydrogels were prepared by free-radical crosslinking copolymerization of acrylamide (AAm) with N,N'-methylene bisacrylamide (BIS) as crosslinker in the presence of ammonium persulfate (APS) as an initiator. Pyranine (P) was introduced as a fluorescence probe and the intensity of pyranine was monitored during in situ drying at various temperatures. It was observed that the fluorescence intensity of pyranine increased during the drying process. A supporting, gravimetrical experiment was also performed. A phenomenological equation was introduced to determine the desorption coefficient, D, of water molecules from the drying hydrogels at various temperatures. The desorption activation energy, triangle E-d, values were measured for the drying processes and found to be 91.08 and 36.82 kJ mol(-1) by fluorescence and gravimetrical methods, respectively. This difference most probably originates from the origin of the techniques; the fluorescence technique measures the parameters at a molecular level, whereas the gravimetrical technique measures a parameter in the bulk.Yayın Small molecule sorption and desorption in and out of PAAm hydrogels at various temperatures(Prous Science, SA, 2007-07) Evingür, Gülşen Akın; Karslı, Kadir; Pekcan, Mehmet Önder[No abstract available]
