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Yayın In situ fluorescence study of swelling, sorption and desorption processes in and out of PAAm gels(Wiley-V C H Verlag GMBH, 2008-05) Evingür, Gülşen Akın; Karslı, Kadir; Pekcan, Mehmet ÖnderSmall molecule sorption and desorption in and out of polyacrylamide (PAAm) gels were studied at various temperatures. Pyranine (P(y)) dissolved in water used as a probe. Fluorescence emission intensity, I(p) from P(y) was monitored for studying sorption and desorption processes. Scattered light intensities, I(SC) from PAAm gel was also monitored to observed structural variations during sorption and desorption process. Li-Tanaka model was applied to produce the swelling time constants, tau(C) and sorption coefficients, D(C) for the swelling processes. on the other hand, sorption and desorption processes were studied and coefficients were produced by using Fickian model. Related activation energies were also calculated from the corresponding physical processes.Yayın Universal behaviour of gel formation from acrylamide-carrageenan mixture around the gel point: A fluorescence study(Taylor & Francis Group, 2006-08) Kaya Aktaş, Demet; Evingür, Gülşen Akın; Pekcan, Mehmet ÖnderThe steady state fluorescence (SSF) technique was used to study the sol-gel transition, for the solution free radical crosslinking copolymerization of acrylamide (AAm) with various carrageenan content. N, N'- methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) are used as crosslinker and an initiator, respectively. Pyranine (8-hydroxypyrene-1, 3,6-trisuffonic acid, trisodium salt, HPTS) was added as a floroprobe for monitoring the polymerization. Pyranine molecules start to bind to acrylamide polymer chains upon the initiation of the polymerization; thus, the spectra of the bonded pyranines shift to the shorter wavelengths. Fluorescence spectra from the bonded pyranines allows one to monitor the sol-gel transition, without disturbing the system mechanically, and to test the universality of the sol-gel transition as a function of some kinetic parameters like polymer concentration. Observations around the critical point show that the gel fraction exponent P obeyed the percolation result for low carrageenan concentrations (< 2.0%) however classical results were produced at higher carrageenan concentration (> 2.0%).Yayın Studying on the small molecule diffusion into hydrogels: a fluorescence study(Amer Inst Physics, 2007) Evingür, Gülşen Akın; Karslı, Kadir; Pekcan, Mehmet ÖnderIn situ steady state fluorescence experiments (SSF) were reported during the diffusion of water molecules into PAAm in gels at various temperatures. The fluorescence emission intensities, Ip increased continuously as water molecules diffused into gels. I-sc, scattered light intensities, from the gel was also monitored to detect the variation in the gel structure during diffusion process. Swelling and diffusion experiments were quantified by Li-Tanaka and Fickian models.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]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.
