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Yayın Small molecule sorption and desorption in and out of iota-carrageenan gels(Taylor & Francis Group, 2007-08) Ataman, Evren; Pekcan, Mehmet ÖnderSmall molecule sorption and desorption in and out of Iota-Carrageenan was studied by using steady-state fluorescence (SSF) technique. Pyranine dissolved in water used as fluorescence probe. Fluorescence emission intensity, I-p from pyranine was monitored for studying sorption and desorption processes at various temperatures. The Fickian model was applied to produce sorption, D-s, early desorption, D-ed, and desorption, D-d, coefficients. Corresponding activation energies were obtained and found to be 20.5 kJ mol(-1), 7.0 kJ mol(-1) and 34.9 kJ mol(-1), respectively. The observed D-ed value is an order of magnitude smaller than the D-s and D-d coefficients. On the other hand, sorption processes were shown to be twice as fast as desorption processes.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.
