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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 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 Sorption and slow release kinetics of PAAM gels at various temperatures(Freund Publishing House Ltd, 2007-11) Akın Evingür, Gülşen; Pekcan, Mehmet ÖnderSmall molecule sorption and slow release in and out of polyacrylamide (PAAm) gels were studied by using steady state fluorescence (SSF) technique. Pyranine (P-y) dissolved in water used as a probe. Fluorescence emission intensity, I-p from P-y was used to monitor for studying sorption and slow release processes at various temperatures. Sorption and slow release processes were analyzed by using Fickian diffusion model and coefficients were obtained. Related activation energies were also calculated for the corresponding physical processes.Yayın Eco-friendly bacterial cellulose/castor oil hydrogels: physicochemical behavior and biocompatibility(Sakarya University, 2025-10-27) Işıkçı Koca, Elif; Pınar, Orkun; Yalçın Çapan, Özlem; Çaylı, Gökhan; Kazan, Dilek; Çakır Hatır, PınarIn the present work, novel thermoresponsive hydrogels were developed from renewable resources, and the influence of bacterial cellulose molar ratio on their chemical structure, thermal properties, swelling behavior, morphology, and biocompatibility was systematically investigated. The hydrogels were fabricated using castor oil, 4,4'-diphenylmethane diisocyanate, bacterial cellulose, Nisopropylacrylamide, and N,N'-Methylenebisacrylamide. Structural and physicochemical characterizations were performed by Fourier-transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry, and thermogravimetric analysis. The highest equilibrated swelling degree was achieved as 592.6% at the maximum bacterial cellulose content. SEM images revealed that the formation of spongy architecture is caused by the increase in the bacterial cellulose content. In vitro biocompatibility studies revealed that the hydrogel with the highest bacterial cellulose content exhibited the greatest cytocompatibility, with an IC50 value of 11.16 mg/ml. Overall, the findings demonstrate the successful fabrication of a novel bio-based thermoresponsive hydrogel through an eco-friendly approach, highlighting its potential for diverse biomedical applications.
