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Yayın Reordering of polystyrene gel due to multiple swelling in organic vapor fast transient fluorescence technique study(Elsevier Science SA, 2006-07-31) Erdoğan, Matem; Pekcan, Mehmet ÖnderReordering of disc-shaped polystyrene (PS) gels due to multiple swelling, under organic vapor was studied by using Fast Transient Fluorescence (FTRF) technique. Disc-sbaped polystyrene gels were prepared by free radical copolymerization (FRC) of styrene (S) with ethylene glycol dimethacrylate (EGDM) as a crosslinker. Pyrene (P) was introduced as a fluorescence probe during polymerization. Swelling experiments were performed by using P doped PS gels under chloroform vapor. After each swelling step, gels were left to dry in an oven at 30 degrees C for consecutive reswelling experiments. Decay curves of P were measured and pyrene lifetimes, tau, were determined. It was observed that tau values decreased as swelling recycles were repeated. It was observed that after the fifth swelling step, two different regimes appeared in the swelling processes in PS gels. Swelling time constant, tau(c), and cooperative diffusion coefficients, D-c were determined by using Li-Tanaka equation for each swelling step in both regimes. It was observed that D-c values decreased up to tenth swelling step and then remained unchanged in both regimes.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.
