Biyoinformatik ve Genetik Bölümü Koleksiyonu

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Browsing Biyoinformatik ve Genetik Bölümü Koleksiyonu by Author "Aktaş, Demet Kaya"

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    Fluorescence technique for monitoring swelling of PAAm-kappa-carrageenan gel composites
    (Shaker Publishing, 2009) Evingür, Gülşen Akin; Aktaş, Demet Kaya; Pekcan, Önder
    Steady-state fluorescence (SSF) technique was employed for studying swelling of polyacrylamide (PAAm) gels with various content of kappa- carrageenan. Disc shaped composite gels were prepared by free-radical cross/inking copolymerization of acrylamide (AAm) with various amounts of kappa-carrageenan (kappa C) using N N'- methylenebis (acrylamide) (BIS) as crosslinker in the presence of ammonium persulfate (APS) initiator. Pyranine was introduced as a fluorescence probe. Fluorescence intensity of pyranine was monitored during in situ swelling processes of composite gels. It was observed that fluorescence intensity values decreased as swelling is proceeded. The Li-Tanaka equation was used to determine the swelling time constants tau and cooperative diffusion coefficients D from intensity variations during the swelling processes. It was shown that tau decreased and D increased as the kappa C content in the composites are increased.
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    Steady state fluorescence technique for studying phase transitions in PAAm-PNIPA mixture
    (Taylor & Francis, 2009) Evingür, Gülşen Akın; Aktaş, Demet Kaya; Pekcan, Önder
    The steady state fluorescence (SSF) technique was used to study the sol-gel phase transition during free radical crosslinking copolymerisation of various amounts of acrylamide (AAm) and N-isopropylacrylamide (NIPA) mixtures. NN'-methylenebis (acrylamide) (BIS) and ammonium persulfate (APS) were used as crosslinker and an initiator respectively. Pyranine (8-hydroxypyrene-1 3 6-trisulfonic acid trisodium salt HPTS) was added as a fluoroprobe for monitoring the polymerisation. It was observed that pyranine molecules bind to AAm and NIPA chains upon the initiation of the polymerisation thus the fluorescence spectra of the bonded pyranines shift to the shorter wavelengths. Fluorescence spectra from the bonded pyranines allowed us to monitor the sol-gel phase transition without disturbing the system mechanically and to test the universality of the sol-gel transition as a function of polymer concentration ratios. Observations around the gel point of PAAm-PNIPA mixtures show that the gel fraction exponent obeyed the percolation result.