Browsing by Author "Tari, Özlem"

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Citation Count: 0
Comparison of cation effects on phase transitions of kappa and iota carrageenan
(European Polymer Federation, 2010) Tari, Özlem; Pekcan, Önder
Phase transitions of kappa and iota carrageenan in KCl NaCl and CaCl2 solutions were separately studied during heating and cooling processes by using fluorescence technique. Scattered light I-SC and fluorescence intensity I was monitored against temperature to determine the critical transition temperatures and exponents. Kappa and iota carrageenans with monovalent (KCl NaCl) salt system presented only coil to double helix (c-h) and double helix to coil (h-c) transitions upon cooling and heating processes respectively. Two transition regions were observed in both heating and cooling of the iota carrageenan in CaCl2 solution while in kappa carrageenan only (c-h) and (h-c) transitions was detected. During heating dimers decompose into double helices by making (d-h) transition. At the high temperature region (h-c) transition takes place. During cooling back transitions repeat themselves. A hysteresis was observed between (h-c) and (c-h) for the kappa and iota carrageenan salt system (except CaCl2) respectively. Dimer to double helix (d-h) and double helix to dimer (h-d) transitions were observed for iota carrageenan in CaCl2 salt. The gel fraction exponent beta was measured and found to be in accord with the classical Flory-Stockmayer Model for both kappa and iota carrageenan salt systems.
Citation Count: 1
Fluorescence study on drying of iota-carrageenan gels at different temperatures prepared with various CaCl2 content
(Springer, 2011) Tari, Özlem; Pekcan, Önder
The influence of temperature and salt content on drying was investigated by using steady-state fluorescence (SSF) technique. Supporting gravimetric and volumetric measurements were also carried out during drying of gels at various temperatures. iota-Carrageenan gels were prepared with various CaCl2 content. Pyranine was introduced as a fluorescence probe during gel preparation. Apparent fluorescence intensity I was measured during in situ drying process at each temperature and it was observed that fluorescence intensity values decreased for all gel samples. A simple model consisting of Case II diffusion was used to produce the packing constants k(0) for helixes. It was observed that k(0) increased as the drying temperature was increased. On the other hand at each temperature it was seen that k(0) decreased as CaCl2 content was increased. Packing energies for drying processes were obtained from fluorescence volumetric and gravimetric measurements separately.
Citation Count: 4
Modelling of Swelling by the Fluorescence Technique in Kappa Carrageenan Gels
(Amer Inst Physics, 2011) Tari, Özlem; Pekcan, Önder
Kappa (-kappa) carrageenan gels prepared with various carrageenan concentrations in pure water were completely dried and then swelled in water vapor. Steady state fluorescence measurements were performed using a spectrometer equipped with temperature controller. Pyranine was embedded in kappa-carrageenan gels as a fluorescence probe during gel preparation. The fluorescence intensity I increased exponentially as swelling time is increased for all gel samples. The increase in I was modelled using Li-Tanaka equation from which swelling time constants tau(c) and cooperative diffusion coefficients D-c were determined. It was observed that D-c increased as the swelling temperature was increased. On the other hand at each temperature it was seen that D-c decreased as kappa carrageenan concentration was increased. Activation energies for swelling were obtained and found to be 57.4 58.3 and 62.73kJ mol(-1) for the gels with increasing amount of kappa-carrageenan content.