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Öğe Cation effects on sol-gel and gel-sol phase transitions of ?-carrageenan-water system(Elsevier Science Bv, 2003) Kara, S; Tamerler, C; Bermek, H; Pekcan, ÖSol-gel and gel-sol phase transitions Of K-carrageenan in pure water and in KCl solution were studied using photon transmission technique. Photon transmission intensity, I-tr was monitored against temperature to determine the sol-gel and gel-sol temperatures (T-sg and T-gs) and activation energies (DeltaH(sg) and DeltaH(gs)). It was observed that T-gs was notably higher than T-sg due to the hysteresis on the phase transition loops. T-gs and DeltaH(gs) values were also higher for gels containing KCl than for those without KCl. The increase in carrageenan content caused an increase in both critical temperatures and activation energies for the gels prepared in pure water and in KCl solution. Increases in the KCl/carrageenan ratio, raised both T-gs and T-sg. Similarly DeltaH(sg) was elevated by the increase in cation content of the gel. These results were interpreted as the formation of stronger gels in the presence of KCl in water. (C) 2002 Elsevier Science B.V. All rights reserved.Öğe Cation effects on swelling of k-carrageenan(John Wiley & Sons Inc, 2003) Kara, S; Tamerler, C; Pekcan, ÖSwelling behavior of kappa-carrageenan gels in water and KCl solutions was investigated by photon transmission experiments following the preparation of gels in the presence and absence of externally added K+ ion as a gel promoting agent. Transmitted photon intensity, I-tr, increased continuously during swelling depending on the carrageenan and ion content in the gel. This increase in I-tr was modeled using the Li-Tanaka equation. Both the experimental work and the model showed that the swelling of low carrageenan and ion content gels took less time than that of high ion content gels. It is confirmed that double helices in a swollen gel move much faster in pure water than in KCl solution during swelling processes. Swelling time constants, tau(I), and collective diffusion coefficients, D-o, were measured for the gels swollen in water and KCl solutions. (C) 2003 Wiley Periodicals, Inc.Öğe Hysteresis during sol-gel and gel-sol phase transitions of ?-carrageenan(Sage Publications Ltd, 2003) Kara, S; Tamerler, C; Bermek, H; Pekcan, ÖPhoton transmission techniques were used to study sol-gel and gel-sol transitions in kappa-carrageenan-water systems with various carrageenan contents. The photon transmission intensity, I-tr was monitored against temperature to determine critical phase transition temperatures and transition rates. It was observed that the sol-gel transition temperatures, T-sg, were found much lower than the gel-sol, T-gs, transition temperatures based on the hysteresis of the phase transition loops. Sol-gel and gel-sol activation energies were determined and it was found that a carrageenan-water system required less energy for the gel-sol transition than for the sol-gel transition.Öğe Photon transmission study on swelling of ?-carrageenan gels prepared in various concentrations(Elsevier Science Bv, 2003) Kara, S; Tamerler, C; Arda, E; Pekcan, Ökappa-Carrageenan gels prepared with various carrageenan concentrations in pure water were completely dried and then swelled in pure water. Photon transmission measurements were performed using a UV-Vis (UVV) spectrometer during the swelling of kappa-carrageenan gels. Transmitted photon intensity, I-tr, increased exponentially as swelling time is increased for all gel samples. The behaviour of I-tr was interpreted by Monte-Carlo Simulation. The increase in I-tr was quantified by employing Li-Tanaka equation, from which time constants tau(l) and collective diffusion coefficients, D-O were determined for the gels in various carrageenan concentrations. Gravimetric and volumetric measurements were also carried out during swelling of gels. It is observed that gel with high carrageenan content possess more double helices and more lattice dislocations and swell slower than gels with low carrageenan content which may contain less double helices and less lattice imperfections. Increase in I-tr was interpreted by the homogeneous distribution of double helices in the carrageenan gel system. (C) 2003 Elsevier B.V. All rights reserved.
