E-POLYMERS, 2010 (SCI-Expanded)
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.