Universality of sol-gel phase transition of κ-carrageenan in various salts:: a steady state fluorescence study

Thermal phase transitions of kappa-carrageenan in NaCl, KCl and CaCl2 solutions were studied using steady state fluorescence (SSF) technique. Pyranine was introduced as a fluorescence probe for studying sol-gel phase transitions. Scattered light, I-sc and fluorescence intensity, I was monitored against temperature to determine the sol-gel (T-sg) phase transition temperatures. It was observed that T-sg values are strongly correlated to NaCl, KCl and CaCl2 contents. The weight average degree of polymerization, DPw, and gel fraction G, exponents (gamma and beta) were measured and found to be in accord with the classical Flory-Stockmayer model, i.e., gamma and beta were found to be close to 1.0, independent of salt content.