Critical behavior of thermal phase transitions of iota-carrageenan in CaCl₂ solution

In situ photon transmission method was applied to study thermal phase transitions of ι-carrageenan in CaCl₂ solution. Coil-to-helix (c-h) and helix-to-dimer (h-d) transitions were detected upon cooling. An extra dimer-to-dimer (d-d) transition was observed as well during cooling at low-temperature region. Upon heating only dimer-to-helix (d-h) and helix-to-coil (h-c) transitions were detected. Photon transmission intensity, I_tr was monitored against temperature to determine several phase transitions and transition temperatures. It was observed that the c-h transition in ι-carrageenan-CaCl₂ system performs a crossover between 3D percolation to classical theory. Upon heating, the specific heat exponent over the d-h transition was extracted from the transmitted intensity data and was found to be 0.045.