Critical behavior at sol–gel transition in gellan gum aqueous solutions with KCl and CaCl2 of different concentrations

The sol–gel transition in aqueous gellan gum solutions with added KCl or CaCl2 upon cooling was investigated using rheology measurements. The gelation temperature Tgel (gel point) and the relaxation critical exponent n were successfully determined according to the Winter's criterion. With increasing salt concentration, Tgel increased while n decreased. The scaling for the zero shear viscosity η0 in the sol phase and the equilibrium modulus Ge in the gel phase were established against the relative distance ɛ (ɛ = |T − Tgel|/Tgel) from the gel point, which gave the critical exponents k and z. No universal critical exponent n was found for this sol–gel transition because this gelation belonged to the cross-linking of existing macromolecules and the concept of random connectivity failed. The fractal dimension df calculated from n without hydrodynamic interaction nor excluded volume suggested a denser filling structure in the critical gel at higher salt concentration.