Critical behavior at sol–gel transition in gellan gum aqueous solutions with KCl and CaCl 2 of different concentrations

Abstract

The sol–gel transition in aqueous gellan gum solutions with added KCl or CaCl 2 upon cooling was investigated using rheology measurements. The gelation temperature T gel (gel point) and the relaxation critical exponent n were successfully determined according to the Winter's criterion. With increasing salt concentration, T gel increased while n decreased. The scaling for the zero shear viscosity η 0 in the sol phase and the equilibrium modulus G e in the gel phase were established against the relative distance ɛ ( ɛ = | T − T gel|/ T gel) 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 d f calculated from n without hydrodynamic interaction nor excluded volume suggested a denser filling structure in the critical gel at higher salt concentration.