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 To (gel point) and the relaxation critical exponent n were successfully determined according to the Winter's criterion. With increasing salt concentration. To increased while n decreased. The scaling for the zero shear viscosity go in the sol phase and the equilibrium modulus G(e) in the gel phase were established against the relative distance epsilon (epsilon = vertical bar T - T-gel vertical bar 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 df calculated from n without hydrodynamic interaction nor excluded volume suggested a denser filling structure in the critical gel at higher salt concentration. (C) 2010 Elsevier Ltd. All rights reserved.