Critical exponents for sol–gel transition in aqueous alginate solutions induced by cupric cations

Abstract

The sol–gel transition in aqueous alginate solutions of four alginate samples having different molecular weights ( M W) and M/G ratios induced by cupric cations was monitored by rheology measurements. The gel point f gel and the relaxation critical exponent n were determined using the Winter’s criterion over the alginate concentration C Alg of 1–4 wt%. The scaling for the zero shear viscosity η 0 before the gel point and the equilibrium modulus G e after the gel point was established against the relative distance ε from the gel point at the concentration of C Alg = 1 wt%, giving the critical exponents k and z. The results indicated that f gel was almost independent of the alginate concentration and became higher for the sample with lower molecular weight. The critical exponent n decreased with the increase in C Alg for these four Cu-alginate samples and the fractal dimension d f estimated from n suggested a denser structure in the critical gel with high G content. The critical exponent n evaluated from k and z agreed well with n determined from the Winter’s criterion.