SOLVENT EFFECTS ON SOL-GEL TRANSITION OF ALGINATE SOLUTIONS BY ADDITION OF CUPRIC IONS

Polyelectrolyte concentration dependence of critical exponents and gel points induced by addition of cupric ions to alginate solutions has b een examined experimentally. Solvent effects have been taken into acco unt when the gelation process is considered as the percolation of blob s. The critical exponents of relative viscosity, kappa, are found to b e in the range of 1.14-1.32, showing only a slight dependence on algin ate concentration. The kappa values are in good agreement with the pre diction of Rouse clusters of percolation theory in which the hydrodyna mic interaction is ignored in calculating the viscosity. A power-law r elation has been found between the gelation point, f(c), and alginate concentration C with an exponent of -0.70 +/- 0.05. Concentration depe ndence of gel point shows that the experimental results can be explain ed by a combination of scaling theories developed for vulcanization pr ocesses and polyelectrolytes in semi-dilute solutions. Based on the sc aling analysis, good agreement has been obtained between the experimen tal exponent, -0.70 +/- 0.05, and theoretical exponents, -0.625 and -0 .75, for semi-dilute polyelectrolyte solutions without and in the pres ence of an added salt, respectively.