Kinetics and mechanism of sol-gel transformation on polyelectrolytes of some transition metal ions, especially cobalt alginate ionotropic membranes

Abstract

The kinetics of gelation have been studied complexometrically at temperatures between 25 and 40°. The pseudo-first order plot of exchange between Na + ions of the macromolecular chains of alginate sol and Co 2+ ions gives a sigmoidal curve with two distinct portions. The initial part was fast and curved significantly at early times followed by a decrease in the rate of exchange at longer times. The rate of gelation conforms to the expression ( C ∞ - C t ) = B 0 e − Rft + P 0e − Rs t , where R f and R s are the first order rate constants of gelation for the fast and slow reactions, respectively. There is discussion of the factors which affect the rate of exchange such as the concentrations of metal ions and alginate sol, the diameter of the formed capillaries and the orientation of the macromolecular chains and the solvent molecules toward the metal ions. The kinetic parameters have been evaluated and a consistent gelation mechanism is suggested.