Abstract
Linear viscoelasticity was studied for aqueous solutions of poly(acrylic acid) (PAA) complexed with ferric ion (Fe3+). Concentration of PAA was fixed in the semidilute regime, and concentration of Fe3+ varied within a wide range. Sol-to-gel transition was observed at low Fe concentration, and syneresis was observed at high Fe concentration. In between, the system was reversible gel with relaxation time governed by the effective breakup of the complexing sites. Analysis of stress relaxation behavior and temperature dependence enabled consistent determination of the association energy of ~ 75 kJ/mol. Syneresis at high Fe3+ concentration was associated with a decrease in solvent quality and increase in elastic energy with increasing density of the PAA/Fe3+ complexing sites.
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