Stress Relaxation of Alginate Gels Crosslinked by Various Divalent Metal Ions

Abstract

Rheological properties of Alginate (Alg) gels were studied by measuring tensile stresses under small strains. The Alg gel rods were prepared in CaCl2, SrCl2, BaCl2, and Pb(NO3)2 solutions in the range of 0.03–1.0 mol dm−3. Their stresses showed long relaxation processes. By curve fitting method, equilibrium elastic moduli Ge, spontaneous elastic moduli Ge+Gr and relaxation times τ were obtained. The results Ge were independent of strains γ, and Gr and τ increased as increasing γ. The effects of Ca ion concentrations CCa on the elasticities were discussed by taking account of the ratio of Ca ion bindings obtained by dialysis equilibrium and that of junction formation obtained by circular dichroism. The values of Ge were analyzed by the theory of swollen gels. The number of the junctions was found to be constant in the region of CCa>0.03 mol dm−3, and slight increases of Ge to be due to changes of the water content and the density of the Alg gels. The magnitudes of Ge and Gr depended on the kind of counterions, and decreased in the order, Ba->>Ca->Sr-> PbAlg; this was almost the same as that of the ion selectivities.