Temperature dependence of the elastic properties of alginate gels

The moduli of elasticity of calcium and lead alginate gels increase with time after preparation, and the temperature dependence of the rate of syneresis suggests an activation energy of 8?12 x 10⁴ J.mol?¹ for the formation of new junctions. At zero time, a negative temperature-dependence was found for the elastic force measured at a low degree of deformation (4%). Deformation of the gels was associated with an increase in entropy and internal energy. When the calcium ions in a preformed calcium alginate gel were exchanged for lead ions, which have a higher affinity for alginate, the modulus increased due to an enhanced increase in internal energy with deformation. Reversal of the sequence of introducing the two types of ions gave the opposite effect. The data suggest that the junctions are “weak points” in the gels, and that even small deformations can cause partial rupture.