Viscoelastic properties of gelatin solutions near the gel point

A lime-processed gelatin was separated into alpha(1) and alpha(2) component s by alcohol precipitation and the viscoelastic properties were measured fo r the solutions at different concentrations. When the concentration exceeds some critical values, the frequency-dependent curve of storage modulus sho ws a plateau, which arises from the three-dimensional network. The critical concentration was theologically determined to analyse the sol-gel transiti on as a percolation process. The storage modulus of gels is scaled on the d ifference between the concentration and the critical concentration. The cri tical exponents are about 1.9 for all systems, showing that the network of gelatin gels can be modelled by an isotropic elasticity. The entropy effect of flexible chains is primarily responsible for the isotropic elasticity. Since the gels are broken down when subjected to large deformation, the mec hanical properties of cross-links were discussed on the basis of non-linear viscoelasticity. The alpha(1) component contributes to the high strength o f cross-links, and the alpha(2) component to the narrow distribution of str ength. By a combined effect, the original gelatin constructs the network in which the cross-links have a high strength and uniform distribution.