Viscoelastic properties of gelatin solutions near the gel point

Abstract

A lime-processed gelatin was separated into α1 and α2 components by alcohol precipitation and the viscoelastic properties were measured for the solutions at different concentrations. When the concentration exceeds some critical values, the frequency-dependent curve of storage modulus shows a plateau, which arises from the three-dimensional network. The critical concentration was Theologically determined to analyse the sol gel transition as a percolation process. The storage modulus of gels is scaled on the difference between the concentration and the critical concentration. The critical 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 mechanical properties of cross-links were discussed on the basis of non-linear viscoelasticity. The α₁ component contributes to the high strength of cross-links, and the α₂ component to the narrow distribution of strength. By a combined effect, the original gelatin constructs the network in which the cross-links have a high strength and uniform distribution.

Key Words:

• Non-linear viscoelasticity
• Gelatin gels
• Percolation
• Scaling analysis