All gelatin networks: 2. The master curve for elasticity

The rheological properties of gelatin gels from various sources (fish and mammalian) were followed in the course of the sol-gel transition and during gel maturation, by performing dynamic measurements under very small deformations. Different concentrations and molecular weights were investigated. The solvent was mainly water, but mixed solvents containing water and glycerol were also considered. Blends of gelatins from fish and mammalian in aqueous solutions were prepared and rheologically characterized. A systematic comparison was established between these measurements and those presented in paper 1 of the series. The comparison between the storage modulus and the concentration of helices leads to a master curve valid for all the samples investigated. This master curve is analyzed in terms of the percolation regime, near the threshold and in terms of a homogeneous network far from the threshold. In the percolation regime, a critical exponent of 2 is found for the storage modulus versus the distance to the threshold, in agreement with previous results. The theoretical models for rigid networks are briefly presented. The fully developed network appears as an entangled assembly of rigid rods (triple helices) connected by flexible links. This study shows that gelatin networks under small deformations do not behave like rubber-like networks, where long random coils are connected by local cross-links or entanglements.