Large amplitude oscillatory shear studies on the strain-stiffening behavior of gelatin gels

Linear and nonlinear viscoelasticity of gelatin solutions was investigated by rheology. The dynamic mechanical properties during the sol-gel transition of gelatin followed the time-cure superposition. The fractal dimension df of the critical gel was estimated as 1.76, which indicated a loose network. A high sol fraction ws = 0.61 was evaluated from the plateau modulus by semi-empirical models. Strain-stiffening behavior was observed under large amplitude oscillatory shear (LAOS) for the gelatin gel. The strain and frequency dependence of the minimum strain modulus GM, energy dissipation Ed, and nonlinear viscoelastic parameter NE was illustrated in Pipkin diagrams and explained by the strain induced helix formation reported previously by others. The BST model described the strain-stiffening behavior of gelatin gel quite well, whereas the Gent and worm-like chain network models overestimated the strain-stiffening at large strains.