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 d(f) of the critical gel was estimated as 1.76, which indicated a loose network. A high sol fraction w(s) = 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 G(M), energy dissipation E-d, and nonlinear viscoelastic parameter N-E 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.