Nonlinear Rheology and Cavitation of a Triblock Copolymer Gel

Polymer gels are subjected to large-strain deformation during their applications. Here, we report the large-strain deformation behavior of a physically cross-linked, swollen polymer gel, which was obtained by dissolving a triblock copolymer poly (methyl methacrylate) - poly (n-butyl acrylate) - poly (methyl methacrylate) [PMMA-PnBA-PMMA] in 2-ethyl 1-hexanol, a midblock selective solvent. Investigations were performed using large amplitude oscillatory shear (LAOS) and custom developed cavitation rheology techniques.  The gel displays unique strain-stiffening response at large-strain and stress vs strain responses have been captured using Gent constitutive model. In cavitation experiments a syringe-needle was inserted into the gel and a growth of cavity at the tip of the needle was captured. The critical pressure for cavitation scales with the local modulus of the gel. Both analytical method and finite-element based modeling have been implemented to capture the pressure response in cavitation experiments. Our results provide new understanding of gel failure mechanism at large-strain.