From thermally activated to viscosity controlled fracture of biopolymer hydrogels
Abstract
We report on rate-dependent fracture energy measurements over three decades of steady crack velocities in alginate and gelatin hydrogels. We evidence that, irrespective of gel thermo-reversibility, thermally activated "unzipping" of the non-covalent cross-link zones results in slow crack propagation, prevaling against the toughening effect of viscous solvent drag during chain pull-out, which becomes efficient above a few mm.s-1. We extend a previous model [Baumberger et al. Nature Materials, 5, 552 (2006)] to account for both mechanisms, and estimate the microscopic unzipping rates.
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