Strain hardening and fracture of heat-set fractal globular protein gels

Non-linear mechanical behavior at large shear deformation was been investigated for heat-set β  -lactoglobulin gels at pH 7 and 0.1 M NaCl using both oscillatory shear and shear flow. These gels have a self-similar structure at length scales smaller than the correlation length of the gel with fractal dimension df=2df=2. Strain hardening is observed that can be well described using the model proposed by Gisler et al. [T.C. Gisler, R.C. Ball, D.A. Weitz, Phys. Rev. Let. 82 (1999) 1064] for fractal colloidal gels. The increase of the shear modulus normalized by the low strain value (G0G0) is independent of G0G0. For weak gels the elasticity increases up to a factor of ten, while for strong gels the increase is very small. At higher deformation irreversible fracture occurs, which leads eventually to macroscopic failure of the gel. For weak gels formed at low concentrations the deformation at failure is about 2, independent of the shear modulus. For strong gels fracture occurs at approximately constant stress (2×103 Pa2×103 Pa).

Graphical abstractHeat set globular protein gels show strain hardening followed by fracture. The strain hardening can be modelled by utilizing the fractal structure of the gels. Microscopic fracture precedes failure so that the minimum of the loss angle precedes the maximum of the storage modulus.Figure optionsDownload full-size imageDownload as PowerPoint slide