Year: 2020
Type: article
Abstract: Although phenomenologically simple to define, the yield stress is often difficult to quantify unambiguously in practice, especially for thixotropic materials with complex shear histories. Here, we identify a stress-controlled bifurcation in the yielding response of cellulose nanofibril gels, which we show can rigorously localize the yield stress in disordered materials with time-dependent behavior. After an initial yielding event, the fibrillar networks subsequently yield faster and at lower magnitudes of stress. For low stresses, the time to yielding increases with waiting time ${t}_{w}$ and diverges once the network has restored sufficient entanglement density to support the stress. For higher stresses, the yield time instead plateaus at a finite value because the developed network density is insufficient to support the applied stress. We quantitatively relate the yielding and aging behavior of the network to the competition between stress-induced disentanglement and dynamic fluctuations of the fibrils rebuilding the network. The critical stress ${\ensuremath{\sigma}}_{c}$ that bifurcates the response of the material between these two states identifies the intrinsic yield stress in these disordered materials, independent of aging, thixotropic effects, or shear history.
Source: Physical Review Materials
Institution: University of Pennsylvania
Language: English
Subfield: Biomaterials
Field: Materials Science
Domain: Physical Sciences
Open Access status: green
Awards: G1870677656, G2567800894, G4481177325
OpenAlex ID: W3045468070