(391d) The Role of Brittility in the Yielding of Polymeric, Colloidal, and Composite Materials

Many concentrated polymeric, colloidal, and composite materials show a transition from solid-like behavior to liquid-like behavior under applied loads, but how this yielding transition occurs can vary significantly. Understanding the physics behind yielding is of great interest for the behavior of biological, environmental, and industrial materials. Some materials yield smoothly and gradually while others yield abruptly. We refer to abrupt yielding as being “brittle”. The key rheological signatures of brittle yielding include a stress overshoot in steady-shear-startup tests and a sharp increase in loss modulus during oscillatory tests. We account for brittility within our recently proposed continuum model for yield stress materials (Kamani et al., Phys. Rev. Lett. 126, (2021)). The original formulation describes the plastic viscosity as being dependent on the total strain rate; plastic flow is aided by the rate at which elastic deformation is acquired. We account for brittility by reducing the contribution of the recoverable component, which impacts the rate at which yielding occurs. The model predictions are successfully compared to results of different rheological protocols from several polymeric, colloidal, and composite yield stress fluids. Our study shows that the brittility plays a critical role in the transient nonlinear rheology of soft materials and could function as a design parameter for future smart polymeric, colloidal, and composite materials.