Failure is a topic that has received a lot of attention in the community of soft matter from a scientific and industrial point of view. Among soft systems, understanding failure in biopolymer gels is crucial as they are used extensively in food and biomedical applications. Biopolymers form polymeric networks made of fibrils, whose stiffness is responsible for the development of negative normal stresses and strain hardening under shear.
At CNRS Montpellier, we have studied the microscopic mechanisms leading to failure in biopolymer gels and their interplay with the gel’s distinctive features by using a novel setup coupling dynamic light scattering to rheology. The setup allows time- and space-resolved measurements of the microscopic dynamics to be made during gel formation within the rheometer plates, and also the successive creep test which eventually leads to failure.
We have evidenced the presence of several types of failure precursors in the microscopic dynamics during the creep test (see figure), but also during gel formation, and have found that gels which eventually fail are characterized by irreversible rearrangements of the bond distribution during gelation. These rearrangements are driven by negative normal stresses developed during gelation and reduce the gel resistance to shear stress. In this way, we have demonstrated that the ultimate fate of biopolymer gels under constant shear load can be inferred by the behaviour of normal stresses developed by the gels during their formation.
Pommella A. et al., Phys. Rev. Lett. 125, 268006 (2020)
CNRS/University of Montpellier