Plasticity and yielding of soft matter

This review examines and compares two transitions characteristic of soft matter: solid-to-solid and solid-to-liquid transitions. The first, a transition from an elastic (or viscoelastic) state to plastic deformation, has rarely been associated with soft matter, although it is well known for various solids, such as soft metals and rocks. The second type of transition is typical for colloidal systems. It is characteristic of multicomponent compositions belonging to the class of yielding liquids. This phenomenon consists of a transition from a gel-like (solid-like) state to a relatively low-viscosity liquid. A common feature of both these transitions is the reorganization of the original structure at the mesoscale level. For crystalline solids, there is a transformation of the crystal lattice. In amorphous solids, the decisive factor is the presence of free volume due to a loose packing of the dispersed phase with the existence of long-lived metastable structures. Plastic deformations in transitions in the solid-to solid transitions are irreversible. Examples of plastic deformations of various soft matter are given. In polymers, this includes necking under uniaxial tension and irreversible deformations of ultra-high molecular weight polyethylene. In dilute hydrogels formed by intermolecular interactions of biopolymers, elastic and irreversible (plastic) deformations overlap. In yielding stress liquids obtained from these gels, steady-state flow with very high viscosity is possible in the gel-like state (at stresses below the yield point). Plasticity is the dominant component of deformation in highly filled suspensions such as raw materials (feedstocks) and wet sand.