Fracture and Adhesion of Soft Materials: A review

Fracture and adhesion of soft materials:a review

Costantino Creton and Matteo Ciccotti
Reports of Progress in Physics, vol 79, 40616, 2016.

Postprint

Abstract

Soft materials are materials with a low shear modulus relative to their bulk modulus and where
elastic restoring forces are mainly of entropic origin. A sparse population of strong bonds connects
molecules together and prevents macroscopic flow. In this review we discuss the current state of
the art on how these soft materials break and detach from solid surfaces. We focus on how stresses
and strains are localized near the fracture plane and how elastic energy can flow from the bulk of
the material to the crack tip. Adhesion of pressure-sensitive-adhesives, fracture of gels and rubbers
are specifically addressed and the key concepts are pointed out. We define the important length
scales in the problem and in particular the elasto-adhesive length Γ/E where Γ is the fracture energy
and E is the elastic modulus, and how the ratio between sample size and Γ/E controls the fracture
mechanisms. Theoretical concepts bridging solid mechanics and polymer physics are rationalized
and illustrated by micromechanical experiments and mechanisms of fracture are described in detail.
Open questions and emerging concepts are discussed at the end of the review.