Fracture of polymer interfaces: what are the relevant length scales?

While it is tempting to relate directly the molecular structure of an interface (between glassy or between semi-cristalline polymers) with its fracture toughness, these two parameters are simply the two end-points of a complex network which needs to be understood in order to control the mechanical strength of the interface. The important mechanisms occur at three different length scales: the molecular scale (stress-transfer across the interface), the microscopic scale (plastic deformation at the crack tip) and the macroscopic scale (loading geometry and elastic constants of the polymers). The couplings existing between these length scales in glassy polymer interfaces are reviewed in this paper in light of the latest experimental studies.