Environmental Stress Cracking of Glassy Polymers

When a glassy polymer is exposed to an organic solvent, it can crack spontaneously or fail more readily under extension. This is environmental stress cracking. When the solvent diffuses into the polymer, stresses develop because of swelling of the polymer. In addition, fluctuations give rise to stresses, because of the variation in surface tension from changes in the surface concentration of the solute, which is the Marangoni effect. A linear stability analysis is performed to show that such a system is unstable to infinitesimal disturbances. Large tensile stresses arise locally, leading to failures, which will be observed in the interfacial region of the solid. In particular, the unstable disturbances of smaller wavelengths grow faster. This is consistent with the observation that the microscopic cracks that emanate from the surface are more profuse in cracks that are more closely spaced as seen in experiments.