(216o) 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 phenomenon is called environmental stress cracking and a model is proposed here.  When the solvent diffuses into the polymer, stresses are developed due to the swelling of the polymer.  In addition, infinitesimal fluctuations give rise to stresses due to the variation in surface tension from changes in the surface concentration of the solute, which is known as the Marangoni effect.  A linear stability analysis is performed to show that such a system where the above effects are included, is unstable to infinitesimal disturbances.  The analysis is confined to very short times following the initial contact between the solid and the fluid phases. The main cause is seen to be the Marangoni effect.  As a result, 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 in keeping with the observation that the microscopic cracks that emanate from the surface are more profuse in cracks that are more closely spaced.