Optical studies of void formation and healing in styrene-isoprene-styrene block copolymers

Abstract

Void formation is shown to be a significant response of styrene‐isoprene‐styrene block copolymers under conditions of tensile stress relaxation. When brought to zero stress, these voids are observed to close and heal, restoring the original mechanical properties of the undamaged material. Dark‐field optical microscopy and light‐transmission photometry have been used to study void formation and healing in the size regime appropriate to optical techniques. As meaured from a reference state of damage, healing was found to increase with time and temperature in the zero‐stress state, with an apparent activation energy of 9 kcal/mole. The Mie theory of particle scattering was used to analyze changes in void size and size distribution during the healing process. The results are discussed in terms of possible mechanisms for healing.