Advanced Vibrational Microspectroscopic Study of Conformational Changes within a Craze in Poly(ethylene terephthalate)

Crazes constitute one of the most common failure mechanisms in polymers. They act as fracture precursors, severely degrading the mechanical properties of the material. Thus, a deep understanding of the chain rearrangement occurring inside crazes is of utmost fundamental and practical importance. We have employed synchrotron infrared microspectroscopy (SIRMS) and Raman microspectroscopy to investigate the conformational changes inside micron-sized crazes in poly­(ethylene terephthalate), PET. A promotion of the full-extended chain conformational structure at the expense of mainly the trans amorphous mesomorphic phase along with an increase in crystallinity of around 4% has been found. These results differ from what we observed across the deformation neck during PET cold drawing, where no promotion of the all-trans crystalline conformation occurred for slow drawing speeds at temperatures well below the glass transition. Our results show the tremendous capabilities of advanced vibrational microspectroscopy techniques to investigate microscale phenomena in polymer science.