Stretch-Induced Stable-Metastable Crystal Transformation Of Pvdf/Graphene Composites

Deformation-induced crystalline structure transformation of poly(vinylidene fluoride) (PVDF)/graphene composites from stable alpha-crystal to metastable beta-crystal at different temperatures was investigated by means of in situ synchrotron radiation wide-angle and small-angle X-ray scattering (SAXS). The obtained results of lamellar and crystalline structures during tensile deformation shown that the alpha-beta crystal transformation relies on the evolution of orientation and there is a threshold value (similar to 0.5) of orientation function for structure transformation. The mechanism of alpha-beta crystal transformation was interpreted based on an indirect approach via the intermediate state of tensile deformation-induced fragmentation and recrystallization process. The fragmentation and recrystallization process was verified by the analysis of four-point and then six-point SAXS patterns. The formation of beta-phase at 160 degrees C was confirmed as a "recrystallization (alpha-crystal -) beta-phase transformation." The loaded appropriate stress guarantees the stable-metastable phase transformation of PVDF. While at 30 degrees C, the adequate stress concentrated on the crystal phase results in formation of beta-crystal from the initial recrystallization. The addition of graphene is beneficial to enhance the mechanical property of PVDF at both 30 degrees C and 60 degrees C, but the compatibility of PVDF/graphene composites does not favor high temperature such as deformation at 160 degrees C.