Structure evolution of PVDF/PBSU interpenetrating crystal frameworks during deformation investigated by in-situ synchrotron radiation SAXS/WAXS

The structure evolution of interpenetrating crystal frameworks during deformation has been investigated with the help of in-situ small angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) by taking poly(vinylidene fluoride)/poly(1,4-butylene succinate) (PVDF/PBSU) blend as an example. During deformation, crystal slip, fragmentation and recrystallization of PVDF occur, leading to the formation of its fibrillar structures and the newly-formed PVDF crystalline lamellae with their normal parallel to stretching direction. In this process, the enriched chains or crystals of PBSU are reorganized accompanying the structure evolution of PVDF and finally enrich among newly-formed PVDF fibrils. The phase segregation and consequent connection of crystalline lamellae, dominated by the composition in blends, play important roles in the structure evolution of PVDF/PBSU interpenetrating crystal frameworks. On the one hand, higher PBSU content in blend contributes to the poor connection and weakens stress transfer among neighboring PVDF crystalline lamellae, corresponding to the larger critical strains for lamellar-to-fibrillar transition and alpha-to-,8 transformation of PVDF. On the other hand, higher PBSU content also leads to its lamellar stack in PVDF crystal framework. The fragmentation and recrystallization of these well-connected PBSU crystals yield newly-formed PBSU crystalline lamellae with their normal parallel to the stretching direction. On the contrary, the well connection of PVDF crystalline lamellae in the case of lower PBSU content corresponds to the fast lamellar-to-fibrillar transition and alpha-to-,8 transformation of PVDF crystal framework. The PBSU crystalline lamellae in this case exhibits poor connection and results in its crystalline lamellae with caxis perpendicular to the stretching direction. Our results are significant for the fundamental understanding of the deformation mechanism.