Nanostructured nanofibers based on PBT and POSS: Effect of POSS on the alignment and macromolecular orientation of the nanofibers

Electrospun well aligned nanofibers based on poly(butylene terephtalate) (PBT) and polyhedral oligomeric silesquioxane (POSS) were prepared starting from polymeric solutions at different POSS contents (namely 0, 3, 6 and 10 wt.%). The chemical and physical properties as well as the orientation and the polymorphic behavior of the nanostructured nanofibers were investigated by several experimental techniques, including scanning electron microscopy, wide and small angle synchrotron X-ray scattering and differential scanning calorimetry. Morphological characterization demonstrated the possibility to obtain defect free PBT/POSS nanofibers, with silsesquioxane dispersion at a submicron level, conversely to cast films where the presence of μm-sized POSS crystals was evident. Moreover, the nanofiber alignment was improved in presence of POSS. Furthermore, real time WAXS and SAXS investigations during the annealing of nanofibrous films demonstrated that electrospun nanofibers suffer from retarded crystallization. In order to assess the role played by POSS in the macromolecules self organization and packing, the post-deposition cold crystallization process of the porous films was investigated. We found that the presence of POSS affects not only the fiber alignment but also the macromolecular orientation during the annealing process.