Crystalline Block Copolymer Decorated, Hierarchically Ordered Polymer Nanofibers

We report the formation of hierarchically ordered polymer nanofiber structures, named as nanofiber shish kebabs (NFSKs), by combining electrospinning and controlled polymer crystallization. Nanofibers were produced by electrospinning polycaprolactone (PCL), which was used as the shish, and a secondary polymer [either PCL or PCL-b-poly(ethylene oxide)] was decorated on the nanofiber by an incubation (slow crystallization) or a solvent evaporation (fast crystallization) method to form kabab lamellae. Selected area electron diffraction experiment showed that the PCL crystal c axis is parallel to the fiber axis in both shish and kebabs. The formation mechanism was attributed to soft epitaxy where crystallographic registration between the shish and the kebab was not needed. In block copolymer NFSKs, nanofiber-induced polymer crystallization brings the block copolymer to the vicinity of the nanofibers, and the block copolymer further phase separated into lamellar structure templated by the nanofiber. The resultant hierarchical architecture is of technological interest because it provides a platform for incorporating different functionalities into nanoscale polymer fibers in an ordered fashion.