Hierarchical Polymer Blend Fibers of High Structural Regularity Prepared by Facile Solvent Vapor Annealing Treatment

In this study, a facile solvent vapor annealing (SVA) method is utilized to inscribe hierarchical secondary nanostructures onto electrospun poly(ε-caprolactone)(PCL)/poly(ethylene oxide) (PEO) blend fibers. By carefully understanding the phase separation and crystallization behavior of PCL/PEO blends during the electrospinning process, one can tune the spatial distribution of the PCL phase, the growth of the PCL crystalline regions, and therefore the amount and even the sensitivity of free amorphous PCL chains in response to acetone vapor. Here, the PEO domains serve as mini-dividers to restrict the growth of the semicrystalline PCL phase. During acetone vapor annealing, the PEO phase remains largely unchanged while swollen-free amorphous PCL chains are deposited on pre-existing PCL or even PEO crystalline lamellae, giving rise to hierarchical structures of high regularity. The morphologies of PCL/PEO hierarchical structures reported in this study are of striking uniformity, further demonstrating the reliability of the facile SVA method, not only for a few layers of thin fiber mats but also for thicker fiber mats.