Confined crystallization and chain conformational change in electrospun poly(ethylene oxide) nanofibers

Abstract

This study focused on understanding the confined crystallization of poly(ethylene oxide) (PEO) in electrospun nanofibers. The effect of thermal treatment on PEO crystallization was also studied. An electrospinning process with a rotating drum collector enabled stretching and aligning of polymer chains, which resulted in the formation of a planar zigzag conformation. The confined environment in nanofibers facilitated an ordered crystal arrangement, resulting in an increase in the degree of crystallinity with a decrease in the fiber diameter. By contrast, large fibers extended solvent evaporation, which resulted in large crystallite sizes. The confined geometry and mechanical force provided by a rotating collector induced the preferred crystal orientation parallel to the fiber axis. Upon thermal annealing, the stretched PEO chains relaxed, resulting in a change from the metastable zigzag conformation to a stable helical conformation. Thermal treatment monotonically increased the melting temperature, degree of crystallinity, and crystallite size of PEO nanofibers regardless of the fiber diameter but did not influence the orientation of the organized crystals. The confinement effect on the chain conformation and crystallization behavior of poly(ethylene oxide) (PEO) in electrospun nanofibers was investigated. The PEO chains in electrospun nanofibers were tightly packed and exhibited a zigzag conformation. Increasing the fiber diameter reduced the packing of polymer chains, resulting in increases in the melting temperature and crystallite size. Thermal treatment relaxed the stretched chains, which induced a change from the metastable zigzag conformation to a stable helical conformation. Additionally, the melting temperature, degree of crystallinity, and crystallite size increased with increasing annealing temperature.