Frustrated Crystallization behavior of Poly(ethylene oxide) in Electrospun Core-Shell Nanofibers and Beads

Confined crystallization behavior of poly(ethylene oxide) (PEO) was studied in electrospun core-shell nanofibers and beads, respectively, using DSC. The core-shell structure consisted of PEO core and polystyrene (PS) shell. It was observed that the morphology of PEO core changed from continuous to discrete domains when the core spinning solvent was switched from water to chloroform. This significantly influenced the crystallization behavior of PEO such that whereas the crystallization nucleation mechanism was heterogeneous for nanofibers with continuous PEO core, it became fractionated for nanofibers with discontinuous PEO core. The relaxation of the PEO domains, in the nanofibers with discontinuous core, via thermal annealing above the glass transition temperature of PS shell, markedly increased homogenous nucleation contribution in the crystallization. This plausibly was due to relaxation of PEO domains through domain breakup and coalescence process resulting in higher fraction of nanosized PEO domains.