Polyethylene glycol (PEG)/polyvinylidene fluoride (PVDF) core/shell nanofibers were fabricated using coaxial electrospinning. In the core/shell composite nanofibers, melted PEG and PVDF solutions were coaxially electrospun (e-spun) through a double spinneret as a core layer and as a shell layer, respectively. The PEG of the core layer in the e-spun composite nanofibers is a phase-change material (PCM) that is able to store and release large amounts of thermal energy at a constant phase transition temperature. PEG was encapsulated with a PVDF shell to prevent its leakage and reduce the effect of the external environment during usage. The core/shell structure of the e-spun composite nanofiber was confirmed using water contact angle (WCA) measurements, X-ray photoelectron spectroscopy (XPS) analysis, and transmission electron microscopy (TEM). Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) showed that the e-spun composite nanofibers had good thermal stability and energy storage capacity. PEG of three different molecular weights (MWs: 1000 Da, 2000 Da and 4000 Da) was used as the core material to prepare e-spun composite nanofibers with different melting/crystallization temperature ranges and thermal storage capacities. Among these PEGs, the WCA value of 106 degrees of e-spun PEG4000/PVDF core/shell nanofibers is similar to that of e-spun PVDF nanofibers confirming that the core/shell nanofibers could completely encapsulate 4000 Da PEG at the highest core feed rate of 0.210 mL/h. Regarding in terms of energy storage capacity, core/shell nanofibers, fabricated at the core feed rate of 0.210 mL/h, had the largest content of PEG in the core up to 42.5 wt% with a latent heat of 68 J/g and a melting temperature of 62.8 degrees C. These shape-stabilized core/shell nanofibers showed good thermal reliability and sufficiently high tensile strength, leading to various potential applications related to energy storage. (C) 2012 Elsevier B.V. All rights reserved.