Embedding Lauric Acid into Polystyrene Nanofibers To Make High-Capacity Membranes for Efficient Thermal Energy Storage

This article describes a simple and reliable approach to the fabrication of lauric acid (LA)-containing polystyrene (PS) nanofibers with LA/PS weight ratios up to 4 to 1 in the final dry mass of nanofibers. The obtained LAPS composite nanofibers achieved an unprecedented thermal energy storage capacity up to 78.4% of pristine LA because of the high LA loading as well as the lightweight and porous nature of the PS matrix. To the best of our knowledge, our result was higher than the previously reported values, which were generally less than 50%. The direct scanning electron microscopy (SEM) observation, IR spectra, Raman spectra, and differential scanning calorimeter (DSC) thermograms of LAPS nanofibers indicated that majority of LA was encapsulated inside the composite nanofibers. The X-ray diffraction (XRD) patterns showed that the crystal size of LA domains enlarged with the increase of LA loading in the composite nanofibers. In addition, the DSC run in T4P mode unveiled that the released latent heat during crystallization could raise the temperature of LAPS composite nanofibers above the onset temperature of crystallization, which was different from the reported results obtained from DSC run in traditional T1 mode. Furthermore, the undesirable supercooling effect was suppressed by increasing the percentage of LA in the composite nanofibers. Also, the LAPS composite nanofibers showed robust cycling stability and reusability during 100 continuous heating–cooling cycles in the temperature range of 0–80 °C. The LAPS composite nanofibers demonstrated excellent structural stability after solvent extraction and prolonged heat treatment. The entrapped LA was locked in the PS matrix without leaking out of the nanofibers even after continuous and repeated heating above the melting point of LA.