Solvent-induced crystallization of electrospun syndiotactic polystyrene nanofibers and its reversible desorption/sorption of volatile organic vapors

Electrospun fiber mats are promising media for chemical separation because of their porous interior and high surface area, which enhance penetrant permeation and provide a large number of active sites. The application of this technology was fulfilled in the present study, wherein syndiotactic polystyrene (sPS) fibers were prepared by high-temperature solution electrospinning to absorb volatile organic compounds. The as-spun sPS fibers had an average radius of ~360 nm and were amorphous as revealed by Fourier transform infrared spectroscopy (FTIR) and wide-angle X-ray diffraction. When the electrospun fibers were exposed to different solvent vapors, solvent-induced crystallization occurred in these submicron-sized fibers to form δ- or γ-form sPS crystals, depending on the solvent used. To trace the microstructure transformation of sPS chains induced by the solvent vapors, in situ FTIR spectral measurements were performed. The absorbance of crystallization-sensitive IR bands was plotted against time, from which the crystallization kinetics were analyzed based on the Avrami equation. Results showed that the rate of solvent-induced crystallization was higher for solvents with a higher saturated vapor pressure. Subsequent solvent desorption from the crystallized sPS fibers was also studied under ambient conditions by monitoring the absorbance variation of the solvent-sensitive IR band. Two-stage solvent desorption was observed in the δ-form sPS fibers; this process consisted of initial rapid desorption from the amorphous region, followed by slow desorption from the crystalline region. Notably, all the solvent molecules in the treated fibers can be completely removed in this manner, thereby leading to the formation of δ_e-form crystals for repetitive sorption/desorption applications.