The crystallization and crystal transition of PVDF in PAN nano-tube

One-dimensional confinements were fabricated by coaxial electrospinning and confined crystallization as well as crystal transition of poly(vinylidene fluoride) (PVDF) were studied. It was found that the PVDF can be confined in the nano-tube with the diameter from 50 nm to 350 nm, formed by polyacrylonitrile (PAN). Since the crystallization temperature of PVDF is higher than the glass transition temperature of PAN, the crystallization of PVDF took place in the soft PAN nano-tubes. The confinement weakened the ability of PVDF crystallization, resulting in the crystallinity (Xc) decreasing sharply in the confined condition and the crystallization temperature (Tc) shifted to very low temperature when the confinement diameter was smaller than 75 nm. The observation by FTIR indicated that there was transition in absorption for during cooling where the absorption abruptly rose up at certain temperature and ended immediate raise at a low temperature. The change of temperature range for transition was similar with the Tc checked by DSC, which was related to the crystallization. Also, it was observed that the crystalline structure in as-spun fibers was almost β-phase, and β-crystal transformed into α-crystal at different degrees in confined and un-confined PVDF. These results inferred the chain orientation in company with confinements affected the crystallization of PVDF.