Tailoring the polyvinylidene fluoride phase structure in high permittivity <scp>MXene</scp>/polyvinylidene fluoride composite films via supercooling of the polymer melt

Abstract In this study, we report a distinct phase tailorable solution cast polyvinylidene fluoride (PVDF)‐based composite films with transition metal carbides and nitride (MXene) fillers achieved by supercooling of the PVDF melt and their dielectric energy storage performance. An unusual thermal treatment temperature higher than the widely used T m was used to realize supercooling. Phase structure analysis by using attenuated total reflection infrared spectroscopy (ATR‐IR), X‐ray diffraction (XRD) and differential scanning calorimetry (DSC) indicated that a small amount of added MXene induced a considerable fraction (76%) of β ‐phase PVDF and a 10‐fold increase in dielectric permittivity (100 Hz) due to filler induced crystallization and super confinement effect when a processing temperature around melting temperature (T m ) is used. Surprisingly, although chain packing and crystallization of the macromolecules occur below T m , a higher processing temperature even induced a double polar ( β + γ ) phase PVDF as a consequence of supercooling and increased crystallization rate. Interestingly, a nonpolar α phase dominant structure was formed again when the processing temperature was 190°C. These findings indicate that the moderate fast crystallization facilitates the polar phase formation, which may be attributed to their higher intermolecular dipole interaction within the geometry confined by the 2D fillers. The results imply a simple way to tailor PVDF phase structure, offering insights into polymer polymorph formation. Highlights A phase tailorable PVDF‐based composite film with MXene fillers was fabricated. Phase structure of MXene/PVDF film was analyzed via ATR‐IR, XRD, and DSC. MXene induced an increase in dielectric permittivity and high β ‐phase in PVDF. Thermal treatment at various temperatures tailored the phase structure of PVDF.