Preparation and characterization of a novel ionic conducting foam-type polymeric gel based on polymer PVdF-HFP and ionic liquid [EMIM][TFSI]

Poly(vinylidenefluoride-co-hexafluoropropylene) (PVdF-HFP)/ionic liquid (IL) (1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide [EMIM][TFSI]) polymer gels have been prepared by solvent volatilization with and without ultrasound irradiation, respectively. The gel structure and electrochemical property are characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC), Fourier transform infrared (FT-IR), and complex impedance spectroscopy (CIS). It is found that a novel foam-type polymer-ionic liquid gel is prepared with ultrasound irradiation. And, the ultrasound-induced polymer-ionic liquid gel has a higher crystallinity and more diverse crystal size polymer network, comparing with that prepared without ultrasound irradiation. The foam-type gel structure can be explained by the formation of pre-ordered aggregation of molecular chain during the ultrasound irradiation process. The ionic conductivity of the PVdF-HFP/[EMIM][TFSI] gel decline after ultrasound irradiation, which can be attributed to the high crystallinity and looser microstructure. Furthermore, it is found that the ultrasound irradiation can promote the crystalline transition of PVdF-HFP from β to α phase and improve its crystallinity.