Crystallization monitoring of semicrystalline poly(vinylidene fluoride)/1-Ethyl-3-methylimidazolium hexafluorophosphate [Emim][PF6] ionic liquid blends

The electroactive characteristics of poly(vinylidene fluoride) (PVDF) are widely and increasingly being used in technological applications, where controlling the crystallization of the PVDF is of utmost importance. The nucleation and growth of crystals in the β or γ electroactive phases, or in the nonelectroactive α phase, depends on a number of factors that, despite the studies carried out, are still to be properly understood, in particular, when blended with specific active fillers. In this context, the crystallization of PVDF blended with the ionic liquid (IL) 1-ethyl-3-methylimidazolium hexafluorophosphate ([Emim][PF6]) has been analyzed. Both components are capable of crystallizing from the melt. The growth of the crystalline phases of PVDF during isothermal crystallization at different temperatures has been monitored using Fourier transform infrared (FTIR) spectroscopy. The isothermal crystallization kinetics of PVDF and the melting temperatures of both PVDF and IL were characterized by differential scanning calorimetry, and the microstructures of the blends were analyzed by optical and electron microscopy. It is observed for [Emim][PF6]/PVDF blends that the isothermal crystallization from the melt between 120 and 162 °C produces PVDF crystallites in the β and γ electroactive phases, while the formation of α-phase crystals is nearly suppressed. The morphology of the blends is altered by the addition of IL, which results in the separation of solid phases at room temperature. In addition, [Emim][PF6] remains liquid when mixed with the amorphous PVDF chains due to the cryoscopic descent.This work was supported by the Portuguese Foundation for Science and Technology (FCT) in the framework of the Strategic Funding UID/FIS/04650/2019. The authors thank FEDER funds through the COMPETE 2020 Program and National Funds through FCT under the projects PTDC/BTM-MAT/28237/2017, PTDC/EEI-SII/5582/2014, and PTDC/FIS-MAC/28157/2017. D.M.C. thank the FCT for grant SFRH/BPD/121526/2016 and C.M.C. for the Investigator FCT Contract 2020.04028.CEECIND. The work of the Spanish groups has been funded by the Spanish State Research Agency (AEI) through the PID2019-106099RB-C41/AEI/10.13039/501100011033 project and from the Basque Government Industry and Education Departments under the ELKARTEK and PIBA (PIBA-2018-06) programs, respectively. CIBER-BBN is an initiative funded by the VI National R&D&I Plan 2008-2011, Iniciativa Ingenio 2010, Consolider Program. CIBER Actions are financed by the Instituto de Salud Carlos III with assistance from the European Regional Development Fund