Decoupling of segmental relaxation from ionic conductivity in [DEMM][TFSI] room temperature ionic liquid incorporated poly(vinylidenefluoride-co-hexafluoropropylene) membranes

Abstract

Herein, thermophysical and electrical properties of different polymer membranes, prepared by incorporating different amounts of room temperature ionic liquid (IL), N,N-diethyl-N-(2-methacryloylethyl)-N-methylammonium bis(trifluoromethylsulfonyl) imide ([DEMM][TFSI]), in poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) polymer, have been studied. The study reveals that [DEMM][TFSI] IL essentially reduces the crystal growth and promotes electroactive β-phase transformation within the polymer matrix by the interaction between the polymer chains and IL cations. The ionic conductivity of polymeric membranes increases with increasing IL content and attains a maximum value of 4.0×10−4S·cm−1 for highest fraction of ionic liquid (50%) at room temperature (303K). Correlation between ion transport and segmental relaxation in polymer membranes has been analyzed using dielectric spectroscopy. The analysis shows that with increasing faction of the ionic liquid the ionic conductivity gradually decouples from the segmental dynamics of the polymer. This is attributed to the higher diffusivity of relatively free anions at lower temperatures, where the segmental dynamics of polymer significantly slow down.