Low-Temperature Phase Transitions of 1-Butyl-1-methylpyrrolidinium Bis(trifluoromethanesulfonyl)imide Swelling a Polyvinylidenefluoride Electrospun Membrane

We studied the temperature behavior of 1-butyl-1-methylpyrrolidinium bis(trifluoromethanesulfonyl)imide (PYR14TFSI) swelling a polyvinylidenefluoride (PVdF) electrospun membrane by means of differential scanning calorimetry and dynamic mechanical analysis. The pure ionic liquid undergoes a glass transition around -85 degrees C independently of the cooling rate (4 or 0.5 degrees C/min). However, when PYR14TFSI swells the polymer membrane crystallization can be induced, either by cooling with a slow temperature rate (0.5 degrees C/min) around -52 degrees C or by prolonged isothermal treatments at -40 degrees C. The kinetics of the crystallization can be described by the usual Johnson-Mehl-Avrami-Kolmogorov equation, for both the isothermal and nonisothermal process. An Avrami index n = 3.78 +/- 0.09 and an activation energy for the crystallization on cooling of the ionic liquid (IL) in the PVdF membrane of 16.0 +/- 0.4 kJ/mol (37.9 +/- 0.1 J/g) are obtained from our experimental data.