Abstract
Light scattering and dielectric spectroscopy measurements were performed on the room temperature
ionic liquid (RTIL) [C4mim][NTf2] in a broad temperature and frequency range. Ionic conductivity
was used to estimate self-diffusion of ions, while light scattering was used to study structural
relaxation. We demonstrate that the ionic diffusion decouples from the structural relaxation process
as the temperature of the sample decreases toward Tg. The strength of the decoupling appears to
be significantly lower than that expected for a supercooled liquid of similar fragility. The structural
relaxation process in the RTIL follows well the high-temperature mode coupling theory (MCT) scenario.
Using the MCT analysis we estimated the dynamic crossover temperature in [C4mim][NTf2]
to be Tc ∼ 225 ± 5 K. However, our analysis reveals no sign of the dynamic crossover in the ionic
diffusion process.
