Measurement of ultraslow rotational dynamics of probes in imidazolium-based ionic liquids near and below the glass transition temperature: Study the role of structural heterogeneity on dynamic heterogeneity

Room temperature ionic liquids have many favorable properties, such as low volatility, low melting points, high ionic conductivity, and a wide liquid range. They are typically composed of a bulky, organic cation paired with an organic or inorganic anion. The large number of potential anion and cation combinations offers task-specific customization, and the low vapor pressure and non-flammability of ionic liquids bring forth safety advantages. Ionic liquids supercool easily, and their wide liquid range makes it possible to study the glass transition. Ionic liquids have the potential to replace conventional solvents, but before they may be put to wide use, a full inquiry of their physical properties must be carried out. In this experimental study, we studied the ultra-slow rotational dynamics of organic probes in three imidazolium-based ionic liquids containing the bistriflate anion near their glass transition temperatures by utilization of the fluorescence recovery after photobleaching method. Near the glass transition, the dynamics of supercooled liquids slow down dramatically and become spatially heterogeneous. Ionic liquids exhibit structural heterogeneity as a result of being composed of a negatively charged anion and a cation with a polar headgroup and non-polar alkyl tail. The purpose of this study was to observe the role of structural heterogeneity on dynamic heterogeneity.