Temperature-dependent structure measurements of imidazolium-based ionic liquids with varying alkyl chain length

Room-temperature ionic liquids (RTILs) are organic compounds attracting a great deal of attention as solvents in a wide variety of applications including as electrolytes in Li-ion batteries. An understanding of the nanoscale structure in these RTILs is essential for understanding their solvency and their electrochemical properties hopefully leading to new high-performance materials. We report on the static structure factors from high-energy synchrotron and laboratory source x-ray diffraction experiments on a series of four homologous ionic liquids. The ionic liquids are 1-alkyl-3-methylimidazolium paired with the triflate anion, with alkyl chain lengths of 4, 6, 8, and 10 carbons. While all structure factors show a distinct prepeak and main peak, a so called ``first sharp diffraction peak'' is observed for alkyl chain lengths of 6, 8, and 10. In this talk, we discuss the association of these features with structures in the liquid and the possible implications for transport mechanisms associated with AC and DC conductivity measurements. The temperature dependence of these features indicates a complicated interplay between entropic and enthalpic tendencies on the evolution of intermolecular structures.