Comparison of thermodynamics properties of ionic liquids with those of simple electrolytes, polymers,cationic surfactants and tetraalkylammonium salts in aqueous and non-aqueous solutions

Ionic liquids (ILs) are organic salts that are liquids at temperatures below 373.15 K. Because of their interesting physical and chemical properties, such as negligible vapor pressure, unique permittivity,high thermal stability, good solvents for both organic and inorganic substances, high electrical conductivity, and wide electrochemical window, ILs have been widely used as reaction media, separation solvents, and novel electrolytes [1-2]. In solution, the solvation and the interactions of the ions or ion pair with the solvent determine the unique properties of these systems [3]. The volumetric and acoustic properties of electrolytic and nonelectrolytic solutions have proved particularly informative in elucidating the solute-solute and solutesolventinteractions that exist in these solutions. In spite of their importance, there is limited information on the thermodynamic properties of ILs in aqueous or non-aqueous solutions. In the present work, the alkyl chain length of 1-alkyl-3-methylimidazolium bromide ([Rmim][Br], R = propyl (C3), hexyl (C6), heptyl (C7), and octyl (C8)) was varied to prepare a series of room-temperature ionic liquids (RTILs), and experimental measurements of density and speed of sound at different temperatures ranging from 288.15 to 308.15 K for their aqueous and methanolic solutions in the dilut