The experimental measurements of the speed of sound and density of aqueous solutions of imidazolium based ionic liquids (IL) in the concentration range of 0.05 mol . kg(-1) to 0.5 mol . kg(-1) at T = 298.15 K are reported. The data are used to obtain the isentropic compressibility (beta(S)) of solutions. The apparent molar volume (Phi(v)) and compressibility (phi(KS)) of ILs are evaluated at different concentrations. The data of limiting partial molar volume and compressibility of IL and their concentration variation are examined to evaluate the effect due to IL-water and IL-IL interactions. The results have been discussed in terms of hydrophobic hydration, hydrophobic interactions, and water structural changes in aqueous medium. (C) 2007 Elsevier Ltd. All rights reserved.
