Effect of hydrophobic phenomena over the volumetric behavior of aqueous ionic liquid solutions

Abstract

To explore the effect of ionic liquid hydrophobicity over the volumetric properties, density has been determined for six of these compounds in aqueous solution in the temperature interval (293.15–308.15) K, covering the diluted region. For three of these binary systems, density at 298.15 K in the pressure interval (0.1–95) MPa has been also measured. The atmospheric pressure density is used together with high pressure data to calculate excess volumes as a function of pressure with high accuracy through an integration scheme based on the excess volume derivative against pressure. Since hydrophobic phenomena is known to have a greater effect over second and third order derivatives of the thermodynamic potential, partial molar volume as well as the its derivative against mole number of the ionic liquid are calculated. Clear anomalies are detected in these magnitudes for all binary systems, very similar to those found for low molecular weight amphiphiles. Dependencies of this anomalous behavior against temperature and pressure are also analyzed.