Mixtures of ionic liquids with similar molar volumes form regular solutions and obey the cross-square rules for electrolyte mixtures

The mixing of ionic liquids of similar and dissimilar molar volumes was studied using molecular dynamic simulations. Binary mixtures of liquids with similar molar volume have negligible enthalpies of mixing, form regular solutions, and obey the cross-square rules for the mixing of electrolytes. In the case of binary mixtures of ionic liquids with significantly different molar volumes, the excess enthalpy is positive and the solution structure shows some dependence on the composition. One particular system exhibited a positive free energy of mixing as a function of the composition of the solution. This suggests the existence of a demixing region in the phase diagram. (C) 2011 Elsevier B.V. All rights reserved.