| Abstract
| - The nature of the interactions between a representative room-temperature ionic liquid, namely 1-butyl-3-methyl imidazolium tetrafluoroborate ([BMIM][BF4]) and a common organic solvent, acetonitrile (CH3CN)has been investigated by means of Brillouin light scattering, over the whole concentration range and in thetemperature range from −20 to 45 °C. Negative deviations from the ideal behavior of both molar volumesand adiabatic compressibility have been observed. This result has been interpreted within the framework ofa well-established theoretical model, namely a nonadditive hard-sphere mixture. Despite that similar findingswere rationalized in terms of enhanced interactions between molecules, a more detailed analysis of excessthermodynamic functions indicates that they are mainly due to excluded volume effects and that the differencesin local intermolecular interactions act as higher order contributions: we have found that this can be a generalfeature of liquid mixtures. On this basis we present a reconsideration for excess thermodynamic data and fortheir role in providing direct information on intermolecular interactions.
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