Structural and compositional effect on the acoustic and volumetric properties of ammonium based ionic liquids with water and N-methyl-2-pyrrolidone

Understanding the volumetric behavior of ionic liquids with molecular solvents is essential for the development of industrial applications. In the present work, attempts have been made to explore and understand the effect of various structurally different protic ionic liquids upon the volumetric and acoustic behavior, when mixed with polar protic solvent (water) and polar aprotic solvent (N-methyl-2-pyrrolidone). Density and speed of sound for ten binary mixture containing five protic ionic liquids namely, propylammonium formate, propylammonium acetate, 3-hydroxypropylammonium formate, 3-hydroxypropylammonium acetate and 3-hydroxypropylammonium trifluoroacetate have been investigated over the whole range of composition at temperature from (293.15 to 333.15) K and at atmospheric pressure. The experimental density and speed of sound data have been used to calculate coefficient of thermal expansion, isentropic compressibility and excess molar volume of studied binary mixtures. In most of the studied binary systems the excess molar volumes were found to be negative and the experimental excess molar volumes have been correlated with Redlich-Kister equation. The protic and aprotic nature of molecular solvents along with its shape and size found to affect the studied volumetric properties. Moreover, the effect of anionic chain length, functionalization of cationic side with hydroxyl group and temperature upon studied properties has also been discussed. The results were analyzed on the basis of ion-dipole interaction, interstitial packing and hydrogen bonding between ionic liquids and molecular solvents.