Analysis of the structure of acetonitrile aqueous solutions based on study of their volumetric elastic properties

The evolution of the structure of acetonitrile aqueous solutions is investigated by analyzing the concentration and temperature dependences of density, ultrasound velocity, adiabatic compressibility, excess molar volume, and excess adiabatic compressibility. It is shown that, the region in which solutions exist can be divided into five intervals that differ by solution structure. The structural features are described for each of them. It is found that in the 0.1 ≤ x ≤ 0.9 range of acetonitrile mole fractions, excess adiabatic compressibility isotherms behave abnormally: its absolute value increases with temperature, testifying to the important role played by the CH3 group of the amide residue of acetonitrile in molecular interactions.