Nonlinear acoustic investigation of intermolecular interactions in binary mixtures of 2-ethoxyethanol with 2-pyrrolidinone and N-methylacetamide

The acoustic nonlinearity parameter and its excess values were evaluated for binary mixtures of 2-ethoxyethanol with 2-pyrrolidinone and N-methylacetamide over the complete composition range at 303.15, 313.15 and 323.15 K using Tong – Dong, Beyer, Beyer – Tong – Dong, Hartmann, Ballou, Lu, Endo, Moelwyn – Hughes, and Sharma models. The excess nonlinearity parameter exhibited predominantly negative deviations for most models, indicating significant heteromolecular interactions and non-ideal mixing behaviour in both systems. The observed nonlinear acoustic behaviour therefore reflects the combined influence of molecular compressibility, structural rearrangement and relaxation effects. The magnitude of deviations increased with temperature, indicating weakening of molecular association due to thermal agitation. Redlich – Kister polynomial fitting was employed to correlate the excess values, and the fitted coefficients showed good agreement. The results demonstrate the usefulness of acoustic nonlinearity parameters in understanding nonlinear compressibility behaviour, structural rearrangement and intermolecular association in associating liquid mixtures.