Impact of isomeric steric hindrance on the thermodynamic excess properties of 3-aminopropyl (dimethyl)amine + dimethylaniline binary systems

This study investigates the non-ideal thermo physical behaviour of binary mixtures containing 3-(dimethylamino)propan-1-amine (DMAPA) and three dimethylaniline isomers (2,6-, 2,5-, and 2,4-DMA) across a temperature range of 303.15 K to 313.15 K. Experimental results reveal significant negative excess molar volumes and positive viscosity deviations, highlighting strong inter-association through hydrogen bonding, dipole-dipole alignments and acid-base interactions. The magnitude of these deviations is governed by the pKa differential and the specific orientation of methyl groups, with 2,6-DMA showing unique steric hindrance effects. To theoretically validate these findings, the PFP theory was applied to dissect the relative contributions of interactional, free volume, and internal pressure effects. Furthermore, the Jouyban-Acree model was successfully employed to correlate the experimental density, speed of sound and viscosity data, demonstrating high predictive accuracy for these complex amine systems. These insights elucidate the structural-solvative relationships essential for industrial chemical processing and molecular modelling.