Volumetric, Thermophysical, Thermodynamic, and Spectral Properties of Pseudobinary Mixtures of Dimethylbenzene Isomers (Xylol) + Butanone at <i>T</i> = (298 to 338 K): An Experimental Study with Complementary DFT Insights

This study comprehensively investigates the thermophysical, volumetric, and spectral properties of pseudobinary xylol + butanone mixtures. Experimental measurements, conducted at T = (298 to 338) K and xylol molar fractions (x1= 0.0–1.0, Δx1 ≈ 0.1), included absolute density (ρ), dynamic (η) and kinematic viscosity (ν), viscosity deviation (Δη), excess molar volume (VmE), excess thermal expansion coefficient (αE), and viscous flow excess properties (ΔGm‡,E, ΔSm‡,E, and ΔHm‡,E). Complementary density functional theory (DFT) simulations provided insights into geometric optimizations, molecular electrostatic potentials, and interaction energies. Results indicate that density and viscosity increase monotonically with the xylol content, reflecting enhanced London dispersion interactions and molecular packing efficiency. All excess properties (VmE, ΔGm‡,E, ΔSm‡,E, and ΔHm‡,E) exhibited negative deviations, signaling favorable dipole-induced dipole interactions and more efficient molecular packing within the mixture. Spectroscopic analyses (FTIR, UV–vis, and photoluminescence) supported these findings, revealing weak, noncovalent interactions and confirming the physical nature of the mixture. DFT calculations further correlated experimental observations with the electronic stability and interaction energies. These findings significantly advance the understanding of xylol + butanone systems, providing critical insights for solvent selection in polymer chemistry and optimizing industrial processes.