Microscopic Structure and Macroscopic Properties of Mesitylene and 2-Alkanol Binary Mixtures: A Combined Experimental, Molecular Dynamics, and DFT Study.

Abstract

This study provides a detailed microscopic and macroscopic investigation into the intermolecular interactions and thermophysical properties of binary mixtures containing mesitylene and a homologous series of 2-alkanols (from 2-propanol to 2-octanol). A combined approach utilizing molecular dynamics (MD) simulations, density functional theory (DFT) calculations, and experimental measurements of density and viscosity was employed. Microscopic structural analyses, including radial, spatial, and combined distribution functions, alongside quantum chemical tools (QTAIM, NBO, and RDG) reveal that alcohols strongly prefer self-association via cohesive O-H···O hydrogen bonds over cross-association. While specific O-H···π interactions between the alcohol and the aromatic ring do occur, they are notably weaker. As the alkanol chain length increases from C3OH to C8OH, growing steric hindrance significantly disrupts packing efficiency and fragments the hydrogen-bond networks, while van der Waals dispersion forces become increasingly dominant. Macroscopically, all binary mixtures exhibit exclusively positive excess molar volumes (VE) and negative viscosity deviations (Δη). These thermophysical behaviors corroborate the theoretical findings, demonstrating that mesitylene acts as a potent structure breaker that disrupts the alcohol networks. The magnitude of this disruption, leading to greater volume expansion and reduced flow resistance, becomes more pronounced with heavier alcohols due to increased steric interference. Ultimately, this work successfully establishes a direct link between atomic-level solvation geometries, competitive binding interactions, and bulk macroscopic thermodynamic behavior.