Temperature dependent behavior of hydrogen-bonded liquids: bridging experiments with molecular dynamics and DFT

Temperature strongly influences the structure and dynamics of hydrogen-bonded liquids, with direct implications for their thermodynamic and transport behavior. In this study, we investigate binary mixtures of heptanal with a homologous series of 1-alkanols (C3-C7) by combining experimental measurements with molecular dynamics (MD) simulations and density functional theory (DFT) calculations. Our results demonstrate that increasing temperature progressively disrupts hydrogen-bonded networks, leading to systematic changes in both microscopic organization and macroscopic properties. Radial distribution functions and hydrogen-bond statistics reveal thermal weakening of directional interactions, while rising self-diffusion coefficients indicate enhanced molecular mobility. Temperature-resolved RDFs were further converted into distance-dependent free energies, allowing separation of enthalpic and entropic contributions and showing that local contacts are primarily enthalpy-driven with small negative entropic penalties. Voronoi-based void analysis shows that heating broadens cavity-size distributions and increases void connectivity. Thermodynamic and transport data display negative excess molar volumes and positive viscosity deviations across all systems, with both effects diminishing with temperature and alcohol chain length. DFT calculations further confirm that thermal disruption is more pronounced in mixtures with shorter-chain alcohols, reflecting stronger aldehyde–alcohol interactions at lower temperatures. Together, these findings provide a consistent thermal perspective: low temperatures promote dense packing and higher resistance to flow, whereas elevated temperatures reduce contraction and viscosity. This integrated framework advances understanding of hydrogen-bonded liquids and supports rational solvent selection and thermal process optimization.