Molecular dynamics study on the role of hydroxyl groups in heat conduction in liquid alcohols

On the basis of non-equilibrium molecular dynamics (NEMD) simulation for alcohols from ethanol to tetracosanol, the present study analyzes the molecular-level energy transfer in associated liquids for the first time. Direct evaluation of the energy transfer by each interatomic interaction reveals a counterintuitive result that in liquid alcohols the Coulomb interaction does not transfer heat more than the van der Waals interaction even for short chain species like ethanol. In addition, by comparing the NEMD analysis on alcohols with those of alkanes, we discuss a molecular mechanism by which alcohol has a higher thermal conductivity than alkane in view of molecular heat transfer. It is shown that hydroxyl OH, not only provides heat paths for the Coulomb interaction, but also increases the number of heat paths for the vdW and the intramolecular interactions. Consequently, the part of the heat transfer by the vdW interaction is replaced with more efficient transfers by the Coulomb and intramolecular interactions, and therefore a higher thermal conductivity occurs. The insights obtained from the present study update the view of microscopic heat transfer in associated liquid towards the molecular theory of thermal conductivity of liquids, which is currently immature in comparison with those of gases and solids.