Hitoshi Washizu

Vapor-liquid equilibrium (VLE) data of fragrance components are crucial for product development and separation processes. However, experimentally obtaining these data can often be a high-cost and challenging task. In order to address this issue, simulations of VLE data using molecular dynamics (MD) methods have gained attention, though there are still relatively few studies about the vapor-liquid equilibrium calculations of fragrance components using MD. In this study, we focused on a mixture of d-limonene and 1-pentanol as representative components and conducted MD simulations. The VLE data obtained by varying the molar fraction of d-limonene, including x-y phase diagrams and activity coefficients, showed a high degree of agreement with the experimental data. Additionally, an analysis of the density profiles on a molecular level revealed a slight increase in the concentration of 1-pentanol at the vapor-liquid interface.

A reactive force field (ReaxFF) molecular dynamics simulation is performed for the sliding of diamond-like carbon (DLC) and yttria-stabilized zirconia (YSZ) under an ethanol gas environment, motivated by the previous experiment of ultralow friction phenomenon (friction fade-out). We observe (i) dissociation of ethanol into ethoxy and hydrogen, both of which simultaneously adsorb on the YSZ surface, and (ii) dissociation of ethanol into ethyl and hydroxy, the former of which forms a bond with another ethanol molecule and the latter of which adsorbs on the DLC surface. Reaction (i) is enhanced by the sliding motion, but occurs even without it, while reaction (ii) only occurs during sliding with a sufficiently high load pressure. The potentials of mean force for the two reactions are also calculated combining the steered MD and Jarzynski equality. It is shown that the activation energies of reactions (i) and (ii) are significantly lowered by the YSZ and DLC surfaces, respectively, as compared to those in a vacuum. The resultant activation energy is higher for reaction (ii) than for reaction (i).