New article in Phys. Rev. E on nonlocal entropic contributions to interfacial properties

Our paper entitled: Temperature anisotropy at equilibrium reveals nonlocal entropic contributions to interfacial properties has been accepted for publication in Physical Review E.

In the work, we show that the configurational part of the temperature has different contributions from the parallel and perpendicular directions at the vapor-liquid interface, even at equilibrium. This has been illustrated in the figure below. Let us assume that north/south are the directions perpendicular, and east/west are the directions parallel to the vapor-liquid interface. Particles located about 1 nanometer towards the vapor-side of the equimolar surface would feel contributions to the configurational temperature from the north/south direction which, if they would have been in a single-phase fluid, would correspond to a hot temperature. These directions would perhaps feel like the Sahara desert. From the east/west directions on the other hand, the contributions would be equivalent to those of a cold temperature in a single-phase fluid. These directions would perhaps feel like the arctic winter. The hot and cold contributions compensate each other, such that the particle at the interface experiences the equilibrium temperature overall.

The article starts by explaining why anisotropy in the contributions to the configurational temperature is expected across the vapor-liquid interface from a theroretical point of view. We next show that the anisotropy can also be found in molecular dynamics simulations and obtain a qualitative agreement between theory and simulations. The theory shows that the temperature anisotropy originates in nonlocal entropic contributions, which are missing from the classical description of interfacial phenomena.

The nonlocal entropic contributions discussed in this work are likely to play a role in the description of both equilibrium and nonequilibrium properties of interfaces. At equilibrium, they influence the temperature- and curvature-dependence of the surface tension. Across the vapor-liquid interface of the Lennard Jones fluid, we find that the maximum in the temperature anisotropy coincides precisely with the maximum in the thermal resistivity relative to the equimolar surface, where the integral of the thermal resistivity gives the Kapitza resistance. This links the temperature anisotropy at equilibrium to the Kapitza resistance of the vapor-liquid interface at nonequilibrium.

I believe the work to be of importance to future research on interfacial phenomena, in particular for the description of nonequilibrium interfacial processes. The work was performed in in collaboration with Thuat T. Trinh and Anders Lervik from the Department of Chemistry at the Norwegian University of Science and technology.

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