Liquid-liquid phase separation of binary Lennard-Jones fluid in slit nanopores

Molecular Dynamics Simulation of Tolman Length and Interfacial Tension of Symmetric Binary Lennard–Jones Liquid

The Tolman length and interfacial tension of partially miscible symmetric binary Lennard–Jones (LJ) fluids (A, B) was revealed by performing a large-scale molecular dynamics (MD) simulation with a sufficient interfacial area and cutting distance. A unique phenomenon was observed in symmetric binary LJ fluids, where two surfaces of tension existed on both sides of an equimolar dividing surface. The range of interaction εAB between the different liquids and the temperature in which the two LJ fluids partially mixed was clarified, and the Tolman length exceeded 3 σ when εAB was strong at higher temperatures. The results show that as the temperature or εAB increases, the Tolman length increases and the interfacial tension decreases. This very long Tolman length indicates that one should be very careful when applying the concept of the liquid–liquid interface in the usual continuum approximation to nanoscale droplets and capillary phase separation in nanopores.

Population inversion, selective adsorption, and demixing of Lennard-Jones fluids in nanospherical pores

The density functional theory has been employed to investigate the population inversion, selective adsorption, and demixing of confined mixture fluids in a spherical nanocavity. In the case of hard sphere fluids for which only the entropy effect has the dominant role, the selective adsorption process strongly depends on size ratio, population of the adsorbed component, and pore size. The effects of such parameters as interaction strength, size ratio, and thermodynamic state on population inversion and selective adsorption have been investigated for L-J mixture fluids. The results for L-J asymmetric binary mixture fluids indicate that the mole fraction of large species (molecules with bigger radii) inside the cavity becomes greater with increasing size ratio or with decreasing temperature than does that for the other component despite its lower population in the bulk fluid (i.e., the so-called population inversion phenomenon). Our results indicate that the inversion population density decreases with size ratio, and the mole fraction of the component with the bigger radius in the pore increases with temperature. Thus, by selecting a small spherical cavity under special conditions, it will be possible to give rise to the selective separation of component 2 in spite of its lower concentration in the bulk asymmetric L-J mixture. Finally, we have investigated the phase separation, demixing phenomenon, of an asymmetric L-J mixture inside a spherical cavity. Also we investigated the cases for which the layered demixing phenomenon occurs in the asymmetric L-J fluid in a nanospherical pore as a result of the difference between the entropy and energy effects.