Binary Lennard-Jones mixtures with highly asymmetric interactions of the components. 2. Effect of the particle size on phase equilibria and properties of liquid-gas interfaces

The method of molecular dynamics simulation has been used to investigate phase equilibrium and properties of liquid-gas interfaces in two-component Lennard-Jones systems in which at the equality of the energy parameters of the interaction potential (ε11 = ε22) the ratio of the particle sizes of the dissolved substance and the solvent σ22/σ11 varied from 0.1 to 0.2. Calculations were made in the temperature range from T∗ = kBT/ε11 = 0.7 to 1.0. The concentration dependences of orthobaric densities, saturation pressure, surface tension, relative absorption, and the effective thickness of interface have been obtained. A uniform distribution of a substance in bulk phases is observed at concentrations of the second component in the liquid up to cl < 0.65. An increase in the content of small-sized particles in a mixture above this value leads to the formation of clusters. The orthobaric densities of liquid and gas phases depend only slightly on the value of the ratio σ22/σ11. It has been found that at the cost of location of small-sized particles (of the substance dissolved) between particles of larger sizes (of the solvent) there may be states in which the density of the liquid phase exceeds its value in the pure solvent several times. The enrichment of a mixture with small-sized particles leads to a monotonic increase in the surface tension and desorption of particles of this kind from the interfacial layer.