Effect of size disparity on the gas-liquid interfacial properties of Lennard-Jones monomer plus dimer mixtures

The interfacial properties of Lennard-Jones monomer plus dimer mixtures at the gas-liquid (gl) interfaces are determined by the direct molecular dynamics (MD) and the density gradient theory (DGT), coupled with the soft-SAFT (soft-statistical associating fluid theory) equation of state. It is demonstrated that both approaches exhibit excellent mutual agreement in the entire pressure and concentration ranges. According to the presented results, the leading effect of increasing the geometrical disparity between the constituent dimer and monomer (σ₂₂ ³/σ₁₁ ³) at the gl state is sharpening of the interface increase and expansion of the biphasic coexistence region. Besides that, decreasing of the size disparity and increasing the mixture asymmetry result in a wider phase envelope in terms of densities and molar fractions. In addition, the interfacial thickness and the surface tension grow with reduction of σ₂₂ ³/σ₁₁ ³, which is a direct consequence of increasing the system asymmetry.