Molecular Origins of Philicity: How Atomic Interactions Determine Miscibility and Diffusivity

We present a computational study on the microscopic origin of molecular philicity, which determines the miscibility and diffusivity of binary liquids. Our simulations reveal how the miscibility of an alkane-perfluoroalkane system responds to variations in the philicity of the two components, which is controlled by tuning the Lennard-Jones force-field parameters. One particular challenge is measuring the instantaneous degree of mixing of the two components. Here, we use two criteria: one based on the pair correlation function and one based on the instantaneous configurational entropy of mixing. We observe a characteristic linear dependence of the critical temperature of mixing on the interaction energy values. The critical temperature is considerably more sensitive to changes in the aliphatic alkanes than in the fluorinated ones. In contrast, the size parameter has a negligible influence on either molecule.