Available States Versus Available Space: Which Predicts the Self-Diffusivity of Dense Confined Fluids?

Confining a fluid to length scales on the order of few particle diameters changes both its static and dynamic properties. Classical density functional theories can often make reliable predictions concerning the former, but implications of confinement for dynamics remain challenging to forecast for even the most basic models. Recent computer simulations of simple, equilibrium fluids show that the relationship between excess entropy, a static property, and self-diffusivity, a dynamic quantity, is approximately independent of the degree of confinement. Do other static measures, such as those that characterize free or available volume, also strongly correlate with single-particle dynamics? Using computer simulations and theory, we investigate this question for a variety of fluids and fluid mixtures, namely the hard-sphere and the Gaussian core fluids confined to channels with strongly interacting boundaries. In particular, we critically analyze the validity of correlations between various static structural and dynamical properties for the above mentioned systems in dense as well as super-cooled regimes.