Simulation and theory of fluid-fluid interfaces in binary mixtures of hard spheres and hard rods

We consider the free interface between demixed fluid phases in a mixture of hard spheres and vanishingly thin hard rods using Monte Carlo simulations and density functional theory. Both approaches treat the full binary mixture and hence include all rod-induced many-body depletion interactions between spheres. The agreement between theoretical and simulation results for density and orientation order profiles across the interface is remarkable, even for states not far from the critical point. The simulation results confirm the previously predicted preferred vertical (parallel) alignment of rod orientation to the interface plane at the sphere-rich (sphere-poor) side. This ordering should be experimentally observable in phase-separated colloidal rod-sphere mixtures.