Hard body amphiphiles at a hard wall

We investigate the structure of amphiphilic molecules exposed to a substrate that is modelled by a hard wall. Our simple model amphiphiles consist of a hard sphere head group to which a vanishingly thin needle tail is radially attached, resulting in a lollipop shape. Such particles act as amphiphiles when added to a binary fluid of hard spheres and needles. Focusing on the pure amphiphile system we compare the results for the positional and orientational order profiles obtained from a recent density functional approximation to those of our computer simulations and find good agreement. For low densities the structure is ruled by the loss of orientational free volume near the wall, while for higher densities packing of the spherical heads dominates. Furthermore, we test the wall sum rule explicitly for this model fluid and find rich structure of the contact distribution which can be interpreted in terms of typical particle configurations.