Density Functional Theory for Fluids at the Nanoscale

The interplay of thermal noise and molecular forces is responsible for surprising features of liquids on sub-micrometer lengths in particular at interfaces. Not only does the surface tension depend on the size of an applied distortion [1], but also the dispersion relation of capillary waves differ from the familiar macroscopic behaviour and nanoscopic thin liquid films dewet faster than would be expected from hydrodynamics [2]. Also in equilibrium, fluids open up new astonishing perspectives when confined to small containers. Nanobubbles seem to be more stable than thermodynamically allowed and free energies of confined fluids seem to depend only on four thermodynamically relevant shape variables [3]. This allows the modeling of solvation energies of proteins [4] and of nematic phases in liquid crystals [5]. Some answers to these phenomena can be given by density functional theory, which has become the standard approach to describe fluids at the nanoscale.