FLUID CUSPS AT THE MOLECULAR SCALE

Recent experiments and calculations have exhibited apparent steady cus ps in certain fluid free surfaces driven by a converging subsurface fl ow. Molecular dynamics simulations are used to elucidate some of the i ssues raised by this phenomenon, with emphasis on the behavior of the fluid on very small scales. The similar but different situation of two immiscible fluids of equal viscosity driven by solid rollers is consi dered. Molecular scale simulations of the evolution of the separating interface exhibit a gradual increase of curvature with rotation rate. However, high curvature interfaces do not reach a steady state, but in stead drops of the fluid above the free surface are detached. In no ca se does a true cusp form, and the stress tensor is never unusually lar ge in the near-cusp region.