Diffusive spreading of rodlike molecules on surfaces

We study the diffusion and submonolayer spreading of rigid rodlike molecules on smooth surfaces. The molecules interact through a short-range repulsive potential and their motion is described through molecular dynamics simulations. We concentrate on the behavior of the collective diffusion coefficient DC(θ) as a function of the surface coverage θ. Through analysis of spreading profiles of circular droplets, and rectangular density profiles we determine DC(θ) for rods of varying lengths. We demonstrate that in analogy to experiments and simulations on chainlike flexible molecules, DC(θ) initially increases with θ due to entropic repulsion and displays a peak at intermediate coverages.