Monolayer spreading in confined immiscible fluids: A molecular dynamics simulation

Molecular dynamics simulations have been performed for two immiscible fluids confined in a slit pore. It is observed that in the regime of complete wetting, the wetting fluid spreads at the solid surface through a penetrating monomolecular layer intercalated between the solid wall and the nonwetting fluid. In particular, the penetration length of this monolayer increases as L(t)∼t. Therefore, the monolayer spreading observed for the confined immiscible (simple) fluids is very similar to the terraced spreading observed for nonvolatile polymeric liquids. We propose a simple model to explain the diffusive manner of monolayer spreading, taking into account the capillary driving force and the interfacial dissipation caused by the slipping of monolayer at the solid surface. The diffusive behavior of L(t)L(t) is recovered and the value for the diffusion coefficient is evaluated, in semi-quantitative agreement with our observation.