Terraced spreading of nanometer-thin lubricant using molecular dynamics

Abstract

Ultra-thin lubricant films are essential in the design of nanoscale systems and devices as surface effects become increasingly important on the nanoscale. We have used molecular dynamics simulations to quantify terraced spreading of perfluoropolyether lubricant on a flat substrate as a function of polymer chain length, lubricant thickness, and functional end groups of the lubricant and the substrate. In addition, we have investigated the physical mechanisms that drive terraced lubricant spreading on a flat substrate. The results show that terraced lubricant spreading follows a process of diffusion and instability, where functional lubricant end groups are attracted to other functional end groups to form clusters that organize into layers. These distinct layers of functional end groups cause the lubricant thickness profile to take on a terraced shape, where layers correspond to the locations at which terraced formations occur. The presence of functional end groups determines the locations of both layer and terrace formations, and greatly affects lubricant spreading.