Terraced Spreading of Nanometer-thin Lubricant Using Molecular Dynamics

Brooklyn Noble, University of Utah

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Ultra-thin lubricant films are essential in the design of nanoscale systems and devices as surface effects become increasingly important on the nanoscale. Experiments with polymer-based lubricants terminated with functional end groups have documented terrace-shaped formations when a nanometer-thin lubricant film spreads on a substrate. While critical to the design of nanoscale lubricant systems, the origins of these terrace formations are not well understood. 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 occurs due to a sequential diffusion and instability mechanism around molecular lubricant layers formed by functional end groups that are attracted to each other, cluster, and 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. This research has implications for nanoscale systems and devices that involve the design of complex, ultra-thin lubricant systems in extreme environments, including micro and nanoelectromechanical devices, nano-imprint lithography, anti-biofouling/fouling-resistant coatings and hard disk drives.

Abstract Author(s): B. Noble, B. Raeymaekers