A Spreading Study of Lubricant Films via Optical Surface Analyzer and Molecular Dynamics

The spreading capability of perfluoropolyether (PFPE) films is critical to handling the intermittent contacts, as well as the long-term reliability of hard disk drives. We first investigated the spontaneous spreading of PFPE nanofilms on carbon overcoats via optical surface analyzer, where we captured the square-root dependence of monolayer thickness on molecular weight, as well as the evolution of monolayer interface inside the thick film for functional PFPEs. Molecular simulation with the Langevin equation was also performed to understand how the molecular motion contributes to the film spreading process. Via the histogram of molecular transfer between layers based on the simulated spreading profiles, we noticed that functional PFPEs are more confined to diffuse than nonfunctional PFPEs. The anisotropic mobility entropy was defined to supplement our understanding of the spatially dependent mobility for functional PFPEs