Modeling of lubricant spreading on a solid substrate

The spreading of nonfunctional or functional perfluoropolyether (PFPE) on a solid substrate is important for the service durability and reliability of computer head-disk devices. Molecular-dynamics simulations based on a coarse-grained, bead-spring model have been adopted to investigate the spreading process. For nonfunctional PFPE, molecules in the fluid interface region of the droplet will flow down to form a cap structure on the substrate. Simultaneously molecules at the liquid front will diffuse along the substrate to form a precursor film, and molecules above the diffusion layer will move downward to fill the cavities created by diffusion. For functional PFPE, interactions between end beads, and between end beads and the substrate complicate the spreading process, giving rise to a hat structure with a vertical step and a precursor film with slower flux.