Simulation of ultrathin lubricant films spreading over various carbon surfaces

The mathematical modeling of the dynamics of ultrathin perfluoropolyalkylether (PFPE) films, taking into consideration both the disk carbon surface composition and lubricant endgroup functionality, is described. Theoretical development based on the Monte Carlo method was employed to emulate experimental spreading data. In this model, we construct a system Hamiltonian based on a lattice-gas model by explicitly incorporating four classes of interactions: molecule/ molecule, molecule/surface, endgroup/endgroup, and endgroup/surface, where a molecule is denoted as a backbone in the absence of endgroups. Spreading properties are investigated by tuning the lubricant interactions to model PFPE Z (without polar endgroups) and PFPE Zdol (with polar endgroups) on several surfaces. The simulations qualitatively describe the spreading profiles for molecules with and without polar endgroups. Acquired from N-frame animations, L-t plots are constructed and provide a qualitative comparison with the experimental data obtained from scanning microellipsometry.