Coarse-Grained Molecular Dynamics Simulations of UV Patterning of Nanometer-Thick Liquid Lubricant Films(Machine Elements, Design and Manufacturing)

The characteristics of monolayer liquid lubricant films coated on magnetic disks are basically determined by their interactions with disk surfaces. If the strength of the interactions could be patterned by ultraviolet (UV) irradiation through a photomask, it would be possible to attain desired tribological performance by rational design of the pattern. In this research, we developed coarse-grained molecular dynamics simulations to investigate the effect of masked UV irradiation on the distribution of monolayer lubricant films coated over solid surfaces. Consistent with experimental results, the simulation results showed that masked UV irradiation induces molecular flow from non-irradiated toward irradiated areas, and thereby a patterned surface structure with thicker lubricant in the irradiated area than in the non-irradiated area. The lubricant films, however, remained monolayer even in the UV-irradiated area. Our simulation results demonstrated that, rather than stacking of lubricant molecules, the patterned surface structure is caused by the stretch of the lubricant molecules in the film thickness direction following the increase of molecule density in the irradiated area.