Molecular Dynamics Simulation of Thermal-Induced Local Heating and Depletion of Ultrathin Perfluoropolyether Lubricant Under Moving Laser Heating

Molecular dynamics simulations of nanostructured perfluoropolyether lubricant are performed to investigate localized heating and lubricant depletion instability under moving laser heating. The evolution of the lubricant surface morphology indicates that a valley-like depletion track is formed along the path of the laser beam, resulting in aggravated depletion with heating time. The depletion profiles at various laser durations are characterized by the film thickness, in which a raised ridge is formed around the depletion zone signifying that the thermocapillary stress has a non-negligible effect on lubricant depletion. The recovery process is studied as well by further equilibrating the entire system with the laser beam turned off. During the cooling stage, the lubricant undergoes a slow recovery when compared with the laser-induced depletion. In addition to the attractive lubricant-to-disk interaction, the strong polar coupling between end beads prevents the recovery of lubricant beads back to the depleted surface. Moreover, the nonuniform surface tension and the nonequilibrium thermocapillary stress are expected to account for the mechanisms of lubricant depletion under moving laser heating.