Molecular Dynamics Simulations of Perfluoropolyether Lubricant Degradation in the Presence of Oxygen, Water, and Oxide Nanoparticles using a ReaxFF Reactive Force Field

The degradation of a perfluoropolyether lubricant, i.e., D4OH, was studied in the presence of a number of different components in a computer hard disk drive using ReaxFF reactive force field-based molecular dynamics simulations. The chemical reaction between nine D4OH strands with oxygen, water, oxide nanoparticles including SiO₂, goethite (FeO(OH)), and Fe₂O₃ was simulated by using reactive molecular dynamics simulation at T = 1500 K. All oxide nanoparticles were used in three different configurations: (1) untreated - cut from the crystalline structure without further treatment; (2) pretreated with dry air; and (3) pretreated with wet air to simulate a realistic environment. It was observed that water molecules strongly affect the degradation rate of the D4OH lubricant while oxygen molecules do not play a significant role. Moreover, the results indicated that the presence of these nanoparticles in any form accelerates the lubricant degradation. Untreated silica and Goethite nanoparticles have stronger effects on the degradation rates of lubricant strands in comparison to dry-air-treated and wet-air-treated nanoparticles, while in the case of Fe₂O₃ nanoparticles wet-air-treated nanoparticles have the strongest effect on the degradation rates of lubricant strands.