Lubricant Pickup of Ultra-Thin PFPE Lubricants With Different Backbone Structures

Lubricant pickups on different perfluoropolyether (PFPE)-lubricant (Z-tetraol, D-4OH, and QA-40) films were compared by using a slider surface analyzing (SSA) tester developed to observe the lubricant thickness mapping on the slider surfaces after the heads slide on the disk surfaces. These lubricants have the same four OH functional end-groups but different backbones. Z-tetraol showed the least lubricant pickup among the four lubricants. D-4OH and QA-40 showed considerable pickup at a large clearance of 30-mW back-off. The pickup volumes of each lubricant disk with a similar mobile lubricant thickness were different, and D-4OH showed the largest pickup volume among these lubricants. An MD simulation was performed to understand the difference in the lubricant pickup of the three types of lubricants. The intermolecular force between the slider and the lubricant molecules was different for these lubricants. This difference in the intermolecular force depended on the dipole-dipole interaction between the end-groups and the slider surface, and the dipole-dipole interaction was affected by the conformation of the lubricant molecules. Therefore, it is estimated that the lubricant pickup phenomenon is influenced by the conformation of the lubricant molecules, and D-4OH with a strong -OH function at the lubricant surface exhibited considerable lubricant pickup.