Formation of Lubricant “Sierra” at Boundary Between Perfluoropolyether Solution Dipped and Undipped Zones over Diamond Like Carbon Coated Magnetic Disks

An unstable phenomenon arising at the boundary between perfluoropolyether (PFPE) solution dipped and undipped zones over diamond like carbon (DLC) coated magnetic disks was studied. The formation conditions of a ridge of lubricant, or “sierra,” at this boundary and the structure of the “sierra” were clarified. It was found that the “sierra” structure of the lubricant suddenly formed when withdrawing the disk from the lubricant solution was decreased to less than a specified value of around 1 mm/s. The “sierra” was less likely to form for a lower lubricant concentration and a longer elapsed time after making the lubricant solution. It was also revealed that, along the ridgeline of the “sierra,” peaks formed periodically and the peak feet propagated in the direction perpendicular to the boundary, forming convex fronts and leaving multiplex bead chains of lubricant accumulations inside the convex.