The replenishment characteristics of PFPE polar lubricant films after sliding-induced depletion arising on lubricant-coated magnetic disks have been clarified by measuring the profile changes of the lubricant film incurring in-contact sliding against a glass pin. Lightly loaded and slowly rotated test conditions were selected so that the molecular layering structure would not be strongly disturbed or destroyed. An unrecoverable phenomenon was first found to occur in which the replenishment function of lubricant films failed. This phenomenon was observed to occur when depletion depth reaches the monolayer surface or when the residual film thickness is only slightly thicker than the monolayer; when depletion depth invades the monolayer, unrecoverable features changed into recoverable features. Compared with the same tests performed using a nonpolar lubricant, the unrecoverable phenomenon was found to be peculiar to polar lubricants. In addition, replenishment characteristics were compared with diffusion characteristics currently obtained from step-boundary flow, which spreads outward from a step-shaped lubricant boundary, and the similarities and differences between the two were clarified.
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