Takayuki Nakakawaji

Adsorption isotherms of perfluorocarbon surfactants from aqueous and non-aqueous solutions and friction measurements of perfluorosurfactant-adsorbed alumina

Abstract The adsorption of a series of perfluorocarbon surfactants C n F 2n + 1 COONa (n = 6, 7, and 8) and C n F 2n + 1 COOH (n = 6, 7, and 8) on aluminum oxide surfaces has been studied experimentally. Isotherms from aqueous and non-aqueous solutions, respectively, were measured, and the effects of pH and fluorocarbon chain length on the adsorption behavior and the maximum level of adsorption determined. Contact angles and friction coefficients for adsorbed films of surfactant on alumina chips were also measured as a function of pH and surfactant concentration. Friction coefficients were reduced while contact angles increased.

Ultrafiltered Perfluoropolyether lubricant under molecular weight distribution control

There are many problems to be overcome when storage devices are used at high-speed rotation and very small spacing between the head and disk. One of them is lubricant spin-off. Lubricant spin-off and lubricity have a close relation to the molecular weight distribution. The commercial Perfluoropolyether (PFPE), which is widely used as a lubricant for magnetic disks, has a wide molecular weight distribution from several hundred to over ten thousand. In order to improve performance regarding spin-off and lubricity, it is necessary to control the molecular weight distribution. This paper discusses the relation between molecular weight of lubricants and spin-off, and stiction. The molecular weight at which spin off occurs easily is found to cause a high stiction. Furthermore, molecular weight distribution control by ultrafiltering is investigated. Presented as a Society of Tribologists and Lubrication Engineers Paper at the ASME/STLE Tribology Conference in Seattle, Washington, October 1–4, 2000

Reversed Micelle Structures in PFPE Lubricant Thin Films on Magnetic Disk Surface Observed by Non-Contact AFM

PFPE lubricants (Fomblin Z-dol) for hard disk surface lubrication have two hydroxyl groups, one at each end of the molecules, and form stable insoluble monolayers at the water surface. In this study, molecular weight-fractionated PFPE lubricant monolayers were transferred from the water surface to solid substrates such as a hydrophilized silicon wafer, gold-sputtered mica, and a hard disk after adjusting the two-dimensional density of the lubricant molecules. The molecular structures of the PFPE lubricant molecules at the solid surfaces were observed by the cryogenic non-contact AFM under ultra-high vacuum. At the hydrophilic silicon wafer surface we could observe a single lubricant molecule in a random coil sphere shape. However, at the non-polar gold surface we confirmed the formation of reversed micelle structures. At the hard disk surface we detected various sizes of reversed micelles of PFPE lubricant in a flat oval shape.

Microstructures in Lubricant Thin Layers at the Magnetic Disk Surface, Observed Using Cryogenic Atomic Force Microscopy

Cryogenic Atomic Force Microscopy (AFM) was used to observe perfluoropolyether (PFPE) lubricant molecules at atomically flat solid surfaces and at a magnetic disk surface to understand the lubricity of ultra-thin (1 nm) lubricant layers at the hard disk surface. Molecular imaging of PFPE lubricant molecules reveals the formation of reversed micelle structures at comparatively non-polar solid surfaces such as gold or the carbon overcoat of magnetic disks.