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Experiments reveal perfluoropolyelher magnetic hard-drive lubricants react with dangling bonds on the surface of crevices in the carbon overcoat.
THE REMARKABLE PROPERTIES OF MAGNETIC HARD DISK DRIVES rely on the presence of 3 thin (1-2 nm) layer of lubricant that is chemically bonded to the surface. These perfluoropolyether (PFPE) lubricants invariably comprise a backbone containing low-surface-energy tetrafluoroethylene oxide (-CF2-CFj-O-) and difiuoromethylene oxide KF2-O-) units that provide lubricity. Their hydrophobicity also protects against corrosion. The molecules are terminated at both ends by hydroxyl (-OH) groups that form weak hydrogen bonds with the surface.
Stronger bonds are also formed by a chemical reaction between the hydrogen atoms of the -OH group with so-called dangling bonds present on the surface of the carbon overcoat. The hydroxyl hydrogen atoms react with one dangling bond, and the resulting reactive terminal oxygen atom reacts with another to form a strong chemical bond with the surface.
The dangling bonus in the carbon overcoat can be detected using a technique known as electron spin resonance (esr), and it has been found that they disappear when the overcoat is exposed to the...