Bonding of Hard Disk Lubricants with OH-Bearing End Groups

Abstract

Typical lubricants for magnetic hard disks comprise the central perfluoropolyether section and the short hydrocarbon end groups bearing hydroxyl unit(s). It had been shown earlier that chemical bonding of these lubricants to the carbon overcoat of disks involves (1) dangling bonds shielded inside the carbon, (2) transfer of the hydrogen atom of the hydroxyl unit to a dangling bond site, and (3) attachment of the remaining alkoxy system, R–CF₂–CH₂–O^·, to the carbon surface as a pendant ether unit. Dangling bonds at or near the surface react immediately with H₂O or O₂ in the atmosphere. It follows that, in order to bond, the hydrocarbon end group must move into crevices of the carbon film. It was postulated that the bonding rate would depend on the length of the hydrocarbon end-group, –(CH₂) _n –OH. The longer the hydrocarbon sector is, the faster and the more extensively the bonding would proceed. Bonding rates were examined for a set of samples differing only in the dimension of the hydrocarbon end-group. Results clearly in accordance with the postulate were obtained. The sample set included two novel lubricants, D-2TX2 and D-2TX4, with the following end-groups, –O–CF₂–CH₂–O–(CH₂) _n=2,4–OH. Excellent bonding rate, coverage, and potential anticorrosion property were revealed for these lubricants.