Z-dol and carbon overcoat: the bonding mechanism

Abstract

Molecular dispositions of Z-dol (linear perfluoropolyether with hydroxyl termini, –O–CF₂–CH₂–OH) applied over the carbon overcoat of magnetic hard disks are often depicted by an arrangement based on the hydrogen bonding interaction between the hydroxyl ends and some polar units of the carbon surface. The hydrogen bonding interaction is weak. The arrangement based on this mechanism is attained rapidly, but is slowly replaced (if partially) by a bona fide chemical bond. The issue of the exact nature of this chemical bond has been left unanswered in most of the reports. Past works deemed to have explored and elucidated the identity of the bond in question are gathered, reviewed and deductively presented. The review, we believe, clearly shows that the bonding in question involves (1) dangling bonds shielded within the sputter-deposited carbon, (2) transfer of the hydrogen atom of the hydroxyl unit of Z-dol to the dangling bond site, and (3) attachment of the remaining alkoxy system, Z–O–CF₂–CH₂–O•, to the carbon surface as a pendant ether unit. The Z-dol moiety thus attached is held by a bona fide chemical bond, and cannot be replaced by water molecules nor removed by solvent extraction.