Disk Lubricant Additives, A20H and C2: Characteristics and Chemistry in the Disk Environment

Abstract

Disk lubricant additives A20H and C2 are Fomblin Z type perfluoropolyether with the hydroxyl endgroup, -O-CF 2 -CH 2 -OH, at one end, and the cyclo-triphosphazene end-group, R 5 (PN) 3 -O-, at the other end. Here, R is an m-trifluoromethyl-phenoxy group for A20H and a trifluoroethoxy group for C2. These additives were examined for miscibility with benzene, spin-off rate, water contact angle, and the diffusion rate over the carbon overcoat. It is revealed that A20H adheres to the carbon overcoat spontaneously. The attractive interaction arises from the charge-transfer type interaction between the aromatic rings of the phosphazene end and the graphitic regime of the carbon overcoat. No spontaneous adherence occurs between the lubricant C2 and the carbon overcoat. A TOF-SIMS study of disks coated with A20H and C2, respectively, with and without subsequent curing by short-UV (185 nm) was performed. It is revealed: (1) if presented with a low energy electron, the phenoxy groups of A20H readily undergo the dissociative electron capture, while the trifluoroethoxy group does not, and (2) photoelectrons generated by short-UV have little kinetic energy and the electron capture occurs only if an electrophilic molecular sector is in intimate contact with the carbon. Thus, in the case of disks coated with A20H, UV-curing results in detachment of a phenoxy group in contact with the carbon, generation of a radical center at the phosphorus atom and subsequent formation of a bona fide chemical bond between the phosphor and the carbon overcoat. No reaction of consequence occurs when disks coated with C2 are irradiated with short-UV.

Improvement in Heat Resistance of Perfluoropolyether Lubricant Films on Magnetic Disks by UV Irradiation with a Bias Voltage on the Disk Surface

“…The bonded ratio of Z-tetraol increased slightly with photoelectron-assisted UV irradiation; however, that of ADOH increased drastically with UV irradiation. This result agrees with the results of previous work, where the cyclo-triphosphazene end group of ADOH was more sensitive to photoelectron chemical reaction than the hydroxyl end groups of other lubricants [10].…”

“…Z-tetraol has hydroxyl end groups, and ADOH has a cyclo-triphosphazene end group with an m-trifluoromethyl-phenoxy single end group. Kasai and Wakabayashi [10] indicated that the cyclo-triphosphazene end group of ADOH was more sensitive to photoelectron chemical reaction than hydroxyl end groups. Thus, ADOH should show a higher bonded ratio with photoelectron-assisted UV irradiation than Z-tetraol, because cyclo-triphosphazene end groups are easily dissociated by photoelectrons.…”

Disk Lubricants for Spontaneous Adsorption and Grafting to Carbon Overcoat by UV Irradiation

“…Separately we reported on characterization of lubricant additives A-20H and C2 [2]. Shown below are their chemical formulae.…”

“…(1) Lewis basicity (electron donating property) of the triphosphazene moiety of these lubricants prevents the catalytic degradation of PFPE backbone. (2) A20H adheres to the carbon overcoat spontaneously while C2 does not. (3) Irradiation of disks lubricated with A20H with short UV (k = 185 nm) results in detachment of phenoxy unit(s) and attachment of the remaining molecular chain to the carbon overcoat.…”

“…For comparison, disks coated with Z-tetraol were also examined. The disks were tested for (1) spin-off rate, (2) diffusion of lubricants over the disk surface, (3) facility for photo-grafting by UV (k = 185 nm), (4) water contact angle (before and after UV exposure), and finally (5) the on-track time-to-failure test. Also reported are results of TOF-SIMS study of disks coated with D-SA1 and D-SA2.…”