Investigation of a New Cyclotriphosphazene-Terminated Perfluoropolyether Lubricant. Properties and Interactions with a Carbon Surface

Wakabayashi

2008

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.

“…The peak at 814 amu is assigned to (CF 3 -C 6 H 4 -O-) 4 , F(NP) 3 -O -. It is believed to be generated when F -replaces a phenoxy group on one of the phosphorus atoms.…”

Section: A20h and C2: Tof-sims Studymentioning

confidence: 99%

“…Consequently efforts were made to chemically link the cyclotriphosphazene moiety to the PFPE molecular chain and led to development of the lubricant A20H [4]. Shown below are the formulae of X1P and A20H.…”

Section: Introductionmentioning

confidence: 99%

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

Wakabayashi

2008

“…3. Here A20 is a derivative of Z-dol in which one of the hydroxyl end-groups is replaced by a cyclotriphosphazene [7]. It is clearly revealed that those lubricants photo-grafted are indeed strongly bound.…”

Section: Grafting Pfpe Chains By the Maya Processmentioning

confidence: 99%

Grafting Lubricant Molecular Chains to the Carbon Overcoat

Wakabayashi

2008

It was conceived and demonstrated that irradiation of magnetic disks coated with PFPE (perfluoropolyether) lubricants terminated with a carboxylic group at one terminus with long-UV (254 nm) would lead to grafting, via a bona fide C-C chemical bond, of genuine PFPE molecular chains to the carbon overcoat all at one terminus with all the remaining chain segments being free to sway. The water contact angle of disks coated with PFPE lubricants terminated with end-groups having hydroxyl unit(s) (e.g., Z-dol and Z-tetraol) decreases gradually, after the initial contact of the droplet, reaching an asymptote in 20-30 s. The gradual temporal change is accounted for by shifting of the equilibrium disposition of hydroxyl units of the lubricant molecules from that determined by the interaction with the surface of the carbon overcoat to that determined by the interaction with surfaces of both the carbon overcoat and the liquid droplet. The water contact angle of disks prepared by the presently conceived photografting method is high ([110 degrees) and shows no temporal change. In a preliminary spin-stand drag test, disks with PFPE chains photo-grafted by this method and also the heads (for the read/write process) with similar photo-grafted PFPE chains exhibited extraordinary durability.

“…A mixture of Z-dol and X1P, however, has a miscibility issue. The PFPE lubricant receiving topical attention, known by the brand name A20H, is a derivative of Z-dol having an X1P-like cyclotriphosphazene unit attached to one end and retaining the original hydroxyl unit at other end [11]. It may be an ideal lubricant meeting all the requirements listed above.…”

Section: Summary and Commentsmentioning

confidence: 99%

Hydrogen bonding in lubricants for hard disk drives

Raman

2006

Hydrogen bonding interaction within a small ensemble of water molecules, that within a group of water molecules and endgroups of Z-dol and Z-tetraol, and the effect of electrolyte ionic pair such as LiCl upon these interactions were examined by the molecular dynamics method based on the potential given by a semi-empirical SCF quantum mechanics. It was revealed that the strength of the hydrogen bond increased rapidly as the size of droplet increased, relating to the population density of hydroxyl units, and that such interaction was amplified significantly by the presence of electrolyte ionic pair. An extraordinary interaction was thus predicted between Z-tetraol and aqueous solution of alkali halide. An experimental study thence conducted revealed that Z-tetraol and aqueous NaCl solution (2 M) formed an extremely stable water-in-oil type emulsion. The emulsion consists of spheroids of several nanometers across wherein several thousands of water molecules are encased by several tens of Z-tetraol endgroups. The interfacial layer of each spheroid is formed and stabilized by the hydrogen bonding interaction between the hydroxyl units of the tetraol-ends and water molecules enhanced by the electrolyte ionic pairs. When disks coated with Z-tetraol were tested for flyability at high humidity, the head-disk interaction detected acoustically increased with time. Spontaneous formation of globules resulting from interaction of tetraol end-groups and water molecules assisted by ubiquitously present alkali halide contaminant would account for the observed increase of the head-disk interaction. Possible structures of perfluoropolyether lubricants ideal for magnetic disk application are discussed.