Hard Disk Surface

At the present, perfluoropolyether or PFPE, a random copolymer with a linear principal chain structure, has been widely used in HDD as the lubricant. Its chemical structure can be described by A-[(0CF2CF2)p-(0CF2)g]-0-A (p/q s2/3), with the average molecular weight ranging from 2,000 to 4,000 g/mol. Here, the symbol -X denotes the end-bead (eb), corresponding to -CF3 (nonfunctional) in PFPE 

Novotny et al. [41] used p-polarized reflection and modulated polarization infrared spectroscopy to examine the conformation of 1 -1,000 nm thick liquid polyperfluoropropy-lene oxide (PPFPO) on various solid surfaces, such as gold, silver, and silica surfaces. They found that the peak frequencies and relative intensities in the vibration spectra from thin polymer films were different from those from the bulk, suggesting that the molecular arrangement in the polymer hlms deviated from the bulk conformation. A two-layer model has been proposed where the hlms are composed of interfacial and bulk layers. The interfacial layer, with a thickness of 1-2 monolayers, has the molecular chains preferentially extended along the surface while the second layer above exhibits a normal bulk polymer conformation. 

Mate and Novotny [42] studied the conformation of 0.5-13 nm thick Z-15 on a clean Si (100) surface by means of AFM and XPS. They found that the height for PFPE molecules to extend above a solid surface was no more than 1.5-2.5 nm, which was considerably less than the diameter of gyration of the lubricant molecules ranging between 3.2-7.3 nm. The measured height corresponds to a few molecular diameters of linear polymer chains whose cross-sectional diameter is estimated as 0.6-0.7 nm. The experimental results imply that molecules on a solid surface have an extended, flat conformation. Furthermore, they brought forward a model, as shown in Fig. 28, which illustrates two 

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Spreading of PFPE films on amorphous carbon surfaces 

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This chapter introduces three kinds of surface organic modihcation hlms on a magnetic head that we have studied. These are polyfluoroalkylmethacrylate films, X-1P films, and self-assembled monolayers (SAMs). It also reviews the works of surface lube on a hard disk surface. In the last, the challenges on the development of a magnetic recording system are discussed. 

Standard computer hard disk surfaces (substrates used in this experiment were industrial hard disk surfaces that have been sputter-coated with nominally 100 A of hydrogenated amorphous carbon) can be coated by dip coating with nm thin films of perfluoropolyethers, such as Fomblin ZDOL, from solutions in perfluorohexane. For films thicker than several nm dewetting occurs spontaneously over a period of days to weeks due to the autophobic effect [43]. 

The concept of overcoating PFPE onto SAMs is similar to that of magnetic harddisk lubrication, where a combination of both bonded and mobile PFPEs is routinely used to better protect the hard-disk surface. For example, in the studies by Katano et al. [48], Chen et al. [49], and Sinha et al. [50], a combination of both bonded and mobile PFPEs on hard-disk surfaces has shown higher wear durability than the use of either bonded or mobile PFPEs alone. In a study by Choi et al. [51], PFPE overcoating onto SAMs-modifled hydrogenated amorphous carbon surface has shown higher wear durability than only a SAM-coated or PFPE-coated carbon surface. 

TFL is an important sub-discipline of nano tribology. TFL in an ultra-thin clearance exists extensively in micro/nano components, integrated circuit (IC), micro-electromechanical system (MEMS), computer hard disks, etc. The impressive developments of these techniques present a challenge to develop a theory of TFL with an ordered structure at nano scale. In TFL modeling, two factors to be addressed are the microstructure of the fluids and the surface effects due to the very small clearance between two solid walls in relative motion [40]. 

Zhang, B. and Nakajima, A., "Possibility of Surface Force Effect in Slider Air Bearings of 100 Gbit/in. Hard Disks, Tribal Int., Vol. 36,2003, pp. 291-296. 

Partially fluorinated X-IP has been used for a number of years as an additive in the inert lubricant PFPE film on the surface of a magnetic hard disk to enhance start/stop durability of PFPE lubricants [29,30]. Recently it has been used as a vapor lubricated film on the surface of the disks [31 ]. In order to avoid the PFPE being catalyzed to decomposition by the slider material AI2O3 (refer to Section 3.4), XI -P was also examined as a protective film on the surface of the magnetic heads [25,32]. The results of CSS tests indicate that the thermal stability of the lubricant was greatly improved in the presence of X-1P, and the thickness of X-1P film on the slider surface has an important influence on HDD lubrication properties. 

The second contribution spans an even larger range of length and times scales. Two benchmark examples illustrate the design approach polymer electrolyte fuel cells and hard disk drive (HDD) systems. In the current HDDs, the read/write head flies about 6.5 nm above the surface via the air bearing design. Multi-scale modeling tools include quantum mechanical (i.e., density functional theory (DFT)), atomistic (i.e., Monte Carlo (MC) and molecular dynamics (MD)), mesoscopic (i.e., dissipative particle dynamics (DPD) and lattice Boltzmann method (LBM)), and macroscopic (i.e., LBM, computational fluid mechanics, and system optimization) levels. 

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