Spreading and dewetting in nanoscale lubrication

Abstract

This article critically reviews the fundamental scientific tools, as well as constructs cohesive schemes for potential applications, relevant to the molecularly-thin liquid film technology. Our focus is to understand the nanoscale dynamic behavior of thin lubricant films, relevant to the emerging field of nanotechnology, especially for achieving durability and reliability in the nanoscale devices. Our goal is to present a unified and hybrid description of perfluoropolyether (PFPE) experiment, mesoscopic interpretation, microscopic simulation tools, and molecular design tools available up to now. The experimentation and theory for the physicochemical properties of ultra-thin PFPE films are used to examine liquid film in the sub-monolayer to multilayer regime. Methods for extracting spreading properties from the scanning microellipsometry (SME) for various PFPE/solid surface pairs and the surface rheological characterization of PFPEs are examined. The interrelationships among SME spreading profiles, rheology, surface energy, and tribology, are given. Mesoscopic theories, including thermodynamics of evaporation and flow, stability analysis, microscale mass transfer, and capillary waves are introduced to describe thin PFPE film dynamics. Estimation of thin film viscosity enhancement from vapor pressure suppression by dispersion force is reviewed. The method for experimental derivation of lubricant spreading profiles from contact angles is summarized. The implications of capillary waves, or thermal fluctuations, at the surface of polymeric lubricant films are also discussed. The lattice-based, simple reactive sphere Monte Carlo (MC) technique for examining the fundamentals of PFPE dynamics is illustrated. An off-lattice based bead-spring MC model is also introduced to capture a detailed internal structure of the PFPE molecules, and the molecular dynamics method is implemented for a full-scale nanostructural analysis of PFPE ultra-thin films. By systematically tuning the endgroup strengths of PFPE, we examined the physicochemical properties for thin liquid films of the various PFPE/solid surface pairings. These tools accurately describe the static and dynamic behavior of ultra-thin liquid films consistent with experimental findings and thus are suitable for examining the fundamental mechanisms of lubrication in nanoscale devices. Application of the next generation head-disk interface design in information storage device is briefly considered.

Bonding Mechanism of Perfluoropolyether Lubricant Film with Functional Endgroup on Magnetic Disks by Ultraviolet Irradiation

“…We could estimate the more particular mechanism as following. It has been shown by many studies [8][9][10][11][12] that the disposition of PFPE with OH-containing end groups of the first monomolecular layer in contact with the carbon overcoat is such that the end groups are held to the carbon surface via hydrogen bonding with the OH units of the carbon surface. Thus, the conduction band of the carbon on anti-bonding orbitals extends into the OH-containing end group.…”

Direct Observation of PFPE Lubricants on Magnetic Disks

“…We studied the lubricant film confirmation of Fomblin Z-dol2000 by direct atomic force microscopy observations using a fluoride-coated probe. Several other studies on PFPE lubricants by using atomic force microscopy have been conducted [2]- [5]. Kumagai et al observed the PFPE lubricant distribution on magnetic disks by using atomic force microscopy to detect the adhesion between the probe and the lubricant layer [2].…”

Laser-Induced Thermo-Desorption of Perfluoropolyether Lubricant from the Surface of a Heat-Assisted Magnetic Recording Disk: Lubricant Evaporation and Diffusion

“…These mechanisms cause the HAMR lubricant to undergo dynamic changes in thickness (thicker and thinner) that may lead to the onset of lubricant dewetting the COC surface [35,36]. The net removal of lubricant from the HAMR disk surface during writing is due to desorption, which ejects lubricant molecules from the disk surface with high velocity (approximately 70 m/s, obtained by equating the thermal energy at 773 K and the kinetic energy of a single desorbed Ztetraol molecule with mass 2700 amu).…”