It is important to evaluate the lubrication and replenishment effects of the submonolayer mobile lubricant in hard disk drives because increased recording density can only be achieved through near-contact or surfing recording without head wear. It is known that the minimum friction coefficient can be obtained at a specific bonding ratio . In recent times, the lubricant thickness has been reduced to one monolayer and the thickness of the mobile lubricant layer, to less than 0.3 nm to reduce lubricant pickup on the head surface. Matthes et al.  shown that a certain fraction of the layer of currently used mobile lubricants with multiple polar groups is important for reducing head wear. Canchi and Bogy  experimentally studied the depletion caused by thermal flying height control (TFC) head contact and reflow speed for various lubricants. Although the diffusion characteristics of perfluoropolyalkylether (PFPE) lubricants layers with a thickness of a few nanometers can be evaluated by a diffusion equation based on continuum mechanics , the validity of the conventional equation in the submonolayer lubricant region is not clear. Mate  showed that the spreading of a pancake-shaped Z-dol lubricant layer with subnanometer thickness can be quantitatively evaluated by a diffusion equation based on continuum mechanics. Ono  showed that the replenishment process of a depleted groove generated by slider touchdown operation can be fairly evaluated by the conventional diffusion equation if the effective ratio of the Hamaker constant to the lubricant viscosity is properly chosen. However, the identified effective viscosity is too high to be estimated from other experimental data [5, 7]. Moreover, the validity of the diffusion equation based on continuum mechanics remains unclear in the submonolayer region.
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Diffusion Equation for Spreading and Replenishment in Submonolayer Lubricant Film
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Ono, K. "Diffusion Equation for Spreading and Replenishment in Submonolayer Lubricant Film." Proceedings of the ASME 2014 Conference on Information Storage and Processing Systems. 2014 Conference on Information Storage and Processing Systems. Santa Clara, California, USA. June 23–24, 2014. V001T01A005. ASME. https://doi.org/10.1115/ISPS2014-6915
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