Lubricant-Induced Spacing Increases at Slider–Disk Interfaces in Disk Drives

Abstract

In this article, we explore the physical mechanisms for lubricant migration on recording head slider surfaces and how this migration leads to increased sliderdisk spacing during disk drive operations. This is done using both a new experimental methodology, called the ''droplet stress test,'' and through simulation. In our simulations, we compare the air shear-induced lubricant migration modeled either as viscous flow of a continuum liquid film with zero slip or as wind driven slippage of molecules across the surface. The experimental data are best fitted using the viscous flow model to determine an effective viscosity for the sub-nanometer thick lubricant films. This effective viscosity tends to be somewhat less than the lubricant bulk viscosity due to air shear promoting the slippage of lubricant molecules across the surface. Our experimental results also indicate that the potential spacing increase from the pickup of disk lubricant on the slider is limited by the mobile fraction of the dewetting thickness of the lubricant film on the slider.

Taking a Fresh Look at Disjoining Pressure of Lubricants at Slider-Disk Interfaces

“…The induced roughness not only degrades the slider-disk clearance, but also promotes the transfer of lubricant to the slider, where it can frequently lead to reliability problems [26], [27]. If we hope in the future to maintain subnanometer clearances, this induced roughening will need to be kept to less than a few angstroms.…”

Numerical Analysis of Surface Force of Diamond-Like Carbon Surface Coated with Monolayer Lubricant Film

“…Experimental evidence of the formation of a macroscopic lubricant bridge between the head surface and the spinning disk was also reported in some papers [21,22]. The lubricant pickup and transfer to the head surface caused by van der Waals forces have been big obstacles to achieving a smaller flying height [23,24]. Saeki et al [25] theoretically revealed the tendency of the speed of lubricant bridge formation at an asperity to increase as the asperity radius decreases.…”

Investigation of lubricant transfer and distribution at head/disk interface in air-helium gas mixtures

“…Wong et al [4] used a molecular dynamics simulation to study lubricant redistribution and transfer (and its relationship with intermolecular force) when the head makes near contact with the disk interface. In addition, Mate et al [5] experimentally studied lubricant migration at the slider surface and found that an effective viscosity could be obtained by fitting the measured data with a viscous flow model. Li et al [6] experimentally investigated lubricant transfer from the disk surface to the slider surface, and their results showed that molecular polarity, the bonding ratio, and the main chain stiffness of the lubricant play roles in lubricant transfer.…”