Effect of van der Waals forces on molecularly thin lubricant in the magnetic storage head-disk interface

The disjoining pressure of lubricant in the magnetic storage device head-disk interface (HDI) was obtained using Lifshitz theory [Sov. Phys. JETP 2, 73 (1956)] and multilayer film stack model. For this purpose the normal-air-gap-centered calculation of the disjoining pressure was replaced by the lubricant-layer-centered system. In the air-centered system the attractive force between the head and media was found to increase as the lubricant layer was thinned. By switching to the lubricant-centered system the disjoining pressure in a thin film of lubricant in the HDI was found to be negative at small head-to-media separation. By equating the free lubricant disjoining pressure with the lubricant in the head-disk interface, a thinning of the lubricant in the interface due to the presence of the head was calculated. A detailed thermodynamic analysis of the disjoining pressure of the lubricant in the interface revealed that the calculated negative disjoining pressure was due to the dominance of the air-gap-centered interaction energy for small air gaps. The impact on the lubricant film in the operating hard disk drive is discussed, and the possible role of negative disjoining pressure on the lubricant accumulation rate on the slider is highlighted. (c) 2005 American Institute of Physics.