Viscosity increase due to confinement of mobile molecules of perfluoropolyethers measured by fiber wobbling method

Near-contact recording or contact recording is an ultimate system to achieve higher receding density of hard disk drives (HDDs). The problems are friction and wear at contact. Contact between a magnetic head and a disk results in confinement and high speed shearing of lubricants within an extremely narrow gap. To clarify the viscous friction force generated by the lubricants under such conditions, we developed a novel shear force measuring method called the "fiber wobbling method". In this study, to clarify the mechanism of the viscosity increase, we investigated the relationship between the viscosity and the end group of the lubricants. The FWM measurements demonstrate that the increase in viscosity at a wider gap is due to the confinement of mobile molecules, and the increase in viscosity at a narrower gap depends on the types of end group. These results are very important for designing the head-disk interface of the high density HDDs.