This paper describes the effect of end-group functionality and molecular weight of ultra-thin liquid lubricant films on contact slider dynamics in hard disk drives. In the experiments, the contact slider dynamics as well as ultra-thin liquid lubricants behavior are investigated using three kinds of lubricants which have different end-groups and molecular weight as a function of lubricant film thickness. The dynamics of a contact slider is mainly monitored using Acoustic Emission (AE). The disks are also examined with a scanning micro-ellipsometer before and after contact slider experiments. It is found that the lubricant film thickness instability due to de-wetting occurs as a result of slider-disk contacts, when the lubricant film thickness is thicker than one monolayer. Their unstable lubricant behavior depends on the chemical structure of functional end-groups and molecular weight. In addition, it is also found that the AE RMS values, which indicate the contact slider dynamics, are almost equivalent, independent of the end-groups and molecular weight for the lubricants, when the lubricant film thickness is around one monolayer. The molecular weight, however, affects the contact slider dynamics, when the lubricant film thickness is less than one monolayer. In other words, the AE RMS values increase remarkably as the molecular weight for the lubricant increases. When the lubricant film thickness is more than one monolayer, the AE RMS values decrease because of the effect of mobile lubricant layer, while the lubricant de-wetting instability affects the contact slider dynamics. Therefore, it would be concluded that the lubricant film thickness should be designed to be around one monolayer thickness region in order to achieve contact recording for future head-disk interface.
Effects of the Mass and Load Force of a Spherical Contact Slider on Wear and Jumping Characteristics.
