High-Speed Friction Measurements for a Molecularly Thin Lubricant Film Using a Fiber Wobbling Method

Flying height between magnetic heads and magnetic disks must be minimized to realize high-recording-density hard disk drives. To lubricate the head-disk interface, the magnetic disks are coated with a molecularly thin lubricant film. Optimal design of the lubricant film is essential to ensure durability and reliability of hard disk drives. The mechanical properties of such a thin film are quite different from those in the bulk state. In our previous study, we developed highly sensitive shear force measuring method, which we called the fiber wobbling method (FWM), and revealed that the viscosity decreases with increasing sliding speed, known as shear thinning. However, the sliding speeds were much slower than those at the head disk interface. In this study, we utilized resonant oscillation of the probe and realized the high-speed friction measurements using FWM. Sliding speed achieved was 0.12 m/s, which is more than 100 times faster than that of conventional study. Our experimental results showed that the effect of shear thinning still remains at a sliding speed of 0.12 m/s and that the viscous friction forces are greatly decreased.