Measurement of Nanorheological Properties of Molecularly Thin Confined Lubricant Film Using Fiber Wobbling Method

An understanding of nanorheological properties of molecularly thin lubricant film is necessary to clarify the head-disk interface (HDI) of high-recording-density hard disk drives. The lubricant molecules are extremely confined to the head and disk surfaces, and the surfaces slide at a high sliding speed. The lower the flying height, the more the confinement affects the flying characteristics. However, few attempts have been made at clarifying the dynamic nanorheological properties of confined lubricant molecules. This is because the method for measuring the dynamic shear force has not been established. So, we have developed a new method of measuring dynamic shear force called “fiber wobbling method”. This method enables us to measure the shear force with a detection limit of about 1 nN. The frequency of shear is able to set to several kHz. The gap is controlled with a resolution of 0.1 nm. Using this method we investigated the effect of confinement on the dynamic viscoelastic properties of perfluoropolyether lubricant film on a magnetic disk. The results show that both viscosiy and elasticity of the lubricant film increase drastically when the gap is less than 13nm.