Tribochemistry of the decomposition mechanisms of perfluoropolyether lubricants at the head-disk interface of hard disk drives in UHV

The successful operation of a hard disk drive requires the presence of a monolayer Perfluoropolyether (PFPE) film at the head-disk interface. The adhesion, mobility, and physical properties of this lubricant can significantly affect the tribological reliability of the hard-disk drive. The physical properties of this PFPE film, and hence its lubricity, are dictated by the interplay of the intramolecular cohesive interactions between PFPE molecules, and by the adhesive interactions between the PFPE lubricant and the underlying surface.; The mechanical properties of the contacting materials are important parameters to study in order to understand the friction and wear at the head-disk interface. The tribochemistry of the involved contacting surfaces is another important issue.; This dissertation focuses on the study of the tribochemistry at the head-disk interface in a computer hard disk drive. An effort is made to understand the lube decomposition mechanisms and the wear and friction mechanisms at the interface in order to enhance the wear durability.; Drag tests and thermal desorption tests were conducted in an ultra-high vacuum (UHV) tribochamber equipped with a mass spectrometer. The tribochemical tester can be used to monitor the tribochemistry at the head-disk interface in real time along with friction and temperature measurements. An optical surface analysis (OSA) system was also used to observe the lube migration behavior.; The results show that the deposited carbon films on the Al2O 3/TiC sliders' air bearing surfaces can significantly improve the wear durability at the interface. Different lube decomposition mechanisms are found for the coated and uncoated sliders.; The hydrogen evolution from the CHx carbon overcoat initiates lube catalytic decomposition with an Al2O3/TiC slider. But for CNx films, catalytic reactions are prevented due to less hydrogen evolution from the CNx overcoat, resulting in a better wear durability as compared to the CHx films.; The studies also demonstrate that the catalytic degradation process of ZDOL in the presence of Lewis acid occurs most readily at the acetal units (-O-CF2-O-) within the internal backbones of the lubricant.; In addition, this catalytic reaction is also shown to be prevented by using X-1P as an additive in ZDOL, thereby passivating the activity centers (Lewis acid) of Al2O3. The X-1P additive also increases the mobility of PFPE lubricants because X-1P molecules preferably occupy the bonding sites on the carbon surface.; The effect of the lube molecular weight is studied by testing fractionated ZDOL. With higher molecular weight, the poorer mobility causes higher viscosity and higher friction. However, the degradation rate is slower with the higher molecular weight.; Lubricant interaction with the carbon overcoat varies as a function of lubricant thickness. In the sub-monolayer regime, adhesion of the lubricant to the carbon surface is much stronger. When the lubricant thickness is above a monolayer, cohesion among the lube molecules plays a greater role.; The lubricant performance is also a function of the bonded fraction. The wear durability of disks improves with increased mobile lube fraction up to a point because the mobile layers provide a reservoir to constantly replenish the ZDOL displaced in the test track.