MEASUREMENT OF RHEOLOGICAL PROPERTIES OF ULTRATHIN LUBRICANT FILMS AT VERY HIGH-SHEAR RATES AND NEAR-AMBIENT PRESSURE

In liquid-lubricated bearings used in experimental near-contact magnetic recording devices, rheological properties of lubricant films at very high shear rates (up to about 10(9) s(-1)) and at near-ambient pressure are required. In this extremely high shear rate regime, shear thinning (non-Newtonian behavior) becomes extremely important. A rheometer is designed and constructed that makes it possible to study the rheology of lubricants at extremely high shear rates. Since traditional rheometers are limited to moderate shear rates due to viscous heating, the design used in this study is based on a magnetic disk drive configuration in which an ultrathin film of lubricant is sheared between a magnetic disk and a slider at relatively low sliding speeds. By monitoring the film thickness between the slider and the disk using a capacitive method, it is possible to accurately measure the shear rate. Two different types of perfluoropolyether lubricants have been studied up to shear rates of 10(7) s(-1), and these data have been compared to previously published data. (C) 1995 American Institute of Physics.