Measurement of lubricant viscosity and detection of boundary slip at high shear rates

A novel rheometer with the maximum shear rate of 105 s−1 has been fabricated to measure lubricant viscosity and to detect solid/liquid boundary slip. The gap between two parallel plates is controlled in the range from 20 to 500 μm and the viscous shear torque is measured with a feed-backed laser reflection technique. Test results of the perfluoropolyethers (PFPE) coated sample indicated that the viscous shear resistance is reduced by about 15-20% compared with the bare plate, implying that possible boundary slip occurred at the liquid/solid interface and a slip length of order 10 μm was extrapolated.