Abstract
Using a lateral force microscopy with a dual-axis micromechanical probe of our own design and fabrication, we measured the friction force of nanometer-thick films of perfluoropolyether (PFPE) lubricants with different bulk viscosities at low sliding speeds of 1-400 μm/s. With increasing sliding speed, the friction force decreased for the less viscous films, whereas it decreased initially and then increased for the more viscous films. From these results and our previous results at high sliding speeds, we infer that, in a wide range of sliding speeds, nanometer-thick PFPE films display a similar trend of an initial decrease followed by an increase in the friction force as the sliding speed increases, and the sliding speed at the inflection point decreases with increasing bulk viscosity of the PFPE.
