Evaluation of practical performance of molecularly thin lubricant films having textures of nano-plateaus and nano-recesses

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To evaluate practical performance of perfluoropolyether (PFPE) lubricant films having texture of nano-plateaus and nano-recesses formed by ultraviolet (UV) ray irradiation, we clarified the mechanism of formation of the texture and optimum conditions for forming the texture on diamond like carbon (DLC) surface. For this purpose, an ultra-high sensitive friction tester was developed. Based on the sliding-induced depletion and replenishment tests, the present textured lubricant film was found to have a special advantage of adjustable tribo-performances. The results are summarized as follows.1) Mechanism of formation of nano-texture i) Experimental approach: For three kinds of PFPE lubricants (UV reactive; Fomblin AM type, polar; Zdol and non-polar; Z) coated on DLC surfaces for magnetic disk use, the irradiation time was optimized and the effects of UV irradiation were compared. In addition, both of irradiation methods; UV irradiation after/before lubricant coating, were confirmed to be … More effective.ii) Molecular simulation approach : Using the smart Monte Carlo method, formation of lubricant texture was reproduced using a local distribution of solid and liquid molecules interaction caused by solid surface irregularity. Applying the molecular-dynamic simulation to solid/liquid interface, formation of lubricant texture was reproduced using a local distribution of the interaction potential between polar end groups of lubricant molecules and carbon molecules of solid surface.2) Evaluation of depletion and replenishment of nano-texture lubricant film. From the results of the sliding test, IN irradiation was confirmed to provide advantages of suppressed depletion without decreasing replenishment performance. Comparing parallel/perpendicular patterns and no pattern, it was found that, as for depletion, the with-pattern case was equivalents to the no-pattern case, while as for depletion, the relationships where the perpendicular case ≒ no pattern>the parallel case held.3) Development of ultra-high sensitive friction tester A new friction tester was constituted by an accurate disk rotation spindle supported by an air bearing and driven by a build-in direct DC motor, and a precise sliding pin-loading mechanism driven by a compact PZT actuator with displacement magnification mechanism. This attained high resolutions of 2.5 μN for the adhesion force and 4μN for the friction force. Less