Recent progress in the physical research of friction is reviewed. We discuss some mechanisms proposal for Amonton and Coulomb's law that is applied well in various systems. The energy dissipation process associated with dynamical friction is also discussed. New experimental techniques that aim to observe the sliding interfaces between solid surfaces and lubricants are introduced.
Superlubricity, a phenomena of vanishing friction, has been studied theoretically and experimentally. It is theoretically shown that certain unique cases exist where friction force exactly vanishes when the atomic arrangements on the contacting surfaces satisfies the condition for the appearance of superlubricity. The experiments agree with the theoretical predictions. The measurements on atomically clean surfaces show that friction forces decrease as the contacting conditions approach those for the appearance of superlubricity. Friction is not observed in the superlubricity regime in the measurements capable of resolving a friction force of 3 nN by scanning tunneling microscopy.
Surface reactions on magnetic recording disks have been studied using our sliding test machine with ceramics slider under high vacuum conditions. Chemical changes of perfluoropolyether (PFPE) lubricant oils in the wear track were observed by time of flight secondary ion mass spectroscopy (TOF-SIMS). It was found that lubricant oils were decomposed even under very low loads less than 1 mN. The decomposition reaction was affected by the coating materials such as Al2O3, diamond like carbon (DLC), TiN or c-BN on the slider. Lubricant oils reacted also with Al2O3 and TiN slider surfaces. Metal (Al, Ti) fluorides were detected by TOF-SIMS in the sliding track after friction experiments. Material transfer is comfirmed by chemical wear of the slider material. The decomposition of lubricant molecules was initiated at the end group of molecules. On the other hand, DLC and c-BN sliders suppressed the decomposition of oil. With these materials, chemical wear was not observed. In conclusion, hard and chemically inert materials are suitable to develop a long-life head-disk interface.
Friction drive CVT that evolved to traction drive CVT (T-CVT) was designed toward the end of 19th century, in a short period after automobiles were on the market. The T-CVT was made practicable in Japan in 1999 after approximately 100 years in advance of the world. Automobiles with the T-CVT have been accomplished as an integrated result of the progress of the following components: various machine elements, mechanism, design, processing technology, manufacturing technology, system control technology, material development, and traction oil development. The traction oil has an important function as one of the elements for the T-CVT unit. Its development and practical use have been the key to make T-CVT automobiles practicable. I would like to introduce out research and development of the traction oil showing the related characteristics.
We here introduce how surface dynamics in polymer films can be examined by lateral force microscopy. Since the manifestation of lateral force is strongly related to energy dissipation during a tip sliding, lateral force can be regarded as an index of dynamic loss modulus at the surface. As a sample, monodisperse polystyrene (PS) films were used. On the basis of the temperature dependence of lateral force, glass transition temperature at the surface was determined. In addition, by measuring scanning rate vs. lateral force curves at various temperatures, activation energy of the surface segmental motion corresponding to glass transition could be successfully obtained via time-temperature superposition principle. The results of these experiments made it clear that thermal molecular motion at the surface was much more vigorous than that in the interior bulk region. Finally, it is also described that LFM was applied to surface segregation phenomenon in polydisperse PS films.
This article briefly reviews our recent works on the characterization of glass and functional thin films using isotopes such as 18O2 gas and deuterated molecules. The topics cover industrial glass used for architectural and automotive applications, photocatalytic TiO2 thin films and organic thin films (Langmuir-Blodgett films). Based on the results obtained, the effectiveness of the materials characterization using isotope is discussed.
The liquid-solid interface motion and the temperature history of thin Si films during short pulse (FWHM = 25 ns) excimer laser annealing are observed by in-situ diagnostics. Substantial supercooling (> 200 K) followed by spontaneous nucleation into fine-grained material is observed. Lateral crystal growth is limited by the triggering of spontaneous nucleation in supercooled liquid Si, and the lateral solidification velocity is measured to be about 7.0 m/s. To enhance the lateral growth, the pulse-duration-controlled solid-state laser is utilized. This sequential crystal growth is found to extend over 5 μm in the lateral direction. The validity of the method is confirmed by superior TFT characteristics of high field-effect mobility (n-ch μ > 460 cm2/Vs).