It is well-known empirically and routinely utilized that adsorbed water reduces friction on material surfaces. However, the initial stages of the wetting process at the nanoscopic level remain unclear. Previous study using nonlinear spectroscopy has reported the heterogeneous wetting behavior of silica glass in response to humidity. Based on this premise, in situ observation of the wetting dynamics of silica glass surfaces was conducted under different humidity conditions using high-resolution atomic force microscopy. As a result, the formation of nano-sized water droplets spontaneously at relative humidities above 50% was observed. Additionally, adhesion force mapping on the glass surfaces was performed using peak force tapping atomic force microscopy, revealing significant differences from traditional wetting models. Specifically, coexistence of nano water droplets and liquid film was observed. These measurements clarified the dynamic behavior and reversible formation processes of nano water droplets. Thus, the potential as controllable lubricants for friction control on material surfaces is suggested, with further understanding of the formation mechanisms expected in future research.

In this study, we characterized the adsorption of several phosphorus-type anti-wear agents on an iron oxide surface in hexane. The phosphorus-type anti-wear agents employed in this study were triphenyl phosphate and its derivatives. The quartz crystal microbalance with dissipation monitoring technique revealed that the adsorption of the phosphorus-type anti-wear agents was strongly dependent on their chemical reactivity; i.e., the anti-wear agents with reactive functional groups result in large adsorption amount on the iron oxide surface. Additionally, (i) the polarity of the anti-wear agents as well as (ii) the presence of a benzene ring in their chemical structure may also affect the adsorption behavior. Adsorption energy of the anti-wear agent was also estimated by an atomistic level simulator “MATLANTIS^TM”and the simulation results well supported the experimental findings. Four-ball tests further demonstrated that the chemical or physical adsorption film formed on the iron oxide surface resulted in the wear resistance, as expected. This study provides fundamental knowledge on the structure-performance relationship of phosphorus-type anti-wear agents, giving future perspectives for lubricant formulations.

Generally, the permissible rotational speed of rolling bearings is listed in the catalog, and it is recommended that they are used within the listed range. When lubricated with grease, the speed is set to be about 20% lower than that with oil lubrication due to the lack of cooling effect. However, some bearings for cleaner motors can exceed 100 000min ^-¹. Although it seems to have a special internal design, it is used at higher rotational speeds than that of oil lubrication. Originally, the permissible rotational speed of rolling bearings was determined by taking into account the heat generation associated with an increase in torque, but there were also reports that with grease lubrication, the torque decreased as the rotational speed increased. Therefore, in this study, firstly the authors measured torque at rotational speeds exceeding the allowable rotational speed using small ball bearing 696. As a result, at high rotational speeds, the torque was low and the temperature did not rise. Then a long-term rotation test was conducted to evaluate the durability. It was concluded that it had sufficient durability even at a rotational speed of 1.5 times the limiting speed.

本会記事，次号予告，特集号企画主旨，コーヒーブレイク