Friction Control at the Molecular Scale

For gentle cleansing of the skin and hair, it is important to minimize friction of the surfaces during washing. When cleaning windows or bathroom fixtures, reducing friction enables easy removal of dirt and stains on the surfaces. On the other hand, the surface of a bathtub or floor must have some amount of friction in order to prevent slipping and sliding accidents. The activity of “rubbing/sliding” occurs everywhere in our daily lives, and it is important to provide desirable friction properties to the target surfaces by suitable use of our products.
Kao has been precisely studying the friction and lubrication properties of surfaces treated with surfactants, oils, and polymer-based materials used in wide variety of our products. The relationship between the structure of lubricating films and resulting friction properties has been investigated in detail, which reveals the sliding mechanisms of the lubricant materials at the molecular scale. On the basis of the findings, we design/utilize friction properties for optimal use.
Our recent study clarified that the dilute aqueous solution of a block copolymer lubricant used for hair cosmetics has an extremely low friction coefficient μ, of the order of 10^-5 (Langmuir 35, (2019) 15784). Few studies have reported on such a low μ value. For comparison, typical μ value for biological synovial fluids (one of the representative examples of low friction systems) is approximately of the order of 10^-3.
Advancements in friction control technologies on the basis of the precise investigation of the structures and properties of lubricant films are directly linked to the efficient energy utilization in machinery industries such as automobile technologies. Kao will apply our findings to the development/improvement of industrial chemical products.