Changes in Friction Properties of Monolayer Lubricant Films Induced by Development of Molecules’ Bonding Available to Purchase

Functional perfluoropolyether (PFPE) films consisting of bonded and mobile molecules are widely used for lubrication of magnetic disk. To clarify the effect of film composition (mobile/bonded) on tribological performance, we measured the time-dependent friction properties of two types of monolayer PFPE films (functional Zdol2000 and nonfunctional Z03) under lightly loaded (loading force: 0–1 mN) and quasi-static (low rotational speed: 2.1 mm/s) conditions. The friction force of Z03 remained unchanged with time and it increased linearly with external loading force. In contrast, induced by the development of molecules’ bonding with time, the friction force of Zdol2000 increased and transited to a nonlinear increase with external loading force as the time proceeded.