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

Abstract

Functional perfluoropolyether (PFPE) films consisting of mobile and bonded molecules are widely used for lubrication of magnetic disks. In order to clarify the influence of film composition (mobile/bonded) on tribological performance, we measured the friction properties of two types of 2 nm-thick 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 as a function of elapsed time. The friction force of Z03 remained unchanged with time and increased linearly with loading force as described by Amontons' law. In contrast, induced by the development of the molecules' bonding in time, the friction force of Zdol2000 increased and transited to a nonlinear increase with loading force as time proceeded. The nonlinear friction-load relationship of Zdol2000 in the equilibrium state was characterized by the Johnson-Kendall-Roberts model.

Adhesion and Friction Properties of Molecularly Thin Perfluoropolyether Liquid Films on Solid Surface

“…They observed that there is a sudden transition to high friction and vibration (bridged state) at some low touchdown pressure when the ambient pressure is decreased with the magnetic recording slider initially flying over the lubricated disk surface; they also discussed the HDI phenomena at the slider contact on the disk surface. On the other hand, to measure the tribological properties, He et al developed a pin-on-disk-type micro-tribotester that can measure adhesion and friction forces. , Their tester mainly consists of a spindle motor, a friction sensor, a slider load/unload switching mechanism, an incremental loading actuator mechanism, and an optical displacement sensor. The friction force is measured on the rotating disk surface, and the pull-off force is measured on the stationary disk surface.…”

“…On the other hand, to measure the tribological properties, He et al developed a pin-on-disk-type micro-tribotester that can measure adhesion and friction forces. 12,13 Their tester mainly consists of a spindle motor, a friction sensor, a slider load/unload switching mechanism, an incremental loading actuator mechanism, and an optical displacement sensor. The friction force is measured on the rotating disk surface, and the pull-off force is measured on the stationary disk surface.…”

Physics of the Sub-Monolayer Lubricant in the Head-Disk Interface

“…In the period before TFC slider technology, when the flying clearance of pico-sliders was 5 nm or more, Z-dol with a single OH polar group at both ends of the main chain was commonly used in monolayers or more, and the bonded ratio was about 40%. In order to achieve stable flying conditions with a clearance of 1-2 nm or less, research on the functions of the bonded and mobile layers of various lubricants, surface energy, adhesion and friction force characteristics in relation to lubricant thickness has been actively conducted since around 2000 [5,6,[31][32][33][34]. Lubricants such as Z-tetraol and D-4OH with two OH polar groups at each end of the main chain, and ZTetraol MultiDentate (ZTMD) with multiple OH groups in the middle of the main chain have been developed to improve the bonding function of lubricants [35,36].…”

Analysis of elastic contact due to meniscus adhesion force

“…筆者ら の動的吸着力の測定実験では， 半径が 1 および 2 mm のガラス球を用いており， また Tani らの論文 Tagawa, 2012, Tani, et al, 2013)では半径 1.82 mm のガラス球を， Zhang らの実験 (Zhang, et al, 2007) (Zhang, et al, 2011 Iteration number Penetration  [10 nm]…”