3 - Surface phenomena in thin-film tribology

Abstract

With miniaturisation of mechanisms and devices, load-bearing and transmitting conjunctions are progressively reducing in size. At the same time the gap size between contiguous solids is continually decreasing. These conjunctions are also subject to quite low loads. A whole new era in tribology has dawned which encompasses a wide area of interest from micro-electromechanical systems to data storage devices (ultra-smooth surfaces) to biological and bio-inspired systems, such as microfibres mimicking contacts of insects and geckos with very smooth surfaces. The field of study is broadly termed nano-tribology, but for biomimetics may be referred to as nano-biotribology. Relatively lightly loaded contacts also occur, for example in fairly rough elastomeric seals, prevalent in drug dispensing devices such as syringes and inhalers with low viscosity biocompatible compounds. Also, gels and cosmetic creams are applied with low load on fairly rough surfaces. Therefore, another new area of nano-tribology is emerging, which may be regarded as pharmaceutical tribology. In nearly all such conjunctions surface energy effects, adhesion, van der Waals interaction, electrostatic effect, meniscus action, hydration or solvation play more significant roles than the usual hydrodynamic viscous action as mechanisms of lubrication/tribology.