We are pleased to present to you this themed RSC Advances collection on Tribology. The field of tribology is where chemistry and mechanics meet. It represents a challenging cross-disciplinary arena focusing on the widely recognized problems associated with friction, adhesion and wear that impact a range of materials systems, from machined engine parts, to space craft and satellites, to medical implants, to micro and nanoscale machine technologies. The energy losses in machines through friction and wear also represent a significant economic impact, solutions to which could dramatically aid in the ever increasing challenges of the energy needs of modern society.
In this themed collection, work in the area of tribology is presented across the spectrum from applied to fundamental and computational studies of materials systems.
On the more applied side, work is presented examining wear behaviour (RSC Adv., 2014, 4, 19034), the role of lubricant additives (RSC Adv., 2014, 4, 6074; RSC Adv., 2014, 4, 20940; RSC Adv., 2014, 4, 25118) and friction modifiers (RSC Adv., 2014, 4, 4278; RSC Adv., 2014, 4, 21238) for chemical modification of surfaces and interfaces, as well as micro/nano-engineering of surfaces (RSC Adv., 2014, 4, 20548) to modulate surface frictional properties. A relatively new comer to the area of lubricant additives and friction modifiers is the use of ionic liquids (RSC Adv., 2014, 4, 19396; RSC Adv., 2014, 4, 30617) whose packing and specific ionic interactions can significantly impact and reduce frictional losses. While much focus has been given to applications in machined engine components, tribological problems abound in a number of other areas as well, including orthopaedic implants (RSC Adv., 2014, 4, 19987) and in tools for nano-imprint lithography (RSC Adv., 2014, 4, 29474).
The articles in this themed issue also present many fundamental aspects of understanding shear at interfaces including the effects of boundary slip on elastohydrodynamic lubrication (RSC Adv., 2014, 4, 20821) and thermal effects on the mechano- and tribochemical reactions that occur at interfaces (RSC Adv., 2014, 4, 24059). Detailed studies of model systems such as self-assembled monolayers examined by surfaces forces and atomic force microscopy (RSC Adv., 2014, 4, 18801) allow one to gain insight into how basic molecular properties such as chain length and chemical functionality influence frictional properties. A similar approach has been applied to polymeric materials (RSC Adv., 2014, 4, 21497) and for vapor phase lubricants using alcohols, which have been shown to be effective for boundary lubrication in microscaled devices (RSC Adv., 2014, 4, 26081). A critical challenge in many such studies is the need for metrology tools that can evaluate both frictional and chemical changes in situ. In this issue, approaches combining tribometry with Raman spectroscopy are shown to hold promise (RSC Adv., 2014, 4, 22205). Another rapidly developing area in tribology is the application of 2-D nanomaterials such as graphene and graphene oxide as friction modifiers at interfaces. The unique 2-D structure of these materials and their ability to form layered interfaces have been shown to produce surprising and promising frictional properties (RSC Adv., 2014, 4, 15937; RSC Adv., 2014, 4, 26721).
The coupling of detailed measurements such as those outlined above with simulations has also led to exceptional insight into many fundamental questions in tribology. For example, how basic chemical functionality, i.e. H- vs. F- passivation of diamond-like carbon films impacts frictional properties, has been examined (RSC Adv., 2014, 4, 33739). Dry adhesion effects, such as those present in natural systems (e.g. gecko feet), can be explored using peeling simulations (RSC Adv., 2014, 4, 25447). Also the organization of molecular adlayers, entailing the balance of forces acting between adsorbates and adsorbate and substrate, have been explored in great detailed using molecular dynamics simulations (RSC Adv., 2014, 4, 16803) to aid in picturing energy dissipation in nanoscopic contacts.
Again, tribology is a very challenging interdisciplinary field and we hope that you find the work presented in this themed issue an inspiring snapshot of the many fascinating problems and challenges that remain to be explored where chemistry and mechanics meet.
James D. Batteas, Texas A&M University
Graham J. Leggett, University of Sheffield
Scott S. Perry, University of Florida