Smooth Sliding through Feedback Control

ribology is the science and technology of contacting solid surfaces in relative motion, including the study of lubricants, lubrication, friction, wear, and bearings. It is estimated that friction and wear cost the U.S. economy 6% of the gross national product [1]. For example, 5% of the total energy generated in an automobile engine is lost to frictional resistance. The study of nanoscale friction has a technological impact in reducing energy loss in machines, in microelectromechanical systems (MEMS), and in the development of durable, low-friction surfaces and ultra-thin lubrication films. Friction between contacting surfaces is a longstanding and crucially important scientific problem, which is characterized by the interplay of energy, stress, and chemistry at many length scales. To understand friction and to meet technology needs, knowledge from the fields of chemistry, material science, physics, mathematics, and engineering must be applied. Fundamental scientific questions include how energy is dissipated in nonequilibrium processes and how the course of energy dissipation can be intentionally controlled. The road map between friction, which is an ensemble-averaged quantity, and molecular-level dynamics remains open. These issues are relevant to the development of energy-efficient technologies, such as ultra-thin lubricant films for ultra-high-temperature lubrication as well as for control and manipulation of frictional properties during sliding. Friction is intimately related to both adhesion and wear, which are nonequilibrium, multiscale phenomena, from the atomic level to the molecular level to the microscopic level. As such, multidisciplinary studies are required to reveal the nature of sliding on a variety of surfaces (smooth or rough; elastic, viscoelastic, or plastic; dry or lubricated) that possess different types of chemistry. Some of the outstanding issues and questions are the following: » experimental and theoretical elucidation of the linear characteristics of friction at or near an equilibrium and their relation to statistical-mechanical theories of solids and liquids at equilibrium Nanotribology and Nanoscale Friction