Published: Jan 2008
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STUDY ON ADHESION AND FRICTION IN MICROscopic scale has received great attention in recent decades. The development of Micro Mechanical Electrical System (MEMS) and nanotechnology, for instance, requires a better understanding of the interfacial phenomena which significantly affect performance of micro and nano-devices. Meanwhile the inventions of new scientific instruments, such as the Scanning Tunnel Microscope (STM), Atomic Force Microscope (ATM), Surface Force Apparatus (SFA), Quartz Crystal Microbalance (QCM), etc., and rapid progress of computer simulation technology allows scientists to explore and resolve the secrets of adhesion and friction in more efficient ways than ever before. This chapter intends to give an introduction to the fundamental studies in the area of atomic-scale adhesion and friction. The emphasis will be focused on molecular origin of friction and connection between adhesion and friction. The chapter was written based on experiences from the present author in studying the fundamental of friction for years. Section 2 describes the surface forces that are responsible for origin of adhesion, and presents an atomic scale analysis by the present author to show how mechanical instability occurs in a process of approach/separation. Section 3 discusses the wearless friction models, both in atomic and asperity levels, which interpret the origin of friction in terms of instable atomic motion and energy dissipation. Section 4 provides the author's own view on interrelations between friction and adhesion, and the role of adhesion hysteresis in particular. Section 5 compares static friction with stick-slip transition to show the similarity and difference between the two events, which provides important information for the understanding of static friction on the basis of the principle of energy optimization. Finally, a summary is given in Section 6 with an expectation that the energy approach presented in this chapter has to be combined with a nonequilibrium thermodynamic model in order to provide a satisfactory solution to the mystery of friction.
Tsinghua University, Beijing,