Friction -adhesion aspects

Friction - adhesion aspects A D ROBERTS Influence of adhesion on friction Schallamach waves... 

V.F. Petrenko, Ice adhesion and friction fundamental aspects and applications. Proceedings 11 International Conference on the Physics and Chemistry of Ice, Bremerhaven, July 2006 (this volume). 

This chapter and the two that follow are introduced at this time to illustrate some of the many extensive areas in which there are important applications of surface chemistry. Friction and lubrication as topics properly deserve mention in a textbook on surface chemistiy, partly because these subjects do involve surfaces directly and partly because many aspects of lubrication depend on the properties of surface films. The subject of adhesion is treated briefly in this chapter mainly because it, too, depends greatly on the behavior of surface films at a solid interface and also because friction and adhesion have some interrelations. Studies of the interaction between two solid surfaces, with or without an intervening liquid phase, have been stimulated in recent years by the development of equipment capable of the direct measurement of the forces between macroscopic bodies. 

An interesting aspect of friction is the manner in which the area of contact changes as sliding occurs. This change may be measured either by conductivity, proportional to if, as in the case of metals, it is limited primarily by a number of small metal-to-metal junctions, or by the normal adhesion, that is, the force to separate the two substances. As an illustration of the latter, a steel ball pressed briefly against indium with a load of IS g required about the same IS g for its subsequent detachment [37]. If relative motion was set in, a value of S was observed and, on stopping, the normal force for separation had risen to 100 g. The ratio of 100 IS g may thus be taken as the ratio of junction areas in the two cases. 

R.W. Caipick and M. Salmeron, Scratching the Surface Fundamental Investigations of Tribology with Atomic Force Microscopy,in Chem. Rev. 97 (1997) 1163. (Review relevant technical aspects using AFM for nanotiibology, results on bare interfaces and model lubricant films (SAM s and LB films), aimed at atomic-scale understanding of processes such as friction, the onset of wear, nanometer-scale elasticity, plasticity ind adhesion.)... 

If the circumstances require the use of a pre-applied solid film, then in addition to the tribological properties of the film (x,.e. its intrinsic friction and wear and its interaction with the countersurface against which it rubs) the adhesion of the film to the substrate surface comes into consideration. An important aspect of practical lubrication... 

Probably the most important aspect of ToF-SIMS analysis involves the use of the technique to understand the variation in surface properties, such as wettability, adhesion, and friction, which are sensitive to suhmonolayer coverage of molecular species. ToF-SIMS is imique in its sensitivity and molecular speciation capability. However, imlike the situation with gas-phase organic molecule identification by electron impact mass spectrometry, there are, as yet, no well-estahhshed rules which allow molecular identification directly from the spectra. The situation is also complicated, in most cases, by the superposition of the spectrum of the substrate and the potential presence of more than one organic molecule. 

Most published evidence on polymer friction led one to believe that the adhesion mechanism can explain many unrelated phenomena provided that the relaxation aspect is taken into account. It appears that as long as polymers are concerned, relaxation controls both adhesion and friction. Thus, a clear demarcation between adhesion and deformation components is unattainable, and many unnecessary arguments about mechanisms can be avoided if relaxation is considered to be the intrinsic property of polymer. 

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