Nanoscale Boundary Lubrication Studies
Boundary films are formed by physisorption, chemisorption, chemisorption and chemical reaction. With physisorption, no exchange of electrons takes place between the molecules of the adsorbate and those of the adsorbant. The physisorption physisorption pro
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Boundary films are formed by physisorption, chemisorption, and chemical reaction. With physisorption, no exchange of electrons takes place between the molecules of the adsorbate and those of the adsorbant. The physisorption process typically involves van der Waals forces, which are relatively weak. In chemisorption, there is an actual sharing of electrons or electron interchange between the chemisorbed species and the solid surface. The solid surfaces bond very strongly to the adsorption species through covalent bonds. Chemically reacted films are formed by the chemical reaction of a solid surface with the environment. The physisorbed film can be either monomolecularly or polymolecularly thick. The chemisorbed films are monomolecular, but stoichiometric films formed by chemical reaction can have a large film thickness. In
28.1 Lubricants Details ................................. 862 28.2 Nanodeformation, Molecular Conformation, and Lubricant Spreading . 864 28.3 Boundary Lubrication Studies ................ 28.3.1 Friction and Adhesion.................. 28.3.2 Rest Time Effect........................... 28.3.3 Velocity Effect ............................. 28.3.4 Relative Humidity and Temperature Effect................ 28.3.5 Tip Radius Effect ......................... 28.3.6 Wear Study .................................
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28.4 Closure ................................................ 880 References .................................................. 881
grip solid surfaces (or be adsorbed). In this chapter, we focus on PFPEs. We first introduce details of the commonly used PFPE lubricants; then present a summary of nanodeformation, molecular conformation, and lubricant spreading studies; followed by an overview of nanotribological properties of polar and nonpolar PFPEs studied by atomic force microscopy (AFM) and some concluding remarks.
general, the stability and durability of surface films decrease in the following order: chemically reacted films, chemisorbed films, and physisorbed films. A good boundary lubricant should have a high degree of interaction between its molecules and the sliding surface. As a general rule, liquids are good lubricants when they are polar and, thus, able to grip solid surfaces (or be adsorbed). Polar lubricants contain reactive functional groups with low ionization potential, or groups having high polarizability [28.1–3]. Boundary lubrication properties of lubricants are also dependent upon the molecular conformation and lubricant spreading [28.4–7]. Self-assembled monolayers (SAMs), Langmuir– Blodgett (LB) films, and perfluoropolyether (PFPE) films can be used as boundary lubricants [28.2, 3, 8–10].
Part D 28
Boundary films are formed by physisorption, chemisorption, and chemical reaction. With physisorption, no exchange of electrons takes place between the molecules of the adsorbate and those of the adsorbant. The physisorption process typically involves van der Waals forces, which are relatively weak. In chemisorption, there is an actual sharing of elec
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