Self-Assembled Monolayers for Controlling Adhesion, Friction and Wear
Reliability of micro- and nanodevices, as well as magnetic storage devices require the use of lubricant films for the protection of sliding surfaces. To minimize high adhesion, friction, and because of small clearances in the devices, these films should b
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Self-Assemble
Reliability of micro/nanodevices, also commonly referred to as micro/nanoelectromechanical systems (MEMS/NEMS), as well as magnetic storage devices (which include magnetic rigid disk drives, flexible disk drives, and tape drives) require the use of molecularly thick films for protection of sliding surfaces [27.1–8].
27.1 A Primer to Organic Chemistry................ 27.1.1 Electronegativity/Polarity .............. 27.1.2 Classification and Structure of Organic Compounds .................. 27.1.3 Polar and Nonpolar Groups ...........
834 834 835 838
27.2 Self-Assembled Monolayers: Substrates, Head Groups, Spacer Chains, and End Groups.................................... 839 27.3 Tribological Properties of SAMs .............. 27.3.1 Surface Roughness and Friction Images of SAMs Films .................... 27.3.2 Adhesion, Friction, and Work of Adhesion ................................. 27.3.3 Stiffness, Molecular Spring Model, and Micropatterned SAMs.............. 27.3.4 Influence of Humidity, Temperature, and Velocity on Adhesion and Friction .............. 27.3.5 Wear and Scratch Resistance of SAMs .......................................
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27.4 Closure ................................................ 856 References .................................................. 857
properties of SAMs, having alkyl and biphenyl spacer chains with different surface terminal and head groups, are surveyed. The friction data are explained using a molecular spring model in which the local stiffness and intermolecular force govern its frictional performance. Based on the nanotribological studies of SAM films by AFM, they exhibit attractive hydrophobic and tribological properties.
A solid or liquid film is generally necessary for acceptable tribological properties of sliding interfaces. However, a small quantity of high surface tension liquid present between smooth surfaces can substantially increase the adhesion, friction, and wear as a result of formation of menisci or adhesive bridges [27.9, 10]. It
Part D 27
Reliability of micro- and nanodevices, as well as magnetic storage devices require the use of lubricant films for the protection of sliding surfaces. To minimize high adhesion, friction, and because of small clearances in the devices, these films should be molecularly thick. Liquid films of low surface tension or certain hydrophobic solid films can be used. Ordered molecular assemblies with high hydrophobicity can be engineered using chemical grafting of various polymer molecules with suitable functional head groups, spacer chains and nonpolar surface terminal groups. The classical approach to lubrication uses multi-molecular layers of liquid lubricants. Boundary lubricant films are formed by either physisorption, chemisorption, or chemical reaction. The physiosorbed films can be either monomolecularly or polymolecularly thick. The chemisorbed films are monomolecular, but stoichiometric films formed by chemical reaction can be multilayered. A good boundary lubricant should have a high
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