ABSTRACT
Abstract ....................................................................................................................98 6.1 Introduction ....................................................................................................98 6.2 Design and Construction of Self-Assembled Ordered Films ....................... 100
6.2.1 Self-Assembled Monolayers ............................................................. 101 6.2.1.1 Monolayers of Organosilicon Derivatives ......................... 102 6.2.1.2 Monolayers of Organosulfur Compounds ......................... 103 6.2.1.3 Monolayers of Fatty Acids ................................................. 105
6.2.2 Self-Assembled Multilayers .............................................................. 107 6.2.2.1 Reactions of NH2-Terminated SAMs ................................. 108 6.2.2.2 Reactions of OH-Terminated SAMs .................................. 109 6.2.2.3 Reactions of COOH-Terminated SAMs ............................ 110 6.2.2.4 Reactions of Halide-Terminated SAMs ............................. 111
6.2.3 Mixed Monolayers ............................................................................ 111 6.2.4 Nanocomposite Ultrathin Films ....................................................... 112 6.2.5 Polymer Thin Films .......................................................................... 114
6.3 Microtribological Properties of Self-Assembled Ordered Films.................. 117 6.3.1 Inuence of Interactions between Head Groups
and Substrate Surfaces ...................................................................... 120 6.3.2 Inuence of Molecular Chain Length and Structure ........................ 120 6.3.3 Inuence of Surface Terminal Groups ............................................. 123 6.3.4 Inuence of Components in Mixed Films ........................................ 127 6.3.5 Inuence of Tribological Conditions ................................................ 130
6.4 Macrotribological Properties of Self-Assembled Ordered Films ................. 135 6.4.1 Macrotribological Properties of Dual-Layer Films .......................... 135 6.4.2 Macrotribological Properties of Nanocomposite Ultrathin Films ................................................................................. 136 6.4.3 Tribological Properties of Polymer Films ........................................ 136
6.5 Conclusion and Outlook ............................................................................... 137 References .............................................................................................................. 139
The rapid developments in microelectromechanical/nanoelectromechanical systems (MEMS/NEMS) and high-density storage technologies have dramatically increased the demand for ultrathin boundary lubricants, which can improve the tribological properties between contacting surfaces on micro-and nanoscales. Unfortunately, these miniaturized devices cannot be lubricated with conventional liquid lubricants. Molecular lubricants are considered to be prospective candidates to resolve the tribological problems of microdevices. This chapter focuses on designing and constructing self-assembled lms and their frictional properties, including self-assembled monolayers, self-assembled multilayers, mixed monolayers, nanocomposite ultrathin lms, and polymer thin lms. Furthermore, the relationship between the structure and composition of self-assembled lms and their frictional response are discussed in detail. Selfassembled lms are ordered and densely packed molecular assemblies formed by chemical adsorption of active precursor molecules from solution onto solid surfaces. The interfacial properties of self-assembled lms, such as adhesion, friction, wear, and wettability, are strongly inuenced by their chemical composition, structure, assembly order, and packing density. The nature and strength of the binding forces between head groups and substrate surfaces dominate the stability and wear resistance of lms. Results from experimental investigations and molecular dynamics simulations consistently show that molecules with longer alkyl chains can provide ordered and densely packed structures and enhance lateral interactions and, thus, exhibit improved frictional properties. Molecules with shorter chains tend to form disordered and less packed lms, which possess poor frictional properties owing to the large amount of energy dissipation in the less ordered structures. Introducing functional groups into alkyl chains to form hydrogen bonds, dipole interaction, π-stacking, or covalent attachment, can construct robust lms with enhanced mechanical and tribological stability. Surface terminal groups of the lms control their wettability, adhesion force, friction force, and shearing force. Investigations on the self-organization and structureproperty relationships will contribute to better design and construction of robust lms with excellent frictional properties and loading-carrying capacity.
