Self-assembled monolayers mechanism

Salmeron M, Liu G-Y and Ogletree D F 1995 Molecular arrangement and mechanical stability of self-assembled monolayers on Au(111) under applied load Force in Scanning Probe Methods ed H-J Guntherodt et al (Amsterdam Kluwer)... 

As mentioned earlier, the contact-mechanics-based experimental studies of interfacial adhesion primarily include (1) direct measurements of surface and interfacial energies of polymers and self-assembled monolayers (2) quantitative studies on the role of interfacial coupling agents in the adhesion of elastomers (3) adhesion of microparticles on surfaces and (4) adhesion of viscoelastic polymer particles. In these studies, a variety of experimental tools have been employed by different researchers. Each one of these tools offers certain advantages over the others. These experimental studies are reviewed in Section 4. 

Section 4.1 briefly describes some of the commonly employed experimental tools and procedures. Chaudhury et al., Israelachvili et al. and Tirrell et al. employed contact mechanics based approach to estimate surface energies of different self-assembled monolayers and polymers. In these studies, the results of these measurements were compared to the results of contact angle measurements. These measurements are reviewed in Section 4.2. The JKR type measurements are discussed in Section 4.2.1, and the measurements done using the surface forces apparatus (SFA) are reviewed in Section 4.2.2. 

As reviewed so far, the contact-mechanics-based techniques (JKR and SFA methods) have been effective in the understanding molecular level mechanisms related to the adhesion of elastomers and in measuring the surface and interfacial energies of polymers and self-assembled monolayers. The current work in this area is aimed at understanding contact induced interfacial rearrangements and the role of specific interactions. The recent progress of these studies is discussed in this section. 

Interest in the adsorption of sulfur-containing molecules at metal surfaces been stimulated by a desire to elucidate the decomposition mechanisms of thiols during the catalytic removal of sulfur from feedstocks and the position of thiols as the favoured head groups for adsorbates used to construct self-assembled monolayers. We shall not survey the extensive self-assembled film literature but restrict our discussion to the simpler thiols. 

Mechanical Properties of Functionalized Alkanethiol Self-Assembled Monolayers. 

Wang W, Lee T, Reed MA (2003) Mechanism of electron conduction in self-assembled monolayer devices. Phys Rev B 68 035416... 

Amylose brushes (a layer consisting of polymer chains dangling in a solvent with one end attached to a surface is frequently referred to as a polymer brush) on spherical and planar surfaces can have several advantageous uses, such as detoxification of surfaces etc. The modification of surfaces with thin polymer films is widely used to tailor surface properties such as wettability, biocompatibility, corrosion resistance, and friction [142-144]. The advantage of polymer brushes over other surface modification methods like self-assembled monolayers is their mechanical and chemical robustness, coupled with a high degree of synthetic flexibility towards the introduction of a variety of functional groups. 

Houston IE Kim HI, Adhesion friction, and mechanical properties of functionalized alkanethiol self-assembled monolayers, Acc. Chem. Res., 2002, 35, 547-553. 

Figure 10. A self-assembled monolayer comprised of terminal porphyrins, intermediate ferrocences, and surface thiols attached on gold surface. The sold line is the photoaction spectrum, the dashed line is the absorption spectrum. Panels a) and b) show the proposed mechanisms, and c) provides the structure of the thiol ferrocene-porphyrin complex.

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