Macroscopic self-assembled monolayers

Several examples of catenanes and rotaxanes have been constructed and investigated on solid surfaces.1 la,d f 12 13 26 If the interlocked molecular components contain electroactive units and the surface is that of an electrode, electrochemical techniques represent a powerful tool to study the behavior of the surface-immobilized ensemble. Catenanes and rotaxanes are usually deposited on solid surfaces by employing the Langmuir-Blodgett technique27 or the self-assembled monolayer (SAM) approach.28 The molecular components can either be already interlocked prior to attachment to the surface or become so in consequence of surface immobilization in the latter setting, the solid surface plays the dual role of a stopper and an interface (electrode). In most instances, the investigated compounds are deposited on macroscopic surfaces, such as those of metal or semiconductor electrodes 26 less common is the case of systems anchored on nanocrystals.29... 

The first oxidation-reduction V " " V is completely reversible in bulk solutions as well as immobilized on various surfaces. The redox-active unit has been incorporated as a backbone component in self-assembled monolayers [289-292], or in a nanometer scale electronic switch [293] and various functional materials [294,295]. For a detailed characterization of the macroscopic electrochemical and structure properties of the various viologen-type adlayers on solid electrodes we refer to [231,296] and the literature cited therein. 

Macroscopic Tribological Testing of Alkanethiol Self-assembled Monolayers (SAMs) Pin-on-disk Tribometry with Elastomeric Sliding Contacts... 

The interactions could be based on electrostatic interactions determined by the electric doublelayer forces or specific interactions (e.g., chemical bonding, chelation, covalent-coordinate bonds, hydrophobic interactions, salvation forces, hydrogen bonding, and steric forces). The adsorption of the surfactant at the interface results in certain desirable changes in macroscopic properties such as wettability and colloidal stability. For example, the self-assembled monolayers at the interface... 

An interesting approach to control self-assembly of macroscopic objects coated with monolayers was described by Whitesides and coworkers. Millimeter-sized gold objects made hydrophobic by the thiol coating self-assemble in water in such a way as to minimize hydrophobic interactions with water. Objects of complimentary shapes recognize each... 

In principle, we can distinguish (for surfactant self-assemblies in general) between a microstructure in which either oil or water forms discrete domains (droplets, micelles) and one in which both form domains that extend over macroscopic distances (Fig. 7a). It appears that there are few techniques that can distinguish between the two principal cases uni- and bicontinuous. The first technique to prove bicontinuity was self-diffusion studies in which oil and water diffusion were monitored over macroscopic distances [35]. It appears that for most surfactant systems, microemulsions can be found where both oil and water diffusion are uninhibited and are only moderately reduced compared to the neat liquids. Quantitative agreement between experimental self-diffusion behavior and Scriven s suggestion of zero mean curvature surfactant monolayers has been demonstrated [36]. Independent experimental proof of bicontinuity has been obtained by cryo-electron microscopy, and neutron diffraction by contrast variation has demonstrated a low mean curvature surfactant film under balanced conditions. The bicontinuous microemulsion structure (Fig. 7b) has attracted considerable interest and has stimulated theoretical work strongly. 

Figure 7 In surfactant-oil-water systems there is a segregation into oil and water domains and surfactant films. In (a) one can distinguish between cases of uncorrelated surfactant films (monolayers) and pairwise correlated films (bilayers), (b) Surfactant self-assembly can lead to discrete structures in which one of the solvents is enclosed or to structures that extend over macroscopic distances in one, two, or three dimensions. The bicontinuous structure, introduced by Scriven [34], in which both solvents form domains that are connected in three dimensions has stood in the foreground of microemulsion research. (Courtesy of Ulf Olsson.)...

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