Monolayer coating

Yamada S and Israelachvili J N 1998 Friction and adhesion hysteresis of fluorocarbon surfactant monolayer-coated surfaces measured with the surface forces apparatus J. Rhys. Chem. B 102 234-44... 

Self-assembled monolayers are formed spontaneously by the immersion of an appropriate substrate into a solution of active surfactant in an organic solvent. After the substrate is immersed for a time from minutes to hours, it is rinsed with ligroin, methanol, distilled water, and dried in a steam of nitrogen. An apparent effect of the monolayer coating is the drastic change in wettability of the surface so that the measurement of the contact angle can be considered as an effective way to detect the formation of the SAMs. 

Gauging catalysis by reference to an electrode where electrons are delivered (or eaten up) in an outer-sphere manner, redox catalysis is not expected to operate at a monolayer coated electrode (Figure 4.10), since, as discussed in Section 4.2.1, redox catalysis results from the three-dimensional dispersion of the catalyst. In contrast, there is no reason that chemical catalysis could not be operative at a monolayer coated electrode. For the same reasons, both redox catalysis and chemical catalysis are expected to function at multilayer electrode coatings (Figure 4.10). 

Although cyclic voltammetry could fruitfully be applied to the kinetic analysis of these catalytic systems, it has mostly been investigated by means of rotating disk electrode voltammetry (Section 1.3.2). The simplest case is that of an irreversible catalytic reaction at a monolayer coating. The next section is devoted to the analysis of these systems by the two techniques. 

In zone R, all three phenomena that take place in the film are fast compared to the diffusion of the substrate from the bulk of the solution to the film-solution interface. The concentrations of both Q and A are constant through the film. The RDEV response is similar to that of a monolayer coating (Section 4.3.2), except that more catalytic material is present on the surface of the electrode (it is multiplied by the number of layers in the multilayered coating). A linear Koutecky-Levich plot is obtained from the intercept, from which the kinetics of the catalytic reaction can be characterized. 

The formation of a 4-MBA SAM on the gold surface of the cantilever was achieved by immersing the cantilever into a 6 x 10-3 M solution of 4-MBA (97%, from Aldrich Chemical Company) in absolute ethanol for 2 days. Prior to SAM immobilization, the cantilevers were thoroughly cleaned and coated on one side with 3 nm of titanium followed by 30 nm gold. Upon removal from the solution, the cantilever was rinsed with ethanol and then dried before use in the experiments. The monolayer coating was shown to be quite stable for several months under normal operating conditions. 

Yang H, Lazos D, Ulbricht M. Thin, highly crosslinked polymer layer synthesized via photo-initiated graft copolymerization on a self-assembled-monolayer-coated gold surface. J Appl Polym Sci 2005 97 158-164. 

DOPC) monolayer-coated mercury electrodes in contact with different electrolytes, using electrochemical impedance spectroscopy and a multivariate analysis of impedance data. Rueda et al. [181] have analyzed impedance spectra of DOPC-coated mercury electrodes. 

SnOi was deposited on hydrolyzed Si and on Si coated with sulphonate-terminated self-assembled monolayers from a solution of SnCU in dilute HCl at 80° [45]. The films, up to 65 nm thick and consisting of a dense-packed aggregate of SnOi nanocrystals (5-10 nm) together with some amorphous basic tin oxide, contained ca. 3 at.% Cl. They were adherent on all substrates, although the adherence and homogeneity on Si was less reproducible than on the monolayer-coated Si. Films were also deposited using a continuous flow system. The films were sim-... 

We have investigated the photocurrent behavior of multilayers of a Chi a-DPL (molar ratio 1/1) mixture on platinum in an aqueous electrolyte without added redox agents (80). Cathodic photocurrents with quantum efficiencies in the order of 10- were obtained with films consisting of a sufficient number of monolayers. The photocurrent was increased in acidic solutions. However, no appreciable photocurrent was observed with a single monolayer coated on platinum. The latter fact most probably results from minimal rectifying property of the metal surface and/or an efficient energy quenching of dye excited states by free electrons in... 

Other aggregates can also allow for control of rates of electron exchange. Inclusion of a donor or acceptor within a cyclodextrin (277), a zeolite (278), a monolayer coating on an electrode (279), or on a polymer-coated metal colloid (280)... 

At the same time, this particular lipid-monolayer coating causes (cf. Chapter 14 below) LCM to display the marked tumortargeting abilities described in Chapters 12 and 13. 

Both compounds reach an equilibrium adsorption within one minute of reaction. This reflects the quick adsorption of the amine group, forming hydrogen bonds with the surface silanols. The lack of further deposition indicates that an equilibrium is reached. Because the reaction is performed in a dry solvent, on a dehydrated substrate, no oligomerization of the silane molecules can occur. It may be concluded, accordingly, that the equilibrium situation reflects the formation of a monolayer coating on the silica surface. 

For the monofunctional APTS, the observed deposition profile is identical to that reported by Vandenberg et al., using liquid/solid ellipsometry.15 The rapid, first equilibrium is followed by an additional adsorption. The equilibrium situation is related to the localized adsorption of silane molecules on the surface hydroxyls. Thus forming a monolayered coating on the surface. The extent of the additional adsorption was found to be not very reproducible and not strictly correlated to the initial silane concentration. At any time it showed not to have the step-wise profile, as found for the bifunctional aminosilane. Therefore, this last adsorption appears to be of a nonspecific type. We will discuss this further below. 

Summarizing, aminosilanes show a fast adsorption on the silica surface. An equilibrium monolayer coating is formed. Modification in aqueous solvent causes polymerization on top of the initial monolayer. For modification from organic solvent, the reactions can be better controlled. With the bifunctional AEAPTS, a secondary silane layer adsorbs on the free primary amine groups of the first monolayer. At high concentration and after long reaction times, for both aminosilane types, a further non-specific deposition occurs. 

The use of self-assembling peptides is also explored beyond the medical, pharmaceutical, or cosmetics industry. Areas of interest are among others functional foods, electronics, functional coatings, and catalysis (but different from enzyme research). As an example, peptides can be designed to switch from a random coil-like primary structure organization into an a-helix or [3-sheet secondary structure with unique properties. Short peptides align to form [3-sheet tapes with different functionalities, for example, hydrophilic and hydrophobic on either side of the tape to form monolayer coatings (Boden et al., 1996). 

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