Functional coating techniques

It is beyond the scope of this Chapter to discuss all kinds of various coating techniques, properties of the supports, properties of the coatings and the various fields of application of the composites in catalysis, separation techniques, materials science, colloid science, sensor technology, biocompatible materials, biomi-metic materials, optics etc. The scope had to be restricted to the fundamental properties of ultrathin organic layers on solid supports followed by some examples, outlining the benefit of the tailored functional surfaces such as SAM and polymer brushes for catalysis. 

In Eastern Europe, parallel to the development of ALE, a quite similar coating technique was developed, called Molecular Layering.12,13,14,15 The principles of Molecular Layering are based on the irreversible chemical reactions of the substrate with a functional reagent. In this way, monolayers can be created to be used as such or to undergo further reaction with a second reagent. Its principles are visualized in figure 13.12. 

An alternative approach to producing a differently functional surface is to use spin coating techniques. This was done by Turner et al. [68], who spun cast layers of polystyrene onto a silica surface. They investigated the nature of the surface and of SDS adsorbed to that surface by neutron reflectivity and IR-ATR. A thin layer of polystyrene, 275 A, was established. The subsequent SDS adsorption was consistent with a monolayer 15 A thick and an adsorbed amount similar to that observed at the air-solution interface. Measurements above the cmc of SDS showed clearly the effects on the adsorption pattern of dodecanol impurities in the SDS. 

Stearic acid has been reported to cause pitting in the film coating of tablets coated using an aqueous film-coating technique the pitting was found to be a function of the melting point of the stearic acid. ... 

Fluidised-bed CVD is a special technique to coat nuclear-fuel particles for high-temperature gas-cooled nuclear reactors which was developed in the late 1950s. This technique has also been used in other applications, such as the production of biomedical components (e.g. heart valves deposited by pyrolysis carbon) and some special functional coatings on ceramic particles. 

The most convenient and most popular analytical methodology to assess enantiomer purity is the direct separation of enantiomers on so-called chiral stationary phases (CSPs). CSPs consist of an (ideally) inert chromatographic support matrix incorporating chemically or physically immobilized SO species. CSPs may be created by a variety of SO immobilization techniques, including (i) covalent attachment onto fhe surface of suitably pre-functionalized carrier materials, (ii) physical fixation employing coating techniques, and (iii) incorporation into polymeric networks by copolymerization, or combinations of these procedures. 

I. van Driessche, S. Hoste, Encapsulations through the sol-gel technique and their applications in functional coatings. In Functional Coatings, Ghosh, S.K., (Ed.) Wiley-VCH, Weinheim, Germany, 2006. 

All diffusion coatings, irrespective of the coating technique, are characterized by the existence of an alloy layer in many cases, this comprises several discrete layers [42]. The extent of alloying is dependent on the coating process, and the precise nature of this layer is discussed below. In addition, part of the coating may be of the unalloyed coating metal (e.g., as obtained by conventional hot-dip processes). The properties of the coating will therefore be a complex function of the individual properties of the discrete layers and their interfaces. 

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