Polymer coating method approach

Another method to synthesize hollow nanocapsules involves the use of nanoparticle templates as the core, growing a shell around them, then subsequently removing the core by dissolution [30-32]. Although this approach is reminiscent of the sacrificial core method, the nanoparticles are first trapped and aligned in membrane pores by vacuum filtration rather than coated while in aqueous solution. The nanoparticles are employed as templates for polymer nucleation and growth Polymerization of a conducting polymer around the nanoparticles results in polymer-coated particles and, following dissolution of the core particles, hollow polymer nanocapsules are obtained. 

Special electrochemical sensors that operate on the principle of the voltammetric cell have been developed. The area of chemically modified solid electrodes (CMSEs) is a rapidly growing field, giving rise to the development of new electroanalytical methods with increased selectivity and sensitivity for the determination of a wide variety of analytes [490]. CMSEs are typically used to preconcentrate the electroactive target analyte(s) from the solution. The use of polymer coatings showing electrocatalytic activity to modify electrode surfaces constitutes an interesting approach to fabricate sensing surfaces useful for analytical purposes [491]. 

To prepare ultrathin polymer films on the surface of wafers, especially those of large diameter (6 or 8 inch), uniformity and defect density become important factors in determining the resist quality. The conventional spin coating method has been reported to introduce interference striations (11) and high defect densities (2.31 when used to prepare ultrathin polymer films. As an alternative approach, the LB technique has been proposed as being suited to the preparation of more uniform ultrathin polymer films (2). Using this technique monolayer polymer films can be transferred layer by layer to the surface of a solid substrate from the water surface. An important feature of the LB technique is that the accumulation of monolayer films allows the thickness of the built-up film to be controlled in a precise manner. Consequently, extremely uniform and ultrathin polymer films can be prepared. 

In 1978, Miller s group and Bard s group independently showed that chemically modified electrodes could be prepared by coating electrode surfaces with polymer films [20,21]. This has since proven to be the most versatile approach for preparing chemically modified electrodes. Indeed, until the recent rebirth of chemisorption and new covalent-attachment schemes (see earlier discussion), the polymer-film method had essentially supplanted all other methods for preparing chemically modified electrodes. 

Surface silylation of solid supports, glass columns, inserts, or even glass-wool spacers and glassware for the sake of surface deactivation remains highly recommended in biochemical GC. An alternative approach to surface deactivation is the method of Aue et al. [93], in which thermal treatment of polymer-coated supports results in a partial linkage of the macromolecule to the surface. This approach has been successfully employed with both packed and capillary columns. 

The complex surface chemistry of the metal oxides (section 4.2.1.2) is incompatible with their use in a number of chromatographic techniques. Polymer coated metal oxides are seen as an important approach to extending their scope. Alumina and zirconia particles coated with poly(butadiene), poly(styrene), poly(ethylene oxide), a copolymer of chloromethylstyrene and diethoxymethylvinylsilane and succinylated poly(ethyleneimine), for example, have been prepared for use in reversed-phase, size-exclusion and ion-exchange chromatography [44,46,54,120,134-137]. The methods of preparation are similar to those used for porous silica. 

The detection of the current generated by reaction at the surface of (usually) carbon fiber or copper microelectrodes at a fixed voltage is capable of low detection limits for electroactive compounds using amperometry, Table 8.14. Several approaches that allow the full possibilities of multiple electrode and pulsed amperometric detection (established techniques in liquid chromatography (section 5.7.4)) have been proven for capillary electrophoresis [508,511]. These methods are not widely used, possibly due to a lack of commercial products and support. Potentiometric detection with polymer-coated wire microelectrodes containing relatively non-specific ion exchange ionophores was used for the detection of low-mass anions or cations [510,511]. 

In overall, the use of polymer-coated CNTs produced by in situ polymerisation, whether by covalent or non-covalent methods leads to the production of polymer nanocomposites displaying much better thermomechanical, flame retardant and electrical conductive properties, even at very low nanotube loadings. As mentioned above, the covalent approach allows the formation of a strong interface between the nanotube and polymer matrix due to strong chemical bonding of polymer molecules to the CNT surface. The in situ polymerisation technique also enables the preparation of composites with very high nanotube loadings. 

Reliable methods for preventing electrode fouling are needed for long-lived amperometric biosensors. In some cases gamma irradiated polymer coated electrodes such as PNVP could provide a simple and effective way to accomplish this goal. The increased response due to the incorporation of the analyte into the polymer film observed for some compounds makes this approach particularly attractive. 

This chapter introduces in a tutorial manner some numerical methods for solving mass transport equations for specific electrochemical systems. These are applied to polymer coatings on electrode surfaces containing redox species. Unlike some theoretical approaches, numerical methods are considerably more straightforward and require only some knowledge of programming. For a typical mass transport situation, the equation to be solved is... 

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