TECHNIQUES USING COLLOIDAL SOLUTIONS

In all the above cases, the sols obtained display a translucent nature due to the small particle sizes usually obtained. 

Again using a very similar chemical-polymerization-within-aqueous-polymeric-stabilizer procedure, Wiersma et al. [284] describe a procedure for the preparation of P(ANi) and P(Py) colloidal suspension within polyurethane dispersions. The procedure follows the now-familiar technique of adding monomer and oxidant (Fe(N03)3 in this case) solutions to the readymade polymeric stabilizer (polyurethane) dispersion or solution in water. In this case, rather than using dialysis, centrifugation of the colloid followed by redispersion in water is used. The sol obtained can then be used to successfully coat various woven textiles. 

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M/SC nanoparticles in size from 1 to 10 nm are of greatest interest because their electronic structure depends markedly on the particle size [4-6]. There are now a lot of methods for a deposition of M/SC and dielectric on solid substrates from liquid or gaseous phase to produce composite films containing M/SC nanoparticles inside or on a surface of a dielectric matrix. Liquid-phase technique uses colloidal solutions of M/SC nanoparticles. Such solutions are formed by chemical reactions of various precursors in the presence of stabilizers, which are adsorbed on the surface of nanoparticles and preclude their aggregation. But it is necessary to take into account, that... 

CONDUCTING POLYMERS Fundamentals and Applications 8.9 TECHNIQUES USING COLLOIDAL SOLUTIONS... 

In 1997, a Chinese research group [78] used the colloidal solution of 70-nm-sized carboxylated latex particles as a subphase and spread mixtures of cationic and other surfactants at the air-solution interface. If the pH was sufficiently low (1.5-3.0), the electrostatic interaction between the polar headgroups of the monolayer and the surface groups of the latex particles was strong enough to attract the latex to the surface. A fairly densely packed array of particles could be obtained if a 2 1 mixture of octadecylamine and stearic acid was spread at the interface. The particle films could be transferred onto solid substrates using the LB technique. The structure was studied using transmission electron microscopy. 

In addition to the preparation of Langmuir and Langmuir-Blodgett films, the use of self-assembly techniques also plays an important role in the formation of particle films. Both physisorption, as, for example, electrostatic adsorption of charged particles from colloidal solution, and chemisorption onto a substrate have been investigated. In Section V.A, electrostatic adsorption will be reviewed chemisorption is the subject of Section V.B. 

An important technique for the qualitative and quantitative analysis of different macromolecular materiafs is based on the efectrophoretic separation of particfes having different transport vefocities (e.g., because they have different zeta potentiafs). This technique is used for the anafysis of proteins, pofysaccharides, and other naturally occurring substances whose molecular size approaches that of colloidal particles (for more details, see Section 30.3.4). It is an advantage of the electrophoretic method that mild experimental conditions can be used—dilute solutions with pH values around 7, room temperature, and so on—which are not destructive to the biological macromolecules. 

The stability of most colloidal solutions depends critically on the magnitude of the electrostatic potential ( /o) at the surface of the colloidal particle. One of the most important tasks in colloid science is therefore to obtain an estimate of /o under a wide range of electrolyte conditions. In practice, the most convenient method of obtaining /q uses the fact that a charged particle will move at some constant, limiting velocity under the influence of an applied electric field. Even quite small particles (i.e. <1 xm) can be observed using a dark-field illumination microscope and their (average) velocity directly measured. The technique is called microelectrophoresis . 

Esters and ethers of cellulose, and especially nitrocellulose, are most widely used in the form of a colloidal solution. This technique is applied in the manufacture of smokeless powder, nitrocellulose varnishes, film and celluloid. 

Nanostructures primarily result from polyelectrolyte or interpolyelectrolyte complexes (PEC). The PEC (also referred to as symplex [23]) is formed by the electrostatic interaction of oppositely charged polyelectrolytes (PE) in solution. The formation of PEC is governed by physical and chemical characteristics of the precursors, the environment where they react, and the technique used to introduce the reactants. Thus, the strength and location of ionic sites, polymer chain rigidity and precursor geometries, pH, temperature, solvent type, ionic strength, mixing intensity and other controllable factors will affect the PEC product. Three different types of PEC have been prepared in water [40] (1) soluble PEC (2) colloidal PEC systems, and (3) two-phase systems of supernatant liquid and phase-separated PEC. These three systems are respectively characterized as ... 

The first studies that intentionally used colloidal nanocatalysts were reported independently by Beller et al. [50] and Reetz et al. [51] using chemical reduction and electrochemical techniques, respectively, to synthesize colloidal palladium nanoparticles for the Heck reaction. Both Beller and Reetz concluded that the solution-phase catalysis occurred on the surface of the nanoparticle, without confirming that a homogeneous catalytic pathway was nonexistent. Le Bars et al. [52] demonstrated an inverse relationship between the size of Pd nanoparticles and the TOF (normalized to the total number of surface atoms) for the Heck reaction (Fig. 18.4a). After normalizing the rate to the density of defect sites (for each nanoparticle size) (Fig. 18.4b), the TOF for all particle sizes was identical. Colloidal PVP-capped palladium nanoparticles synthesized by ethanol reduction are effective catalysts for Suzuki cross-coupling reactions in aqueous solution [53]. The El-Sayed group reported that the initial rate of reaction increased linearly with the concentration of Pd nanoparticles [53] and the catalytic activity was inversely proportional to the... 

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