Colloidal systems applications

Although the remainder of this contribution will discuss suspensions only, much of the theory and experimental approaches are applicable to emulsions as well (see [2] for a review). Some other colloidal systems are treated elsewhere in this volume. Polymer solutions are an important class—see section C2.1. For surfactant micelles, see section C2.3. The special properties of certain particles at the lower end of the colloidal size range are discussed in section C2.17. 

Overbeek, JTG Lijklema, J, Electric Potentials in Colloidal Systems. In Electrophoresis, Theory, Method and Applications Bier, M, ed. Academic Press New York, 1959 1. 

While the nuclear magnetic resonance (NMR) technique has widely been used to study diffusion processes of normal liquids, solids, or colloidal systems, there are only a few applications to molten salts. The spin echo self-diffusion method with pulsed field gradients was applied to molten salts by Herdlicka et al. "" There is no need to set up or maintain a concentration gradient. 

Measurements of the chemical composition of an aqueous solution phase are interpreted commonly to provide experimental evidence for either adsorption or surface precipitation mechanisms in sorption processes. The conceptual aspects of these measurements vis-a-vis their usefulness in distinguishing adsorption from precipitation phenomena are reviewed critically. It is concluded that the inherently macroscopic, indirect nature of the data produced by such measurements limit their applicability to determine sorption mechanisms in a fundamental way. Surface spectroscopy (optical or magnetic resonance), although not a fully developed experimental technique for aqueous colloidal systems, appears to offer the best hope for a truly molecular-level probe of the interfacial region that can discriminate among the structures that arise there from diverse chemical conditions. 

The major disadvantages of colloidal catalysts studied so far can be attributed to problems in controlling the metal colloid formation (control of particle size, particle size distribution, structure of metal colloids) and stabilization of the prepared particles, which are not yet completely solved. But it is exactly the stability of the nanoparticles, that is decisive for long-term usage during catalytic processes. Moreover for catalytic application, it is extremely important to preserve the large surface of such colloidal systems. 

A.S. Kabalnov, A.V. Pertsov and E.D. Shchukin Ostwald Ripening in Two-Component Disperse Phase Systems Application to Emulsion Stability. Colloid Surfaces 24, 19 (1987). 

In the past few decades, a specific kind of colloidal system based on monodis-perse size has been developed for various industrial applications. A variety of metal oxides and hydroxides and polymer lattices have been produced. Monodisperse systems are obviously preferred since their properties can be easily predicted. On the other hand, polydisperse systems will exhibit varying characteristics, depending on the degree of polydispersity. 

In drug studies, of main interest is the application of colloidal systems, which show specific and unspecific interaction with mainly lipophilic substances. An obvious application is the study of highly lipophilic and poorly absorbable drugs that are administered orally or transdermally (2). Such interactions with surface-active agents may either cause a diminution of the... 

Hotta,Y Ozeki, S. Suzuki,T. Imal, S. Ka-neko, S. (1991) Surface characterization of titanated a-Fe203. Langmuir 7 2649—2654 Howe, A.T. Gallagher, K.J. (1975) Mossbauer studies in the colloidal system P-FeOOH — P-Fe20j Structures and dehydration mechanism. J. Chem. Soc. Faraday Trans. I. 71 22-34 Hsi, C.D. Langmuir, D. (1985) Adsorption of uranyl onto ferric oxyhydroxides Application of the surface complexation site-binding model. Geochim. Cosmochim. Acta 49 1931-1941... 

To sum up, the choice of operating conditions for a specific FFF application is made in a way that recalls the general criteria used in chromatography. An accurate search of literature addressed to similar samples that have been already analyzed by FFF techniques is very useful. A number of specific reviews have been published concerning, for example, enviromnental, pharmaceutical, and biological samples (see Section 12.5). As previously mentioned above, one of the most important factors is the stability of the considered colloidal system, for which a great deal of information can be obtained from specialized literature, such as colloid, polymer, and latex handbooks [33], For example, the use of the proper surfactant (e.g., Fl-70) is common for SdFFF applications. Polymer analysis with ThFFF requires solvent types similar to those employed in size exclusion chromatography. 

M.P. Krafft, J.G. Riess, Highly fluorinated amphiphiles and colloidal systems, and their applications in the biomedical field—A contribution, Biochimie 80 (1998) 489-514. 

When the relation between D and M is established, we can easily convert G(D) obtained by dynamic LLS into a differential molecular weight distribution, such as fw(M). We have successfully applied the above methods to various kinds of polymeric and colloidal systems, such as for Kevlar [15, 23], fluoropolymers (Tefzel Teflon) [12,30-35,52], epoxy [53-55],polyethylene [56,57], water-soluble polymers [18,50-51,58,59], copolymers [60-62], thermoplastics [63-65] and colloids [66-72]. Three of those applications are illustrated below. 

Similar incorporation of ligand-based targeting motifs is applicable to colloidal systems. In the final analysis, the effectiveness of ligand-based targeting drug delivery systems depends on the density of the target receptor on the cell surface, the rate in which the systems are internalized into the cell, and recycling and reexpression of the receptor on the cell surface after internalization. 

As we shall see, the intensity, polarisation and angular distribution of the light scattered from a colloidal system depend on the size and shape of the scattering particles, the interactions between them, and the difference between the refractive indices of the particles and the dispersion medium. Light-scattering measurements are, therefore, of great value for estimating particle size, shape and interactions, and have found wide application in the study of colloidal dispersions, association colloids, and solutions of natural and synthetic macro-molecules. 

The application of light scattering to the characterisation of colloidal systems has advanced rapidly over the last few decades. This has been made possible by the development of (a) lasers as intense, coherent and well-collimated light sources, (b) sophisticated electronic devices for recording data, and (c) computers for the complex data processing that is involved. 

One widespread application, which has been much researched in recent years, is the use of colloidal systems for controlled uptake and release purposes. 

In fact, the SFA was initially developed for practically probing the DLVO theory, and DLVO forces were successfully measured in electrolyte solutions and colloidal systems [4,22]. However, the applications of the apparatus were not restricted to this. Detailed and accurate information was obtained on thickness and refractive index profiles of thin films [6], simple liquid molecular structuring... 

Fluorocarbons and fluorinated amphiphiles have found a variety of applications in materials science and medicine [1-5]. As many of these applications involve colloidal systems stabilized by a monolayer of fluorinated amphiphiles, it is essential to understand the structure and properties of these interfacial films. Such knowledge can provide improved control over the engineering and properties of highly fluorinated colloids and interfaces [6]. 

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