Dispersion formation, practical aspects

While a great deal of information has been pubhshed over the years on the theoretical and practical aspects of emulsion formation and stabilization, until recently little has been said about more complex systems generally referred to as multiple emulsions. Multiple emulsions, as the name implies, are composed of droplets of one liquid dispersed in larger droplets of a second liquid, which is then dispersed in a final continuous phase. Typically, the internal droplet phase will be miscible with or identical to the final continuous phase. Such systems may be w/o/w emulsions as indicated in Figure 11.13, where the internal and external phases are aqueous or o/w/o, which have the reverse composition. Although known for almost a century, such systems have only recently become of practical interest for possible use in cosmetics,... 

Tribological tests have been performed and are supported by post-test examination using X-ray Photoelectron Spectroscopy (XPS), and Environmental Scanning Electron Microscope (ESEM) with Energy Dispersive X-ray analysis (EDX). Preliminary results show that fully formulated lubricant oils are effective in the reduction of wear and friction for ferrous-based systems but not for aluminium systems. Initial XPS and EDX data suggests that a relatively thick anti-wear film is formed on ferrous materials but is thin (and therefore unstable) for steel on aluminium systems. In completely non-ferrous systems the wear film is absent. In this paper the fundamental aspects of the film formation as well as the practical aspects of the results will be discussed. 

The existence of electrical charges at any interface will give rise to electrical effects, which will, in many cases, determine the major characteristics of that interface. Those characteristics will affect many of the properties of a multicomponent system, including emulsion and foam formation and stability, solid dispersions, and aerosols. The theoretical and practical aspects of electrical double layers are the subject of a vast amount of literature and for that reason have not been addressed in any detail so far. Such details can be found in bibliographic references cited for this chapter. 

Yet another important aspect is the change in the fractal dimension of polymers when they are simulated on fractal rather than Euclidean lattices. This fact is also important from the practical standpoint for multicomponent polymer systems. The introduction of a dispersed filler into a polymer matrix results in structure perturbation in terms of fractal analysis, this is expressed as an increase in the fractal dimension of this structure. As shown by Novikov and co-workers [25], the particles of a dispersed filler form in the polymer matrix a skeleton which possesses fractal (in the general case, multifractal) properties and has a fractal dimension. Thus, the formation of the structure of the polymer matrix in a filled polymer takes place in a fractal rather than Euclidean space this accounts for the structure modifications of the polymer matrix in composites. 

The previous chapters have introduced several classes of colloids and some of the important surface aspects of their formation, stabilization, and destruction. Emulsions, foams, and dispersions are the most commonly treated and intensely studied examples of colloidal systems. They constitute the majority of practical and ideal systems one encounters. There exists one other class of true, lyophobic colloids—the aerosols—which, although seemingly less important in a theoretical or applied sense, are of great practical importance. 

Aerosols, like foams, emulsions, and dispersions, may be either advantageous or detrimental, depending on the situation. The previous discussion introduced some of the fundamental aspects of aerosol formation. Of equal or perhaps greater practical importance is the question of the suppression of aerosol formation, the destruction of unavoidable aerosols, or the controlled deposition of aerosols onto surfaces. Perhaps the best approach to solving such problems is through an understanding of some of the general principles involved in their stabilization and destruction. In that context, some of the mechanisms of destruction involved will be essentially the same as those for other colloidal systems flocculation and coalescence. 

The influence of particle size distribution in the use of latex dispersions is shown to be of great practical importance. The practical consequences are examined of bimodal particle size distribution with respect to coatings applications. The introduction of polydispersity in acrylic dispersions is examined as a way of obtaining a lower dispersion volume loading at an equivalent viscosity as for monodisperse spheres. Aspects such as film formation, rheology, and drying behaviour are discussed. 39 refs. 

Although nano-emulsions are thermodynamically imstable systems, they may possess high kinetic stability. This property together with their transparent or translucent visual aspect and a viscosity similar to that of water makes them of special interest for practical applications. Nano-emulsions are used in the pharmaceutical field as drug delivery systems [8,17, 18,25,28-33], in cosmetics as personal-care formulations [2,4,6,7,10,19-21,23,24,27], in agrochemical applications for pesticide delivery [3,34,35], in the chemical industry for the preparation of latex particles [9,22,26,36-38], etc. In addition, the formation of kinetically stable liquid/liquid dispersions of such small sizes is of great interest from a fimdamental viewpoint. 

Considering only mechanical energy aspects, nano-emulsion formation should be considerably costly. However, it is well known that by taking advantage of the physicochemical properties of the system, dispersions can be produced almost spontaneously [3,6,14]. This is the case with the so-called low-energy emulsification methods that are described next. In practice, the two types of methods are often combined. 

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