Colloidal dispersions, destruction

What is a colloidal dispersion Give some examples of colloids. The Tyndall effect is often used to distinguish between a colloidal suspension and a true solution. Explain. The destruction of a colloid is done through a process called coagulation. What is coagulation ... 

Figure 12.1 Casein is the protein that has the function of emulsifier in milk. Without the casein (milk s "natural polymer"), the milk would be destabilized, since the fat globules, via coagulation or coalescence, would result in destruction of the colloidal dispersion. Reprinted from Walstra et al. f / 984), with permission from John Wiley Sons, Ltd...

Not all colloid systems are stable. The most stable involve solid dispersion media, since movement through a solid host will be slow. Emulsions also tend to be stable think, for example, about a glass of milk, which is more likely to decompose than undergo the destructive process of phase separation. Aerosols are not very stable although a water-based polish generates a liquid-in-air colloid, the particles of liquid soon descend through the air to form a pool of liquid on the table top. Smoke and other solid-in-gas aerosols are never permanent owing to differences in density between air and the dispersed phase. 

Flocculation The destruction of a colloidal suspension by bringing the dispersed particles together. 

This barrier can be caused either by the hydrophilicity of the particles, by the availability of a boundary water layer near the particle surface (cf. Section 10.5) or by a surfactant adsorption layer hydrophilising the particle. Since hydrophilicity of many dispersed systems has been studied in colloid chemistry, independent information can be used to identifying the nature of the barrier at the particle surface. Broad experience in flotation of large particles can be used for selecting surfactants to destruct the boundary layer of particles of a concrete nature. 

In Chapter 1 the importance of the various classes of colloidal systems to modern science and technology was indicated in a general way. Because of the wide variety of colloidal systems one encounters, each having certain unique features that distinguish it from the others, it is convenient to discuss each major classification separately. For that reason, chapters have been devoted to specific systems such as solid dispersions, aerosols, emulsions, foams, lyophilic colloids (i.e., polymer solutions), and association colloids. There is a great deal of overlap in many aspects of the formation, stabilization, and destruction of those systems, and an effort will be made not to repeat more than is necessary. However, for purposes of clarity, some repetition is unavoidable. 

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. 

An emulsion is a dispersion of one liquid in another where each liquid is immiscible, or poorly miscible in the other [1]. Emulsions exhibit all classical behaviors of metastable colloids Brownian motion, reversible phase transitions as a result of droplet interactions that may be strongly nradified and irreversible transitions that generally involve their destruction. They are obtained by shearing two immiscible fluids to the fragmentation of one phase into the other. From diluted to highly concentrated, emulsions exhibit very different internal dynamics and mechanical properties. Emulsifiers are usually added to oU/water mixture to enhance the formation of stable monomer emulsions. The molecules of emulsifier adsorb to the surface of oil droplets during homogenization and provide a protective membrane... 

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