Types of Colloids

Many colloids are two-phase dispersions. Systems where a dispersed phase is distributed within a continuous dispersion medium are called simple colloids or colloidal dispersions. Table 3.1 lists examples of various types of 

Disperse phase Dispersion medium Name Examples 

Solid Liquid Sol, colloidal dispersion or suspension, paste (high solid content) Silver iodide in photographic film, paints, toothpaste 

Gas Solid Solid foam Polyurethane foam, expended polystyrene 

Liquid Solid Solid emulsion Tarmac, ice cream 

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Samples that contain suspended matter are among the most difficult types from which to obtain accurate pH readings because of the so-called suspension effect, ie, the suspended particles produce abnormal Hquid-junction potentials at the reference electrode (16). This effect is especially noticeable with soil slurries, pastes, and other types of colloidal suspensions. In the case of a slurry that separates into two layers, pH differences of several units may result, depending on the placement of the electrodes in the layers. Internal consistency is achieved by pH measurement using carefully prescribed measurement protocols, as has been used in the determination of soil pH (17). 

Figure 6.2. (a). Colloidal silica network on the surface of spores from Isoetes pantii (quill wort). Scale = 20 pm. (b). Polystyrene networks and foams produced as a biproduct of colloidal latex formation. Both types of colloidal system are typical of the diversity of patterns that can be derived from the interactions of minute particles. Scale (in (a)) = 50pm. 

There are eight different types of colloid, each of which has a different name according to the identity of the dispersed phase and the phase acting as the dispersion medium. 

We are dealing here with a new type of colloid the micelle. 

Table 7.1 Type of Colloids present in Natural Systems... 

Transmission electron microscopy (TEM) can provide valuable information on particle size, shape, and structure, as well as on the presence of different types of colloidal structures within the dispersion. As a complication, however, all electron microscopic techniques applicable for solid lipid nanoparticles require more or less sophisticated specimen preparation procedures that may lead to artifacts. Considerable experience is often necessary to distinguish these artifacts from real structures and to decide whether the structures observed are representative of the sample. Moreover, most TEM techniques can give only a two-dimensional projection of the three-dimensional objects under investigation. Because it may be difficult to conclude the shape of the original object from electron micrographs, additional information derived from complementary characterization methods is often very helpful for the interpretation of electron microscopic data. 

A colloid is also called a colloidal dispersion. A colloid dispersion consists of two components similar to a solution. The particles themselves are the dispersed phase and are analogous to the solute in a solution. The dispersing medium is similar to the solvent. Some examples of different types of colloids are summarized in Table 11.5. 

One type of colloidal system has been chosen for discussion, a system in which the solid metal phase has been shrank in three dimensions to give small solid particles in Brownian motion in a solution. Such a colloidal suspension consisting of discrete, separate particles immersed in a continuous phase is known as a sol. One can also have a case where only two dimensions (e.g., the height z and breadth y of a cube) are shrank to colloidal dimensions. The result is long spaghettihke particles dispersed in solution—macromolecular solutions. 

The terms used to distinguish colloidal particles on the basis of their affinity to the fluid in which they are dispersed are lyophilic and lyophobic. These terms mean, literally, solvent loving and solvent fearing, respectively. When water is the medium or solvent, the terms hydrophilic or hydrophobic are often used. This terminology is very useful when considering surface activity such as wettability of a surface however, when used to classify colloids, the distinction is not always clear-cut. We consider these two types of colloids separately in the following subsections. 

The entire picture is still more confusing because of the fact that several different types of colloids are distinguished—i.e., radiocolloids, pseudo-colloids (7, 8, 28, 33), and true colloids. Radio-colloids refer to systems of radiotracers which appear to be in colloidal form although they are in concentrations well below their ionic solubility (25, 26). The term pseudo-colloid is used to describe the formation of a colloid system... 

Fig. I. One type of colloid mill. Rotor blades A break up slurry. Serrations in rotor and stator provide mechanical shear and force material into adjustable gap (0.0005-0.125 inch 0.013- 3 2 millimeters) between rotor and stator B for intense hydraulic shear. Lower pan of rotor C adds further whirling action...

The present accumulated data for various types of colloidal proplnts permits one to det approximately their rate of burning if composition and/or some properties(such as calorimetric value or temp of expln) are known. This knowledge, is purely empirical and does not explain the process of burning as would a good theory of burning. The teal value of a theory lies in its physical and chemical picture of the process. If a theory is close to the truth it helps one to understand not only the burning itself... 

A Pearls are a type of colloid, a mixture of large particles consisting primarily of calcium carbonate. 

Set up a circus of gels, sols, emulsions and foams, e.g. jelly , milk, pumice stone, polyurethane foam, bread, emulsion paint, cola, hair cream, aerosol dispenser, salad cream. A silica gel can be made from sodium silicate and hydrochloric acid. Classify the examples according to type of colloidal system. 

Fig. 33 Various types of colloid DNA-mediated interactions, either conventional or self-protected - switched off - through intra-particle hybridization, (a, b) Normal, hairpin-free pair of complementary sticky ends, either grafted to separate beads (a) or mixed on the same bead (b). (c, d) Self-complementary sticky ends. Besides self-protective loops as in (b), this sequence can form two hairpin structures the sticky end sequence can fold on itself (1), or it can bind to the backbone (2). (e, f) As in (a), but each of the sticky ends can fold into a protective hairpin. Adapted with permission from [140]...

Sols and emulsions are by far the most important types of colloidal dispersion. The term sol is used to distinguish colloidal suspensions from macroscopic suspensions there is, of course, no sharp line of demarcation. When the dispersion medium is aqueous, the term hydrosol is usually used. If the dispersed phase is polymeric in nature, the dispersion is called a latex (pi. latices or latexes). 

In particular, the full potential to control colloids is not presently realized. There are several types of complex, mixed colloid that are only poorly understood. For example, the properties of colloids in which more than one type of colloidal species is dispersed may be dominated by the behaviour of the minor dispersed-phase component. The nature and properties of colloids within colloids, such as suspended solids in the dispersed phase of an emulsion, or emulsified oil within the aqueous lamellae of a foam, are only beginning to be understood [2-4]. 

This book provides an introduction to the colloid and interface science of three of the most common types of colloidal dispersion emulsions, foams, and suspensions. The initial emphasis covers basic concepts important to the understanding of most kinds of colloidal dispersions, not just emulsions, foams, and suspensions, and is aimed at providing the necessary framework for understanding the applications. The treatment is integrated for each major physical property class the principles of colloid and interface science common to each dispersion type are presented first, followed as needed by separate treatments of features unique to emulsions, foams, or suspensions. The second half of the book provides examples of the applications of colloid science, again in the context of emulsions, foams, and suspensions, and includes attention to practical processes and problems in various industrial settings. 

Colloid science books available up to now have been either principally theoretical (such as the classic and standard colloid chemistry texts), or they focus on specific types of colloidal dispersion (like van Olphen s classic book on clay colloid chemistry [1]), or on applications of a specific type of dispersion in a specific industry, like the author s petroleum industry series ... 

Emulsions and suspensions are colloidal dispersions of two or more immiscible phases in which one phase (disperse or internal phase) is dispersed as droplets or particles into another phase (continuous or dispersant phase). Therefore, various types of colloidal systems can be obtained. For example, oil/water and water /oil single emulsions can be prepared, as well as so-called multiple emulsions, which involve the preliminary emulsification of two phases (e.g., w/o or o/w), followed by secondary emulsification into a third phase leading to a three-phase mixture, such as w/o/w or o/w/o. Suspensions where a solid phase is dispersed into a liquid phase can also be obtained. In this case, solid particles can be (i) microspheres, for example, spherical particles composed of various natural and synthetic materials with diameters in the micrometer range solid lipid microspheres, albumin microspheres, polymer microspheres and (ii) capsules, for example, small, coated particles loaded with a solid, a liquid, a solid-liquid dispersion or solid-gas dispersion. Aerosols, where the internal phase is constituted by a solid or a liquid phase dispersed in air as a continuous phase, represent another type of colloidal system. 

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