Colloids, classification

Nomenclature. Colloidal systems necessarily consist of at least two phases, the coUoid and the continuous medium or environment in which it resides, and their properties gready depend on the composition and stmcture of each phase. Therefore, it is useful to classify coUoids according to their states of subdivision and agglomeration, and with respect to the dispersing medium. The possible classifications of colloidal systems are given in Table 2. The variety of systems represented in this table underscores the idea that the problems associated with coUoids are usuaUy interdisciplinary in nature and that a broad scientific base is required to understand them completely. 

Figure 1, Classification of principal areas of colloidal particle chromatography...

With foams, one is dealing with a gaseous state or phase of matter in a highly dispersed condition. There is a definite relationship between the practical application of foams and colloidal chemistry. Bancroft (4) states that adopting the very flexible definition that a phase is colloidal when it is sufficiently finely divided, colloid chemistry is the chemistry of bubbles, drops, grains, filaments, and films, because in each of these cases at least one dimension of the phase is very small. This is not a truly scientific classification because a bubble has a film round it, and a film may be considered as made up of coalescing drops or grains. ... 

Another classification scheme is based on the size of the dispersed particles within the dispersion medium (Table 2). The particles of the dispersed phase may vary considerably in size, from large particles visible to the naked eye, down to particles in the colloidal size range, and particles of atomic... 

Table 3 Classification of Protective Colloids (gums, thickeners, and polymers) According to Their Origins... 

Sheng R.S., Zhu L., Morris, M.D., Sedimentation classification of silver colloids for surface-enhanced Raman-scattering, Anal. Chem. 1986 58 1116-1119. 

The classification of wastewater in terms of size distribution is normally done from a practical point of view. Typically, a distinction is made between soluble, colloidal and suspended components (Figure 3.6). While this definition for determining what solids are is rational as far as physical transport processes in sewers are concerned, when dealing with the microbial processes for sewer conditions, an extension of the solids definition is required. Particles larger than about 10-4 pm cannot be transported through the cell wall and are, therefore, from a microbial point of view, considered particles. 

Colloids are introduced in the second half of the chapter. The various classifications of colloid types are discussed, together with ways of forming, sustaining and destroying colloids, i.e. colloid stability. Finally, association colloids ( micelles ) are discussed. 

Queste S, Salager JL, Strey R, Aubry JM (2007) The EACN scale for oil classification revisited thanks to fish diagrams. J Colloid Interface Sci 312 98-107 Cayias JL, Schechter RS, Wade WH (1976) Modeling Crude Oils for Low Interfacial tension. Soc Petrol Eng J 16 351-357... 

CLASSIFICATION OF COLLOIDS BASED ON AFFINITY TO CARRIER FLUID... 

Colloids are also often classified on the basis of the affinity of the surfaces of the particles to the continuous phase. This classification is also ambiguous in some respects, but deserves a brief mention. 

As in the case of lyophilic colloids, the use of the adjective lyophobic does not necessarily mean that the surfaces of the colloids are uniformly liquid repelling. For example, ceramic sols such as silica and alumina powders in liquids do have surfaces with varying degrees of affinity to the liquid. Despite the ambiguities in the use of the terms lyophobic and lyophilic, such a classification is convenient. 

The object in undertaking such a series of preparations is twofold (1) the acquisition of a certain degree of skill in dealing with the difficulties that are encountered in the process of making pure compounds and (2) the extension and classification of information regarding types of compounds, acquaintance with the methods available in their preparation, and acquaintance with their chief reactions. This should include familiarity with the colloidal state of matter which any material may assume. 

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