Colloid system, 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. 

Colloidal systems may be grouped into three general classifications ... 

Definition and Classification of Emulsions. Colloidal droplets (or particles or bubbles), as they are usually defined, have at least one dimension between about 1 and 1000 nm. Emulsions are a special kind of colloidal dispersion one in which a liquid is dispersed in a continuous liquid phase of different composition. The dispersed phase is sometimes referred to as the internal (disperse) phase, and the continuous phase as the external phase. Emulsions also form a rather special kind of colloidal system in that the droplets often exceed the size limit of 1000 nm. In petroleum emulsions one of the liquids is aqueous, and the other is hydrocarbon and referred to as oil. Two types of emulsion are now readily distinguished in principle, depending upon which kind of liquid forms the continuous phase (Figure 2) ... 

This section presents an overview of the great variety of soft particles encountered both in fundamental science and in applications. We propose a classification based on composition and architecture, distinguishing colloidal-like particles, network particles, polymer-colloid systems, and surfactant particles, as illustrated in Fig. 1 and discussed below. 

Colloidal systems and dispersions are of great importance in many areas of human activity such as oil recovery, coating, food and beverage industry, cosmetics, medicine, pharmacy, environmental protection etc. They represent multi-component and multiphase (heterogeneous) systems, in which at least one of the phases exists in the form of small (Brownian) or large (non-Brownian) particles (Hetsroni 1982, Russel et al. 1989, Hunter 1993). One possible classification of the colloids is with respect to the type of the continuous phase (dispersions with solid continuous phase like metal alloys, rocks, porous materials, etc. will not be consider). 

For the classification of the different kinds of single colloid systems the elimination procedure is used to characteri2 e them. It enables us to divide the liquid single systems into two kinds, which will be called Sols (in the restricted sense) and Coacer-vateSf though both fulfil the definition of sol in the larger sense of 1 b (p. 2). 

It is possible therefore to subdivide the complex systems according to the latter principle of classification into various cases but it does not strike the essential point which is characteristic of complex systems and indeed produces no rational order in the mutually very varied behaviour of the complex colloid systems. 

In the first place one should distinguish reversible and irreversible systems, that is to say, colloid systems which can undergo phase change or phase separation reversibly or otherwise. A thermodynamically definable stability difference is thus the basis of this classification. It is for this reason more logical than the old classification into lyophobic and lyophilic systems (and to a still greater degree than that into suspensoids and emulsoids). 

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. 

As mentioned earlier, colloidal systems are composed of two phase of matter. The dispersed phase, also called the discontinuous or internal phase is made up of colloidal particles while the dispersion medium, also called the continuous or external phase is made up of the solvent in which the dispersion takes place. Numerous types of combinations of these two phases are possible (Table 3.1) and it is difficult to classify colloids strictly. However, various attempts have been made and the classification of colloidal systems as two distinct types - the lyophillc colloids and the lyophobic colloids, based upon the Interaction of phases has found wide acceptance. 

Although the classification of colloids covers an extremely diverse array of materials, in general colloidal systems can be identified by the following characteristics ... 

In Table 5.1, different colloidal systems are summarized for different combinations of the dispersed and continuous phase. This table should give you an idea of the diversity of this classification of material. The word colloid was first coined by the chemist Thomas Graham in 1861 from the Greek word for glue. Colloids tend to stick to each other unless mediated by another force, so this name is appropriate (Figure 5.3). Incidentally, Graham also introduced the words e/ and sol to the scientific vocabulary. A sol is a dilute dispersion of solid colloidal particles in a liquid phase, whereas d gel in the colloidal sense is a concentrated dispersion that does... 

Soft materials such as liquid crystals, polymers, biomaterials, and colloidal systems touch every aspect of our lives. Not surprisingly, the rapid growth of these fields over the past few decades has resulted in an explosion of soft matter research groups worldwide. Fundamentals of Soft Matter Science introduces and explores the scientific study of soft matter and molecular self-assembly, covering the major classifications of materials, their structure and characteristics, and everyday applications. 

Classification of Colloidal Systems.— Unlike true solutes, the various components of a colloidal system can be any one or more of the three states of matter. 

CLASSIFICATION OF COLLOID SYSTEMS ACCORDING TO THE MATERIAL OF THE PARTICLES... 

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