Colloidal dispersions classification

There are numerous ways in which viscosities are expressed in the literature. Some of the most common are defined Table 6.8. There is an entire lexicon of terms used to describe the different rheological classifications of colloidal dispersions [9-11,353,355]. 

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) ... 

Latex is a dispersion of polymer particles in a liquid medium, where the particles will remain suspended indefinitely. This property means that latices are colloidal dispersions. By nature of its origin, latex is classified into natural latex for dispersions obtained from plants, and synthetic latex for dispersions that are man made, typically by a process called emulsion polymerization. Blackley discusses a number of further classifications including artificial latex for dispersions in which the polymer is dispersed after synthesis, and modified latex where a chemical modification of existing latex is made. 

Further subdivision of the colloids concerned many researchers. For example, studies of coagulation processes lead Miiller to connect suspensions with physical disintegration processes and large molecules with chemical precipitation methods. He designated as high molecular such substances as albumin and colloidal silica. The later classification by Staudinger into colloidal dispersions, micellar colloids (assocation colloids), and colloidal molecules (macromolecules) proved to be very suitable and forms the foundation of modern textbooks on colloid science. ... 

A particular focus of this chapter is colloidal dispersions of solid particles in a liquid. These are both industrially important but also scientifically interesting since model systems can be prepared with which we can probe the intermolecular interactions responsible for colloidal aggregation. As indicated in Table 3.1, such systems are termed sols. Sometimes they are also known as lyophobic solids. This reflects a now-outmoded classification of colloids into those that are solvent hating (lyophobic) and those that are solvent loving (lyophilic). Some examples of sols are described in Section 3.9, whilst the aggregation of model sols is discussed in Section 3.15. Other examples of commonly encountered colloids are described in Sections 3.10 to 3.14. 

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. 

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... 

The components of soils and rocks have different size, shape, and quality. The particle size of organic components usually is in the colloid range (<500 nm) mineral components have different dispersity. The first classification system of soils on the basis of particle size was done by Atterberg (1905). Practically, this classification has been used until now, though some countries have their own classifications, considering their widespread soil types. The size of soil particles will also determine how the soil fraction is named (e.g., clay, sand, silt, rock, etc.). Table 1.6 provides these names along with the standard diameter of the particles for the international classification system. 

A classification of the colloids with respect to the state of aggregation of the disperse and the continuous phases is shown in Table 5.1. Some examples follow ... 

Along with the classification of disperse systems based on the phase state of the dispersed phase and the dispersion medium, and their classification as coarse dispersed or colloidal, structured or unstructured, dilute or concentrated, one can also subdivide disperse systems into lyophilic or lyophobic types. Systems belonging to these principally different classes differ in the nature of colloid stability and in the intensity of interfacial intermolecular interactions. High degree of similarity between the dispersed phase and the dispersion medium, and, consequently, compensation of the... 

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). 

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. 

Crude oil has been characterized as a colloid (1,2) in which high molecular weight, asphaltic particles are dispersed. Such particulates—known as asphaltenes—are held in solution via peptization by lower molecular weight components—classified as resins. This association forms a micellar type structure (3-5). Classification of the asphaltic constituents in crude oil is based primarily upon each component s solubility in various solvents (e.g., the pentane soluble, propane insoluble resin or maltene fraction and the benzene soluble, pentane insoluble asphaltene fraction) (6,7). 

Colloids are broadly classified as lyophobic and lyophilic, depending on the affinity of the particles toward the dispersing medium the former refers to particles with low affinity for the medium, whereas the latter conveys great solvent affinity particles (Verwey and Overbeek 1948). This classification, thus, should in fact be applied not to the particles themselves but to the suspension as a whole, because obviously the nature of the interactions will be dependent on both the particle and the dispersing... 

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. 

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... 

When we distinguish colloid systems according to the state of aggregation we should separate that of the colloid system as a whole and that of the dispersed particles. We shall begin with the first classification and shall successively take into account the second. 

Heterogeneous oligomer blends are subdivided according to the size of dispersed particles (therefore, the classification used in colloidal chemistry of polymers is here applicable [98, 109, 110]), aggregative state of dispersion media or dispersion phase, temporary stability (or instability) of morphology, and etc. Many questions arise from this classification, and they have no definite answers at present. Fixrther discussion on these problems is provided in fmther chapters in the third part of this monograph. 

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