What are Colloids

To some the word colloidal conjures up visions of things indefinite in shape, indefinite in chemical composition and physical properties, fickle in chemical deportment, things infilterable and generally unmanageable. 

The above remarks reflect the impression created by many textbooks of physical chemistry — if they deign to mention colloids at all. In fact, in both its experimental and theoretical aspects, and no less important in its technological applications and in the appreciation of its biological implications, colloid science has made impressive progress in the last few decades. In the following chapters an attempt is made to summarise the basic concepts of colloid science and to dispel some of the doubts expressed in the above quotation. 

Nevertheless, despite the sophistication needed for the development of a complete quantitative theory of colloids, the basic 

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What are colloids Referring to Table 12.4, why is there no colloid in which both the dispersed phase and the dispersing medium are gases ... 

The surface-active agents (surfactants) responsible for wetting, flotation and detergency exhibit rather special and interesting properties characteristic of what are called association colloids or, in the older literature, colloidal electrolytes. These properties play an important role in determining, at least indirectly, the detergency of a given surfactant and are therefore considered here... 

What are nanostructured colloidal particles What are hydrosols and organosols ... 

What are the advantages of Bonnemann s method of colloidal nanoparticle synthesis ... 

This is the expression we were looking for. What does it tell us For one thing, that the potential decays exponentially as the distance from the electrode increases pig. 6.64(b)], Further, as the solution concentration c0 increases, k increases and falls more and more sharply. This potential-distance relation [Fig. 6.64(b)] is an important and simple result from the Gouy-Chapman model. It forms a valuable basis for thinking about the interaction of the diffuse charges around what are called colloidal particles (see Section 6.10.2). 

Under what conditions are colloids stable Explain qualitatively (with schematic diagrams) the forces between colloidal particles. How does the force of repulsion between them vary with concentration As the concentration of the colloid increases, there is the tendency to coagulate and in fact the critical concentration for coagulation gets less as the valence of the ions present increases (Schulze-Hardy rule). Give a detailed, although qualitative, rationalization of this law. (Bockris)... 

What are lyophilic colloids What are lyophobic colloids Give some examples. 

What are the difficulties with the characterization of colloids as lyophilic or lyophobic ... 

More often than not one deals with colloidal objects immersed in a liquid or other such media, and therefore interactions between similar or dissimilar materials in an arbitrary medium are of importance in colloid science. Moreover, it is very useful to relate such dissimilar interactions to those between identical particles in vacuum. In the last section (Section 10.8) we present what are known as combining relations for accomplishing this. The van der Waals forces between macroscopic objects are usually attractive, but under certain circumstances they (and, as a consequence, the Hamaker constant) can be negative, as noted in Vignette X. A brief discussion of this completes Section 10.8. 

What are the factors that are relevant for extending the theories of coagulation presented here to (a) polydisperse colloids, (b) nonspherical colloids, and (c) conditions for which fluid flow is important ... 

In one report, there are three blocking agents used for channel wall, colloidal gold, and polystyrene bead to reduce non-specific binding. What are they [1021] (3 marks)... 

In this chapter, we have tried to review the recent literature on trace elements in rivers, in particular by incorporating the results derived from recent ICP-MS measurements. We have favored a field approach by focusing on studies of natural hydrosystems. The basic questions which we want to address are the following What are the trace element levels in river waters What controls their abundance in rivers and fractionation in the weathering - - transport system Are trace elements, like major elements in rivers, essentially controlled by source-rock abundances What do we know about the chemical speciation of trace elements in water To what extent do colloids and interaction with solids regulate processes of trace elements in river waters Can we relate the geochemistry of trace elements in aquatic systems to the periodic table And finally, are we able to satisfactorily model and predict the behavior of most of the trace elements in hydrosystems ... 

Integration of such two-body interactions to the scale of aquatic systems is not done without difficulties. At least three types of questions are encountered. What is a What are the inputs to the system In addition to colloid chemical reactions, what other processes may be important As suggested subsequently in this chapter, laboratory experiments can provide estimates of a(/, /)t.M> and a(p, c)CM, for use in simulations. Inputs of particles to aquatic environments are usually... 

The term colloid does not define a molecular species as do the names acids, bases, salts, and esters. Instead the name colloid describes a state in which practically any substance can abide if suitable conditions are provided. In brief, colloid describes a characteristic manner in which one substance can be dispersed in another. Our interest is primarily in what are known as organic colloids. As this is a vast subject for which comprehensive texts are available, here we will give only a brief outline of aspects known to be factors in the industrial use of activated carbon. 

The presence of attractive colloidal forces becomes apparent in the black spots." The black film appears to be in a sort of metastable equilibrium state with a finite thickness in the colloidal size range. What are... 

What is a Microemulsion - As shown in Table 2, microemulsions, as well as emulsions, are colloidal systems. An emulsion is a thermodynamically unstable suspension of liquid droplets in a second immiscible liquid. 

Household Paint Some types of paint are colloids composed of pigment particles dispersed in oil. Based on what you know about colloids, recommend an appropriate location for storing cans of leftover household paint. Justify your recommendation. 

What are the roles of the surfactants in the colloidal chemical synthesis of... 

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