Properties of Colloids

A beam of lights is visible in a colloid solution (left) but not in a true solution. The size of the particles in the colloid is large enough to scatter the light beam, making it visible. 

Another important characteristic of colloids is that the particles have relatively huge surface areas. We saw in Section 14.4 that the surface area is increased 10-fold when a 1-cm cube is divided into 1000 cubes with sides of 0.1 cm. When a 1-cm cube is divided into colloidal-size cubes measuring 10 cm, the combined surface area of all the particles becomes a million times greater than that of the original cube. 

Colloidal particles become electrically charged when they adsorb ions on their surfaces. Adsorption should not be confused with absorption. Adsorption refers to the adhesion of molecules or ions to a surface, whereas absorption refers to the taking in of one material by another material. Adsorption occurs because the atoms or ions at the surface of a particle are not completely surrounded by other atoms or ions as are those in the interior. Consequently, these surface atoms or ions attract and adsorb ions or polar molecules from the dispersion medium onto the surfaces of the colloidal particles. This property is directly related to the large surface area presented by the many tiny particles. 

Colloidal particles become electrically charged when they adsorb ions on their surface. 

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Fig. XIII-10. Properties of colloidal electrolyte solutions—sodium dodecyl sulfate. (From Ref. 102a.)...

In practice, sedimentation is an important property of colloidal suspensions. In fonnulated products, sedimentation tends to be a problem and some products are shipped in the fonn of weak gels, to prevent settling. On the other hand, in applications such as water clarification, a rapid sedimentation of impurities is desirable. 

Many properties of colloidal suspensions, such as their stability, rheology, and phase behaviour, are closely related to the interactions between the suspended particles. The background of the most important contributing factors to these interactions is discussed in this section. 

Klein R and D Aguanno B 1996 Scattering properties of colloidal suspensions Light Scattering, Principles and Development ed W Brown (Oxford Clarendon) pp 30-102... 

Russel W B, Seville D A and Schowalter W R 1989 Colloidal Dispersions (Cambridge Cambridge University Press) General textbook, emphasizing the physical equilibrium and non-equilibrium properties of colloids Shaw D J 1996 Introduction to Colloid and Surface Chemistry (Oxford Butterworth-Heinemann)... 

It was assumed throughout that the compound which separated out from the solution was chemically pure, but this is not always the case. The purity of the precipitate depends inter alia upon the substances present in solution both before and after the addition of the reagent, and also upon the exact experimental conditions of precipitation. In order to understand the influence of these and other factors, it will be necessary to give a short account of the properties of colloids. 

Chapter 8 presents evidence on how the physical properties of colloidal crystals organized by self-assembly in two-dimensional and three-dimensional superlattices differ from those of the free nanoparticles in dispersion. 

AlSalman,A.,Tortschanoff, A.,Mohamed, M. B., Tonti, D., van Mourik, F. and Chergui, M. (2007) Temperature effects on the spectral properties of colloidal CdSe nanodots, nanorods, and tetrapods. Appl. Phys. Lett., 90, 093104. 

There have been other MPC dynamics studies of hydrodynamic effects on the transport properties of colloidal suspensions [61-64]. In addition, vesicles that can deform under flow have also been investigated using hybrid MPC-MD schemes [65-69]. 

Ueltmam, R.N. and Green, H. "Rheological Properties of Colloidal Solutions, Pigment Suspensions, and Oil Mixtures," J. Applied Physics. 1943, 14, 569-576. 

Khan-Lodhi, A. Robinson, B. H. Towey, T. Herrmann, C. Knoche, W. Thesing, U. In The Structure, Dynamics and Equilibrium Properties of Colloidal Systems Bloor, D. M. Wyn-Jones, E., Eds. Kluwer Academic Publishers, 1990 p 373. 

A state of subdivision of matter with a particle size between 10"7 and 10 5 cm (1 nm to 100 nm). The properties of colloids lie between those of true solutions and coarse suspensions. 

Blue skies and the Tyndall effect by M. Kerker in/. Chem. Educ., 1971, 48, 389 is a nice introduction. Alternatively, try Chapter 7 Some important properties of colloids II scattering of radiation in Everett (above), which is extremely thorough. 

The important forces involved in the adsorption of metals on to particles are attractive electrostatic or van der Waals forces. These concepts explain many of the properties of colloids with respect to the adsorption of contaminants or ion-exchange factors and the aggregation of the colloids into larger particles. These larger particulates may then descend the water column to the sediment. This occurs most notably in estuarine environments, as increases in salinity lead to estuarine silting. Binding of electrolytes to hydrophobic colloids is often used to facilitate their coagulation and precipitation. 

The major goal of this chapter is to help you master the concepts associated with solutions—concentration units, solubility, and especially colligative properties. We will also examine the properties of colloids. If you are still unsure about calculations and the mole concept, review Chapters 1,3, and 4. And again, the only way to master these concepts is to Practice, Practice, Practice. 

Brant J, Lecoanet H, Hotze M et al. (2005a) Comparison of electrokinetic properties of colloidal fullerenes (n-C60) formed using two procedures. Environ Sci Technol. 39 6343-6351. 

Kandori, K Hori, I. Yasukawa, A. Ishikawa, T. (1995) Effects of surfactants on the precipitation and properties of colloidal particles from forced hydrolysis of EeCl3-HCl solution. J. Mat. Sci. 30 2145-2152 Kandori, K Kawashima,Y. Ishikawa, T. 

Serpone N, Lawless D and Khairutdinov R (1995) Size effects on the photophysical properties of colloidal anatase TiOz particles size quantization or direct transition in this indirect semiconductor. J Phys Chem 99 16646-16654... 

In addition to the interphase potential difference V there exists another potential difference of fundamental importance in the theory of the electrical properties of colloids namely the electro-kinetic potential, of Freundlich. As we shall note in subsequent sections the electrokinetic potential is a calculated value based upon certain assumptions for the potential difference between the aqueous bulk phase and some apparently immobile part of the boundary layer at the interface. Thus represents a part of V but there is no method yet available for determining how far we must penetrate into the boundary layer before the potential has risen to the value of the electrokinetic potential whether in fact f represents part of, all or more than the diffuse boundary layer. It is clear from the above diagram that bears no relation to V, the former may be in fact either of the same or opposite sign, a conclusion experimentally verified by Freundlich and Rona. 

It will be noted that in the derivation of the transverse potential difference the product ijv should be constant for the same system under uniform conditions. A change in tj can be produced most conveniently by alteration of the temperature. Burton (Physical Properties of Colloidal Solutions, p. 145) gives the following data for colloidal silver solutions in support of the validity of the equation. 

The diminution of charge and eventual reversal of sign produced by the addition of electrolytes is more marked in the case of the polyvalent ions, and has been carefully investigated by Burton The Physical Properties of Colloidal Solutions, pp. 164-169) who in the case of a colloidal solution of copper obtained the following results ... 

Often it is difficult to adjust the mixture proportions to achieve desired design parameters for all properties of concrete. Consequently the properties of colloidal underwater concrete are controlled by the addition of three chemical admixtures. Minimum water-cement ratios range from 0.36 to 0.40. Cement and fine-aggregate contents are usually higher than corresponding mixes placed on land, and silica fume may be used in conjunction with a superplasticizer or conventional water reducers to reduce segregation. The key to a non-dispersible concrete with self-leveling characteristics is the successful optimization of the VEA with the superplasticizer used to increase the slump. 

Khan-Lodhi A, Robinson BH, Towey T, Hermann C, Knoche W, Thesing U (1990) in The structure, dynamics and equilibrium properties of colloidal systems, Bloor DM, Wyn-Jones E (eds), Kluwer Academic, London, p 373... 

The difference between macroscopic and microscopic objects is clear from everyday experience. For example, a glass marble will sink rapidly in water however, if we grind it into snb-micron-sized particles, these will float or disperse freely in water, prodncing a visibly clondy soln-tion , which can remain stable for honrs or days. In this process we have, in fact, prodnced a colloidal dispersion or solution. This dispersion of one (finely divided or microscopic) phase in another is quite different from the molecular mixtures or true solutions formed when we dissolve ethanol or common salt in water. Microscopic particles of one phase dispersed in another are generally called colloidal solutions or dispersions. Both nature and industry have found many uses for this type of solution. We will see later that the properties of colloidal solu-... 

The properties of colloidal dispersions are intimately linked to the high surface area of the dispersed phase and the chemistry of these interfaces. This linkage is well illustrated by the titles of two of the main journals in this area the Journal of Colloid and Interface Science and Colloids and Surfaces. The natural combination of colloid and surface chemistry represents a major area of both research activity and industrial development. It has been estimated that something like 20 per cent of all chemists in industry work in this area. 

A Khan-Lodhi, BH Robinson, T Towey, C Hermann, W Knoche, U Thesing. In DM Bloor, E Wyn-Jones, eds.. The Structure, Dynamics and Equilibrium Properties of Colloidal Systems. Dordrecht Kluwer, 1990, pp 373-383. 

Creative interplay between colloid and polymer chemistries has increasingly contributed to the development of membrane-mimetic systems and advanced materials. On the one hand, the employment of polymer methodologies and/or the addition of polymers have favorably altered the properties of colloidal systems. On the other hand, the introduction of surfactants and surfactant assemblies prior, during, or subsequent to polymerization has resulted in distinctly different polymers. 

As we see in the rest of the book, many of the interesting properties of colloids are the result of their dimension, which lies between atomic dimensions and bulk dimensions. Two of the important consequences of the size range of colloids are (a) colloidal materials have enormous surface areas and surface energies, and (b) the properties of colloidal particles are not always those of the corresponding bulk matter or those of the corresponding atoms or molecules. Let us use a simple exercise or a thought experiment to illustrate these points. 

So far, we have focused on how to deal with the variations in the sizes and shapes of colloidal particles encountered in practice. However, in recent years another equally important and highly useful perspective in the use of colloids has emerged from viewing the variations in size and shape (and surface chemistry) as controllable parameters. The question is, Can we control the shapes and sizes of the particles to produce model particles that can be used to study properties of colloids and to develop new uses for colloids The answer is yes (within reason). 

We have had no occasion as yet in this book to note that colloidal solutes may possess an electrical charge just like their low molecular weight counterparts. Portions of Chapter 4 and Chapters 11-13 are concerned with those properties of colloids that are direct consequences of... 

Materials in a colloidal state are frequently preferred in industrial processing operations because their large surface areas per unit volume enhance chemical reactivity, adsorptive capacity, heat transfer rates, and so on. Therefore, one cannot overlook the importance of the flow behavior and properties of colloids since they exert a significant influence on the performance, efficiency, and economy of the process. Note that some examples of this (e.g., ceramic processing, electrophoretic display devices, and food colloids) were mentioned in the vignettes presented in Chapter 1. In addition, one often uses the flow properties and behavior of the products as measures of the microstructure (or, morphology ) of the products and as a means of quality control (e.g., printing inks, toners, paints, skin creams, blood substitutes,... 

The next topic is Einstein s theory of viscosity of dispersions of rigid, spherical particles. This theory is the starting point for most of the current approaches to flow properties of colloids and plays a practical, pedagogical, as well as historical role. 

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