Characterization of Colloids

The flow behaviour of colloids is very important to many of their applications. To take an everyday example, margarine should be stiff in the tub but flow under the pressure of the knife as it is spread on bread. The structural and dynamical complexity of colloidal systems leads to a diversity of rheological phenomena. The essential features of many of these effects (shear thinning, shear thickening, viscoelasticity) are common to different soft matter systems. Thus, rheology is discussed in Chapter 1 and is not explicitly considered further here. 

Here we consider colloidal sols, where discrete sohd particles are dispersed in a liquid. The sol particles can have three-dimensional (sphere-Uke), two-dimensional (rod-like) or one-dimensional (plate-like) forms, as exemplified by Fig. 3.3. Examples of these structures include dispersions of highly monodisperse spherical particles that can be obtained by emulsion polymerization of latex particles, dispersions of needle-shaped colloidal particles in cement and asbestos and plate-like particles in aqueous solutions that are the structural basis of clays. 

Electron microscopy methods are outlined in Section 1.9.1. Although colloid particles are usually too small to be directly observed in an optical 

Here Ps and p, are the densities of solid particles and liquid respectively, g is the acceleration due to gravity, R is the particle radius (in this context called the Stokes settling radius) and r] is the viscosity of the medium. Thus 

The hydrodynamic radius of colloidal particles can be obtained from dynamic light scattering (DLS), also known as photon correlation spectroscopy (PCS). Here, the temporal fluctuations of scattered light intensity are measured to provide the autocorrelation function, analysis of which provides the translational diffusion coefficient. Then the Stokes-Einstein equation (Eq. 1.9) is used to determine a hydrodynamic radius. This method is described further in Section 1.9.2. 

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Kher S S and Wells R L 1996 Synthesis and characterization of colloidal nanoorystals of capped gallium arsenide Nanostruct. Mater. 7 591... 

Singh K, Siivastava ML, Mishra SSD (2006) Electrochemical deposition and photoelectrochemical characterization of colloidal HgS containing CdSe composites. Sol Energy Mater Sol Cells 90 923-932... 

Duff, D.G. et al., Structural characterization of colloidal platinum by high resolution electron microscopy and EXAFS analysis, Angew. Chem. 101, 610, 1989 Angew. Chem. Int. Ed. Engl., 28, 590,1989. 

Preparation and characterization of colloidal a-FeOOH with a narrow size distri-... 

Fujita, T Sugiyama, D., Swanton, S. W. Myatt, B. J. 2003. Observation and characterization of colloids derived from leached cement hydrates. Journal of Contaminant Hydrology, 61, 3-16. 

McCarthy, J. F. Degueldre, C. 1993. Sampling and characterization of colloids and particles in groundwater for studying their role in contaminant transport. In Buffle, J. van Leeuwen, H. P. (eds) Environmental Particles, Vol. 2. CRC Press, Inc., Boca Raton, 247-315. 

In subsequent chapters, we discuss some in situ techniques for the characterization of colloidal particles, especially with respect to particle size, structure, and molecular weight. 

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

One such consequence is their use in the physical characterization of colloidal dispersions and macromolecular solutions. Let us highlight one such application through one element of a class of analytical separation techniques known as field flow fractionation (FFF). 

Equation (9) is an important result since it describes the relationship among Rs, v, r/, and Ap, the density difference. Any one of these quantities may be evaluated by Equation (9) when the other three are known. Thus, Equation (9) can be used to determine the density difference between two phases or to determine the viscosity of a liquid. In this chapter, however, our interest is in the characterization of colloidal particles by means of observations of their sedimentation behavior. Therefore, we are primarily concerned with Equations (11) and (12), which are specifically directed toward this objective. 

A more detailed characterization of colloid-actinide systems would permit a quantitative interpretation, but this was not within the scope of this effort. 

The characterization of colloids depends on the purposes for which the information is sought, because the total description would be an enormous task. Among the properties to be considered are the nature and/or distributions of purity, crystallinity, defects, size, shape, surface area, pores, adsorbed surface films, internal and surface stresses, stability, and state of agglomeration [57,58],... 

Separation and Size Characterization of Colloidal Particles in River Water by Sedimentation Field-Flow Fractionation, R. Beckett, G. Nicholson, B. T. Hart, M. Hansen, and J. C. Giddings, Wat. Res., 22, 1535 (1988). 

Separation and Characterizing of Colloidal Materials of Variable Particle Size and Composition by Coupled Column Sedimentation Field-Row Fractionation, H. K. Jones and J. C. Giddings, Anal. Chem., 61, 741 (1989). 

Mtiller-Goymann, C. C. (2004), Physicochemical characterization of colloidal drug delivery systems such as reverse micelles, vesicles, liquid crystals and nanoparticles for topical administration, Eur. J. Pharm. Biopharm., 58(2), 343-356. 

Seaman, J.C., Bertsch, P.M., and Strom, R.N., Characterization of colloids mobilized from southeastern coastal plain sediments, Environ. Sci. Technol., 31, 2782, 1997. 

Hunter, R.J., Recent development in the electroacoustic characterization of colloidal suspensions and emulsions, Colloids Surfaces, 141, 37, 1998. 

Scattered light carries information about colloidal particles in both amplitude and phase functions, represented by bjiq, f) and exp /q [ry(/) — r/(/)1. respectively. DLS techniques are based on exploiting the phase function, or more precisely, its variation due to particle motion. The utility of DLS for the characterization of colloidal particles relies upon our ability to describe the mechanisms of colloidal particle motions (Brownian, electrophoretic, etc.) and their dependence on size or other particle properties. 

Lu Wenqing, Cheng Baorong and Deng Haishan, Preparation and characterizations of colloidal BaTlOj superfines. J. Wuhan University (Natural Science Edition). 46(2000) pp. 245-248. 

R.O. James. Characterization of Colloids in Aqueous Systems, in Adv. Ceramics, 21 Ceramic Powders, G.L. Messing, J.W. McCauley, Eds., Am. Ceramic Soc. (1987) 349. (Review emphasizing oxides, site binding models.)... 

Another original approach to the application of electric dichroism for the characterization of colloidal particles is due to Tolstoi et al. ° and, with regard to macromolecular solutions, to Dvorkin et al. ° and later authors. ... 

This attempt to distinguish between the organic and mineral colloidal pools is highly approximate, but it does show that understanding the abundance of REEs and, by extension, other insoluble elements requires a better physical characterization of colloidal phases and association constants with individual elements. Experimental work aimed at determining the association constants of elements with surface sites coupled with field data are necessary. The diversity of colloids, the diversity of associations between elements and colloids, and the existence of filtration artifacts are intrinsic impediments toward a better description and prediction of trace-element concentration in river waters. 

Kingston W. L. and Whitbeck M. (1991) Characterization of colloids found in various groundwater environments in central and southern Nevada. Water Resources Center Publication 45083. Desert Research Institute, University of Nevada System. 

Barratt, G. Characterization of colloidal drug carrier systems with zeta potential measurements. Pharmaceutical Technology Europe 1999, 25-32. 

Field-flow fractionation is a highly promising tool for the characterization of colloidal materials. It is a dynamic separation technique based on differential elution of the sample constituents by a laminar flow in a flat, ribbonlike channel according to their sensitivity to an external held applied in the perpendicular direction to that of the flow. 

Cornell, R. M., Giovanoli, R. and Schneider, W. (1991) Preparation and characterization of colloidal a-FeOOH with a narrow size distribution. I. Chem. Soc. Faraday Trans. 87 869-873. 

Fourest, B., Hakem, N.. and Guillaumont, R.. Characterization of colloids by measurement of their mobilities, Radiochim. Acta. 66/67. 173, 1994. 

Onjia, A.E. et al.. Characterization of colloidal chromia particles obtained by forced hydrolysis, Mater. Res. Bull., 38, 1329, 2003. 

McFadyen, P., and Matijevic, E., Precipitation and characterization of colloidal copper hydrous oxide sols, J. Inorg. Nucl. Chem., 35, 1883. 1973. 

Panda, A.K., Bhowmik, B.B., Das, A.R. and Moulik, S.P. (2001) Dispersed molecular aggregates. 3. Synthesis and characterization of colloidal lead chromate in water/sodium bis(2-ethyl hexyl) sulfosuccinate/n-heptane water-in-oil microemulsion medium. Langmuir, Y7, 1811— 1816. 

METHODS OF CHARACTERIZATION OF COLLOIDAL PROPERTIES OF CRUDE OIL AND ITS PRODUCTS... 

A more modern approach to colloidal dispersions is based on fractal geometry. The fractal approach, as explained later, provides a new basis for the definition and characterization of colloidal systems. 

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