Concentrated Colloidal Dispersions

Latex dispersions have attracted a great deal of interest as model colloid systems in addition to their industrial relevance in paints and adhesives. A latex dispersion is a colloidal sol formed by polymeric particles. They are easy to prepare by emulsion polymerization, and the result is a nearly monodisperse suspension of colloidal spheres. These particles usually comprise poly(methyl methacrylate) or poly(styrene) (Table 2.1). They can be modified in a controlled manner to produce charge-stabilized colloids or by grafting polymer chains on to the particles to create a sterically stabilized dispersion. Charge-stabiHzed latex particles obviously interact through Coulombic forces. However, sterically stabilized systems can effectively behave as hard spheres (Section 1.2). Despite its simpHcity, the hard sphere model is found to work surprisingly well for sterically stabilized latexes. 

Model hard sphere systems can be prepared from sterically stabilized latexes. One system that has been extensively studied is PMMA spheres, grafted with poly(12-hydroxystearic acid). Typically the cores are several hundred nm in diameter, whereas the grafted polymer layer is about 10 nm 

Dickinson, E., An Introduction to Food Colloids, Oxford University Press, Oxford (1992). Everett, D. H., Basic Principles of Colloid Science, Royal Society of Chemistry, Cambridge (1988). 

Fennell Evans, D. and H. Wennerstrom, The Colloidal Domain. Where Physics, Chemistry, Biology and Technology Meet, VCH, New York (1994). 

Hunter, R. J., Foundations of Colloid Science, Oxford University Press, Oxford, Vol. I (1987) and Vol. II (1989). 

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Instead, a semiempirical approach is used to develop equations that describe the viscosity of concentrated colloidal dispersions. One of the most widely used equations was derived by Dougherty and Krieger and is applicable across the whole volume fraction range (Figure 9) (9, 109). 

Small-Angle Neutron Scattering. The intensity of small-angle scattering, I(Q), for a concentrated colloidal dispersion of identical particles is given by (14)... 

In many cases, a comprehensive characterization of the rheological properties of systems, such as concentrated colloidal dispersions, can require measurements of dynamic mechanical behaviour at frequencies outside the range of conventional, commercially available, rheometers (typically 10 Hz to 10 Hz). In particular, consideration of the relative time scales of particle-fluid displacement and interfacial polarization mechanisms in such systems reveals the need for enhanced high frequency ranges (above ca. 10 Hz). 

Faraday Discussions of the Chemical Society, Concentrated Colloidal Dispersions, Royal Society of Chemistry, London, 1983. 

Brady, J. F. The rheological behavior of concentrated colloidal dispersions. J. Chem. Phys. 99, 567-581 (1993). 

D. Qiu, C.A. Dreiss, T. Cosgrove, A.M. Howe, Small-angle neutron scattering study of concentrated colloidal dispersions The intopaiticle interaetions between sterically stabilized particles. Langmuir 21(22), 9964-9969 (2005). doi 10.1021/la050322m... 

In principle, then, through equation (45), light-scattering studies of concentrated colloidal dispersions yield structural information in the form of h(r). In practice, however, the usefulness of equation (45) is severely limited by the fact that it is valid only in the absence of multiple scattering. With concentrated aqueous dispersions of latex particles, this means studying very small sample volumes in which structure could be influenced by the surface properties of the container. Even so, no measurements of this sort have yet been reported due to the experimental difficulties involved. 

Patel VM, Sheth P, Kurz A, Ossenbeck M, Shah DO, Gower LB (2002) Synthesis of calcium carbonate-coated emulsion droplets for drug detoxification. In Markovic B, Somansundaran P (eds) Concentrated colloidal dispersions theory, experiments, and applications. ACS Symposium Series 878. American Chemical Society, Washington DC... 

There are many relative viscometric methods, i.e., those which require calibration with a fluid of known viscosity. Although they may be useful for viscometry of Newtonian fluids and for process and product control, the relative methods are inappropriate for adhesive materials, since concentrated colloidal dispersions and concentrated solutions of macromolecules show non-Newtonian behavior. While macromolecular systems usually exhibit viscoelasticity, colloidal dispersions can often be considered to be purely viscous. Non-Newtonian behavior can be characterized in steady shear, and is usually expressed as the functional dependence of shear stress on shear rate, or of viscosity on shear rate. 

In the case of non-Newtonian behavior and especially in the case of viscoplastic behavior, such as that typical for moderately concentrated colloidal dispersions, Poiseuille s law gradually loses its validity. This happens because in the shear force-free central region close to the capillary axis, the structure of the concentrated colloidal system remains intact, so that the viscous shear exists only in the peripheral regions of the capillary. This process causes serious issues in the pumping of cement slurries or crude oil containing crystallizing phases. In laboratory practice, it is beneflcial to conduct such measurements in combination with other measurements that utilize uniform states. 

J.F. Brady The rheological behavior tf concentrated colloidal dispersion, J. Chem. Phys., 99 (1993) 567-581... 

B.J. Maranzano and N.J. Wagner The effects of panicle size on reversible shear thickening of concentrated colloidal dispersions . Chem. Phys., 114 (2001) 10514-10527... 

V. Degiorgio, R. Piazza, and R. B. Jones. Rotational diffusion in concentrated colloidal dispersions of hard spheres. Phys. Rev. E, 52 (1995), 2707-2717. 

W. van Megen and S. M. Underwood. Tracer diffusion in concentrated colloidal dispersions. II. Non-Gaussian effects. J. Chem. Phys., 88 (1988), 7841-7846. 

Fluidization of Highly Concentrated Colloidal Dispersions by Tailoring of Attractive Interactions... 

CRYSTALLINE AND LIQUID CRYSTALLINE ORDER IN CONCENTRATED COLLOIDAL DISPERSIONS AN OVERVIEW... 

The equilibrium thermodynamic and structural properties of coUoidal dispersions may be treated in the same way as in the case of simple liquids by considering the colloidal particles as "supramolecules dispersed in a continuous (but fluctuating) back-ground. The potential which for the case of fluctuating forces replaces the interaction potential between molecules (in vacuo) is the potential of the average forces which act between the dispersed particles. This effective interaction is the input for statistical mechanical theories. Therefore statistical mechanical theories developed for simple fluids can be applied to colloidal dispersions. The theoretical basis for such a treatment was given by Onsager and Me Millan and Mayer. In recent years concepts of liquid state theory have been applied successfully to understand the behavior of concentrated colloidal dispersions. ... 

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