Rheology of colloidal dispersions

A discussion on kinetic properties and characterization of colloid particles would not be complete without a few words about the rheology of colloids. 

Mathematics may be less important than an appropriate quahtalive understanding of the basic underlying phenomena. The basic characteristics of the rheology of dispersions can be summarized as  

Some few simple liquids like water, petrol, glycerol, ethanol and dilute aqueous solutions follow Newtonian behaviour (constant viscosity value in Equation 8.11). Very few colloidal dispersions follow Newtonian behaviour, i.e. constant viscosity, and moreover the range of shear rates of interest is very broad. Deviations from Newtonian behaviour are even more pronounced in the case of concentrated dispersions and if the particles are asymmetric and/or aggregated. Formation of structure throughout the system and orientation of asymmetric particles cause non-Newtonian flow. 

Most shear-thinning fluids like paints and certain polymer solutions are also thixotropic, i.e. the viscosity decreases with time (at constant shear rate). Yoghurt is also an example of a thixotropic liquid. The opposite, i.e. rheopectic liquids (viscosity increases with time). 

Before and during application, the viscosity of paint has to comply with several requirements  

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Several recent studies demonstrate convincingly the possibilities for adjusting the rheology of colloidal dispersions through the incorporation of polymer. Here we briefly review the effects of grafted polymer, adsorbing homopolymer, and nonadsorbing polymer. The literature abounds with other and more complicated phenomena. 

William B. Russel Controlling the rheology of colloidal dispersions through the interparticle potential Ceramic Transactions, Vol. 12, Ceramic Powder Sdence IB (Garry L. Messing, Shin-ichi Hirano, and Hans Hausner, eds.) The American Ceramic Sodety, Westerville, Ohio (1990) 361-373... 

There are two general approaches to rheology, the first being to set up mathematical expressions which describe rheological phenomena without undue reference to their causes, and the second, with which the following discussion is mainly concerned, is to correlate observed mechanical behaviour with the detailed structure of the material in question. This is not an easy task. The rheological behaviour of colloidal dispersions depends mainly on the following factors ... 

Mourchid, A., Delville, A., Lambard, J., Lecolier, E. and Levitz, P. (1995) Phase Diagram of Colloidal Dispersions of Anisotropic Charged Particles Equilibrium Properties, Structure, and Rheology of Laponite Suspensions. Langmuir 11, 1942-1950... 

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]. 

Mourchid A, Delville A, Lambard J, L 233 colier E and Levitz P 1995 Phase diagram of colloidal dispersions of anisotropic charged particles equilibrium properties, structure, and rheology of Laponite suspensions Langmuir AA 1942-50... 

The presence of copolymer and surfactant together alters the rheological properties of solutions, adsorption on solid particles, solubility, and stability of colloidal dispersions. The solution properties are mainly influenced by... 

The flow properties of colloidal dispersions are of great importance in handling dispersions in various practical situations. Another important aspect is that the viscosity and other rheological parameters can be used to determine the size, shape and interaction potentials of the dispersed particles. For most simple liquids, the viscosity is independent of the shear force. In this case, the liquid is then called Newtonian. For more complicated systems, when the liquid contains colloidal particles and/or polymers, the (apparent) viscosity depends on the shear force, except at very low concentrations of dispersed material. The fluid is then designated non-Newtonian. In this section, only systems containing particles are discussed, without the complicating influence of macromolecules. 

Although the rheological literature may not usually be that easily accessible for traditional chemist, there are a number of readable accounts, with one of these being the text by Barnes et al. (46). The latter is recommended as good introductory book on rheology. In addition, a good overview of the hydrodynamics of colloidal dispersions is given in ref. (47). 

Lionberger R.A. Shear thinning of colloidal dispersions. J. Rheol. 1998 42(4) 843-863 Lionberger R.A., Russel W.B. Microscopic theories of the rheology of stable colloidal dispersions. Adv. Chem. Phys. 2000 111 399-474... 

These relationships are particularly significant in micro- and nanofluidics as well as in other aspects of polymer rheology. Although recent advances in the development of colloidal dispersions at sub-nano-diameter levels are promising, colloidal nanoparticles with versatile morphologies, shapes, and bioactive attributes are of particular interest. 

In this chapter, the rheology of colloids has also been discussed and it was shown that very complex behaviours can be observed depending on the shape and concentration of the colloid particles. In addition, dispersions can show thixotropic (time-dependent) behaviour. The rheology of colloids is important for products such as shampoo, paint, foods and lotions. 

Zackrisson M, Stradner A, Schurtenbeiger P, Beigenholtz J (2(X)6) Structure, dyneunics, and rheology of concentrated dispersions of poly(ethylene glycol)-giafted colloids. Phys Rev E 73 11408-1-11408-8... 

Zackrisson, M., Stradner, A., Schurtenberger, P, and Bergenholtz, J. 2006. Structure, dynamics, and rheology of concentrated dispersions of polyfethylene glycol)-grafled colloids. Phys. Rev. E 73 011408. 

In this section we give a description of the colloidal interactions which govern the state of dispersion and rheology of calcium carbonate slurries. The description is based on a series of fundamental experimental studies that have been described in more detail in previous publications. ... 

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