Particles, colloidal rheological properties

In order to utilise our colloids as near hard spheres in terms of the thermodynamics we need to account for the presence of the medium and the species it contains. If the ions and molecules intervening between a pair of colloidal particles are small relative to the colloidal species we can treat the medium as a continuum. The role of the molecules and ions can be allowed for by the use of pair potentials between particles. These can be determined so as to include the role of the solution species as an energy of interaction with distance. The limit of the medium forms the boundary of the system and so determines its volume. We can consider the thermodynamic properties of the colloidal system as those in excess of the solvent. The pressure exerted by the colloidal species is now that in excess of the solvent, and is the osmotic pressure II of the colloid. These ideas form the basis of pseudo one-component thermodynamics. This allows us to calculate an elastic rheological property. Let us consider some important thermodynamic quantities for the system. We may apply the first law of thermodynamics to the system. The work done in an osmotic pressure and volume experiment on the colloidal system is related to the excess heat adsorbed d Q and the internal energy change d E ... 

It is also important to emphasize that conventional consciousness of colloid or fine particle technology, like better dispersion and control of rheological properties of dipping solution, are not to be overlooked. The growth of nanoparticles in liquid phase is almost exactly regulated by the nuclei-growth theory as well as stability of lyophobic colloids suggested half a century ago. 

In this chapter, we review the rheological properties of suspensions of solids in a liquid medium, under conditions in which the particles do not clump together— that is, do not gel. Gelled colloidal suspension are discussed in Chapter 7, while emulsions md foams—where the suspended phase is another liquid or a gas—are discussed in Chapter 9. Even within these limits, the scope of this chapter is extensive, and there is only room for major topics. Additional detail can be found in Russel et al. (1989), Hiemenz and Rajagopalan (1997), Kim and Karrila (1991), and Chapter 10 of Macosko (1994). For reviews of the most recent work, see Brady (1996) and Mellema (1997). 

The clay component is the main factor controlling the rheological properties and the slip stability. Some part in this respect, hovewer, can also be played by the other very fine components. From the frit particles, water extracts alkalis which affect the colloidal and rheological properties of the slip. Since the extraction is gradual, the suspension is allowed to stand for a certain time before application to stabilize its properties. 

In fact, Equation 5.281 describes an interface as a two-dimensional Newtonian fluid. On the other hand, a number of non-Newtonian interfacial rheological models have been described in the literature. Tambe and Sharma modeled the hydrodynamics of thin liquid films bounded by viscoelastic interfaces, which obey a generalized Maxwell model for the interfacial stress tensor. These authors also presented a constitutive equation to describe the rheological properties of fluid interfaces containing colloidal particles. A new constitutive equation for the total stress was proposed by Horozov et al. ° and Danov et al. who applied a local approach to the interfacial dilatation of adsorption layers. 

The colloidal characteristics of A -alkylacrylamide- or Af-alkylmethacrylamide-based particles are temperature related. In fact, the swelling ability, charge density, charge distribution, hydrophilic-hydrophobic balance, hydration and dehydration properties, particle size, surface polarity, colloidal stability, water content, turbidity, and electrokinetic and rheological properties are indis-cemibly temperature dependent. Such polymer particles can be used as a stimuli-responsive model for the investigation of colloidal properties and for theoretical studies. 

Several colloidal interaction forces can act between particles dispersed in a liquid. If these particles attract each other, they will aggregate, which means that the dispersion is unstable. The interaction forces can also affect the stability of a thin film (e.g., between air bubbles) and the rheological properties of particle gels. 

Flow or deformation involves the relative motion of adjacent elements of the material. As a consequence such processes are sensitive to interatomic or intermolecular forces. In the case of liquids containing dispersed particles, interparticle forces are also important. Because the rheological properties of colloidal suspensions exhibit such a rich variety of phenomena, rheological studies not only provide information on medium-particle and particle-particle interactions but also arc of immense technological importance. 

Free colloidal particles about a micrometer or less in size settle out so slowly under gravity that they may often be considered as suspended in the flow and moving with it. As a result, the principal concern is to determine the rheological properties of the colloidal suspension. 

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... 

Haber, S., and Brenner, H., Rheological properties of dilute suspensions of centrally symmetric Brownian particles at small shear rates, J. Colloid Interface ScL, 97, 496-514 (1984). 

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