Colloid dispersion rheology

Of course, the processing engineer or the colloid chemist seldom worries about the fundamental aspects of the microstructure of the product and its relation to rheology, but many of the topics we discuss in this chapter are useful for gaining the conceptual basis necessary to deal with the practical aspects of dispersion rheology. 

Hunter, R. J., Foundations of Colloid Science, Vol. 2, Clarendon Press, Oxford, England, 1989. (Undergraduate and graduate levels. Along with Volume 1, these two volumes cover almost all the topics covered in the present chapter at a more advanced level. Volume 1 discusses DLVO theory and thermodynamic approaches to polymer-induced stability or instability and is at the undergraduate level. Volume 2 presents advanced topics (e.g., statistical mechanics of concentrated dispersions, rheology of dispersions, etc.).)... 

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]. 

Figure 6.17 Some of the phase separations that may occur during rheological measurements involving colloidal dispersions. The sample shown contains oil droplets ( ), coarse solids (O), and fine solids (-). From Schramm [95]. Copyright 1992, American Chemical Society.

As discussed in Chapters 1-7, diffusion, Brownian motion, sedimentation, electrophoresis, osmosis, rheology, mechanics, interfacial energetics, and optical and electrical properties are among the general physical properties and phenomena that are primarily important in colloidal systems [12,13,26,57,58], Chemical reactivity and adsorption often play important, if not dominant, roles. Any physical chemical feature may ultimately govern a specific industrial process and determine final product characteristics, and any colloidal dispersions involved may be deemed either desirable or undesirable based on their unique physical chemical properties. Chapters 9-16 will provide some examples. 

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. 

While asphalt itself consists of a complex colloidal dispersion of resins and asphaltenes in oils, introduction of liquid elemental sulfur, which on cooling congeals into finely dispersed crystalline sulfur particles and in part reacts with the asphalt, necessarily complicates the rheology of such a SA binder. Differences and changes with SA binder preparation, curing time, temperature etc. must be expected and may be demonstrated by viscosity characteristics. 

This behaviour ean be quahtatively explained by Equation (12.7) since 4>m increases as the width of the size distribution increases. A good example of the ef-feets that particles and polymers have on the rheological behavior of liquids is cloudy apple juice (Genovese and Lozano, 2000). The aqueous milieu of the juice is a solution of sugar, acids and salts (i.e., the clarified juice) that contains charged particles (0.25-5 pm in size) and pectin as a colloidal dispersion. The viscosity of cloudy apple juice has been described by the expression ... 

This section draws heavily from two good books Colloidal Dispersions by Russel, Seville, and Schowalter [31] and Colloidal Hydrodynamics by Van de Ven [32] and a review paper by Jeffiey and Acrivos [33]. Concentrated suspensions exhibit rheological behavior which are time dependent. Time dependent rheological behavior is called thixotropy. This is because a particular shear rate creates a dynamic structure that is different than the structure of a suspension at rest. If a particular shear rate is imposed for a long period of time, a steady state stress can be measured, as shown in Figure 12.10 [34]. The time constant for structure reorganization is several times the shear rate, y, in flow reversal experiments [34] and depends on the volume fraction of solids. The viscosities discussed in Sections 12.42.2 to 12.42.9 are always the steady shear viscosity and not the transient ones. 

At this voliime fraction, the viscosity diverges because the shear stress is now given by the particle-particle contact in the tightly packed structure. As a result, we obtain a fluid with visco-elastic properties similar to polymeric solids. In ceramic processing, we extrude and press these pastes into green shapes. As a result, the rheology of ceramic pastes is of importance. The rheology of very concentrated suspensions is not particularly well developed, with the exception of model systems of monodisperse spheres. This section first discusses visco-elastic fluids and second the visco-elastic properties of ceramic pastes of monodisperse spheres. The material on visco-elastic fluids draws heavily from the book Colloidal Dispersions by Russel, Saville, and Schowalter [31]. 

It was our intention to provide the Soft Matter community with a comprehensive review of some recent approaches on the rheology of polymer-colloid dispersions. We hope that the reader will feel that the different topics discussed in this volume, which each address a particular facet of high solid dispersions, complement each other and help to draw a bridge between microscopic phenomena and macroscopic rheology. 

Keywords Colloidal dispersions Colloidal glasses Dynamics Grafted particles Hairy particles Micelles Nanoparticle-polymer hybrids Phase diagrams Polymers Rheology Soft colloids- Softness Stars... 

Keywords Colloidal dispersion Flow curve Glass transition Integration through transients approach Linear viscoelasticity Mode coupling theory Nonlinear rheology Non-equilibrium stationary state Shear modulus Steady shear... 

Sciortino F (2009) Nonlinear rheological properties of dense colloidal dispersions close to a glass transition under steady shear. Adv Polymer Sci. doi 10.1007/12 2009 30... 

Keywords Colloidal dispersion Confocal imaging Glass transition Nonlinear rheology... 

For higher values of the particle volume fraction, the rheological behavior of the colloidal dispersions becomes rather complex. We will consider qualitatively the observed phenomena, and next we will review available semiempirical expressions. 

Stability in colloidal dispersions is defined as resistance to molecular or chemical disturbance, and the distance the system is removed from a reference condition may be used as a measure of stability. The stability can be analyzed from both energetic and kinetic standpoints. The kinetic approach uses the stability ratio, as a measure of the stability. W is defined as fhe ratio of the rate of flocculation in the absence of any energy barrier to that when there is an energy barrier due to adsorbed surfactant or polymer. These processes are referred to as rapid and slow flocculation with rate constants kj and kg, respectively, such that W = kjlk. The stability of colloidal suspensions can be evaluated using various techniques. In practice, two methods are mainly used sedimentation and rheology measurements. 

W. R. Schowalter, Mechanics of Non-Newtonian Fluids (Pergamon, New York, 1978) W. B. Russell, D. A. Saville, and W. R. Schowlater, Colloidal Dispersions (Cambridge University Press (Cambridge, 1989) R. G. Larson, The Structure and Rheology of Complex Fluids (Oxford University Press, New York, 1999). 

Colloidal dispersion Excellent rheology, film appearance Require solubilizing amines... 

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... 

When De is very large, the system behaves like a solid and has elastic properties when De is very small, it flows like a liquid. The importance of rheology in studying colloidal dispersions arises from the fact that De is often around unity so that a wide range of visco-elastic phenomena are observed. 

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