Bulk rheology

Using the above model, Papenhuizen [21] derived an expression for the viscosity coefficient, rji, resulting from purely hydrodynamic effects, i.e. 

---

The behavior of colloidal suspensions is controlled by iaterparticle forces, the range of which rarely extends more than a particle diameter (see Colloids). Consequentiy suspensions tend to behave like viscous Hquids except at very high particle concentrations when the particles are forced iato close proximity. Because many coating solutions consist of complex mixtures of polymer and coUoidal material, a thorough characterization of the bulk rheology requires a number of different measurements. 

Both of these processes appear to be associated with the glass transition and bulk rheological dissipation. 

Compared to dilute solution viscometry and to some extent to bulk rheology, the flow properties of dendrimers in concentrated solutions have been the least investigated area of dendrimer rheology. In fact, with the notable exception of some recent data on generation 4 PPI in water [22] the only [32] reported... 

The bulk rheological properties of the PFPEs, including the melt viscosity (p), storage modulus (G ), and loss modulus (G"), were measured at several different temperatures via steady shear and dynamic oscillation tests. Note that we denoted p as melt viscosity and r as solution viscosity. An excellent description of the rheology is available in Ferry [99]. 

In terms of the materials used, there is a major difference in the complexity of the feedstocks of food extrusion compared to synthetic polymers when one examines any level below that of the bulk rheology of the mix. For example ... 

In actual situations several processes occur simultaneously. The details of any particular dispersion processes are also affected by the viscosity of each phase, the shear in the system, the interfacial energy, the pressure of solid particles, and dissolved substances. In nonuniform shear flow (e.g., tubular Poiseuille flow), for example, droplet breakup can be related to the bulk rheological properties of the dispersed and continuous phases and the critical Weber number (We ) as shown in Figure 3 (3). The We is a dimensional group defined by... 

Effect of Emulsion Characteristics. As discussed in Chapter 4, the rheology of emulsions is affected by several factors, including the dis-persed-phase volume fraction, droplet size distribution, viscosity of the continuous and dispersed phases, and the nature and amount of emulsifying surfactant present. All of these parameters would be expected to have some effect on flow behavior of the emulsion in porous media. However, the relationship between bulk rheological properties of an emulsion and its flow behavior in porous media is feeble at best because, in most cases, the volume... 

The measurement of rheological properties at the surface of a solution or the interface between a solution and, for example, a biological film is called surface or interfacial rheology. In this technique also, experiments are performed either in tension, compression or shear, and phenomena observed in bulk rheology such as flow and viscoelasticity are also observable. An introduction to the techniques available and some key findings are discussed by Warburton. ... 

That s enough on bulk rheology for now. A more detailed treatment is planned for Volume IV. Several of the above features recur in the following sections on surface rheology. 

Extending the analogy with bulk rheology, for linear shear deformation of an interface it is possible to define a surface (or interfacial) shear viscosity rj° and a surface (or interfacial) shear modulus G°. In a Cartesian co-ordinate system, with again the z-axis normal to the interface... 

For extensions and further elaborations of these principles see Joly s review, mentioned in sec. 3. lOd, and standard textbooks on bulk rheology 1). The translation from three-dimensional to two-dimensional systems is not difficult. 

M. van den Tempel. Surface Rheology, in Journal of Non-Newtonian Fluid Mechanics 2 (1977) 205-19. (Review with a phenomenological emphasis operational definitions and coupling to bulk rheology.)... 

The dependence of the viscous stress on the velocity gradient in the fluid is a constitutive law, which is usually called the bulk rheological equation. The general linear relation between the viscous stress tensor, T, and the rate of strain tensor,... 

Section 5.1 discusses, besides some basic notions, the rheology of liquids and liquidlike systems, i.e., those systems that exhibit flow. Solidlike systems are discussed in Section 17.1. This all concerns bulk rheology. Surface rheology is discussed in Section 10.8. 

Basic aspects of rheology are discussed in Sections 5.1.1 and 2. This concerns bulk rheology. Rheological theory can also and usefully be applied to the deformation of fluid interfaces. A main problem is that an interface cannot exist by itself it is the boundary between two phases and these phases must be deformed with the interface. Surface or interfacial... 

In practice, interfaces are often subjected to a combination of the deformations mentioned. As in bulk rheology, there are some other variables. First, the response of a material to a force can be elastic or viscous. Elastic response means immediate deformation, where the strain (relative deformation, i.e., tan a. in shear and AA/A in dilatation) is related to the force on release of the force, the strain immediately becomes zero. In viscous deformation, the force causes flow or, more precisely, a strain rate (d tan a/dt or d In Ajdty, this occurs as long as the force lasts, and upon release of the force the strain achieved remains. For most systems, the behavior is viscoelastic. Second, deformation can be fast or slow, and time scales between a microsecond and more than a day may be of importance. Third, the relative deformation (strain) applied can be small—i.e., remain close to the equilibrium situation—or be large. 

---