Rheological properties, requirements for

We can see that Eqs. (2 101) (2-104) are sufficient to calculate the continuum-level stress a given the strain-rate and vorticity tensors E and SI. As such, this is a complete constitutive model for the dilute solution/suspension. The rheological properties predicted for steady and time-dependent linear flows of the type (2-99), with T = I t), have been studied quite thoroughly (see, e g., Larson34). Of course, we should note that the contribution of the particles/macromolecules to the stress is actually quite small. Because the solution/suspension is assumed to be dilute, the volume fraction is very small, (p 1. Nevertheless, the qualitative nature of the particle contribution to the stress is found to be quite similar to that measured (at larger concentrations) for many polymeric liquids and other complex fluids. For example, the apparent viscosity in a simple shear flow is found to shear thin (i.e., to decrease with increase of shear rate). These qualitative similarities are indicative of the generic nature of viscoelasticity in a variety of complex fluids. So far as we are aware, however, the full model has not been used for flow predictions in a fluid mechanics context. This is because the model is too complex, even for this simplest of viscoelastic fluids. The primary problem is that calculation of the stress requires solution of the full two-dimensional (2D) convection-diffusion equation, (2-102), at each point in the flow domain where we want to know the stress. 

The two rheological properties required—the yield stress, x , and the high-shear-limiting (or plastic) viscosity, —determine the flow behavior of a Bingham plastic. The viscosity fnnction for the... 

Consequently, a common effort should be made to establish and complete the data basis concerning the numerous thermodynamic, thermophysical, transport and rheological properties necessary for modeling and simulating the different steps of this complex mild drying process. Moreover, the methods available for the characterization of most of these end-use properties should be improved and additional characterization methods should be adapted from other research fields (material science, applied biochemistry, physical chemistry, etc.). Improved characterization methods promise a better description and a safer control of numerous end-use properties for existing freeze-dryers as well as for new machines with more possibilities to better comply with more and more severe quality requirements in the future. The use of non-invasive sensors or of rapid non-intrusive methods for on-line and in situ estimation of the main parameters of the process could also help to overcome the difficulties observed, for example, the artifacts resulting from invasive sensors inserted inside vials and presently commonly used. 

These cements have unusual rheological properties (Wilson, 1975b). They can be mixed to higher powder/liquid ratios (6 1 by mass, or more) than any other dental cements and are very fluid. Whereas pastes of other cements behave as plastic bodies, the EBA cement has the characteristics of a very viscous Newtonian liquid and flows under its own weight, even when mixed very thickly (Wilson Batchelor, 1971). High powder/liquid ratios are required for optimum properties 3-5 g cm for luting and 5 to 6 g cm for linings and bases. 

One of the most difficult parenteral dosage forms to formulate is a suspension. It requires a delicate balance of variables to formulate a product that is easily resuspended and can be ejected through an 18-to 21-gauge needle through its shelf life. To achieve these properties it is necessary to select and carefully maintain particle size distribution, zeta potential, and rheological properties, as well as the manufacturing steps that control wettability and surface tension. The requirements for, limitations in, and differences between the design of injectable suspensions and other suspensions have been previously summarized [17b, 18,19]. 

Favorable rheological properties are an essential requirement for the commercialization of polyolefins like polyethylene. The ease of processability of the polymer melt, obtained through modifications in the microstructural features, is as important as the end use mechanical properties of these polymers. Presence of long-chain as well as short-chain branching, LCB and SCB, respectively, more or less dictates the rheological behavior of most commercial... 

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