Rheology, nonlinear

If a dilute polymer solution is subjected to a imidirectional or steady flow with a velocity gradient large enough to stretch out the polymer molecule, nonlinear viscoelastic effects are observed. The simple Hookean dumbbell model, described in Section 3.4.4, can predict 

Several causes of shear thinning in dilute solutions have been proposed. These include finite extensibility, nonequilibrium hydrodynamic interaction, excluded volume, and internal viscosity (Larson 1988). The most important of these is the finite extensibility of polymer molecules (Bird et al. 1987b) it is discussed in Section 3.6.2.2.I. For a review of the other causes of shear thirming, see Larson (1988). 

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The molecular theory of Doi [63,166] has been successfully applied to the description of many nonlinear rheological phenomena in PLCs. This theory assumes an un-textured monodomain and describes the molecular scale orientation of rigid rod molecules subject to the combined influence of hydrodynamic and Brownian torques, along with a potential of interaction (a Maier-Saupe potential is used) to account for the tendency for nematic alignment of the molecules. This theory is able to predict shear thinning viscosity, as well as predictions of the Leslie viscosity coefficients used in the LE theory. The original calculations by Doi for this model employed a preaveraging approximation that was later... 

Thus, adequate determination of nonlinear rheological parameters can be obtained, using industrial polymer processing-relevant flows, albeit with very substantial computational efforts, virtually assuring the relevance of the use of the constitutive equation for solving other complex processing flows. 

Viscolelastic materials can be divided into viscoelastic solids and viscoelastic, or simply elastic, liquids. All viscoelastic liquids are non-Newtonian, but not all non-Newtonian liquids are viscoelastic. Non-Newtonian liquids show nonlinear rheological behavior, and this may be time dependent (Barnes et al., 1989). 

Wang, C.F. and Kokini, J.L. (1995). Simulation of the nonlinear rheological properties of gluten using the Wagner eonstitutive model. J. Rheol. 39(6), 1465-1482. 

The concept of polymer entanglements represents intermolecular interaction different from that of coil overlap type interaction. However, it is difficult to define the exact topological character of entanglements. The entanglements concept was aimed at understanding the important nonlinear rheological properties, such as the shear rate dependence of viscosity. However, viscoelastic properties could not be defined quantitatively as is possible with the reptation model. Because an entanglement should be... 

Problem 3.6 exercises your ability to compute nonlinear rheological properties of dilute solutions. 

The notation tr stands for the trace of the tensor. These expressions contain parameters, such as and a, that must be obtained by fits to nonlinear rheological data. None of... 

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... 

The described universal scenario of shear-molten glass and shear-thinnig fluid makes up the core of the MCT-ITT predictions derived from (11-14). Their consequences for the nonlinear rheology will be discussed in more detail in the following sections, while the MCT results for the linear viscoelasticity were reviewed in Sect. 3. Yet, the anisotropy of the equations has up to now prevented more complete solutions of the MCT-ITT equations of Sect. 2. Therefore, simplified MCT-ITT equations become important, which can be analysed in more detail and recover the central stability equations (20, 22). The two most important ones will be reviewed next, before the theoretical picture is tested in comparison with experimental and simulations data. 

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