Polymer solutions viscoelasticity

EFFECT OF POLYMER SOLUTION VISCOELASTICITY ON INJECTION AND PRODUCTION FACILITIES... 

This section briefly summarizes the problems and solutions with injection and production facilities that are related to polymer solution viscoelastic properties. For more details, see Wang (2001) and Wang et al. (2004a, 2004c). 

Effect of Polymer Solution Viscoelasticity on Injection and Production Facilities 233 ... 

In this chapter, we will review theories of dilute polymer solution viscoelasticity based on a bead-spring model The purposes of this chapter are to introduce these theories to non-specialists and to see how they might be compared with experimental results. Therefore, we will not examine the validity of the model or the statistical mechanical calculations involved in these theories. A review article by Fixman and Stockmayer (4) and a book by Yamakawa (5) include instructive descriptions on these problems. 

Evaluation of Mechanical Properties Viscosity of Shear-Sensitive Materials Dispersed Systems Polymer Solutions Viscoelasticity... 

Viscoelastic model None Polymer solutions Viscoelasticity Dynamic asymmetry... 

G D. J. PhiUies. Polymer solution viscoelasticity from two-parameter temporal scaling. /. Chem. Phys., 110 (1999), 5989-5992. 

Normal Stress (Weissenberg Effect). Many viscoelastic fluids flow in a direction normal (perpendicular) to the direction of shear stress in steady-state shear (21,90). Examples of the effect include flour dough climbing up a beater, polymer solutions climbing up the inner cylinder in a concentric cylinder viscometer, and paints forcing apart the cone and plate of a cone—plate viscometer. The normal stress effect has been put to practical use in certain screwless extmders designed in a cone—plate or plate—plate configuration, where the polymer enters at the periphery and exits at the axis. 

B. Zimm. Dynamics of polymer molecules in dilute solutions viscoelasticity, low birefringence and dielectric loss. J Chem Phys 24 269-278, 1956. 

For example, at MW = 4 X 10, c = 12 g/liter, and at MW = 5 X 10, c " = 62 g/liter. A polymer solution with concentration c > c is called a semidilute solution because mass concentration is low yet repulsive interactions between solutes are strong. Thermodynamics, viscoelasticity, and diffusion properties of semidilute polymer solutions have been studied extensively since the 1960s. 

Osaki, K. Viscoelastic Properties of Dilute Polymer Solutions. Vol. 12, pp. 1 —64. 

Many materials of practical interest (such as polymer solutions and melts, foodstuffs, and biological fluids) exhibit viscoelastic characteristics they have some ability to store and recover shear energy and therefore show some of the properties of both a solid and a liquid. Thus a solid may be subject to creep and a fluid may exhibit elastic properties. Several phenomena ascribed to fluid elasticity including die swell, rod climbing (Weissenberg effect), the tubeless siphon, bouncing of a sphere, and the development of secondary flow patterns at low Reynolds numbers, have recently been illustrated in an excellent photographic study(18). Two common and easily observable examples of viscoelastic behaviour in a liquid are ... 

Zimm, BH, Dynamics of Polymer Molecules in Dilute Solution Viscoelasticity, Flow Birefringence and Dielectric Loss, Journal of Chemical Physics 24, 269, 1956. 

Some examples where the viscoelastic behaviour of polymer solutions are exploited are their use as thickeners in ... 

First approaches at modeling the viscoelasticity of polymer solutions on the basis of a molecular theory can be traced back to Rouse [33], who derived the so-called bead-spring model for flexible coiled polymers. It is assumed that the macromolecules can be treated as threads consisting of N beads freely jointed by (N-l) springs. Furthermore, it is considered that the solution is ideally dilute, so that intermolecular interactions can be neglected. 

Using this equation an attempt was made to find a critical Re-number which could be correlated to the onset of vortices observed with the naked eye, as has been done, for example, for Newtonian fluids [93], but no correlation could be found [88]. The reason is probably due to the fact that polymer solutions are viscoelastic fluids, also called second-order fluids. 

Factorizability has also been found to apply to polymer solutions and melts in that both constant rate of shear and dynamic shear results can be analyzed in terms of the linear viscoelastic response and a strain function. The latter has been called a damping function (67,68). 

The above model assumes that both components are dynamically symmetric, that they have same viscosities and densities, and that the deformations of the phase matrix is much slower than the internal rheological time [164], However, for a large class of systems, such as polymer solutions, colloidal suspension, and so on, these assumptions are not valid. To describe the phase separation in dynamically asymmetric mixtures, the model should treat the motion of each component separately ( two-fluid models [98]). Let Vi (r, t) and v2(r, t) be the velocities of components 1 and 2, respectively. Then, the basic equations for a viscoelastic model are [164—166]... 

For inelastic fluids exhibiting power-law behaviour, the bed expansion which occurs as the velocity is increased above the minimum fluidising velocity follows a similar pattern to that obtained with a Newtonian liquid, with the exponent in equation 6.31 differing by no more than about 10 per cent. There is some evidence, however, that with viscoelastic polymer solutions the exponent may be considerably higher. Reference may be made to work by Srimvas and Chhabra(15) for further details. 

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