The Rheology of Dilute Polymer Solutions

Dilute Solution Properties. The rheology of dilute polymer solutions has been used extensively to gain insight into the structure and conformation of polymers in solution (11). The intrinsic viscosity provides a measure of the molecular weight of a polymer through a relationship such as the Mark-Houwink-Sakurada equation. Earlier studies of polyacrylamide (PAM) systems and details of the complexity of the characterization of high-molecular-weight water-soluble systems can be found in references 9, 13, and 14. 

The rheology of a polymer solution increases with the polymer concentration. A transition exists at the so-called critical concentration (which decreases with increasing molecular mass) separating "dilute" from "concentrated" solutions. 

Cooke BJ, Matheson AJ (1976) Dynamic viscosity of dilute polymer solutions at high frequencies of alternating shear stress. J Chem Soc Faraday Trans II 72(3) 679-685 Curtiss CF, Bird RB (1981a) A kinetic theory for polymer melts. I The equation for the single-link orientational distribution function. J Chem Phys 74 2016—2025 Curtiss CF, Bird RB (1981b) A kinetic theory for polymer melts. II The stress tensor and the rheological equation of state. J Chem Phys 74(3) 2026—2033 Daoud M, de Gennes PG (1979) Some remarks on the dynamics of polymer melts. J Polym Sci Polym Phys Ed 17 1971-1981... 

In a dilute polymer solution, there are no entanglements of the individual molecules and the molecules can be considered to be essentially isolated from each other, so that treatment of an individual molecule is sufficient. Much work was done to understand the rheological behavior of dilute polymer solutions using the concept that a polymer molecule can be idealized as dumbbells, that is, two beads connected by a spring. The hydrodynamic. Brownian, and intramolecular forces acting on the beads are considered when the dumbbells are suspended in a Newtonian fluid. Because experimental data cannot be taken at concentrations considered to be sufficiently low for the absence of intermolecular interactions, data obtained at low polymer concentrations (e.g., c < 10" gmL ) must be extrapolated to infinite dilution (Ferry, 1980). 

Y arin et al. [29, 111] gave a theory of the capillary breakup of thin jets of dilute polymer solutions and formation of the bead-OTi-the-string structure (some additional later results can be foimd in [90]). The basic quasi-one-dimensional equations of capillary jets (1.49) and (1.50) are supplemented with an appropriate viscoelastic model for the longitudinal stress. Yarin et al. [29, 111] used the Hinch rheological constitutive model, which yields the following expression... 

CapUlaiy instability and breakup of thin jets of dilute polymer solutions considered in section CapUlaiy Breakup of Rheologically Complex Liquid Jets of Chap. 1 represents itself an example of the so-called strong flows, in which coil-stretch transitiOTi of macromolecular coils can happen because the elongation rate is so... 

Concentrated dispersions may be shear thickening, as opposed to the shear thinning of dilute polymer solutions. Some materials, such as latex paints, tend to form a structure. As the structure breaks down with shearing action, the viscosity decreases. Such materials are thixotropic. Some fluids have a yield stress. A thorough characterization of the rheology may require a number of different measurements. 

Larson, R.G., 2005. The rheology of dilute solutions of flexihle polymers Progress and problems, J. RheoL, 49,1-70. 

Lodge, A. S., Wu, Y.-J. Exact relaxation times and dynamic functions for dilute polymer solutions from the bead/spring model of Rouse and Zimm, Report 16. Rheology Research Center, University of Wisconsin (July, 1972). 

They have been developed based on either molecular structure or continuum mechanics where the molecular structure is not considered explicitly and the response of a material is independent of the coordinate system (principle of material indifference). In the former, the polymer molecules are represented by mechanical models and a probability distribution of the molecules, and relationships between macroscopic quantities of interest are derived. Three models have found extensive use in rheology the bead-spring model for dilute polymer solutions, and the transient net work and the reptation models for concentrated polymer solutions and polymer melts. 

Fabula, A.G. The Toms phenomenon in turbulent flow of very dilute polymer solutions. Proceedings of the 4th International Congress on Rheology, Brown University, Providence, Rhode Island, August 26-30, 1963 Lee, E.H., Copley, A., Eds. Interscience New York, 1965 Part 3, 445-479. 

A dilute polymer solution at 293 K flows over a plane surface (250 mm wide X 500 mm long) maintained at 301K. The thermophysical properties (density, heat capacity and thermal conductivity) of the polymer solution are close to those of water at the same temperature. The rheological behaviour of this solution can be approximated by a power-law model with n=0.43 and m = 0.3 — 0.000 33 T, where m is in Pa-s" and J is in K. 

After a preliminary analysis of the influence of the production mode on xanthan characteristics, this study was focussed on the effects of the origin and concentration of proteins on the state of aggregation of xanthan in solution estimated by rheological measurements. In a first while, purification treatments were applied to dilute polymer solutions in order to try to separate proteins from xanthan and thus to evaluate the amount and effect of proteins linked to the polysaccharide backbone. In the second phase of this study, the direct addition of proteins to dilute or concentrated xanthan solutions was analyzed, and the effects of salt, pH and origin of proteins were investigated. 

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