Universal Scaling of Linear and Nonlinear Rheological Properties of Semidilute and Concentrated Polymer Solutions.

Abstract

This dissertation examines the universal rheological behavior of linear polymers in solution. The universality of the dependence of zero-shear viscosity on concentration for both flexible and semiflexible polymers in good solvents is demonstrated by measurements for -phage DNA over the semidilute concentration regime, and comparisons for many other polymers from the literature. All experimental data for >0.5 fall on a single empirical curve with the polymer contribution to the zero-shear viscosity, the hypothetical Rouse polymer viscosity, the polymer concentration, and the entanglement concentration. For polystyrene (PS) solutions in tricresyl phosphate (TCP) with nearly monodisperse molecular weights, at the same below a critical value of around 2.0 for our PS/TCP solutions, linear and nonlinear rheological functions were successfully superimposed after the modulus and the frequency (or shear rate) of each solution were respectively normalized with the concentration-dependent plateau modulus and the equilibration time obtained from the de Gennes scaling relationships. However, we found that once the polymer volume fraction exceeds the “swelling volume fraction” , above which the polymer takes on a random walk configuration on all length scales even in a good solvent, this universal scaling breaks down and the polymer conformation appears to be governed by Colby-Rubinstein’s scaling laws for solutions. By employing this universality for drag-reduction study, we recognized an anomalous rheological behavior of high molecular weight poly (ethylene oxide) (PEO) solutions: the high values of dimensionless zero-shear viscosities for PEO solutions relative to those of other polymers at the same reduced viscosity, and growing high shear rate viscosities with concentration, which is supposed to be the solvent viscosity. These anomalies indicate aggregation of PEO, and call for further research utilizing dynamic light scattering and other methods.