Chain Model for Dilute Solutions

Abstract

Various experimental observations reveal an important aspect of the behavior of polymer solutions which is not captured by FENE dumbbell models. When the experimental data for high molecular weight systems is plotted in terms of appropriately normalized coordinates, the most noticeable feature is the exhibition of universal behavior. By this it is meant that curves for different values of a parameter, such as the molecular weight, the temperature, or even for different types of monomers can be superposed onto a single curve. For example, when the reduced intrinsic viscosity is plotted as a function of the reduced shear rate, the curves for polystyrene in different types of good solvents at various temperatures collapse onto a single curve [4]. There is, however, an important point that must be noted. While polymers dissolved in both theta solvents and good solvents show universal behavior, the universal behavior is different in the two cases. An example of this is the observed scaling behavior of various quantities with molecular weight. The scaling is universal within the context of a particular type of solvent. The term universality class is used to describe the set of systems that exhibit common universal behavior [99]. Thus theta and good solvents belong to different universality classes.