Rheology of Concentrated Macromolecular Solutions

Abstract

A polymer solution is a kind of suspension. As the size of polymers is much larger than the solvent molecules, the surrounding particles of the polymers can be regarded as a continuum Newtonian fluid. Also, in the usual theoretical treatment, polymers are assumed to be made up of some frictional units that are large enough to be regarded as Brownian particles. Therefore the theory of polymer solutions one of interacting Brownian particles. This chapter discusses the system of suspensions. It discusses the classical theory of Kirkwood for the dynamics of polymer solutions and also studies a particular system—the concentrated solution of rod-like polymers. The major purpose of the Kirkwood theory was to calculate the viscoelasticity of dilute polymer solutions. In concentrated polymer solutions, the instantaneous drop in the stress is quite small, which means that the elastic stress is essential in such system. On the other hand, in suspensions of large particle size, the stress vanishes immediately, which indicates the dominant contribution of the viscous stress. In the ideal elastic materials, the stress is given by the variation in the free energy under a hypothetical strain. As the viscous stress is negligibly small in concentrated polymer solutions, the stress in such systems can be calculated from the variation in the dynamic free energy.