Power Laws in the Dynamics of Polymer Solutions

Abstract

The dynamics of polymer solutions in the semidilute to concentrated regimes has been examined, using solutions of poly(methyl methacrylate) in propylene carbonate over the wide concentration range from φ ≈ 0.001 to φ ≈ 0.6. Here φ is the volume fraction of polymer in the solutions. Four power law regimes of the dynamical correlation length, ξh ∼ φ−α are observed when the local viscosity is taken into account. Crossovers from α = 0.75, via α = 0.5, to α = 1 corresponding to transitions from a good solvent, via a marginal solvent, to a theta solvent behavior have been predicted due to the gradual reduction of the segmental flexibility between the entanglement points with increasing φ. For the first time a clear experimental validation of these transitions is found experimentally presented. The fourth regime (α ≈ 2) is observed in the highly concentrated region where the static correlation length reaches the persistence length of the polymer. This dynamical regime was not included in the original theoretical treatment but can be explained within the same framework.