Polyelectrolytes Revisited: Reliable Determination of Intrinsic Viscosities

The linear extrapolation of ( η  −  η 0 )/( η 0 c ) towards c  → 0 constitutes the basis of traditional methods to determine intrinsic viscosities [ η ], where η is the viscosity of polymer solutions of concentration c and η 0 is the viscosity of the pure solvent. With uncharged macromolecules this procedure works well; for polyelectrolytes it fails because of the pronounced non‐linearity of the above dependence at high dilution resulting from the increasing electrostatic interactions. This contribution presents a new method for the determination of [ η ]. It rests upon the application of the laws of phenomenological thermodynamics to the viscosity of polymer solutions and introduces a generalized intrinsic viscosity enabling a comparison of differently charged and uncharged polymers.