Charge density effects on polyelectrolyte dynamic rheology

The dynamic rheological properties of an uncharged polymer and charged polyelectrolytes were evaluated in salt‐free water at various concentrations above the entanglement concentration. A poly(acrylic acid) homopolymer was used as the uncharged polymer and was ionized to anionic poly(acrylic acid‐co‐sodium acrylate) at five levels of ionization (0.05, 0.10, 0.15, 0.30, and 0.50). The polymers exhibited a terminal region at a low frequency and a plateau region at a high frequency. The dynamic data for the nonionic parent and all charged polymers could be reduced to a master curve, which indicated a similar distribution of relaxation times for the nonionic and charged polymers. The shear modulus, relaxation time, and zero shear viscosity properties exhibited a concentration and charge density dependence. Higher power‐law exponents for the rheological properties were noted for the nonionic polymer versus the charged derivatives. The number of mechanically active entanglements per number of chains increased with the polymer concentration and charge density. The total number of mechanically active entanglements per number of chains that occurred because of imposing a charge to the nonionic parent did not change with increased concentration, and this indicated a different entanglement mechanism for charged polymers in comparison with their nonionic parent. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008