Viscoelastic properties of polyelectrolyte solutions. III. Dynamic moduli from terminal to plateau regions

Viscoelastic properties of entangled polyelectrolyte solutions in the absence of added salt were measured over a wide range of polymer concentration, C, from the terminal to plateau regions. master curves of storage, G′, and loss, G″, moduli from the terminal to plateau regions are obtained irrespective of polymer concentrations, by using G_x, defined as the modulus at which G′ and G″ coincide with each other, asa characteristic modulus to superinpose the data. The master curves are similar to those of non-ionic polymer solutions, implying that the distribution of relaxation times of entangled polyelectrolyte solutions are not so much different from that of entangled non-ionic polymer solutions. Specific viscosity at zero shear-rate, η_sp^O, steady-state compliance, J_e^O, and G_x of entangled polyelectrolyte solutions can be understood by classifying the solutions into two regions, i.e. semidilute and concentrated regions. In the semidilute regions the polymer concentration dependence is given by and J_e^O ∞ G_x^- ∞ C^-.3 in salt-free solutions. In concentrated regions (C > 0.3 g/cm³), on the other hand, the polymer concentration dependence of η_sp⁰, J_e⁰ and G_x becomes stronger than that in the semidilute regions. The steep increase of η_sp⁰ may be due to the significant increase of concentration dependence of local frictional coefficients, and the concentration dependence of J_e⁰ and G_x may be understood by the uniform network model, like entangled non-ionic polymer solutions at high concentrations.