Solution rheology of polyelectrolytes in organic media*

The solution rheology of polyelectrolytes has been widely studied in aqueous media. Studies in non-aqueous media are less common, in part because of the limited solubility of polyelectrolytes in organic solvents. Here we study the solution behaviour of the tetrabutylammonium salt of carboxymethyl cellulose (TBACMC) in over 20 different solvents. The TBA ions increase the solubility of CMC in linear alcohols, diols etc. compared to more common counterions such as sodium or potassium. 

The overlap concentration of TBACMC is found to scale with the dielectric constant as c* ≈ ε ^-1 in salt-free solution and as c* ≈ ε ^-0.25 in excess added salt. These results indicate that chain dimensions decrease as the solvent permittivity decreases, presumably due to the lower charge density of the chains. In the semidilute non-entangled regime, the specific viscosity scales with concentration with power-law exponents of 0.7-1.1, with higher exponents being observed for less polar media. At high concentrations, strong dependences of the specific viscosity with concentration are observed (η_sp ≈ c^3.5), which are assigned to the onset of entanglements. The entanglement concentration is found to be largely unaffected by ε, the reason for this remains unclear at present.