Conformations of sodium poly(styrene-4-sulfonate) macromolecules in solutions with different ionic strengths

Abstract

Translational friction and viscosity of dilute solutions of sodium poly(styrene-4-sulfonate) with molecular masses of M = (5 × 10⁴)−(85 × 10⁴) are studied at different concentrations of low-molecular-mass salts. Molecular masses of the polymer are determined from the sedimentation-diffusion data. The study of the correlation between molecular masses and hydrodynamic characteristics resulted in ascertainment of the Kuhn-Mark-Houwink-Sakurada relationships for salt-free aqueous solutions of the polymer and solutions of the polymer in 0.2 M NaCl, 4.17 M NaCl, and 1.0 M KCl. It is shown that, as the ionic strengths of solutions are varied from minimum (H₂O) to maximum (4.17 M), macromolecules of the strong polyelectrolyte sodium poly(styrene-4-sulfonate) change their conformations from rigid rods to coils and, then, approach a globular conformation. In terms of the Gray-Bloomfield-Hearst and Yamakawa-Fujii theories and within the framework of the weakly bent cylinder model, the statistical Kuhn segment length and the hydrodynamic diameter of sodium poly(styrene sulfonate) chains are estimated in 0.2 and 4.17 M NaCl, 1.0 M KCl, and salt-free aqueous solutions. The electrostatic component of the equilibrium rigidity is taken into account within the framework of the Odijk-Fixman-Skolnick and Dobrynin theories.