Macromolecules, Vol.31, No.21, 7340-7346, 1998
The ordinary-extraordinary transition revisited : A model polyelectrolyte in a highly polar organic solvent
The "ordinary-extraordinary" transition in the observed diffusivity of polyelectrolyte solutions was studied by dynamic light scattering using the model system of sodium polystyrene sulfonate (SPS) in N-methylformamide (NMF). NMF was chosen because it has a high dielectric constant that varies strongly with temperature, and it was hoped that an organic solvent would better solvate the chain backbone. Two diffusion coefficients corresponding to the previously reported fast and slow modes were observed at all salt concentrations. This is in contrast to previous work where the slow relaxation "appeared" only when the concentration of added salt is less than the critical concentration, C-DD, derived by Drifford and Dalbiez. In this work, the absolute amplitude of the slow mode was nearly constant at salt concentrations both above and below the transition in general agreement with Sedlak's recent survey of aqueous SPS solutions.
Keywords:DYNAMIC LIGHT-SCATTERING;ANGLE NEUTRON-SCATTERING;MOLECULAR-WEIGHT;IONIC-STRENGTH;POLY(METHACRYLIC ACID);POLYIONCONCENTRATION;BIO-POLYMERS;SALT;CHARGE;PHASE