Electrostatic contributions to chain stiffness and excluded-volume effectsin sodium poly(styrenesulfonate) solutions

Intrinsic viscosities for sodium poly(styrenesulfonate) in aqueous sodium c hloride at 25 degrees C have been determined for 15 samples ranging in weig ht-average molecular weight from 3.8 x 10(3) to 6.5 x 10(5) at five salt co ncentrations C-s between 0.05 and 2 M. Their molecular weight dependence at each C-s is fairly satisfactorily explained by the theory of Yoshizaki et al. for unperturbed wormlike chains combined with the quasi-two-parameter t heory for excluded-volume effects. The estimated persistence length q and e xcluded-volume strength B both increase with decreasing C-s. This increase in q is not quantitatively described by the known theories for the electros tatic persistence length when the previously determined q of 0.69 nm in 4.1 7 M aqueous NaCl at the theta point is used for the intrinsic persistence l ength. It is also shown that the values of B computed on the conventional b ead model and the rodlike segment model in the Debye-Huckel approximation w ith the ion condensation hypothesis are too large compared to the experimen tal estimates at lower C-s of 0.05 and 0.1 M though the latter model gives considerably smaller B than does the former one.