Dependence of polyelectrolyte apparent persistence lengths, viscosity, and diffusion on ionic strength and linear charge density

Abstract

Apparent electrostatic persistence lengths (i.e., those found by substituting the perturbed for the unperturbed mean-square gyration radius in the wormlike chain theory) obtained from static light scattering for variably ionized acrylamideJsodium acrylate copolymers varied approximately as the inverse square root of the ionic strength, C,, and linearly with fractional ionization. While this does not agree directly with unperturbed persistence length theories, electrostatic excluded-volume corrections yielded better agreement with the experimental results. Intrinsic viscosity also varied as C,-O.5, and apparent persistence lengths extracted from those data via the Yamakawa model were in fair agreement with those from the light scattering data. In the limit of zero polymer concentration and zero scattering vector q, and equivalent hydrodynamic radius RH was found to be independent of ionic strength, whereas the mean-square radius of gyration, (P), varied strongly. This is at odds with the often-assumed linear relationship between RH and (S2)1/2 for random coils and may imply a partial-draining condition. Finally, the 'extraordinary diffusional phase appears removable by filtration.