Domain structures in low ionic strength polyelectrolyte solutions

A steep upturn at low angles dominates the small-angle neutron scattering profile of low ionic strength polyelectrolyte solutions. This behavior is demonstrated for poly(N-methyl-2-vinylpyridinium chloride) in D2O by measurements that are extended to low angles not typical of most studies. This behavior is consistent with static and dynamic light scattering measurements performed on the same solutions. Specifically, the upturn at low q and the slow diffusive mode in dynamic light scattering indicate the presence of supramolecular structures, which we interpret as large domains of increased polymer concentration. In these same solutions, a shorter wavelength correlation is evident from the presence of a maximum at finite q in the small-angle scattering experiment. Fluctuations on a short wavelength are also apparent from the existence of the fast mode in the dynamic light scattering. The maximum is interpreted as reflecting a characteristic dimension defined by order within domains, while the fast mode results from electrodynamic coupling of fast moving counterions and portions of chains.