A small-angle neutron scattering study of the equilibrium conformation of polyelectrolytes in stoichiometric saloplastic polyelectrolyte complexes

Stoichiometric polyelectrolyte complexes, PECs, from fully sulfonated poly(styrenesulfonate), PSS, as polyanion and poly(diallyldimethylammonium chloride), PDADMA, as polycation, were prepared by mixing them at optimized polyelectrolyte and NaCl concentrations. The complexes were compacted by ultracentrifugtion and then annealed in NaCl solutions at elevated temperatures to allow the polymers to fully intermix and relax. Small-angle neutron scattering, SANS, with contrast matching, was used to study single polyelectrolyte chain dimensions in PECs made from a mixture of deuterated and protonated PSS chains. Two PSS molecular weights in PECs were investigated at various ionic strengths. SANS curves, form factor fits, and corresponding Kratky plots indicate the Gaussian nature of the polyelectrolyte chains in the complexes regardless of molecular weight. PSS coils were slightly larger than the unperturbed dimension, more so for the higher molecular weight material, which was attributed to an effective stiffening of the chain due to ladderlike interactions between polyelectrolytes.