A small-angle neutron scattering study of the structure of gelatin/polyelectrolyte complexes

Mixtures of a fractionated gelatin with very low concentrations of anionic polyelectrolytes have been studied by small-angle neutron scattering. The scattering pattern observed from the system is reminiscent of that from pure polyelectrolyte solutions, with a maximum in the scattering, but at a much greater intensity. The position of the scattering peak is independent of the polyelectrolyte molecular weight, but moves to larger momentum transfer, Q, with increasing concentration. The scattering intensity at higher Q reflects the extent of complexation of the gelatin and polyanion. The addition of salt removes the peak from the scattering pattern and high salt concentrations weaken the complexes. Raising the pH also weakens the complexes. At high pH (greater than or equal to 10), the scattering indicates that there is no interaction between gelatin and the polyanions. The extent of complex formation for similar polyelectrolytes depends on the charge density and distribution in the chain.