Comparison between neutral gels and neutralized polyelectrolyte gels in the presence of divalent cations

The effect of calcium ions on the osmotic and scattering properties of fully neutralized sodium polyacrylamide (PSA) gel was compared to that of changing the cross-link density in the corresponding neutral polyacrylamide (PAA) gel. Changes in thermodynamic properties were investigated using complementary experimental techniques to probe different characteristics length scales. In PAA gel it was found that the third order interaction parameter was independent of cross link density whereas in PSA it was influenced by calcium ions. In PSA systems the intensity of liquidlike component calculated from the macroscopic swelling pressure was greater than that obtained from the decomposition of small-angle neutron scattering spectrum.