Abstract
By quantitatively analyzing small angle neutron scattering (SANS) results of protonated generation 5 (G5) polyamidoamine (PAMAM) dendrimers dissolved in aqueous solution, we have accurately determined their structural characteristics. The investigation has focused on understanding the effect of counterion valency on the counterion association and its effect to the intra-molecular density profile. It is found that the association of extremely large amount of divalent counterions significantly reduces the effective charge of a dendrimer molecule. Similar to the results of G4, we found that there is still an intra-molecular structure transition in G5 when DCl is used to protonate a dendrimer. However, surprisingly, no discernible transition of the density distribution profile is observed for the G5 dendrimer charged by D2SO4. We have attributed the reason to the more effective screening effect of divalent counterions.
