Abstract
In this report, we present a contrast variation small angle neutron scattering (SANS) study of
a series of neutral PAMAM dendrimer in aqueous solutions using three different generations (G4-6) at a
concentration of about 10 mg/ml. Varying the solvent hydrogen-deuterium ratio, the scattering
contributions from the water molecules and the constituent components of PAMAM dendrimer can be
determined. Using an analytical model of the scattering cross section I(Q) incorporating the effect of
water penetration, we have quantified the intra-molecular space of PAMAM dendrimer by evaluating
the number of guest water molecules and we draw a direct comparison to computational predictions. As
expected, the overall available internal cavity was seen to increase as a function of increasing dendrimer
generation. However, the fraction of water accessible volume in the internal cavity of a dendrimer was
found to remain invariant for the three generation PAMAM dendrimers studied in this report. We have
also estimated the average water density inside a dendrimer, which is found to be higher than that of
bulk water.
