From Stars to Spheres: A SAXS Analysis of Dilute Dendrimer Solutions

Abstract

The progression of intramolecular organizations within a series of dilute poly(amido amine) (PAMAM) dendrimer/methanol solutions is examined by use of small-angle X-ray scattering (SAXS) combined with comparisons to electron density models and radial density distributions extracted by the indirect transformation for the calculation of P(r) (ITP) method. The SAXS from generation 3 (G3) dendrimers are shown to possess scattering features similar to those of star molecules. This contrasts with the SAXS of the much larger G9 and G10 dendrimers. The G10 SAXS exhibits at least five resolvable secondary maxima. These features are successfully reproduced for a model consisting of constant-density spheres with a small amount of polydispersity in molecular size. Scattering from the intermediately sized G4 through G8 dendrimers reflects a consistent evolution of internal structure progressing from “starlike” to “hard-sphere-like” organizations.