Reversible Swelling Process of Sixth-Generation Poly(amido amine) Dendrimers Molecule As Determined by Quartz Crystal Microbalance Technique

Dynamic light scattering (DLS) was used to measure the electrophoretic mobility and diffusion coefficients of sixth-generation poly(amido amine), G6 PAMAM, dendrimers in an aqueous solution. The measurements were used to determine the effective charge and the hydrodynamic radius of PAMAM molecules. The physicochemical measurements were supplemented with dynamic viscosity measurements. From these data, the intrinsic viscosity of the PAMAM solutions was determined. The viscosity behavior was discussed in terms of the core/shell dendrimer structure postulated in the literature. Additional information about the structure of the dendrimers was obtained using atomic force microscopy (AFM) and a quartz crystal microbalance (QCM). The latter was used to study the adsorption of G6 PAMAM from aqueous solution on a Au-coated surface. The QCM measurements indicate that the adsorbed dendrimer molecules significantly change their conformation and viscoelastic properties in response to variations in ionic strength and solution pH. We demonstrated that the QCM method detects the reversible swelling of dendrimer molecules in the film due to its adoption of an extended conformation upon the protonation of the dendrimer’s amine groups.