Structure of charged poly(propylene imine) dendrimers: Theoretical investigation

A mean-field model for charged dendrimers has been elaborated and applied to Astramol clenchimers of 5(th) generation in salt-free solution. The free energy of a dendrimer molecule was minimized with respect to the dendrimer size and to the profile of counterion distribution. The model of highly stretched freely jointed chain was used to describe the elasticity of long branches, the dissociated groups were assumed to be localized mostly on the periphery of the molecule, and the electrostatic interactions were described in the Poisson-Boltzmann approximation. It was found that the osmotic pressure of counterions leads to moderate expansion of dendrimer molecules upon charging, and a significant fraction of counterions is localized within the dendrimer molecule under typical experimental conditions.