Simulations of Terminally Charged Dendrimers with Flexible Spacer Chains and Explicit Counterions

Abstract

We study the properties of terminally charged dendrimers under systematic variation of the length of flexible spacers, accompanied by explicit counterions in an athermal solvent using Monte Carlo simulations based on the bond fluctuation model. In our study, both the full Coulomb potential and the excluded volume interactions are taken into account explicitly with the reduced temperature, τ, as the main control parameter. Our calculations confirm that counterions get localized in the molecules’ interior and, in particular, condense on the terminal groups as τ is lowered. This, in turn, affects the conformational properties of the molecules that swell at intermediate τ due to dominating repulsion between the terminal groups and shrink in the limit of high and low τ, respectively. Like for neutral dendrimers, we find a substantial decrease in monomer densities with the radial distance from the dendrimers’ center of mass and backfolding of the terminal groups toward the molecules’ interior. By means of the radius of gyration tensor, we conclude that the mean instantaneous shape of dendrimers is spherical for all τ inspected.