We study the properties of starburst dendrimers with flexible spacers in good solvent using Monte Carlo simulations based on the bond fluctuation model by systematic variation of dendrimers' generation number G and spacer length S. Our simulations support the dense-core picture of dendrimers due to a substantial decrease of monomer densities with the radial distance from the dendrimers' center of mass. The interior of dendrimers is penetrated by the terminal groups due to finite values of the end-group densities in that area indicating backfolding of the terminal groups toward the molecules' interior. The mean instantaneous shape of dendrimers changes monotonously from oblate to spherical as the increase in their molecular weight N is caused by an increase in G, while for fixed G it is hardly affected by variations of S. Using a mean-field model for the dendrimer extension reveals spacers as nearly unperturbed linear chains in good solvent and the dendrimer's conformation is a result of rearrangement of spacer chains up to a limiting generation of about G = 9. In particular, the radius of gyration follows the predicted scaling behavior of R g /S ν ∼ (N/S) 1/5 G 2/5 . Upon appropriate rescaling of length scales, extension measures, monomer distributions, and shape factors display spacer-length scaling. As a result dendrimers in good solvent display universal properties with respect to the length of spacers up to a rather high number of generations.

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.

We study the properties of weak dendritic polyelectrolytes of generation G = 5 with flexible spacers of various lengths and explicit counterions in an athermal solvent using Monte Carlo simulations based on the bond fluctuation model. The calculations are performed for molecules under neutral and low pH conditions. At neutral pH we assume that only the terminal groups of the dendrimers bear positive charges, while at low pH both the terminal groups and the branching units are charged. In our study, the full Coulomb potential and the excluded volume interactions are taken into account explicitly with the reduced temperature τ as the main simulation parameter. We observe an interplay of condensation of counterions, trapping of counterions inside the dendrimer’s volume and evaporation of counterions into the surrounding solution giving rise to a nonmonotonous electrostatic swelling of the dendrimer with temperature. Decreasing pH leads to higher swelling and stronger spacer-length dependence. At low pH spacer length-scaling cannot be applied and longer spacers shift the maximum of the swelling to lower temperature. To explain the swelling effect we apply a Flory-type argument where both trapped but noncondensed counterions and uncompensated charges due to evaporation of counterions are taken into account. This model properly reflects the swelling behavior with respect to temperature, pH and spacer-length variation, but quantitatively underestimates the swelling effect. We further investigate the pH-effects on density and charge profiles of the dendrimer.