The conformational behavior of a single, intrinsically flexible, weakly charged polyelectrolyte chain in poor solvent is analyzed by extensive computer simulations combining Monte Carlo and molecular dynamics techniques. After determining the ϑ point for the charge-free case, we focus on the weak screening limit, corresponding to low salt concentration in the solution. We study the dependence on both the solvent strength, characterized by the relative deviation from the ϑ point, τ, and the fraction of charged monomers in the chain, which is effectively tuned by varying the Coulomb interaction parameter. The conformations are discussed in terms of global properties (such as the end-to-end distance, the inertia tensor components, etc.) and functions revealing more detailed information, such as the density distribution around the center of mass and the structure factor. For chains in the ϑ regime our data confirm the picture of a string of electrostatic blobs. For poorer solvents (up to τ = 0.4) we observe, upon increasing the intrachain Coulomb repulsion, a splitting of the spherical globule into a dumbbell-type structure, accompanied by a sharp increase in the chain's gyration radius. For sufficiently large τ, a further splitting is observed as well. Such a “necklace globule” (a sequence of transitions) had been predicted by Dobrynin, Rubinstein and Obukhov (Macromolecules 1996, 29, 2974), with a nontrivial scaling of the gyration radius with chain length and interaction parameters, which is confirmed by our data. By means of a scaling analysis, we argue that the transitions can be interpreted as thermodynamic first-order phase transformations, when taking the appropriate thermodynamic limit, which implies a scaling of the electrostatic coupling with inverse chain length.

Dynamic properties of dilute solutions of neutral and charged dendrimers with explicit excluded-volume, electrostatic, and hydrodynamic interactions have been investigated by Brownian dynamics simulation. Three different types of motions in dendrimers up to g = 5 generations have been considered:  the motion of a dendrimer as a whole; the size and shape fluctuations (pulsations); the local reorientations of the individual monomers. The influence of the excluded-volume, electrostatic, and hydrodynamic interactions on these motions has been studied. The characteristic relaxation times have been compared with the theoretical predictions of the Rouse and Zimm models. The self-diffusion of a dendrimer can be described with the help of the preaveraged Zimm approach, and a dendrimer may be considered as an impenetrable sphere with the hydrodynamic radius R h. For both neutral and charged dendrimers the hydrodynamic radius is smaller than the gyration radius R g. The dynamics of the size fluctuations for a dendrimer with rigid spacers differs significantly from the theoretical predictions for a dendrimer with flexible spacers. The relaxation of these fluctuations is weakly sensitive to the presence of the hydrodynamic interactions, and the behavior of a dendrimer is close to that of an elastic body in a viscous medium. The local orientational mobility of individual monomers is significantly influenced by the ionization of the terminal groups.