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We present the results of molecular dynamics simulations of net positively charged fullerene nanoparticles in salt-free and salt-added solution. The aggregation of fullerene (C60)-like nanoparticle and counterion are studied in detail as a function of temperatures and a finite salt concentration. Our simulations show that the strong conformation changes as temperature changes. The net positively-charged nanoparticles do not repel each other but are condensed under proper temperatures. If salts are added, the aggregated nanoparticles will be disaggregated due to the Debye screening effect. [ABSTRACT FROM AUTHOR]

Off-lattice molecular dynamics simulations are carried out to study fully charged polyelectrolyte brushes with salt, and a comparison with an off-lattice self-consistent field (SCF) theory including finite stretching and volume effects [Biesheuvel et al. Macromolecules2008, 41, 6254] is presented. The SCF approach is able to reproduce the brush heights at different grafting densities, salt concentrations, and chain lengths on a semiquantitative level. At high grafting densities, the density profiles obtained with both techniques exhibit a particularly close agreement, while at low densities systematic deviations between their shapes are observed. The approximation of local electroneutrality, which the SCF approach is based on, is studied, and its implications are discussed. In this context, the strengths and limitations of the SCF model are analyzed in detail. [ABSTRACT FROM AUTHOR]

Off-lattice computer simulations of polyelectrolyte brushes are carried out using the Debye approximation with explicit counterions but implicit salt. The results are compared with explicit salt ion simulations and self-consistent field theory. We demonstrate that the data generated with these different techniques are in excellent agreement, thereby confirming the validity of the Debye approximation in the context of polyelectrolyte brushes. The efficiency of the Debye approximation is verified through benchmark computations. Further on, we develop an improved Flory-type mean-field model, based on the original argument by Pincus, but taking into account both the excluded volume and finite extensibility of chains. On the basis of this model, we demonstrate how the interplay of counterion pressure and excluded volume repulsion explains the observed effect of salt on the swelling of the brush under good solvent conditions. The brush height as a function of grafting density is investigated, and it is argued that the resulting power law scaling of −1/3 is incapable of distinguishing between excluded volume and electrostatic effects. [ABSTRACT FROM AUTHOR]