Computer simulations of dendritic polyelectrolytes: Effects of solvent quality and adsorption
Zusammenfassung der Projektergebnisse
In the course of executing the project we carried out Monte Carlo simulations based on the bond fluctuation model of dendrimers in various environments. Due to an increasing interest in vehicle-mediated gene and drug delivery based on the dendrimer/DNA binding phenomenon, in the first step we completed the inspection of complexes between charged dendrimers and linear polyelectrolytes. Since DNA molecules are not fully flexible, we included in our calculations another variable parameter referred to as the chain flexibility. Thus, the aim of the study was to understand the interplay between electrostatic effects and chain flexibility. We found that complexes comprised of the dendritic and linear polyelectrolytes of varying rigidity are dominated by electrostatic interactions. For chains much longer than the compensation points conformational transitions occur at strong electrostatic interactions caused by increasing chain rigidity. In particular, long chains show a release of tails from the complex. Next, using the same simulation method, we inspected neutral and charged dendrimers of various generations and spacer length under variation of the solvent quality from athermal to poor. In our study we took into account explicitly counterions, the full Coulomb potential and excluded volume interactions. The effect of solvent was accounted for implicitly by a short range attraction between the monomers. Our simulations confirmed the Flory-type scaling prediction of the dendrimers' size under all solvent conditions for neutral dendrimers. Neutral dendrimers were also shown to display universal scaling properties with respect to the spacer length and spacer self-density. With respect to charged dendrimers the maximum of electrostatically driven swelling, controlled by osmotically active residual counterions, was found to be nearly independent of solvent quality. We demonstrated that under poor solvent conditions the electrostatically driven volume degree of swelling reaches values up to Q = 23, which indicates potential applications for dendrimers as stimuli-responsive nano-particles. For the sake of design of nanodevices with optimal transport properties it is crucial to understand the behavior of dendrimers near surfaces. Thus, in frames of the project, we also studied adsorption of dendrimers with flexible spacers onto a flat surface in a wide range of molecular weight, generation number, spacer length, and the monomer-surface interaction strength parameter. Our calculations indicated that for dendrimers with high molecular weight the molecules exist in three temperature-dependent regions referred to as non-adsorbed, critical and adsorbed. Slightly below the critical point of adsorption a weakly adsorbed state is approached in which the molecules stick to the surface and are spherical in shape. We also found that by further lowering the reduced temperature below its certain spacer-length dependent value, a jumphke transition into a strongly adsorbed state occurs. Here, the dendrimers become flat and their lateral size can be described by a 2D mean-field model. Last but not least, in frames of the project, in a review paper we had the opportunity to give an overview of the state-of-the-art knowledge of physical properties of dendrimers as seen from coarse grained computer simulations and analytical theories.
Projektbezogene Publikationen (Auswahl)
-
Simulations of charged dendrimers - linear polyelectrolyte complexes with explicit counterions, DPG Spring Meeting, 26-30 March 2012, Berlin, Germany
J. S. Klos and J.-U. Sommer
-
Simulations of Complexes between a Charged Dendrimer and a Linear Polyelectrolyte with Finite Rigidity, Macromolecular Theory and Simulations 21, 448-460, (2012)
J. S. Klos and J.-U. Sommer
-
Coarse Grained Simulations of Neutral and Charged Dendrimers, Polymer Science, Ser. C, 55, No. 1, 125-153, (2013)
J. S. Klos and J.-U. Sommer
-
Simulations of Neutral and Charged Dendrimers in Solvents of Varying Quality, Macromolecules 46, 3107-3117, (2013)
J. S. Klos and J.-U. Sommer
-
Simulations of the adsorption behavior of dendrimers, International Conference PPAM2013, 8-11 September 2013, Warsaw, Poland
J. S. Klos and J.-U. Sommer
