Computersimulationen und theoretische Beschreibung von Lösungen aus geladenen und ungeladenen Dendrimeren: Konzentrationseffekte und Selbstorganisationsprozesse

• Antragsteller: Professor Dr. Jens-Uwe Sommer
• Fachliche Zuordnung: Experimentelle und Theoretische Polymerphysik
• Förderung: Förderung von 2008 bis 2018
• Projektkennung: Deutsche Forschungsgemeinschaft (DFG) - Projektnummer 57587123

• Erstellungsjahr: 2016

Zusammenfassung der Projektergebnisse

Using a universal lattice based simulation method we test and develop universal theoretical models of the equilibrium statistics of dendrimers with flexible spacers. In the first period of support of the project we have developed theoretical concepts for single dendrimers under various conditions and simple complexes of dendrimers and linear chains. Up to high generations conformational entropy dominates and spacer scaling can be verified. Due to the high self-density of monomers mean-field methods can be applied and provide a quantitative interpretation of the simulation results. For the case of charged dendrimers it is important to discriminate between condensed, bound (residual) and free counterions. Using this information from simulation mean-field models (taking into account the osmotic effect of bound counterions and residual charges due to free counterions) are able to describe non-monotonous swelling behavior of dendrimers with respect to charge temperature. The model can be extended to consider selective and poor solvent. The interplay between poor solvent and osmotic pressure of residual counterions gives rise to high swelling/collapse ratios. The theory relates dendrimers with charged brushes and gels since the basic contributions to the mean-field free energy in all these systems are the elasticity of the strands (threads, i.e. longest paths in dendrimers) and the entropy of counterions. In the second period of funding we studied the concentration effects in dendrimer solutions and obtained first approaches to a scaling model of semi-dilute dendrimer solutions. Dendrimers with flexible spacer appear as mutually penetrable and thus concentration effects are closer to the physics of semi-dilute solutions of linear polymers. This picture was confirmed by simulations of two dendrimers using Umbrella sampling techniques in various environments. By following-up the discontinuous adsorption transition of dendrimers obtained before the start of the second period of funding we also investigated the collapse of a grafted dendrimer in a charged capacitor where we also found a jump-like collapse with increasing external fields. As other effects observed for flexible dendrimers mean-field arguments can explain the observed behavior. The project has been further extended to brushes of dendritic polymers both under static and under conditions of shear. This project has provided substantial understanding of the properties of dendrimers. At the same time the new insights open further interesting topics such as the depletion forces between dendrimers in different environments and the self-organization of dendrimers with modified endgroups (co-dendrimers). Work on the project of dendrimers has spawned several collaborations and new projects such as to understand the synthesis of dendritic polymers by walking catalysts (funded since 2015).

Projektbezogene Publikationen (Auswahl)

• Properties of dendrimers with flexible spacer-chains: A Monte Carlo study. Macromolecules 42, 4878 (2009)
  J. S. Kłos and J.-U. Sommer
  
• Simulations of dendrimers with flexible spacer-chains and explicit counterions in low and neutral pH conditions. Macromolecules 43, 10659 (2010)
  J. S. Kłos and J.-U. Sommer
  
• Simulations of terminally-charged dendrimers with flexible spacer-chains and explicit counterions. Macromolecules 43, 4418 (2010)
  J. S. Kłos and J.-U. Sommer
  
• Monte Carlo simulations of charged dendrimer-linear polyelectrolyte complexes and explicit counterions. J. Chem. Phys. 134, 204902 (2011)
  J. S. Kłos and J.-U. Sommer
  
• Adsorption of branched and dendritic polymers onto flat surfaces: A Monte Carlo study. J. Chem. Phys. 139, 244903 (2013)
  J.-U. Sommer, J. S. Kłos and O. N. Mironova
  
• Simulations of a Grafted Dendritic Polyelectrolite in Electric Fields. Macromoecules 48, 1179 (2015)
  J. S. Kłos and Jens-Uwe Sommer
  
• The structure of brushes made of dendrimers: Recent advances. Polymer, 98, 19 August 2016, Pages 437-447
  C.-W. Li, H. Merlitz, C.-X. Wu and J.-U. Sommer