Dresden 2011 – wissenschaftliches Programm
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 6: Charged Soft Matter
CPP 6.12: Vortrag
Montag, 14. März 2011, 17:15–17:30, ZEU 160
Simulations of charged dendrimers with flexible spacer-chains and explicit counterions — •Jaroslaw Sylwester Kłos1,3 and Jens-Uwe Sommer1,2 — 1Leibniz Institute of Polymer Research Dresden, Germany — 2Institut for Theoretical Physics, TU Dresden, Germany — 3Faculty of Physics, UAM Poznan, Poland
We study the properties of weak dendritic polyelectrolytes with flexible spacer-chains 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. In the first case solely the terminal groups of the dendrimers are protonated, whereas in the second both the terminal groups and branching units are. In our approach the full Coulomb potential and the excluded volume interactions are taken into account with the reduced temperature τ as the main control parameter. Our simulations show an interplay of counterion condensation, trapping of counterions inside the dendrimer’s volume and counterion evaporation into the solution which give rise to a non-monotonous electrostatic swelling of the molecule with τ. Decreasing pH leads to higher swelling and stronger spacer-length dependence. To explain the swelling effect we apply a Flory-type argument where both trapped but non-condensed counterions and uncompensated charges due to counterion evaporation are included. This model properly reflects the swelling behavior with respect to temperature, pH and spacer-length variation, though quantitatively underestimates it. We also investigate the pH-effects on density and charge profiles of the dendrimer.