Fluctuation effects and monomer-counterion correlations in starlike polyelectrolyte systems.
We performed molecular-dynamics simulation to investigate fluctuation effects of monomers and counterions in starlike polyelectrolyte systems. We further study correlations between monomers and counterions. These quantities are systematically studied by variation of two parameters: the functionality f and the degree of dissociation alpha. Fluctuations of monomers and counterions are quantified by comparing the corresponding form factors of the monomers and counterions with a mean-field approximation. Fluctuations being correlated at length scales of the order of the star radius turn out to be negligible with increasing arm number f of the stars. At small arm numbers where fluctuation effects play a significant role, the use of theoretical mean-field models is questionable for a proper description of the monomer- and counterion-form factors. Correlations between monomers and counterions are quantified by a cross-correlation function. At small degree of dissociation alpha this function vanishes and indicates weak correlations. Furthermore, we compare our results with theoretical mean-field models. We give an appropriate analysis of the theoretical form factors and test commonly used counterion density distributions with our form factor analysis.
Jusufi
Arben
A
Physikalische Chemie I, Universität Bayreuth, Universitätsstrasse 30, D-95440 Bayreuth, Germany. arben.jusufi@uni-bayreuth.de