We study the complex formation between one long polyanion chain and many short oligocation chains by computer simulations. We employ a coarse-grained bead-spring model for the polyelectrolyte chains and model explicitly the small salt ions. We systematically vary the concentration and the length of the oligocation and examine how the oligocations affects the chain conformation, the static structure factor, the radial and axial distribution of various charged species, and the number of bound ions in the complex. At low oligocation concentration, the polyanion has an extended structure. Upon increasing the oligocation concentration, the polyanion chain collapses and forms a compact globule, but the complex still carries a net negative charge. Once the total charge of the oligocations is equal to that of the polyanion, the collapse stops and is replaced by a slow expansion. In this regime, the net charge on the complexes is positive or neutral, depending on the microion concentration in solution. The expansion can be explained by the reduction of the oligocation bridging. We find that the behavior and the structure of the complex are largely independent of the length of oligocations, and very similar to that observed when replacing the oligocations by multivalent salt cations, and conclude that the main driving force keeping the complex together is the release of monovalent counterions and coions. We speculate on the implications of this finding for the problem of controlled oligolyte release and oligolyte substitution.
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28 April 2016
Research Article|
April 26 2016
Complex formation between polyelectrolytes and oppositely charged oligoelectrolytes
Jiajia Zhou
;
Jiajia Zhou
a)
1School of Chemistry & Environment, Center of Soft Matter Physics and Its Applications,
Beihang University
, Xueyuan Road 37, Beijing 100191, China
2Komet 331, Institute of Physics,
Johannes Gutenberg-University Mainz
, Staudingerweg 9, D55099 Mainz, Germany
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Matthias Barz;
Matthias Barz
3Institute of Organic Chemistry,
Johannes Gutenberg-University Mainz
, Duesbergweg 10-14, D55099 Mainz, Germany
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Friederike Schmid
Friederike Schmid
b)
2Komet 331, Institute of Physics,
Johannes Gutenberg-University Mainz
, Staudingerweg 9, D55099 Mainz, Germany
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J. Chem. Phys. 144, 164902 (2016)
Article history
Received:
February 04 2016
Accepted:
April 10 2016
Citation
Jiajia Zhou, Matthias Barz, Friederike Schmid; Complex formation between polyelectrolytes and oppositely charged oligoelectrolytes. J. Chem. Phys. 28 April 2016; 144 (16): 164902. https://doi.org/10.1063/1.4947255
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